[From the U.S. Government Printing Office, www.gpo.gov]





















                     State of Alaska
                     Division of Governmental
                     Coordination
                     Assessment of Stormwater
                      Controls in Coastal Alaska
                     June 1995






6575D MONTGOMERY WATSON
.W38
1995








Assessment of Stormwater Controls in Coastal Alaska














                        Prepared for:

                       State of Alaska
              Division of Governmental Coordination




                U. S. DEPARTMENT OF COMMERCE NOAA
                COASTAL SERVICES CENTER
                2234 SOUTH HOBSON AVENUE
                CHARLESTON, SC 29405-2413




                        Prepared by:

                     Montgomery Watson
                     4100 Spenard Road
                   Anchorage, Alaska 99517



                     Property of CSC Library





                         June 1995






U    ~TABLE OF CONTENTS


I    ~~~1.0 Executive Summary ....... .....I..........................1-1
          1.1I Background and Objectives...................................1-1
          1.2 Projections of TSS loadings ..................................1-1
          1. 3 Best Management Practices...................................1-2
          1.4 Costs and Economic Impact ..................................1-2
      2.0 Introduction ...............................................2-1
           2.1 Study Objectives.........................................2-1
          2.2 Background............................................2-3

I       ~~3.0 Baseline Conditions of Indicator Municipalities............................3-1
          3.1 Introduction ............................................3-1
              3.1.1 Typical Year ......................................3-1
  I              ~~~~~~3.1.2 Rainfall .........................................3-1
              3.1.3 Runoff ..........................................3-2
                    3.1.3.1 Rainfall Runoff ..............................3-2
    I                    ~~~~~~~~3.1.3.2 Snowmelt Runoff.............................3-3
              3.1.4 TSS Loadings......................................3-4
                    3.1.4.1 Pre-Development TSS Loadings ....................3-5
                    3.1.4.2 Post-Development TSS Loadings....................3-6
              3.1.5 Summary of Derivation Methods ..........................3-7
              3.1.6 Land Development Scenarios.............................3-8
          3.2 Anchorage.............................................3-9
              3.2.1 Rainfall .........................................3-9
              3.2.2 Runoff.........................................3-10
              3.2.3 Soils and Drainage Conditions...........................3-10
              3.2.4 TSS ..........................................3-10
              3.2.5 Expected Site Development Types.........................3-10
              3.2.6 Typical Year .....................................3-11
              3.2.7 LocaliRegulations ..................................3-13
 3          ~~~~3.3 Bethel...............................................3-13
              3.3.1 Rainfall ........................................3-13
              3.3.2 Runoff.........................................3-14
  3               ~~~~~3.3.3 Soils and Drainage Conditions...........................3-14
              3.3.4 TSS ..........................................3-14
              3.3.5 Expected Site Development Types.........................3-14
  I             ~~~~~3.3.6 Typical Year .....................................3-15
              3.3.7 Local Storm Drainage Regulations.........................3-17
          3.4 Juneau ..............................................3-17
   I             ~~~~~3.4.1 Rainfall.......................I............... .3-17
              3.4.2 Runoff.........................................3-18
              3.4.3 Soils..........................................3-18
              3.4.4 TSS ..........................................3-18
      Siormwater Controls in Coastal Alaska                                                            ,~page i
  IJune, 1995






            3.4.5 Expected Site Development Types ...............................................3-19
            3.4.6 Typical Year ........................................................................3-19
            3.4.7 Local Storm Drainage Regulations ...............................................3-21
      3.5 Local Economic Conditions ................................................................3-21

4.0 Management Practices ................................................................................4-1
      4.1 Survey of Applicable Best Management Practices ..........................................4-1
      4.2 Type of Development and BMP for Each Land Use .......................................4-8

5.0 Cost Estimates ........................................................................................5-1
      5.1  Design Considerations for Selected BMP Construction and Maintenance ..............5-1
      5.2 Cost Estimate for Selected BMPS ...........................................................5-2
      5.3 Measures of Economic Impact ...............................................................5-2

6.0 Conclusions ...........................................................................................6-1

7.0 References .............................................................................................7-1


































Stormwater Controls in Coastal Alaska  page ii
June, 1995






LIST OF FIGURES

1 Location Map ..........................................................................................2-2
2    Anchorage Mean Monthly Precipitation Distribution - 1923-1984 and 1991 ..................3-9
3    Anchorage Monthly Rainfall-Runoff Distribution for Typical Year ..........................3-11
4  Cumulative Pollutograph for Anchorage for Typical Year .....................................3-12
5    Bethel Mean Monthly Precipitation Distribution - 1923-1984 and 1991 .....................3-13
6  Bethel Monthly Rainfall-Runoff Distribution for Typical Year ...............................3-15
7  Cumulative Pollutograph for Bethel for Typical Year ..........................................3-16
8    Juneau Mean Monthly Precipitation Distribution - 1949-1984 and 1987 ....................3-18
9    Juneau Monthly Rainfall-Runoff Distribution for Typical Year ...............................3-19
10 Cumulative Pollutograph for Juneau for Typical Year .........................................3-20
1E1   Particle Size Distribution Analyses for Suspended Sediment in Stormwater ................4-10


LIST OF TABLES

I Summary of Derivation Methods for Runoff and TSS Loadings ...............................3-8
2    Hydrologic Characteristics of Each Land Development Scenario for Anchorage ...........3-12
3    Hydrologic Characteristics of Each Land Development Scenario for Bethel ................3-16
4    Hydrologic Characteristics of Each Land Development Scenario for Juneau ...............3-21
5  Economic Features of Indicator Municipalities ..................................................3-22
6 Non-structural Best Management Practices ........................................................4-3
7 Structural Best Management Practices .............................................................4-6
8 Summary of Target TSS Removal Percentages .................................................4-11
9 Summary Pond Sizes ................................................................................5-1
i 10 Estimated Stormwater Control Costs ...............................................................5-2
11 Measures of Economic Impact ......................................................................5-3
12 Unit Costs for Stormwater Controls ...............................................................5-4


APPENDICES

Appendix A   Runoff and TSS Calculations
Appendix B   Cost Estimates












Stormwater Controls in Coastal Alaska                                                  J page iii
June, 1995






1.0 EXECUTIVE SUMMARY



1.1 BACKGROUND AND OBJECTIVES

The US Environmental Protection Agency (EPA) has established "Management Measures" for
control of Nonpoint Pollution in the Coastal Zone, in conjunction with the National Oceanic and
Atmospheric Administration (NOAA), the agency responsible for regulations of the Coastal Zone
Management Act. The Management Measures have been devised for a variety of land development
activities, including resource extraction, roadways, and urban development.  Management
Measures cover a variety of pollutants. Of particular note is the requirement to control Total
Suspended Solids (TSS) in community development. Specifically, the Management Measure calls
for coastal communities to:

   (a) Reduce the average annual TSS loadings by 80% after construction has been completed
        and the site is permanently stabilized; and/or

   (b) Reduce the postdevelopment loadings of TSS so that the average annual TSS loadings are
        no greater than pre-development loadings.

Previous research by Montgomery Watson on behalf of the Municipality of Anchorage
(Montgomery Watson, 1994) suggests that few "best management practices" (BMPs) have
documented performance sufficient to reliably meet these measures. This is particularly true where
Alaska's sub-arctic and arctic conditions complicate the effectiveness of such practices.

Montgomery Watson prepared this assessment of storm water controls for the State of Alaska,
Division of Governmental Coordination, Coastal Management Program. The work focuses on
Anchorage, Bethel, and Juneau, cities selected to represent the range of conditions typical in
Alaskan coastal communities.

This assessment has been undertaken to accomplish several objectives, as follows:

       Quantify annual pre-development and post-development loadings of TSS
   ï¿½  Determine target load reductions to meet the management measures
   * Determine appropriate best management practices
   * Estimate costs to implement BMP's
   * Determine the economic impacts of such costs

1.2  PROJECTIONS OF TSS LOADINGS

Development scenarios were derived for each city, on scales ranging from 5 acre residential
development to 20 acre industrial development. Total annual combined rainfall and snowmelt
runoff in Anchorage was estimated to range from less than 1.4 inches before development to
approximately 10 inches for commercial development. Similar ranges were 0.27 to 2.52 inches for


Stormwater Controls in Coastal Alaska                                                ~ page 1-1
June. 1995






Bethel, and 1.45 to 20.54 inches for Juneau. Typical runoff TSS concentrations were estimated to
range from SI mg/L (for Bethel) to 224 mg/L (for Anchorage commercial development).I

Loadings were estimated by multiplying TSS concentrations times projected runoff on a daily basis
through the year. Estimates of TSS loadings range from 48 to 56 pounds per acre per year for
"predevelopment" Anchorage, and 140 to 333 pounds per acre per year after development.
Estimates were higher for Juneau, due to more effective mobilization of TSS during runoff, up to
over one-half ton of TSS per acre per year for commercial sites after development.  BethelI
estimates were much lower, due to low intensity rainfall, flat slopes, and well established
vegetation.

1.3 BEST MANAGEMENT PRACTICES

Maintenance of urban runoff facilities was judged to be the best non-structural BMP for
implementation, although costs and benefits were not directly quantifiable. Wet pond type
sedimentation basins were judged to be the best structural controls for Anchorage and Juneau.
These ponds are impractical for Bethel due to permafrost and shallow groundwater. Vegetative
slope protection for embankments appears to provide the best pollution prevention function in low
lying tundra areas, although the effectiveness has not been reliably quantified.5

Sedimentation ponds are not viewed as effective in capturing fine particulates (<10 microns
effective diameter) from runoff. This fraction of TSS typically accounts for more than 20% of theI
TSS load in Alaska's low intensity storms. Therefore, it was concluded that the 80% removal
management measure is not attainable even with the BMP judged most cost effective for Alaska's
commnunities.
1A COSTS AND ECONOMIC IMPACT

In most instances, reduction in loadings to predevelopment conditions was judged to be less
stringent than the 80% reduction level. Costs were estimated for 3 Anchorage and 2 Juneau
development scenarios based on minimum sizing criteria for effective sedimentation pond
development.

Annual costs for sedimentation ponds range from $490 per developed industrial acre to over SI1640
per developed residential acre. This represents approximately 0.5 to 0.75 % of the annual cost of
an industrial or commercial enterprise, or nearly 5% of annual household income for a residence.3

Another measure is on the basis of total cost per pound of pollutant removed. For a twenty acre
industrial development, this can be as low as $3.00 per pound of TSS. Smaller commercial and3
residential developments are limited b~y sizing criteria, forcing costs up to as much as $26.00 per
pound of TSS for a 5 acre residential development in Anchorage.






Stormwater Controls in Coastal Alaska                                                  0 page 1-2I
June, 199S






2.0 INTRODUCTION



2.1  STUDY OBJECTIVES

The purpose of this study is to determine the costs of stormwater quality controls to meet federal
management measures for the reduction of suspended sediments from new urban development.

Suspended sediment from stormwater runoff in urban areas constitute the largest mass of pollutant
loading to surface waters.  NOAA and EPA have established management measures for total
suspended sediment (TSS) for new development in urban areas. The goal of this report is to
present an economic analysis of TSS controls for stormwater in coastal Alaska consistent with
EPA guidelines and to provide useful information to Alaskan communities for management of TSS
in urban stormwater.

Objectives of the study:

   *  Quantify TSS pre and post development loadings
   a Determine target TSS load reductions for two specified management measures:
       - 80% removal
       - removal to predevelopment conditions
      Determine appropriate best management practices (BMPs) to meet both management
       measures and to meet current local stormwater quality standard
   a Estimate the costs to implement appropriate BMP
   o  Determine the economic impacts of these costs

Each objective is carried out for each of three municipalities, Juneau, Anchorage, and Bethel for
new development. The communities are located on the map in Figure 1. New development is
characterized by three scenarios for each municipality: residential, commercial, and industrial land
use. For each scenario, one structural BMP was to be chosen for each of the two TSS reduction
goals. Although this study describes non-structural controls for TSS, there is not enough data to
determine if the controls are sufficient to meet the management measures for new development or
to estimate -the costs associated with them, especially if they are implemented on a site-specific
basis.













Stormwater Controls in Coastal Alaska                                                  3 page 2-1
June, 1995























                     (C~~~~~~~~~~~~~~ 




                                 4-~~~~~~~~~~~~~~~~~~~~~~~~~~~~s


                                            A:-~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~P

     *  I                  *~~~~~~~~~-'- Ovv



           '1*~~~~~~~~~~~BT




                                      ~~~~~~~~~~~~GULFO    L   ,







                                                                      FIGURE I

 MONTGOMERY WATSON
W             ~~~Anchorage, Alaska                                            LOCATION  MAP






22 BACKGROUND

The NOAA and EPA Coastal Nonpoint Pollution Control Program Management Measure for new
urban development, which includes urban redevelopment, new or relocated roads, highways and
bridges, requires:

       (1) By design or performance:

              (a) After construction has been complete and the site is permanently stabilized,
              reduce the average annual total suspended solid (TSS) loadings by 80 percent. For
              the purposes of this measure, and 80 percent TSS reduction is to be determined on
              an average annual basis,* or

              (b) Reduce the post-development loadings of TSS so that the average annual TSS
              loadings are no greater than redevelopment loadings, and

       (2) To the extent practicable, maintain post-development peak runoff rate and average
       volume at levels that are similar to pre-development levels.

       * Based on the average annual TSS loadings from all storm less than are equal to the 2-
       year/24-hour storm. TSS loadings from storms greater than the 2-year/24-hour storm are
       not expected to be included in the calculation of the average annual TSS loadings."

       (in Section II. A. New Development Management Measure (EPA, 1993))

These guidelines do not explicitly included snowmelt TSS loading in the calculation for average
annual TSS loading. However, they don't explicitly exclude it, either. In order to limit the scope
of this study, the following procedure has been adopted.

TSS loading from snowmelt is quantified in Section 3 of the report, in order to present a complete
picture of the annual TSS loading. The TSS removal of the chosen BMP for snow melt runoff is
estimated, but the BMP is not sized to treat snow melt runoff to the (a) and (b) criteria.

The BMPs'are selected and sized to meet the (a) and (b) criteria based on their ability to meet treat
the annual TSS loading for rainfall events up to the 2-year/24-hour storm (May through September
for Anchorage and Bethel; February through October for Juneau).













Stormwater Controls in Coastal Alaska                                                   0 page 2-3
June, 1995






~3.0 BASELINE CONDITIONS OF INDICATOR MUNICIPALITIES3


3.1 INTRODUCTIONI

The purpose of this section is to define the hydrologic and TSS loading conditions in each indicator
municipality. These conditions will provide the bases for BMP selection and cost analyses in
sections 4 and S. TSS loadings for urban basins are caused by runoff events. Runoff events, in
turn, are caused by rainfall and by snowmelt. Annual timing and amounts of runoff and TSS
loading are variable because of the influence of local meteorological conditions.

In the following sub-sections, the rainfall, runoff, soils conditions and TSS loadings are described3
in general and then in particular for each municipality. Local drainage conditions are described and
scenarios are developed that characterize expected site development sizes and conditions for the
three land use categories (residential, commercial and industrial). The typical year's runoff and3
TSS loads for each scenario are quantified. finally, local stormwater quality regulations for each
community are discussed and a summary of local economic conditions is presented.

3..1 Typical Year

In order to obtain annual TSS loadings, a "typical" year, in terms of precipitation, was identified3
from available weather service records for each municipality. A daily runoff rate was estimated
based on the daily rainfall or snowmelt and, from these runoff rates, daily TSS loadings were
generated. Because of the variability of precipitation events and the short record period of readilyI
available data, the "typical" year may vary considerably in individual months from the long term
record. In spite of this discrepancy, the use of actual rainfall records was assumed to be more
representative of actual conditions than a simulated series would have been. The typical year forI
Juneau and Bethel were determined by analysis of annual climatological summaries for years with
complete records during the period 1980 through 1993. A typical year for Anchorage was
suggested by the Municipality of Anchorage (MOA).
3.1.2  Rainfall3

Rainfall events greater than 0.1I inches were identified in the rainfall records for the typical year.
For all three municipalities, no daily rainfall in the chosen typical year exceeded the 2-year 24.-hour
event determined for the location by the U.S. Weather Bureau in Technical Paper 47 (TP 47)
(Miller, 1963). Professional experience in Alaska has found that TP 47 consistently overestimates
rainfall intensities for any recurrence interval. As a consequence, the use of this document often
leads to an overestimate of the number of rainfall-runoff events. This will consequently lead to an
overestimation of the TSS loadings for rainfall events that would be subject to management
measures. Before management measures are implemented, a more refined estimation of the 2-year
24-hour event should be made for specific localities.I




Storm water Controls in Coastal Alaska                                                  Z1 page 3-1 
June, 1995







   3.1.3 Runoff

   TSS loadings from urban basins is mobilized from the ground by runoff events. Coastal Alaska's
   runoff events fall in three general categories: summer/fall rainfall events, winter thaws, and spring
   snow melt.

   3.1.3.1 Rainfall Runoff

   Runoff due to rainfall is influenced by a number of factors, the primary ones being the soil types
   and percent imperviousness of the site, rainfall intensity, and antecedent moisture conditions. In
   developing a rainfall-runoff relationship, site specific data is the most reliable.  For ungaged
   locations, other methods have been developed.

   For Anchorage, some site specific rainfall-runoff data was available for developed urban basins.
   An equation, developed by the USGS (Brabets, 1987) based on data from three basins in the
   Anchorage area, was used to model the rainfall-runoff relationship in the Anchorage area. The
   equation has the following form:

                  VOL = 0.39 * (RF)1-10 (DA)0.14 (PEIA)0.38                        (1)

          where VOL is volume of runoff, in inches
                  RF is total storm rainfall, in inches
                  DA is drainage area in acres
                  PEIA is percent effective impervious area

   This equation has been calibrated for basins of less than 38 acres that have effective
   imperviousness less than 70%, for storm rainfall events that are less than 0.5 inches. Because this
   equation was calibrated for Anchorage, it was used to determine rainfall runoff for Anchorage
   only.

   For Bethel and Juneau, no site specific data was available. For these two municipalities, the
   method described in the USDA Soil Conservation Service's (SCS) Technical Release 55 (TR-55)
   was used to estimate runoff response to rainfall. TR-55 presents a simplified procedure to
   calculate storm runoff volume and is applicable to small urbanizing watersheds. This method
   estimates the runoff volume for a 24 hour storm event, based on two parameters: a factor, or curve
   number (CN), that reflects the soil type and imperviousness of the site, and the depth of rainfall.

                     (P-.2*S)2
                 Q-(P+.8*S)

          where P=rainfall in inches
                 Q=runoff in inches
                     CN
I                 S~~~~~10o010

   There are limitations on the use of this equation; both with respect to precipitation and the CN.

   Stormwater Controls in Coastal Alaska                                                  C page 3-2
   June, 1995







SCS suggests that this equation is less accurate when runoff is less than 0.50 inches. This is the 
case particularly in Bethel, and for a majority of the rainfall events in Juneau. The TR-55 method
predicts lower flows than does another standard method, the Rational method. The Rational
method, which predicts flow as the product of rainfall, basin area, and percent impervious, wasI
developed to estimate peak flows (Sheaffer, 1982). It was not developed for the study of runoff
volume, but approximations can be made by dividing the flow by the basin area. However, it was
used here to serve as a check on the results from the TR-55 method. The TR 55 method accountsI
for two factors that the Rational method does not: antecedent moisture conditions and initial
abstraction. Consideration of these factors tends to more fairly represent actual conditions than
does the Rational method.
The SCS has mapped soils throughout the lower 48 United States and developed a system of soil
types, ranked A through D, that relate to the CN in this equation. A review of the soil surveys of
the Juneau and Bethel areas was made. The soil types in these areas have not been classified within
this system. CN numbers were estimated, based on soils descriptions and their distributions in the
developable areas. The CN is site specific and will vary from location to location within theI
municipality. This is especially true in Juneau; Bethel area soils are more homogenous. The soil
type variability within the Juneau area will cause site specific runoff to be more variable than in
Bethel. Antecedent moisture conditions are taken into account by assigning a higher CN; the
higher CN is prescribed by the SCS and based on the CN for average conditions.

Despite these limitations regarding precipitation and CN values, we felt that TR-55 was the bestI
available method to estimate the runoff from rainfall events. These limitations should be kept in
mind, and the results from this method taken as relative rather than absolute values.

3.1.3.2 Snowmelt Runoff

Snow melt runoff is variable from year to year. Within a year, snow melt is highly variable in
duration and volume. The length of the snow melt period varies, depending on daily and hourly
temperatures, wind speed and direction, and the amount of snow on the ground. Although the3
amount of snow on the ground may influence the length of the snow melt period, it is not directly
correlated to the amount of runoff, either over the snow melt period or on a given day, because of
infiltration. If the ground beneath the snow is frozen, the amount of runoff will be greater. If
freezing temperatures precede snow fall in the fall, the ground will freeze and stay frozen through
the winter. Under these conditions, snow melt runs off rather than infiltrates, because the ground
thaws after the snow melt. These factors influence snow melt runoff in each of the indicatorI
communities to a different extent.

Snow melt runoff data was available for five urban basins in the Anchorage area, but none wasI
available for Juneau or Bethel. The data for Anchorage (Brabets, 1987, and Billman and Bacon,
1990), collected during spring breakup periods, indicate that daily runoff rate lies generally in the
range of 0.01I to 0.20 inches, but is variable from day to day, due to changes in temperatures, windI
velocity, insolation, and other heat transfer components. The rate of runoff is also influenced by
the amount of impervious area (including frozen ground as well as pavement and buildings), but
this relationship has not been quantified. Snowmelt runoff does not occur until the snowpack is

Stormwater Controls in Coastal Alaska                       -- page 3-3I
June, 1995






        saturated. Saturation, or snow pack ripening, is generated by melting snow or rain trickling
        through the snowpack. Ripening may take a week or more, depending on the initial condition of
        the snowpack and the rate of snowmelt. Rainfall on a snow pack will accelerate the ripening
        process.

        Since the day-to-day variability in temperatures during spring breakup is similar in all three
        municipalities, runoff rates for a specific series of days can be reasonably approximated using
        Anchorage data. A sequence of daily snow melt rates was derived from the Anchorage data, using
        a 30% impervious residential area, and applied to the land development scenarios for Anchorage,
        Bethel and Juneau. The length of the breakup period was determined by a combination of daily
        average temperatures above 32ï¿½ F and the daily snow on the ground record for Bethel and Juneau.
        Both sets of snowmelt data (Billman and Bacon, 1990, and Brabets, 1987) showed an increase in
        snowmelt runoff from developed areas with higher imperviousness. A factor was applied to the
        assumed snowmelt rate from the 30% impervious area to account for this increase. This results in
        an equation of the form:

                       VOL = VOL30 *(1 + (PEIA - 30)*.03)                                      (3)

               where VOL = runoff, inches
                      VOL30 = runoff from 30% impervious site, inches
                       PEIA = percent effective impervious area, expressed as a percent

        This adjustment factor was based on basins varying from 30% to 70% impervious. Use of the
        factor for areas with imperviousness greater than 70% may overestimate the runoff; and for areas
        with less than 30% imperviousness, it may tend to underestimate the runoff.

        Days of snow melt for winter months were defined based on the number of days the maximum
        temperature exceeded 32ï¿½ Fahrenheit. No data were available for runoff from winter thaw events;
        but the initial spring snowmelt may be comparable to winter thaws. During the early part of the
        spring snowmelt, flow rates are in the range of 0.01 to 0.04 inches. These values were estimated
        from 1988 data (Billman and Bacon, 1990). Therefore, a constant snow melt rate was assumed on
        winter thaw days. Some winters may have extremely warm periods, causing greater snow melt
        runoff than this assumption covers, leading to an underestimation of snow melt. Conversely, thaw
        days with no runoff may also occur if there is little or no snowpack, and the constant rate
        assumption would overestimate runoff in that case.

        3.1.4  TSS Loadings

        TSS data is sparse in these areas of Alaska. Where it has been collected, it has rarely been
        correlated to antecedent rainfall conditions or to basin area. No daily data is available for an entire
        year at one site. The TSS data is most often collected in streams, which are not representative of
        developed conditions. Where it has been collected, sampling has occurred in the summer, or
        rainfall, months. Winter thaws and spring snow melt data are very limited.

        TSS sampling data is expressed as a concentration of suspended particles per unit volume of water,
        generally, milligrams per liter (mg/l). TSS loadings represent the mass of suspended particles,

        Stormwater Controls in Coastal Alaska                                                Z page 3-4
        June, 1995

I






generally represented by pounds per day or pounds per year. TSS loadings are obtained by
multiplying the TSS concentration times the flow (times appropriate conversions factors for
disparate units). Thus, a low flow with a high concentration can yield a similar load to a high flow
with a low concentration.

3.1.4.1 Pre-Development TSS Loadings

Pre-development conditions in the three indicator municipalities span the spectrum from bare
ground to natural undisturbed vegetation. The guidance manual specifying the New Development
Management Measure (EPA, 1993) describes pre-development it as follows:

       "...the term pre-development refers to the sediment loadings and runoff volumes/velocities
       that exist onsite immediately before the planned land disturbance and development activities
       occur. Predevelopment is not intended to be interpreted as that period before any human-
       induced land disturbance activity has occurred."

It goes on to say that

       %... management measure option II.A.(1)(b) is not intended to be used as alternative to
       achieving an adequate level of control in cases where high sediment loadings are the result
       of poor management of developed sites e.g. ... sites where land disturbed by previous
       development was not permanently stabilized."

From this, it appears that management measure II.A.(1)(a), the 80%  removal measure, is
applicable to bare or unstabilized sites and that management measure II.A.(1)(b) is more likely to
be applied to sites that were stabilized or are in a naturally vegetated state before development.
Therefore, pre-development TSS was estimated for natural or stabilized sites only.

TSS loadings for undeveloped conditions with natural vegetative cover were based on the
Universal Soil Loss Equation (USLE). This equation takes the form:

              A   R x K x LS x C x P                                                     (4)

       where  A = soil loss, tons/(acre)(year)
               R = rainfall erosion index, in 100 ft - tons/acre x in/hr
               K = soil erodibility factor, tons/acre per unit of R
              LS = slope length and steepness factor, dimensionless
               C = vegetative cover factor, dimensionless
               P = erosion control practice factor, dimensionless

This method was originally developed to estimate the annual sediment yield from small cropland
areas. It calculates annual soil loss in tons per acre, based on rainfall, soil erodibility, site slope
and length, and cover and erosion control practices. Because this method is empirical and the
parameters have been calibrated for agricultural conditions in the lower 48 United States, this
method is not directly applicable for developed urban areas in Alaska. It is somewhat applicable
for the "pre-developed" condition, assuming the effects of natural vegetation on soil loss in these

Stormwater Controls in Coastal Alaska                                                  ~2 page 3-5
June, 1995






        indicator municipalities is similar to effects in the lower 48 states. Another drawback of the USLE
        is that it does not differentiate soil losses attributable to rainfall from those due to snow melt
I     ~ ~runoff.  Since the equation is being used to estimate the annual load from soils with natural
        vegetative cover, it is reasonable to assume that snowmelt would not cause soil loss. Thus, the
        loads predicted by the USLE in this application represent pre-development TSS from rainfall
        events only but could reasonably approximate annual loads as well. This equation does not predict
        TSS concentrations or daily loads.

        3.1.4.2 Post-Development TSS Loadings

        TSS data from urban rainfall and snow melt runoff has been collected in the Anchorage area, but
        not for the same basins. This data were used to generate two relationships; one for rainfall and one
        for snowmelt. The rainfall-runoff-TSS load relationship is based on a regression equation using
        the parameters of runoff, drainage area, and percent effective imperviousness as independent
        variables. The snowmelt-TSS loading relationship uses consecutive thaw day as the independent
        variable.

        The relationship between stormwater runoff and TSS concentrations is based on data from three
        urban basins in Anchorage and shows two distinct patterns. The first pattern is an initial peak of
 3      ~~sediment concentration at the beginning of the storm and then a rapid decrease. The other pattern
        shows sediment concentrations following the fluctuations of the storm's runoff. These patterns
 I     ~reflect two TSS mobilization mechanisms.  An initially high intensity storm mobilizes loose
        sediment readily. This observation follows from the USLE theory. A low intensity storm
        mobilizes sediment at a lower but more constant rate as the sediments are wetted and loosened over
        the course of the storm. It is reasonable to assume that the high intensity storm mobilizes particles
   Iof larger diameter, but it is not known whether the distribution of particle size in the TSS between
        the two storm types is significantly different.

   IRecognizing these limitations, a relationship was established between total storm runoff and TSS
        load. Regression techniques applied to data from these three basins were used to calibrate an
        equation that calculates estimated TSS loads based on the runoff volume, drainage area, and

        percent of effective imperviousness for a given basin (Brabets, 1987). The equation is of the form:
                       SSED = 42.6 * (VOL)(-90 (DA) I 0 I (pEIA)0.71              (5)

                where SSED is suspended sediment load, in pounds
                       VOL is volume of runoff, in inches
                       DA is drainage area in acres
                       PEIA is percent effective impervious area

        This equation is considered to have a high standard error of estimation. However, it is used here,
        where no other information is available. It has been calibrated for basins of less than 38 acres that
    I   have effective imperviousness less than 70%, for storm rainfall events that are less than 0.5 inches.

    I   Since rainfall patterns are expected to be quite similar for Anchorage and Bethel, the calibrated
        equation was used for predicting TSS loads in Bethel. This equation is limited to use on rainfall

    I   Stonmwater Controls in Coastal Ala.ska                                                 J page 3-6
        June, 1995






events of less than 0.5 inches. Even though this limitation is exceeded in Juneau, the application
of this equation led to fairly reasonable TSS loadings for Juneau, so it was used for Juneau as
well. There is no data with which to judge the accuracy of these estimates.

During snowmelt, mean TSS concentrations are typically higher than for rainfall runoff. Data from
Chester Creek (Brabets, 1987) indicates that TSS concentrations in urban snowmelt can be 16% to
400% higher than in rainfall runoff.

Spring thaw TSS concentrations for two urban basins showed two concomitant patterns: a diurnal
fluctuation and a trend through the snow melt period (Billman and Bacon, 1990). On a daily basis,
suspended sediment concentrations peak in the afternoon with peak discharge (Brabets, 1989).
Through the month (more or less) of the snow melt period, the daily concentrations are initially
quite high and then decrease. Therefore, a relationship between day of snowmelt and runoff was
developed based on 1988 data from two basins. It is of the form:

              VOL = 215 - 5.48(DAY)                                                    (6)

       where VOL= runoff, in
              DAY = day of snowmelt period

The constants in this equation are calibrated to 1988 data only. These constants vary from location
to location and year to year, but the downward trend was verified by the Chester Creek data
(Brabets, 1987). The relationship between concentration and day of the snowmelt period was
assumed to be the same for thaw periods during winter months. The magnitude of the
concentrations, however, was assumed to vary over the winter. Because the snowpack tends to
accumulate sand and precipitated airborne materials over the course of the winter, TSS
concentrations are expected to be highest in the spring and lower during an early winter thaw.
Thus, for example, November thaw was assumed to exhibit TSS concentrations similar to those on
day 25 of the spring thaw. The concentrations were multiplied times the flow to obtain TSS loads.

These snow melt patterns were considered to be similar in all three municipalities, although the
magnitudes of concentrations vary. In Bethel where there is little street sanding, the snow melt
concentrations were assumed to be half of those in Anchorage. In Juneau, the Anchorage
concentrations were used.

3.1.5 Summary of Derivation Methods

A summary of the methods used for each location is shown in Table 1. Details regarding the
development of the snow melt and rainfall runoff and TSS loading for each community are given in
the following descriptions.








Stormwater Controls in Coastal Alaska                                                0 page 3-7
June, 1995







                                              Table 1
            Summary of Derivation Methods for Runoff and TSS Loadings

          Variable                Rainfall            Spring Breakup             Winter Thaw
                                                  I  I  Snowmelt                Snowmelt
                                           Anchorage
    Runoff                  Equation (1)             Snowmelt runoff rates   flat 0.03' rate
                                                  from Anchorage basins
                                                  with Equation (3)
    Pre Development TSS    Equation (4)              none                     none
    Loading
    Post Development TSS   Equation (5)              Equation (6) for         Equation (6) for
    Loading                                          concentration;           concentration;
                                                  concentration x flow for  concentration x flow for
                                                  load                    load
                                              Bethel
    Runoff                  Equation (2); CNs for D   Snowmelt runoff rates   flat 0.03" rate
                           soils                   from Anchorage basins
                                                   with Equation (3)
    Pre Development TSS    Equation (4)              none                     none
    Loading
    Post Development TSS   Equation (5)              Equation (6) for         Equation (6) for
    Loading                                          concentration;           concentration;
                                                  concentration x flow for  concentration x flow for
                                                   load                    load
                                              Juneau
   Runoff                  Equation (2); CNs for C   flat 0.03" rate         flat 0.03" rate
                           soils
   Pre Development TSS    Equation (4)              none                     none
   Loading
   Post Development TSS   Equation (5)              Equation (6) for         Equation (6) for
   Loading                                          concentration;           concentration;
                                                  concentration x flow for  concentration x flow for
                                                   load                    load
   Equation 1  VOL = 0.39 * (RF)1'10 (DA)0'14 (PEIA)0-38
                 _(P-.2*S)2
   Equation 2  Q-(P.*S)
                 Q~(P+.8*S)
   Equation 3  VOL = VOL.3 *(1 + (PEIA - 30)*.03)
   Equation4 A=RxKxLSxCxP
   Equation 5  SSED = 42.6 * (VOL)0-90 (DA)1-01 (PEIA)0-71
   Equation 6  VOL = 215 - 5.48(DAY)

3.1.6 Land Development Scenarios

The development scenarios outlined for each municipality are those that can reasonably be expected
to occur. An implicit assumption is that there is no runoff into these sites that must be treated. It is
assumed that the stormwater control practices will be implemented by the developer of the site as
part of site development. These construction costs and the annual and periodic maintenance costs
will be passed along to the buyers or leaseholders. Although there may be some component of
municipal involvement for maintenance, we assumed that the municipality would recoup the cost of
this from the property owners.


Stormwater Controls in Coastal Alaska                                                           D page 3-8
June, 1995







For single family residential development, density was taken as four houses per acre. Of the land
available, 90 percent would be used for housing and 10 percent for roads and other infrastructure,
not including the stormwater control. Thus for a 5-acre residential development size, 18 houses
are expected.

Commercial development was assumed to be retail stores. The building size was assumed to be
one-third of the impervious area of the site. The other two-thirds would be paved.

Industrial development was assumed to be equipment yards and warehouses. The building size
was assumed to be one-half of the impervious area of the site. The other one-half would have
equipment or covered storage.

3.2 ANCHORAGE

3.21   Rainfall

Anchorage precipitation averages 15.3 inches.  TP 47 gives the 2-year/24-hour storm for
Anchorage as 1.5 inches (Miller, 1963). The Municipality of Anchorage (MOA) uses 0.66 inches
for a 2-year/6-hour event. MOA has not established a 24-hour event for any return period. Based
on the depth of the 2-year/6 hour storm, however, the 2-year/24 hour storm event would likely be
less than 1 inch. The monthly rainfall distribution is shown in Figure 2. This figure shows that
the peak precipitation period is in the months of July through September. Rainfall greater than 0.5
inches occurs approximately 5 days a year.

                                              Figure 2
    Anchorage Mean Monthly Precipitation Distribution - 1923-1984 and 1991



    7     - - -- -- - --- - --- - -- - - ----- --------  ------ - -- -  --






  0V4 4:                                                               ! /   /\--C-Mean Monthly Total (in);
                                                                             '--Me,/  an No of days > 0.1 In I
  **                             r              /I~  ]                 I X~~ o,---Mean No of days > 0.5 in 
                                                                               !   1965 Month Total tin)


    2




    0-           -    -_
      c                                                              i -   >,    =                           B a,   2i   8
                                      Month

Source: Leslie, 1986 and NOAA, 1965                                                                          1


Stormwater Controls in Coastal Alaska                                                 Q page 3-9
June, 1995







3.2.2  Runoff

The Anchorage spring break up period is generally from mid March through mid April. Summer
rains occur from the end of April through the middle to end of October. A daily runoff relationship
for snow melt and for rainfall was developed for Anchorage, on a depth per unit area basis. The
rainfall runoff relationship was developed on Chester Creek by the USGS (Brabets, 1987). The
snow melt relationship was based on data from two residential basins and adjusted for percent
imperviousness.

3.2.3  Soils and Drainage Conditions

Anchorage lies in a gently sloping bowl, although some developable land is located up stream and
river valleys. The soils in the Anchorage area are glacial till. Some sites are on gravel or sand
where the soils are highly permeable, but the majority of developable sites will be on relatively
impermeable soils or near surface bedrock. The developable areas are drained by well defined
creeks.

3.2.4  TSS

Total suspended solids data has been collected by the United States Geologic Survey (USGS) from
6 creeks in the Anchorage area. Most of the Anchorage area USGS data is based on stream
sampling, which includes base flow, and generally represents runoff from several land use
categories. One USGS report (Brabets, 1987), however, presents rainfall and snow melt runoff
data from one commercial and one residential basin, and some in-stream data from an undeveloped
basin. Snow melt data has been collected from two residential basins by the Municipality of
Anchorage (Billman and Bacon, 1990).

Pre-development TSS loading for Anchorage was based on the Universal Soil loss equation.

Post-development TSS loading for Anchorage was based on the TSS-runoff relationship
developed by the USGS (Brabets, 1987).

3.25  Expected Site Development Types

According to the MOA Department of Community Planning and Development (Weaver, 1995),
Anchorage residential development is generally in the 2.5 to 5 acres range; a 40 acre site is
considered large. Commercial site sizes are dictated by the amount of parking and percentage of
landscaping required. Industrial sites are generally graveled. Assumed land uses and types are as
follows:

          Residential       5 ac     4 houses per acre                38% impervious
          Commercial        10 ac     123,000 sf retail store         85% impervious
          Industrial        10 ac     109,000 sf warehouse/office    50% impervious



Stormwater Controls in Coastal Alaska                                               D page 3-10
June. 1995






3.2.6  Typical Year

The Municipality of Anchorage has identified 1965 as its typical rainfall year (Wheaton, 1995).
The snow melt runoff pattern for March and April, 1988, were used to simulate runoff. Winter
thaw periods in the months of November through February were based on the number of days
that, on a long-term average basis, the maximum daily temperature exceeded 32ï¿½ F. During the
winter thaw days, the number of thaw days per month was reduced by two, to account for the time
it would take for the snowpack to ripen before runoff occurs.

The rainfall-runoff pattern for Anchorage for the typical rainfall year is shown in Figure 3. Two
runoff peaks, one in April and one in August, illustrate the bimodal runoff, from snowmelt and
rainfall.

                                         Figure 3
         Anchorage Monthly Rainfall-Runoff Distribution for Typical Year




           4.5I

           3.5                                                                  __
             3-                                               --- Rainfall
                                                             2--- Residential Runbff
                       x" \ /~\                           ~  r--Commercial Runoffi

                     i1v".5           ~/~,~ ~i,          I  ! X  Industrial Runoff

             0
                 LLO 'M   <.0             0) z.~ 

                                  month


The cumulative TSS loading for the typical Anchorage year is shown in Figure 4. This figure
shows the loadings due to runoff from development for each land use category. It also shows the
total annual predevelopment load from each of the land use categories on the right side of the
graph.











Stormwater Controls in Coastal Alaska                                              'l page 3-11
June, 1995








                                            Figure 4
               Cumulative Pollutograph for Anchorage for Typical Year



     3500                -

     3000 -

    2500

    2000 ---- ---Residential
                                                           2000      =,---- Industrial
  a                                                        .                 -_.___Commercial
                                                      - f......... _-ANNUAL PreDev Res
     1500 So                                                                  .     ANNUAL PreDev Ind & Comrn

     1000 

             Soo C          -       _. rC        0      ï¿½ ._, __ _ . _-
       5                                 =0    0 -'   CP---'~-d
                                            7~~~~~~~~~    '
         .---, .___ . _
       o   ~'--"'*/----

            (sC   e   -  _   _                               --_N_6
                                      date


A summary of the hydrologic characteristics of each land development scenario is shown in Table
 2.

                                            Table 2
  Hydrologic Characteristics of Each  Land  Development  Scenario for Anchorage

                                                               Land Use Type
      Variable         Condition        Units      Residential         Industrial       Commercial
           ~Arem~a  |                   acres           5                 10                 10
  % Impervious                            %             38                 50                85
  Rainfall   (May - Sept)               inches          9.45 9.45                            9.45
  Rainfall Runoff    Pre Development    inches          1.01              1.01               1.01
  Depth
                   Post Development   inches          2.81               3.43              4.20
  Snowmelt Runoff Pre Development    inches            0.35               0.35               0.35
  Depth
                   Post Development   inches          2.74               3.53              5.85
  TSS Loadings      Annual Pre            lbs           240                560               560
                   Development
                   Annual Post           lbs           699               1942              3322
                   Development
                   Summer Post           lbs           338               992               1734
                   Development
  Removal Required for Pre=Post           %             29%               44%                68%
  Conditions - Summer
  Median TSS        Annual Post          mg/l           128                148               187
  Concentrations    Development
                   Summer Post          mg/I           131                157               224
                   Development
  Maximum 6-hr    Summer Post             cfs           0.17              0.43               0.52
  flow              Development
  Median 24-hr flow Summer Post           cfs           0.01              0.02               0.03
                   Development

                       ~~~~~~~~~WIN_
Stormnwater Controls in Coastal Alaska                                                         0 page 3-12
June, 1995








3.2.7  Local Regulations

The population of Anchorage is greater than 100,000 so the MOA must comply with the National
Pollution Discharge Elimination System permit requirements for stormwater runoff. In the course
of applying for this permit, the MOA has modified its Municipal Code to implement regulatory
control over stormwater discharge. In particular, the MOA has identified TSS as a pollutant for
which it can require treatment or removal. The MOA has not established performance objectives
for stormwater control and currently defers to the Alaska Department of Environmental
Conservation (ADEC),which is the agency that can legally enforce its own performance objectives.
In the interim, until the MOA establishes performance criteria, it will not issue a developer the
authority to proceed without review by the state.


3.3  BETHEL

3.3.1  Rainfall

Bethel's annual precipitation is 16.9 inches. The 2-year/24-hour storm for Bethel is 1.5 inches
(Miller, 1963). The rainfall distribution is shown in Figure 5. The highest precipitation occurs in
August, and less than 5 days a year have rainfall depths greater than 0.5.

                                             Figure 5
       Bethel Mean Monthly Precipitation Distribution - 1923-1984 and 1991





    8                                                                                                     I


    71


                                                                               '=l-Mean Monthly Total (in)
                                                                               ?'--Mean No of days 0.1 In
                                                                               i---Mean No of days 0.5 In
                                                                            4 4.199 Month Total (in)

    34                                                                                                    I
    2


      ci                                                                                                   I
    0-

                                      Month

Source: Leslie, 1986 and NOAA, 1991




Stormwater Controls in Coastal Alaska                                               0 page 3-13
June, 1995






3.3.2  Runoff

The TR-55 method was used to generate runoff from rainfall events in Bethel. Since the majority
 of rainfall is of low intensity, this method predicts very low runoff. In Bethel, total snowfall is
somewhat less than Anchorage. Snowpack is also smaller than Anchorage, due to wind effects.
Both of these factors lead to a shorter snow melt runoff period than Anchorage in general. Colder
temperatures in April cause the snow melt period to occur later than in Anchorage.

3.3.3 Soils and Drainage Conditions

Bethel is located on the banks of the Kuskokwim River in southwestern Alaska. Bethel's soils are
predominantly silts underlain by permafrost and are generally impermeable. This, and the lack of
relief in area, create standing water following rainfall and snow melt events. Consideration for
permafrost conditions has necessitated the construction of elevated roadways and above ground
utilities. Scraping and grading of sites is generally limited to work on the constructed pads. Only
one five mile road is paved; the rest are gravel or native soil. Very little, if any, sand is applied to
the streets in the winter. Consequently, the primary source for sediment loading is erosion of the
roadways and embankments. The primary stormwater structures are ditches and culverts. Most of
the drainage is diffuse, with only one well defined creek running through the town.

3.3.4 TSS

There is no suspended sediment data for the Bethel urban area.  Suspended sediment data is
available for the Kuskokwim River, but this data is not representative of urban runoff TSS.

Pre-development conditions were estimated based on the USLE. A generalized regional analysis
indicates that non glacial streams in the region probably do not normally exceed 100 mg/I in
suspended sediment in the summer (Feulner, 1972).

The post development TSS loading for the Bethel area was assumed to be half the rate of the
Anchorage area for snow melt runoff. In Bethel, roads are not typically sanded in the winter and
streets and parking lots are not typically paved.

3.3.5   Expected Site Development Types

Bethel residential development is generally in the 2.5 to 5 acres range. The minimum lot size is
9,000 square feet. Commercial site sizes are small, generally accommodating such individual
enterprises as a store or a bed-and-breakfast. No new industrial sites are likely to be developed;
most industry is maritime and operates off-shore, on the Kuskokwim River. No street or parking
lot paving is required, so the percent impervious is lower than that in more urban communities.

           Residential       5 ac      4 houses per acre                25% impervious
           Commercial        2 ac                                       40% impervious
           Industrial        not anticipated



*Str mwater Controls in Coastal Alaska                                                0 page 3-14
June, 1995






3.3.6 Typical Year

1991 was identified because of its near normal annual precipitation and average March 31
snowpack. The March 31 snowpack was used as an indicator of the snow melt season, and to
evaluate if the chosen year were typical or not. Rainfall and thaw events were taken from the
climatological record for the year. The 2-year/24 hour rainfall was not exceeded on any day in
1991.

The runoff pattern for Bethel is shown in Figure 6. Two peaks, one in April and a smaller one in
September, illustrate the runoff from snowmelt and rainfall.

                                        Figure 6
           Bethel Monthly Rainfall-Runoff Distribution for Typical Year



      1.80
      1.60
      1.40 -
      1.20 -
      10o -                                                                    Rainfall
   t/ \                   :                                                A, Residential
      0./0                                                                ---- Commercial        :
      0.60A/\
      0.40-.
      0.203
      0.00 -


                                  month


The cumulative TSS loadings for the typical Bethel year are shown in Figure 7. This figure shows
the loadings due to runoff from development for each land use category. It also shows the total
annual predevelopment load from each of the land use categories on the right side of the graph.






                        !~~~~~~~~~~~~~~~



Stormrwater Controls in Coastal Alaska                                               0 page 3-S5
June, 1995







                                                 Figure 7
                    Cumulative Pollutograph for Bethel for Typical Year



       1.40 -    -
            1~~~~~.d.O .. ... . ............. ... ........................................

                      1 00 ~ ~         ~         ~         ~        .-
                                              r_   or~~~1~
                                            _~~~~~~~~~~~~~~~~~~~~~~~~~~

        8 0 -                                                                             R|icental.
                                                                                    --- __ _ComnerclSl
                                           /                                        ~~~~~~~~~~-....ANNUAL PfDev ARes
        6 0 --                                          --.-   ANN--J-,-eDev -nmm

        4 0 

                          d.                          '--H
        20

         0                                                                    --
                         - a a g- = = - -               - - - - -
                                            date



 A  summary of the hydrologic characteristics of each land development scenario is shown in
 Table 3.

                                                 Table 3
       Hydrologic Characteristics of Each Land Development Scenario for Bethel

                                                                         Land Use Type
             Variable    I  Condition             Units          Residential       Commercial
         Area             I                        acres               5                 2
         % Impervious     I                         %                 25                40
         Rainfall  (May - Sept)                    inches            6.67               6.67
         Rainfall Runoff   Pre Development         inches            0.03               0.03
         Depth
                           Post Development        inches            0.39               0.55
          Snowmelt Runoff Pre Development          inches             0.24              0.24
         Depth
                           Post Development        inches             1.29              1.97
         TSS Loadings      Annual Pre               lbs                85                15
                           Development
                           Annual Post              lbs               140               45
                           Development
                           Summer Post              lbs               42                 16
                           Development
         Removal Required for Pre=Post               %               -100%               8%
         Conditions - Rainfall
         TSS               Annual Post              mg/l               81                81
         Concentrations    Development
                           Summer Post             mg/l               107               140
                           Development
         Maximum 6-hr    Rainfall Post              cfs               0.13              0.03
         flow              Development
         Average 24-hr flow Summer Post             cfs              0.003             0.001
                           Development


I~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 Stormwater Controls in Coastal Alaska                                                         3 page 3-16
 June, 1995







Calculated TSS loadings in Bethel decreased under developed conditions. We believe this wouldI
not be the case, for two reasons. A good cover of natural vegetation in the predevelopment
conditions limit sediment loss. Developed conditions generally involve pad or elevated road
construction, on which both the side slopes and horizontal surfaces are generally more vulnerableI
to erosion than predevelopment conditions. The predevelopment loads are most likely lower than
those predicted by the USLE, which is especially sensitive to rainfall energy and the slope of the
site. The post development loads are probably underestimated. Even though the sites have lowI
percentages of imperviousness, the native soils are also highly impervious, as well. Because of
the lack of data for Bethel with which to verify these results, they should be considered with
skepticism. They do not provide a strong basis for development of target removal levels of TSS.I
However, because of other site specific conditions, no BMPs that can be designed to meet targeted
removal levels are practical for Bethel.

3.3.7 Local Storm Drainage Regulations

Bethel has a Coastal Management Plan, which requires a review of subdivision plats.  TheI
municipal ordinance requires that drainage channels on private property be preserved and requires
the installation of culverts where these channels are crossed by driveways or roads. There are no
minimum landscaping requirements for commercial or industrial development, although the lots
have minimum setbacks.

34 JUNEAU

3.41   Rainfall

Annual rainfall in southeast Alaska is much greater than in south-central or western Alaska.
Juneau's climate is typically much rainier than either Bethel or Anchorage, but is highly variable
even within the developed area of the City and Borough of Juneau (CBJ). The average annual
rainfall in downtown Juneau (90 inches) is nearly twice that at the airport (52 inches). Data from
the weather station at the airport were used in this study, because published records were moreI
complete in recent years. In addition, new development is more liely to occur north of town than
in the town proper. Use of the airport data will lead to an underestimation of the runoff, and
therefore TSS, in some parts of Juneau. The 2-year/24-hour storm for Juneau is 3.0 inches
(Miller, 1963).

The rainfall pattern for the airport weather station is shown in Figure 8. The maximumI
precipitation occurs in October. Precipitation exceeds 0.5 inches on 28 days a year. Although the
shape of these curves is similar for the downtown weather station, the magnitude, both in inches
and in days of exceedence is higher. There are 61 days a year when precipitation exceeds 0.5
inches.






Sic rmwater Controls in Coastal Alaska                                              C2 page 3-17I
June, 1995







                                               Figure 8
             Juneau Mean Monthly Precipitation Distribution - 1949-1984 and 1987


           18 -,


            14
           12
         a 10                               "-- -Mean Monthly Total (in)
                                                                          -4i--Mean No of days 0.1 in
                                                                           -a-mean No of days 0.5 in
            a ,,-m-,-1987 Month Total (in)


            4



                        . -IC           C   _
                                        Month

       Source: Leslie, 1986 and NOAA. 1987

       3.42  Runoff

       The TR-55 method was used to generate runoff from rainfall events in Juneau. Rainfall tends to
       persist over consecutive days; so adjustments were made (to the assumed CN) to account for
       antecedent moisture conditions, which generally result in higher runoff.

       Juneau's snow melt events include more frequent winter thaw events, including winter rains and
       earlier spring snow melt events than south-central or western Alaska. Some Juneau winters are
       dominated by rainfall runoff events, rather than snow and thaw events..

       3A3  Soils

      The high relief of the Juneau area has led to development along the coast and up stream and river
       valleys. The soils in the flood plains of these streams is silty. Soils on the uplands are either thin,
       underlain by bedrock or thicker glacial till deposits, which are firm and compact. Although there
       are tracts of well drained soil, the soil conditions generally impermeable.  Storm runoff in
       developed areas is handled by a combination of underground storm sewers, ditches, and culverts.
      The developed areas are drained by creeks.

       3A4   TSS

      Total suspended solids data has been collected by the United States Geologic Survey (USGS) from
       creeks in the vicinity of Juneau. The TSS data collected from these streams is associated with
      mining activity and is not applicable to this study because the sites are much higher in elevation
       than the area where development may occur.  Rainfall and snowmelt runoff conditions in

      Stormwater Controls in Coastal Alaska                                               J page 3-18
      June. 1995


 







southeastern Alaska are strongly affected by elevation, which reflects both orographic and
temperature effects. The Alaska Department of Environmental Conservation (Richards, 1993)
presents stream water quality data for 15 streams and rivers in the Juneau area. This data does not
include the drainage area above the sampling point, instantaneous stream flow, or antecedent
rainfall or snow melt conditions. This data can provide general ranges for the summer months.

The rainfall period was taken as the months of February through October. A TSS loading based
on the Anchorage area runoff relationship was used. The snow melt runoff and TSS loading
developed for Anchorage was used for winter thaw periods.

3A5  Expected Site Development Types

According to the CBJ's Department of Planning, Juneau's new development is generally
characterized as in-filling. Its residential development is generally in the range of 5 acres range. A
typical commercial site size is 15 acres. Industrial sites are generally graveled.

          Residential       5 ac      4 houses per acre               40% impervious
          Commercial        15 ac    retail store                     85% impervious
          Industrial        20 ac     218,000 sf warehouse/office    50% impervious

3A.6 Typical Year

For Juneau, 1987 was identified as the year with total rainfall closest to the long term average.
However, the winter snowfall was below average this year, and the winter temperatures above
average. This led to a higher percentage of the runoff due to rainfall, with consequently lower TSS
concentrations through the winter.

The runoff pattern for Juneau is shown in Figure 9. Two runoff peaks, in June and October,
illustrate the runoff from rainfall.

                                         Figure 9
           Juneau Monthly Rainfall-Runoff Distribution for Typical Year



      1o.oo - 
       1.00 -
       8.00 -
       7.00 --                                 /        \
       6.00--                                  /           '   i  i-Raintall
   S  5.00 -                      / A        /      A      XWN~ ii--  Residential Runoff
       e -0                      /  \       J                      -Tin  \  A- ; --lndustrial Runoff
            ago4.00                                                  4-- Commercial Runoff
       3.00-

       I.00 I
       0.00 -

                                  month



Stormwater Controls in Coastal Alaska                                               Q page 3-19
June, 1995









The cumulative TSS loadings for the typical Juneau year are shown in Figure 8. This figure
shows the loadings due to runoff from development for each land use category. It also shows the
total annual predevelopment load from each of the land use categories on the right side of the
graph.

                                        Figure 10
                Cumulative Pollutograph for Juneau for Typical Year





       16000

       14000

       12000 -
                                                        f ....- Residential
     n 10000                                                         ----Industrial
           F                                       J                 -Commercial
                       8O~~~~~~~~~~ .............00             ,ANNUAL PreDev Res
         6000-                                                       - ''ANNUAL Pre Dev Ind
         8  000-         -:~.                                              omeca
                                                        __  ',  ~ -ANNUAL Pre Dev Comm
        4000 -                     _- -

        2000-  -                                            _

           0-,-.- .- ... ...             . .....
             C C .0.0D  - ~- ~- > CC - - 0)0)0. 0. ,  > > C.) C.)
            n n IL tL L    <           M;nnn8 <i  )t    z z D
                C  N _U NC CU -..    N            00_00000N 

                                     date



A summary of the hydrologic characteristics of each land development scenario is shown in
Table 4.





















Stormwater Controls in Coastal Alaska                                                O page 3-20
June, 1995







                                          Table 4
    Hydrologic Characteristics of Each Land Development Scenario for Juneau

                                                            Land Use Type
       Variable     I Condition       Units    Residential      Industrial    Commercial
   Area              I                 acres         5               20             15
   % Impervious                         %            40              50             85
   Rainfall    (Feb-Oct)               inches       38.54          38.54           38.54
   Rainfall Runoff   Pre Development   inches       1.41            1.41            1.41 
   Depth
                     Post             inches        6.59           8.17            19.18
                     Development
   Snowmelt Runoff   Pre Development   inches       0.04            0.04            0.04
   Depth
                     Post             inches        0.67           0.82            1.36
                     Development
   TSS Loadings      Annual Pre         lbs         480             2500            1785
                     Development
                     Annual Post        lbs         1285           7351           17782
                     Development
                     Summer Post        lbs         879            5106           12544
                     Development
   Removal Required for Pre-Post %                  45%             51%             86%
   Conditions - Summer
   Median TSS        Annual Post       mg/l          127            157             214
   Concentrations    Development
                     Summer Post       mg/I         133             163            222
                     Development
   Maximum 6-hr flow Summer Post        cfs         0.53            2.40            3.10
                     Development
   Median 24-hr flow   Summer Post      cfs         0.01            0.03            0.05
                     Development

3.4.7 Local Storm Drainage Regulations

Juneau has a Coastal Management Plan which includes stream setbacks. The CBJ is currently
working with the ADEC on two streams in the borough that have been identified as impaired.
Developers in the CBJ have been required by ADEC to install stormwater controls on their project,
after site specific review.

3.5 LOCAL ECONOMIC CONDITIONS

The economic indicators for each community are summarized in the Table 5. The figures that were
available included population, municipal full value determination, total municipal revenue, median
annual household income, and median owned-house value. Population and tax base extend over
several orders of magnitude, although household income and median home price indicators are
comparable.






Stormwater Controls in Coastal Alaska                                                  C page 3-21
June, 1995







                                                Table 5
                       Economic Features of Indicator Municipalities

                 Feature                     Anchorage              Bethel               Juneau
  Incorporation Type                     Unified Home Rule   Second Class City   Unified Home Rule
                                         Municipality                             Municipality
  Population                             248,296              2,009                29,078
  Area (sq mi)                           1,698                44                   2,594
  Population Density (per sq mi)         146                  46                   11
  Property Tax (mils)                    16.23                none                 14.02
  Total Municipal Revenue                $790,239,935         $9,729,980           $121.312,436
  Municipal Full Value Determination (tax $12,295,898,030     $184,121,800         $1,765,984,100
  base)
  Median Household Income                $43,946              $45,203              $47,924
  Median Owned Home Price                $109,700             $82,000              $113.500
  Source: Alaska Department of Community and Regional Affairs, 1995










































Stormwater Controls in Coastal Alaska                                                           -7 page 3-22
June. 1995






4.0 MANAGEMENT PRACTICES



41 SURVEY OF APPLICABLE BEST MANAGEMENT PRACTICES

In the previous section, typical annual pre and post development TSS loads for coastal Alaska were
estimated. In this section, methods for reducing the TSS loadings, known as best management
practices (BMPs), in coastal Alaska are presented.

Although scores of best management practices have been recommended and used throughout the
lower 48 states, Alaska's climatological conditions limit the applicability of many of them. We
have completed a draft survey of potential BMPs for stormwater pollution prevention, with an
extensive and thorough summary of their applicability to Anchorage conditions, for the
Municipality of Anchorage (MW, 1994). That document and three sources (Scheuler, 1987,
Scheuler, 1992, EPA, 1993) were reviewed for applicability to the municipalities and land
development types targeted in this study.

Twenty best management practices (BMPs) are outlined on Tables 6 and 7. Table 6 includes 11
non-structural practices. Table 7 includes 9 structural practices This list has been developed to aid
in the selection of Best Management Practices (BMPs) for new development projects in coastal
Alaska, particularly for the scenarios used for the cost analysis in this study.

In the first column, a code indicating the function of the BMP is listed. The BMPs are arranged in
the following categories:

       Source            BMPs Which Reduce Pollution at Their Source

       Erosion           Erosion, Sedimentation and Drainage BMPs

       Vegetative        Vegetative BMPs

       Retention         Retention/Detention and Flow Regulation BMPs

       Filtration        Filtration and Infiltration BMPs

The second and third columns gives the name and a description of the BMP.

The fourth column describes site specific constraints, clarifies how the BMP may be applied and
may mention unusual maintenance conditions (e.g. a BMP has a very short life even with proper
maintenance).

The fifth through seventh columns gives a ranking for each municipality. The identified BMPs are
ranked for their applicability to each of the three indicator municipalities and the land use scenarios
developed for the cost analysis. The rankings are based on professional judgment, weighing such
factors as:

Stormwater Controls in Coastal Alaska                                                  D page 4-1
June, 1995







    *   site size
    ï¿½ soil type
    * slopes less than 5%
    * maintenance requirements
    *  climatic conditions
    * community acceptance
    * constructibility in given community
    *  existing storm drainage infrastructure

The ranking for non-structural (NS) and structural (S) BMPs are separate, with 1 being the most
effective in the given category for the given municipality. Entries of N/A indicate that the BMP
would not be applicable to the municipality.






































Stormwater Controls in Coastal Alaska                                                       3 page 4-2
June, 1995





                                                                                  Table 6
                                                            Non-structural Best Management Practices


             Non-structural                   BMP Description                     Constraints, Applications, and Unusual          Rank of         Rank of         Rank of
Function      OPNm
               Function BMP Name Maintenance Conditions                                                                        Applicability   Applicability   Applicability
                                                                                                                               to Anchorage      to Bethel       to Juneau

Source       Maintenance of   Ensure that all urban runoff facilities are
             urban runoff      operated and maintained properly. Maintenance
             facilities        should occur at regular intervals, be performed
                               by one or more individuals trained in proper
                               inspection and maintenance of urban runoff
                               facilities, and be performed in accordance with
                               the adopted standards of the State or local
                               government (EPA, 1993).


Source       Setback           Setback distances should be determined on a      In level or gently sloping terrain, a general        8                4               7
             distances near    site-specific basis since several variables may  rule of thumb is to establish a setback of 50
             wetlands,         be involved such as topography, soils,           to 100 feet from the edge of the wetland or
             waterbodies, and  floodplains, cut-and-fill slopes, and design     riparian area and the right-of-way. In areas
             riparian areas    geometry (EPA, 1993).                            of steeply sloping terrain (20 percent or
                                                                                greater), setbacks of 100 feet or more are
                                                                                recommended. Right-of-way setbacks from
                                                                                major waterbodies (oceans, lakes, estuaries,
                                                                                rivers) should be in excess of 100 to 1,000
                                                                                feet (EPA, 1993).


Source       Residential road  Plan residential roads and streets in accordance   Narrower streets would reduce the quantity         10               6               6
             and street        with local subdivision regulations, zoning       of runoff and accompanying pollutants.
             planning          ordinances and other local site planning
                               requirements.





                                                                                  Table 6
                                                        Non-structural Best Management Practices (cont.)


             Non-structural                   BMP Description                      Constraints, Applications, and Unusual          Rank of          Rank of Rank of
Function      BMP Name                                                                     Maintenance Conditions               Applicability   Applicability   Applicability
                                                                                                                              to Anchorage       to Bethel       to Juneau

Source       Retain existing    Do not alter wetlands or riparian areas to        In general, the location of surface water             I I             2                I
             functions of       improve their water quality function at the       runoff ponds or sediment retention basins in
             wetlands and      expense of their other functions (EPA, 1993).    healthy wetland systems should be avoided
             riparian areas                                                       (EPA, 1993).


Source       Sweep, vacuum,   Sweeper technologies used in conjunction with   Equipment types commonly used for street                  2              N/A               2
             and wash          other BMPs that are effective in trapping fine     sweeping include abrasive brush and vacuum
             parking lots       solids could improve downstream water quality   device sweepers. A newly developed helical
                               (NVPDC, 1987).                                    brush sweeper that incorporates a steel brush
                                                                                with vacuum has been shown to be more
                                                                                effective at removing fine solids and is
                                                                                currently being evaluated (NVPDC, 1987).


Source       Preserve natural   Natural drainage features infiltrate and attenuate                                                     3                3               3
             drainage          flows and filter pollutants. Depressional storage
             features and      areas reduce runoff volumes and trap pollutants
             natural           (EPA, 1993).
             depressional
             storage areas


Source       Snow storage       Sites designated to keep melt water runoff from   Prevent dumping of accumulated snow into             5                7                5
                               overloading streams with pollutants. New sites   surface waters (EPA, 1993).
                               should provide containment and appropriate
                               treatment (HDR and CH2M Hill, 1993).






                                                                                   Table 6
                                                        Non-structural Best Management Practices (cont.)


             Non-structural                   BMP Description                      Constraints, Applications, and Unusual          Rank of          Rank of         Rank of
Function    IBMP Name                                                                      Maintenance Conditions               Applicability   Applicability   Applicability
                                                                                                                               to Anchorage       to Bethel      to Juneau

Source       Alternative        Apply sand in controlled amounts based on                                                              4               N/A               4
             sanding           temperature and road conditions.
             practices


Erosion      Minimize           Restrict paving and the use of non-porous cover                                                        9               N/A              10
             imperviousness   materials in recharge areas (EPA, 1993).


Erosion      Reduce the         Pollutant loading from impervious surfaces may                                                         7               N/A               9
             hydraulic         be reduced if the impervious area does not
             connectivity of   connect directly to an impervious conveyance
             impervious        system (EPA, 1993).
             surfaces


Vegetative   Retain existing    Clear only those areas that are essential for                                                          6                5               8
             vegetation        completing site construction. Avoid disturbing
             wherever          vegetation on steep slopes or other critical areas.
             feasible          Route construction traffic to avoid existing or
                                newly planted vegetation. Protect natural
                                vegetation with fencing, tree armoring, retaining
                                walls, or tree walls (EPA, 1993).






                                                                                   Table 7
                                                                Structural Best Management Practices


                Structural                     BMP Description                      Constraints, Applications, and Unusual          Rank of          Rank of         Rank of
Function      BMP Name                                                                     Maintenance Conditions                Applicability   Applicability   Applicability
                                                                                                                                to Anchorage       to Bethel       to Juneau

Vegetative   Vegetated filter   Low gradient area of land with vegetative cover  In coastal Alaska, vegetated filter strips will        2                4               2
             strip              that is designed to intercept runoff as overland    be limited by a fairly short growing season
                                sheet flow from upstream development (EPA,        and will not be effective during initial
                                1993).                                           snowmelt.



Vegetative   Grassed swale    An earthen conveyance system in which               In coastal Alaska, grassed swales will be             4                3               4
                                pollutants are removed from urban stormwater    limited by a fairly short growing season and
                                by filtration through grass and infiltration      will not be effective during initial snowmelt.
                                through soil (Schueler, Kumble, and Heraty,
                                1992).


Vegetative   Seeding and        Seeding with erosion protection blankets                                                                7                1               7
             mulch/mats for   protects road and pad side slopes while the
             side slope        vegetation becomes established (EPA, 1993).
             protection        Erosion protection blankets are tacked in place
                                and can be made of straw, jute netting or nylon
                                fiber. Seeds can be incorporated into the
                                blanket to provide the necessary ground cover
                                to curb erosion and aid plant establishment.


Vegetative  Vehicle surface   On roads and in parking and storage areas           Gravel caps are the prime example of this             6               2                6
             preparation       where asphalt and concrete are too expensive,      method. Permazyne, a chemical soil
                                an alternative soil cap is beneficial to counter  additive, is in the research stage in rural
                                wind and water erosion.                           Alaska. Soil cement is an older technology
                                                                                 that may serve this function.





                                                                                    Table 7
                                                            Structural Best Management Practices (cont.)


Function    Structural          BMP Description                                     Constraints, Applications, and Unusual          Rank of          Rank of         Rank of
             BMP Name                                                                      Maintenance Conditions                Applicability   Applicability   Applicability
                                                                                                                                to Anchorage       to Bethel       to Juneau

Detention    Extended           A pond which temporarily detains a portion of                                                          5               N/A               5
             detention pond    urban runoff for up to 24 hours after a storm,
                                using a fixed orifice to regulate outflow at a
                                specified rate, allowing solids and associated
                                pollutants the required time to settle out.
                                Normally dry between storm events and does
                                not have any permanent standing water.
                                Provides greater flexibility in achieving target
                                detention times (EPA, 1993).


Detention    Wet pond (also   A basin designed to maintain a permanent pool                                                            I              N/A
             called            of water and temporarily store urban runoff
             sedimentation     until it is released at a controlled rate. (EPA,
             basin)             1993).


Detention   Catch basin         In its simplest form, a catch basin is a single-                                                       3              N/A               3
             (water quality    chambered urban runoff inlet in which the
             inlet)            bottom has been lowered to provide 2 to 4 feet
                                of additional space between the outlet pipe and
                                the structure bottom for collection of sediment.
                                Several designs exist (EPA, 1993).


Detention   Catch basin with  A water quality inlet with a second chamber                                                              8              N/A               8
             sand filter (water  containing a sand filter to provide additional
             quality inlet)    removal of finer suspended solids by filtration.
                                The first chamber provides effective removal of
                                coarse particles and helps prevent premature
                                clogging of the filter media (EPA, 1993).





                                                                                 Table 7
                                                         Structural Best Management Practices (cont.)

Function    Structural         BMP Description                                    Constraints, Applications, and Unusual         Rank of         Rank of         Rank of
            BMP Name                                                                    Maintenance Conditions               Applicability   Applicability   Applicability
                                                                                                                            to Anchorage      to Bethel      to Juneau

Infiltration  Porous           A porous asphalt through which runoff is                                                             9              N/A              9
            pavement and      diverted into an underground stone reservoir,
            permeable         gradually exfiltrating out of the stone reservoir
             surfaces          into the subsoil (EPA, 1993).







4.2 TYPE OF DEVELOPMENT AND BMP FOR EACH LAND USE3

The II.A.(l)(a) management measures for controlling TSS in runoff from new development is
expressed as 80% removal of TSS. The second management measure, prescribing that post3
development TSS load equal predevelopment loads, can also be expressed as a percentage, when
the pre and post development loads are known. The percentage efficiency of the BMP is calculated
by dividing the mass of settled TSS by the mass of the total incoming TSS. These percentages3
establish target levels of TSS removal.

Non-structural BMPs have proved effective in removing TSS, but cannot be managed to meet3
targeted removal levels. Vegetative structural BMPs have also proved effective, even in northern
climates (Marshall, 199 1), but cannot be designed to remove a targeted level of TSS. This is due
both to lack of information to aid in developing design methods as well as the variability of
performance in the field. .Performance is highly dependent on proper construction and
maintenance. The only structural BMPs that can be designed to targeted reduction levels include
detention and infiltration methods.
Infiltration methods, which include retention facilities and infiltration structures, are not applicable
in areas where soils are relatively impervious.  This is always the case in Bethel, which hasI
uniformly silty soils. It is the general case in Anchorage and Juneau. In Anchorage and Bethel,
and to a lesser extent in Juneau, infiltration methods are only functional for the times of the year
when they are neither covered by snow nor frozen. Because of these limitations they were notI
considered to be effective.

Detention methods detain storm water. While the water is detained, sedimentation occurs, whichI
lowers the TSS concentration in the outflow. Gravity detention structures (those not requiring
mechanical equipment such as pumps) require excavation in order for water to flow by gravity. In
Bethel, construction requiring excavation is not feasible due to the high groundwater table andI
permafrost conditions. In Juneau and Anchorage, detention facilities, either water quality inlets or
sedimentation basins, have been used on site specific bases. Since these are considered to prove
more effective than infiltration methods, they were chosen for the cost analysis rather than
infiltration methods.

Detention BMPs remove TSS by settling suspended particles. Under passive treatments (that is,
with no chemical or physical controls), settling occurs by precipitation. Particle set'tling is
influenced by three factors: settling velocity, flow rate and surface area of the detention facility.
These factors are related by the following equation:


              Vs
       where Q = flow rate, cfs3
              Vs = particle settling velocity, ft/sec
              A = basin surface area, sq ft



Storm water Controls in Coastal Alaska                                                  Jpage 4-8            I
June, 1995






        Settling velocity is dependent on water temperature and particle shape and diameter. The colder
        the water, the smaller the particle diameter, and the less spherical the particle, the slower the
        particle settles. The suspended particles that make up TSS vary in diameter and shape. Clay
        particles settle very slowly, if at all, because of their planar shape. Turbulence and wind action
3      ~~create conditions under which smaller particles do not follow this equation, because the lift forces
        counteract gravity and they cannot settle. Experience has shown that it is usually physically
        practical to design for removal of sands, but removal of silts and clays is likely to be physically
3      ~~prohibitive (Walesh, 1989). Clays and silts have particle diameters in the range of <z2 microns and
        2 to 50 microns, respectively. For purposes of this analysis, 10 microns was taken as the
        minimum diameter of a settleable particle.

        Distribution of particle size within the TSS varies, depending on the sources of the TSS, such as
        local soils and road maintenance practices. The distribution also varies based on storm intensity;
I     ~ ~higher intensity rainfalls can mobilize larger particle sizes. (This follows from the Universal Soil
        Loss Equation). If all of the TSS particles are greater than 10 microns, a high removal efficiency
        can theoretically be achieved. Conversely, a large fraction less than 10 microns will place a lower
I     ~ ~limit on the sedimentation efficiency. It follows that the percentage of the TSS particles, by mass,
        greater than IO microns, defines the upper level of removal efficiency that can be achieved.

I      ~~Sediment sampling results are available from stormwater in the Anchorage area (JMM, 1992) and
        are shown in Figure I11. The Basin Inlet Composite #1 in Figure I11 represents the particle range
        of a number of composited samples. The percent of suspended sediment greater than 10 microns
I    ~for Basin Inlet Composite #1 is 72%. Although the other samples show a higher percentage of
        particles greater than 10 microns, Basin Inlet Composite #1 represents the lower bound on the
3     ~~distribution. This 72% value, and the particle size distribution for these small diameter particles,
        compare favorably with the particle size distribution found in stormwater from nationwide sources
        (Pitt, 1985), where 78% of the particles were greater than 10 microns. As mentioned previously,
        rainfall intensity is one factor that determines TSS loading and it follows that higher intensity
        storms mobilize particles of larger diameter. Since rainfall in the Anchorage area is generally of
        lower intensity than the nationwide average, the slightly greater percentage of smaller diameter
        particles is reasonable. Therefore, this distribution was used in evaluating the expe cted efficiency
        of sedimentation basins in Anchorage. This distribution was also used to evaluate the efficiency of
        sedimentation basins in Juneau, because, even though the Juneau area experiences higher annual
   Irainfall, its rainfall intensities are still lower than the nationwide norm.  Because Bethel has
        uniformly silty soils, we would expect an even smaller percentage of particles greater than 10
        microns.

        Based on the particle size distribution, the best removal efficiency that can be expected in Juneau
        and Anchorage is 72%; and even lower in Bethel. Therefore, sedimentation basins will not meet
   3the 80% target of management measure in II.A.(l1)(a) in these locations in coastal Alaska.
        However, for five of the land development scenarios, reducing pre development loads to post
        development levels entails removal rates lower than 72%. For these scenarios, sedimentation
   Ibasins were sized to meet the percent removal rates, and prototype sedimentation basins were
        designed. Cost figures have been calculated for these prototype basins.



        Stormwater Controls in Coastal Alaska                                                 D page 4-9
   IJune. J99S





                       Figure 11. Particle Size Distribution Analyses for Suspended Sediment in Storm Water



               100%







                 75%



         Percent

                                                                                                         ---- 100th Ave. Grab, Q=0.3 cfs
                                                                                                        --  It-  100th Ave. Grab, Q=0.6 cfs
        Passing  50%
         PassBy Weight 5                                                                                          -11- 100th Ave. Grab, Q=0.3 cfs
         By Weight
                                                                                                        --El-- Basin Inlet Composite #1
                                                                                                        -U--1- Basin Inlet Composite #2




                 25%






                                                                                                             Source: (JMM, 1992)
                  0%
                    . 0            10            20             30            40             50             60
                                                  Particle Diameter, microns






II - m m mI -3                                                             m m    m -    m - m -  






    Quantifiable structural BMPs are not feasible for the residential or commercial land development
    scenarios in Bethel. The recommended control methods include gravel capping of parking areas
    and erosion protection on the side slope of pads. There is not enough data to determine whether
    these BMPs will achieve the targeted removal rates, but it is reasonable to assume a 50% removal
    rate.

    Table 8 summarizes the target removal efficiency for each municipality and land use scenario under
    management measure II.A.(1)(b) for rainfall runoff events. There was no municipality in which
    80% removal efficiency (management measure II.A.(1)(a)) could be achieved. The scenarios in
    which these target percentage removal levels were less than 72% were carried forward for cost
    estimates in Section 5.
                                              Table 8
                        Summary of Target TSS Removal Percentages

                         Target Removal Efficiency (%) Required for
                              Pre=Post Development (II.A.(1)(b)
                                                   Municipality
                       Land Use        Anchorage        Bethel    j   Juneau
                       Residential         29      I    -100      I      45
                       Industrial         44   [          8       ]     51
                      Commercial          68   [         NA   ]          86

    Costs were not developed for other removal scenarios for various reasons. Since none of the
    municipalities have specific local ordinances addressing TSS removal levels, no cost estimates
    were developed for meeting existing municipal ordinances.  As mentioned previously, the
    effectiveness of non-structural measures cannot be quantified. Since non-structural measures
    cannot be recommended to meet the management measures, no cost analyses was performed. No
    industrial development scenario for Bethel was considered, because a new industrial site that could
    reasonably be expected to be developed could not be characterized. No cost estimates were
    developed for residential and commercial land development in Bethel, since there are no
    quantifiable BMPs that will work there. As discussed in Section 3.3.6, the TSS loading estimates
    made for pre and post development loads for Bethel are highly uncertain, so any costs developed
    based on the loading estimates would be ambiguous.









I 





    Stormwater Controls in Coastal Alaska                                               Z page 4-11
    June, 1995







5.0 COST ESTIMATES



5.1 DESIGN CONSIDERATIONS FOR SELECTED BMP CONSTRUCTION AND
     MAINTENANCE

Sedimentation basins sizes were estimated for five of the scenarios based on rainfall runoff flows
and TSS loading. The minimum pond surface area was calculated by an iterative technique. A
pond surface area was assumed, and the mass of TSS removed by the pond for each storm in the
typical year was calculated. The total mass removed from all rainfall runoff was divided by the
total TSS for the rainfall season to obtain a summer removal percentage. When the removal
percentage matched the level prescribed in Table 8 (the pre=post management measure), the pond
surface area was established. In all cases, the calculated pond surface areas were too large to be
incorporated into underground facilities, such as water quality inlets. Therefore, sedimentation
ponds were chosen as the BMP for each scenario. Other design considerations, such as maximum
side slopes and minimum storage volume for retained sediment, dictated a larger pond size in three
out of the five cases. These considerations were included in the design on which cost estimates
were based. Appendix B gives details of the assumptions and methodology used to determine the
pond design for each scenario.

                                          Table 9
                                   Summary Pond Sizes

 Land Use                                         Municipality
                             Anchorage                                     Juneau
              Minimum Sedimentation   Estimated Removal    Minimum Sedimentation   Estimated Removal
                    Pond Size             Efficiency             Pond Size             Efficiency

             Theoretical    Practical    Summer   Annual   Theoretical   Practical    Summer   Annual
             Surface Area  Surface Area                   Surface Area  Surface Area

                            sq ft       %         %         sq ft       sq ft        %         %
 Residential     90          1,300       72        44         450         1.300       66        55
  Industrial     400         1,300       67        43        2,600        2.600        51        43
Commercial     1,600        1,600        65       42         NA           NA         NA        NA


Table 9 shows a summary of minimum pond sizes. The theoretical minimum pond surface area
was calculated by the iterative technique described above. The practical pond surface area was
determined by the geometry of the pond design criteria. The summer and annual percentage
removal rates for the practical pond surface areas are also shown. The annual percentage removal
rates were based on the assumption that the pond would be effective during 25% of the snowmelt
runoff events in Anchorage and 50% of the snowmelt runoff events in Juneau. Although we feel
these are reasonably conservative assumptions, there are no data to support them.


Stormwater Controls in Coastal Alaska                                                   Z? page 5-1
June, 1995







52 COST ESTIMATE FOR SELECTED BMPS

Cost estimates for storm water controls are presented in Table 10. The costs for stormwater
controls included land costs and building and site development costs. The sum of these is the total
capital cost (TCC). The costs for construction of the controls were based on a prototype
sedimentation design, and unit prices for construction from Means Heavy Construction Cost Data.
In addition, annual and periodic maintenance costs were estimated. The maintenance tasks were
itemized and unit prices for these were taken from Means Heavy Construction Cost Data. The
annual cost for development was estimated by annualizing the capital costs over 25 years at 10
percent interest rate. The total annualized cost (TAC) of the project includes both the annual
maintenance costs and the annualized capital cost.

For prices taken from the Means Cost Data, the City Cost Index for Anchorage was used to adjust
the unit prices for Anchorage. For Juneau, the 105 percent of the Anchorage City Cost Index was
used.

These methods are consistent with the method used by the EPA in its economic analysis of coastal
nonpoint source pollution controls. (EPA, 1992).

                                         Table 10
                          Estimated Stormwater Control Costs

                  Type of Land Use                         Storm Water Controls
 Municipality  Project Size    Project Type   Total    O&M Cost   Total        Acres    Annual Cost
                (ac)                       Capital      ($)    Annualized  Required  per Developed
                                           Cost ($)              Cost ($)                Acre ($)

  Anchorage       5       Residenutial(38%)    38,231    3,754      7,966      0.34         1,593
                 10       Industrial(50%)   33,695      3,754      7,466       0.34         747
                 10     Commercial(85%)    68,720       4,095      11.666      0.36        1,167
   Juneau        5        Residential(40%)    38,782    3,936      8,208       0.34        1,642
                 20       Industrial(50%)   39,472      5,402      9.751       0.43         488

5.3 MEASURES OF ECONOMIC IMPACT

To measure the control practices' economic impact on development activities, ratios of stormwater
control costs to development costs without stormwater controls were computed, based on costs
derived in Section 5.2. These ratios, consistent with the method used by the EPA (EPA, 1992),
are described as follows:

       Residential development

              TCC/total land price
              TCC/number of housing units / median home price
              TAC/number of housing units / median annual mortgage
              TAC/number of housing units / median household income

Stormwater Controls in Coastal Alaska                                                   a page 5-2
June, 1995








       Commercial and Industrial development                                                               I

              TCC I Total development cost 
              TAC / Annualized development cost

Two costs were used to estimate capital development costs for commercial and industrial 
development, land costs and building and site development costs. Land prices were based on local
knowledge. Building and site development costs were obtained from Means Building
Construction Cost Data. The annual cost for development was estimated by annualizing the capital            |
costs over 25 years at 10 percent interest rate.

Residential housing costs were based on tabulated data from the State of Alaska Department of 
Community and Regional Affairs (1995). This source reports median household income and the
median value of owned homes. The annual mortgage payment was calculated from the owned
home value, assuming a 15% down payment, an 8%, thirty-year note, and 10% for insurance and                 3
taxes.

The storm water control to development costs are shown in Table 11. Also included in Table 11                I
are the range of values for similar ratios as reported by EPA for control costs meeting both
management measures. As pointed out in Section 5.1, no BMP controls are expected to treat storm
water to the 80% removal level. Therefore, the costs and ratios presented here are for meeting the 
pre=post management measure only.

                                         Table 11                                                         3
                             Measures of Economic Impact

                                 Single Family Residential
 Municipality    Project Type    TCC/House/Annual   TCC/Land   TAC/House/    TCC/House/
                                    Mortgage         Price       Household     House Price
                                                                 Income 
                                       (%)             (%)          (%)            (%) 
 Anchorage       Residential            1.94            2.93          4.86           1.01
 Juneau          Residential            1.90            2.97          4.84           0.95
 National Range for Single Family    .31 - .93 %     3.7 - 8.6 %    .45 - 1.3 %   .16 - .32 % 
                                 Commercial and Industrial
 Municipality    Project Type    Capital Development  Annualized   TCC/Capital  TAC/ Annualized
                                      Cost        Capital Cost     Cost            Cost
                                                       ( $)                                            ~~~~~~~I
                                           ($)        ~~~($)        (%)            (%)
 Anchorage       Industrial          9,090,613        1,001,495       0.37           0.75
                Commercial          15,219,444       1,676,697       0.45           0.70 
 Juneau          Industrial          18,654,687       2,055,151       0.21           0.47
 National Range for Commercial Only                               .49 - .67 %     .70 - .95 %

 TCC - total capital cost for storm water control                                                            I
 TAC - total annualized cost. including O&M, for storm water control

                                                                                                        I


Stormwater Controls in Coastal Alaska                                                   ~ page 5-3 -
                          ~Jau~ne, ~1995






As can be seen in Table 11, the measures of economic impact for stormwater controls on
residential development are consistently high compared to the national range, except in the
comparison with land values alone. For commercial land development, the economic impact ratios
are within the national range. The residential economic indicators use the annual household income
and mortgage expense of the eventual owners of the property. The commercial economic
indicators only represent the cost of controls as a portion of the total development cost. The
residential method more accurately reflects the market's willingness to pay than does the
commercial method. In the commercial method, there is no way to determine if the incremental
costs will still make the development an attractive one for investors or buyers. Therefore, even
though the commercial economic indicators in Table 11 compare favorably with national averages
(EPA, 1992), they do not reflect the true conditions that would determine whether the control
measures are economically achievable.

                                        Table 12
                          Unit Costs for Stormwater Controls

 Municipality   Development    Area     TAC       Annual   Removal of   Load      Cost per   Cost per
                  Type                            [Load Annual    Removed   Acre per    Pound
                                                           Load                  Year    Removed
                              ac       $          lbs        %         lbs         $          $
Anchorage    Residential        5      7,966       699         44        308       1,593      25.90
            Industrial        10      7,466      1,942       43         835       747        8.94
             Commercial        10      11,666     3,322       42        1,395      1,167      8.36
Juneau       Residential        5       8,208      1,287       55        708       1,642      11.60
            Industrial        20      9,751      7,403       43        3,183       488       3.06

Table 12 summarizes the annualized unit costs of stormwater controls in cost per developed acre
and cost per pound of sediment removed.























Stormwater Controls in Coastal Alaska 0I page 5-4
June, 1995






6.0 CONCLUSIONS


The 80% TSS removal standard cannot be reliably met in any of the three indicator communities by
any BMP whose performance can be quantified. Since the only quantifiable BMPs that will work
rely on settling and the fraction of settleable solids is less than 80%, there is no way to improve the
removal rate by BMPs.  The methods for removing the remaining unsettleable fraction involve
chemical or physical treatment, such as employed for drinking water supplies. These methods are
much more expensive than BMPs and would fail the economic indicator tests for developments of
the size presented in this analysis.

The pre=post removal standard can be met in Anchorage and for residential and industrial
development in Juneau. Meeting this standard comes at annualized costs, including O&M, ranging
from $490 per developed acre for industrial development to $1640 per developed residential acre.



































Stormwater Controls in Coastal Alaska  page 6-1
June, 1995






I7.0 REFERENCES



Alaska Department of Community and Regional Affairs Community Database. June 1995.
    Community Profile - Juneau. Research and Analysis Section

Alaska Department of Community and Regional Affairs Community Database. June 1995.
    Community Profile - Bethel. Research and Analysis Section

Alaska Department of Community and Regional Affairs Community Database. June 1995.
    Community Profile - Anchorage. Research and Analysis Section

Berglund, E.R. 1978. Seeding to Control Erosion Along Forest Roads. Oregon State University
   Extension Service, Extension Circular 885. In: Guidance Specifying Management Measures
   for Sources of Nonpoint Pollution in Coastal Waters. EPA 840-B-92-002. January 1993.

Billman, Daniel and Thomas R. Bacon. 1990. Spring Breakup Flows in Anchorage Storm
   Drains. Cold Regions Hydrology and Hydraulics. ASCE Technical Council on Cold Regions
   Engineering Monograph. 669-693.

Brabets, Timothy P. 1987. Quantity and Quality of Urban Runoff from the Chester Creek Basin
   Anchorage, Alaska . United States Department of the Interior Geological Survey. Water-
   Resources Investigations Report 86-4312.

City of Bethel. June 1983 Bethel Coastal Management Plan Conceptually Approved Draft

Feulner, Alvin J., Joseph .M Childers, Vernon W. Norman. 1972. Water Resources of Alaska.
   United States Department of the Interior Geological Survey . Water Resources Division.
   Alaska District

Goldman, Steven J., Katharine Jackson, Taras A. Bursztynsky. 1986. Erosion and Sediment
   Control Handbook. McGraw Hill.

HDR and CH2M Hill. 1992. National Pollutant Discharge Elimination System Storm Water
   Discharge Permit Application, Part 1. Prepared for the Municipality of Anchorage and Alaska
   Department of Transportation and Public Facilities. May.

HDR and CH2M Hill. 1993. National Pollutant Discharge Elimination System Storm Water
   Discharge Permit Application, Part 2. Prepared for Municipality of Anchorage and Alaska
   Department of Transportation and Public Facilities. May.

Hinton, Robert B. and Charles L. Girdner, Jr. 1968. Soils of the Bethel Area, Alaska .:United
   States Department of Agriculture, Soil Conservation Service.




Stormwater Controls in Coastal Alaska                   J                          page 7-1
June, 1995







James. M. Montgomery Engineers. 1986. Sedimentation Basin BI-] Decisional Documents.
   Prepared for the Municipality of Anchorage Department of Public Works. December.

Jokela, J. Brett and Thomas R. Bacon. 1990. Design of Urban Sedimentation Basins in
   Anchorage. Cold Regions Hydrology and Hydraulics. ASCE Technical Council on Cold
   Regions Engineering Monograph. 761-789.

Leslie, Lynn D. 1986. Alaska Climate Summaries Alaska Climate Center Technical Note No. 3.
   Arctic Environmental Information and Data Center. September.

Marshall Macklin Monaghan Limited. 1991. Stormwater Quality Best Management Practices.
   Prepared for: Environmental Sciences & Standards/Water Resources, Ontario Ministry of the
   Environment. June.

Miller, John F. 1963. Probable Maximum Precipitation and Rainfall-Frequency Data for Alaska.
   Technical Paper No. 47. U.S. Department of Commerce Weather Bureau.

Montgomery-Watson. 1993. Design Storm Investigation . Prepared for the Municipality of
   Anchorage, Department of Public Works. December.

Montgomery-Watson. 1993. Areawide Water Quality Monitoring Program 1992-1993
   Sedimentation Basin Performance Monitoring Report. Prepared for the Municipality of
   Anchorage, Department of Public Works. July.

Montgomery-Watson.  1994. Potential Best Management Practices for Stormwater Pollution
   Prevention.. Phase 2 Draft. Prepared for the Municipality of Anchorage, Department of
   Public Works. November.

National Oceanographic and Atmospheric Administration. 1987. Climatological Summary for
   Alaska.

National Oceanographic and Atmospheric Administration. 1991. Climatological Summary for
   Alaska.

North Virginia Planning District Commission (NVPDC). 1987. BMP Handbook for the Occoquan
   Watershed. Annadale, VA. In: Guidance Specifying Management Measures for Sources of
   Nonpoint Pollution in Coastal Waters. EPA 840-B-92-002. January 1993.

Pitt, R. 1985. Summarized Guidelines for Wet Detention Pond Design. Wisconsin Department
   of Natural Resources. Nonpoint Source and Land Management Section.

Schoephorster, Dale B. and Clarence E. Furbush. 1974 . Soils of the Juneau Area, Alaska.
   United States Department of Agriculture, Soil Conservation Service. Palmer, Alaska. June.





Stormnwater Controls in Coastal Alaska                                           I page 7-2
June, 1995






Scheuler, Thomas R. 1987. Controlling Urban Runoff: A Practical Manual for Planning and
   Designing Urban BMPs. prepared for Washington Metropolitan Water Resources Planning
   Board. July 1987.

Scheuler, Thomas R., Peter A. Kumble, and Maureen A. Heraty. 1992. A Current Assessment
   of Urban Best Management Practices, Techniques for Reducing Non-Point Source Pollution in
   the Coastal Zones. Prepared for USEPA, Office of Wetlands, Oceans, and Watersheds.
   March.

Sheaffer, John R and Kenneth R. Wright. 1982. Urban Storm Drainage Management. Marcel
   Dekker, Inc. New York.

U.S. Army Corps of Engineers Alaska District. 1979. Soils of the Anchorage Area, Alaska.
   Volume 7 Metropolitan Anchorage Urban Study Final Report.

U.S. Department of Agriculture. 1985. National Engineering Handbook, Section 4, Hydrology
   Soil Conservation Service

U.S. Department of Agriculture. 1986. Urban Hydrology for Small Watersheds Technical
   Release 55. Soil Conservation Service Engineering Division

US EPA. January 1993. Guidance Specifying Management Measures for Sources of Nonpoint
   Pollution in Coastal Waters. EPA 840-B-92-002.

US EPA. December 1992. Economic Analysis of Coastal Nonpoint Source Pollution Controls:
   Urban Areas, Hydromodifications and Wetlands.

Walesh, Stuart G. 1989. Urban Surface Water Management. John Wiley and Sons, Inc.

Weaver, Jerry. June 1995. Personal Communication

Wheaton, Scott. May 1995 Personal Communication

Wiegand, C., T. Scheuler, W. Chittenden, D. Jellick. 1986. Cost of Urban Runoff Quality
   Controls. Urban Runoff Quality - Impact and Quality Enhancement Technology. Proceedings
   of an Engineering Foundation Conference. June, 1986. 366-350.

Williams, Richard. 1993. Juneau Streams - A Water Quality Study. Alaska Department of
   Environmental Conservation July.









Stormwater Controls in Coastal Alaska                                           C page 7-3
June, 1995



I
I
I
I
I


i
I
I
I
I
I Appendix A
I
I
I
I

I
I
I                --TOIMIO
I






Appendix A



Daily Runoff and TSS Load from Rainfall and Snowmelt Events for Typical Year

   ï¿½ Anchorage
   * Bethel
   * Juneau

Derivation of Snowmelt Runoff and TSS Loading from North Arctic/Orbit Data

Derivation of Annual Predevelopment TSS based on Universal Soil Loss Equation






































                             .
Stormwater Controls in Coastal Alaska                                               Zi page A-l
June, 1995



                                                                 I

                                                                 I

                                                                 I
Daily Runoff and TSS Load from Rainfall and Snowmelt Events For Typical
Year
a Anchorage                                                                    I
* Bethel
* Juneau

                                                                 I

                                                                 I

                                                                 I

                                                                  I

                                                                  I

                                                                  I

                                                                  I

                                                                  I
                                    ~~~~~~~~II

                                                                  I
                                                         -  ~ I

                                                                  I

                                                                  I

                                                                  I






                                                             ANCHORAGE




                                                              Residential                                  Industrial
                                               Area:          5 ac                       Area:           10 ac
                                               Au   imp:     38                           % imp:         50
                                     Assumed                                     TSS
                            Snowmelt Snowmelt Rainfall                           concentr
Assumed                     for       TSS conc Runoff  Snowmelt           Runoff  alion   Rainfall   Snowmelt          Runoff
Day of Melt Date    Precip    imp=30  (mo/I)   in       Runoff   TSS lbs cts      mall    Runoff in Runoff   TSS lbs  cfs
       11  12-Jan               0.03      157              0.04        7    0.01    157                 0.05       17      0.02
       12  13-Jan               0.03      151               0.04       6    0.01     151                0.05       16      0.02
       13  14-Jan               0.03      146              0.04        6    0.01     146                0.05       16      0.02
        422-Feb                 0.03      195              0.04        8    0.01     195-               0.05       21      0.02
        523-Feb                 0.03      190              0.04        8    0.01     190                0.05       21      0.02
        6  24-Feb               0.03      184               0.04       8    0.01     184                0.05       20      0.02
        7  25-Feb               0.03      179              0.04        8    0.01     179                0.05       19      0.02
           26-Feb               0.03      173              0.04        7    0.01     173               0.05        19      0.02
        -1 .10-Mar    0      -046799      212              0.06       14    0.01    212.                0.07       36      0.03
        -2 11-Mar          -0.02291       206             -.03         7    0.01_   206                 0.04       17      0.02
        -12-Mar-            0.04679       201 _2I 0.06                13    0.01    201                 0.07       34      0.03
        4   3-Mar           0.03002       195               0.04       8    0.01     195                0.05       21      0.02
        514-Mar             0.01967       190              0.02        5    0.01     190                0.03       14      0.01
        6  15-Mar           0.01967       184               0.02       5    0.01    184                 0.03       13      0.01
        7 _16-Mar           0.01967       179               0.02       5    0.01     179                0.03       13      0.01
        8- 17-Mar           0.01967       173              0.02        5    0.01     173                0.03       12      0.01
        9  18-Mar            0.0352.    168                0.04        8    0.01     168                0.06       21      0.02
       10  19-Mar           0.04037       162               0.05       9    0.01    162                 0.06       24      0.03
       1_-20-Mar            0.04058     157                0.05        9    0.01    157                 0.06       23      0.03
       12 21-Mar_             0.0383      151              0.05        8    0.01    151                 0.06       21      0.03
       1 3 22-Mar           0.03023       1-46              0.04       .-.  0.01.   146.                0.05    16i    0.02
       14 23-Mar          _0.0383         140              0.05        8    0.01     140                0.06       20      0.03
       15  24-Mar           -0.03727      135        ___  0.05         7    0.01     135                0.06       18      0.03
       16  25-Mar           0.02588-      129         _    0.03 5.   0.01    129                        0.04       12      0.02
       17  26-Mar             0.0383      124          __ 0.05    _  7      0.01     124                0.06       17      0.03
       18 -27-Mar           0.03106    __118          _     0.04_    5    0.01       118                0.05        13     0.02
       1 928-Ma-r -         0.03002       113         _     0.04       5    0.01     113                0.05        12     0.02
      20  -29-Mar           0.02588       1 07             0.03-      4    0.01      107               0.04        10     0.02
      21  30-Mar         _0,04017         102             -(0.05      6  (.01    102                   0.06        15     0.03
      22  31-Mar__         0.04617         96              0.06:      6    0.01       96               0.07        16     0.03
      23   1-Apr            0.04617        91             0.06   _  6    0.01         91               0.07        15     0.03
      24.  ?-Apr.          0.06336         85              0.08       8    0.02       85               0.10        20      0.04
      25_- 3-Apr  -          0.0499        80      _       0.06       6    0.01       80               0.08        14      0.03
      26  _4-Apr       -     00_ 354       75              0.04       4    0.01       75               0.06        10      0.02
      27   5-Apr           0.04679         69              0.06:      5    0.01       69               0.07        12      0.03
      28   6-Apr            0.05176        64              0.06       5    0.01       64               0.08        12      0.03
      29   7-Apr         . 0.05176         58         __   0.06       4    0.01       58               0.08        11      0.03
      30.  8-Apr.           0.03894.       53   _          0.05       3    0.01 _    53                0.06         7      0.03
      31   9-Apr_           0.05073        47     ___   0.06          3    0.01       47               0.08         9      0.03
      32  10-Apr     ._   0.06522          42_   _         0.08__  4    0.02          42 -.10                      10      0.04
      33. 11-Apr.           0.0-5176-      36         -.   0.06       3     0.01      36               0.08         7      0.03
      34. 12-Apr._          0.08157      _31               0.10       4    0.02       31               0.13         9      0.05
      35_ 13-Apr_   __       0.0793       25               0.10        3    0.02_ _25                  0.13         7 _   0.05
      36  14-Apr            0.08758        20              0.11,    2    0.02         20               0.14         6      0.06
      37__15-Apr    __ _0.11346            14              0.14    2        0.03      14               0.18         6      0.08
          22-May_  k0.9 _    _                   0.02-                40.01.139'    0.03                           11     0.01
          24-May      0.09 __  0_                _0___ _4                     .01139.    0.03                      11      0.01
          31-May     0.15                        0.04                 6    0.01      132      0.05                 18     0.02
            6-Jun     0.14          __           0.04                  6    0.01    133       0.05                 17      0.02
           19-Jun__  0.16                _        0.05                 7    0.01     131      0.06                 20      0.02
          20-Jun     0.26                        0.08                11    0.02     124      0.09                 32      0.04
           22-Jun      0.1                        0.03                 4    0.01     138      0.03                 12      0.01
           30-Jun     0.12                        0.03                 5    0.01     135      0.04                 15      0.02
             I-Jul    0.28                        0.08                12    0.02     123      0.10                 34      0.04
            9-Jul    0.18        _               0.05                 8    0.01    129       0.06                 22      0.03
           1-3-Jul  _0.1            _ 00.03                           5    0.01    135       0.04                  15     0.02
           l8-Jul    0.55                        0.18                23    0.04    114       0.21                 67      0.09
           24-Jul _   0.09       ___              0.02                4    0.01    139        0.03                 11      0.01
           25-Jul     0.12        _              0.03_                5    0.01      135,    0.04                  15      0.02
           3-Aug_    0.5              _          6.04    _ _          6    0.01    132  _  0.05                    18     0.02
           9-Aug       0.2                       0.06    a           8     0.01    .128. - 0,07                    24     0.03
        -12-Aug      0.11                        0.03         ----5    0.01-   1 36.----.--0.04                    14      0.02
          13-Aua       0.3                       0.09                12    0.02      122      0.11                 37      0.05




                                                             Page 1 of 4






                                                             ANCHORAGEI




                                                              Residential                                   Industrial
                                               Area:          -5_ec                       Area:      I       0 ac
                                               % imp:        3 8 _                        % imp:          50.
                                      Assumed                                     TSS
                            Snowmell Snowmelt Rainfall                            concentrI
Assumed                      for       TSS conc Runoff  Snowmelt           Runoff  ation    Rainfall   Snowmelt          Runoff
Day of Melt Date    Precig)   imv30   (moll   in        Runoff    TSS lbs cts     moll    Runoff in Runoff    TSS lbs  cis5
           14-Aug      0.26                       0.08.  11   0.02                    124      0.09.                 32      0.04
           16-Aug       0.1.                      0.03.                 4_  0.01      138      0.03.                 12      0.01
           23-Aug      0.24                        0.07.  10    0.01                   125      0.09                 29      0.04
            4-Sep     0.16                       -0.05.                7    0.01_  131-   0.06                       2 0     0.02
            6-Sep     0.17                        0.05.                7    0.01      130      0-.06 '21                     0.02
             8-Sep     0.27.                       0.08-               11_  0.021    124   Q. -1 0                    33.    0.04
            iI-Sep     0.14                        0.04.         _      6.  0.01       1 33.-   0.05.                 1 7    0.02
           14-Sep      0.16-                      0.5_   _          _7.  0.01_  131 __         0.06 -2 0_   10.02                     
           I15-.Sep_  0.18                        0._05.         -      8    0._01    129      0.06           .      22 '    0.03
           17-Sep     0.51                     -0. 16.                21   -0.03      11 5     0.20                  62-    0.08
           18-Sep-    0:12                    -- 0.03          _        5    0.01     135      0.04                  1-5    0.02
           19-Sep     0.64                        0.21-  .26__ 0.04                   112,    0.25                   77      0.11
           20-Sep.    0.14                         0.04     6_ _ 6    0.01.   133               0.05                 17      0.02
           23-Sep.     0.34          .             0.10-               14    0.02     120 _    0.13                  41.    0.05
           26-Sep      0.39.                       0.12       _        16__ 0.03      119      0.15             -    47.     0.06
           27-Sep_ -947                           0.5                  19_ 0.03.   116~  0.118                       5 7.    0.08
           29-Sep      0.34                       -0.1I0-              14    0.02     1 20.    0.13 a                41      0.05
           30-Sep      0.29                        0.09 __             12_ 0,02.   123         0.11          a    s          0.04
             6-Oct     0.44                        0.14         I       8    0.03  _117         0.17           .      53      0.07
             a-Oct     0.12           .        . 0.03          _        5    0 .01     135      0.04   .15                    0.02
            10-Oct     0.42                        01                  17    0.03   _118 0.16                         51      0.07
            13-Oct_    0.09               _        0.02                 4.  0.01       139      0.03                  11      0.01
           24-Oct      0.14          _0.04.                             6    0.01     133  -  0.95                   17      0.02
          -25-Oct _ 0.11          -      -- --   0.03-    _____         5  -0.01      136      0.04-                 1 4   'D.02
       26  11-Nov_               0.03 -      75              0.04       3    0.01       75                0.05         8      0.02
       27  12-Nov-003                        6               0.04       3    0.01       69                0.5     a             0.02
       2 8.13-Nov-__             0.03.       64              0.04       3    0.01       64                0.05         7      0.02
       289 14-Nov.               0.0.3       58      a       0.04       2    0.01       58                0.05         6      0.0 2
       3 0  1I5--Nov__    _      0.03.      53          _    0.04       2    0. 1 300                                  6_     0.02
               3 1 16-Nov       0.03        4 7          0.04;         2     0___  _47 ______  _0    02
       321__1-Nov    _     _     0.03       42               0.04       2    0.01       427               0.05         5      0.02
       33  18-Nov      _         0.03       36      .        0.04       2    0.01       36.               0.05.        4      0.02
       1-8  15-Dec               0-.03-    1-18              0.04       5:   0.01 _118:                   0.05  _   13        0.02
       I19__16-Dec               0.03      113               0.04 ~   5    0.01        113                0.05        12      0.02
      26  17-Dec                0.03      107               0.04:       5    0.01     107                0.05        12      0.02

          Total        9.45.                        2.8       2.7    699       1.2               3.4       3.5     1942        2.9
       Median Day     0.16                          0 0.1    0.0      7.1.    0.0    128         0.1      0.1      19.8      0.02
                    Rain 9.  4     5   ~~~         2.4               338    0.01      130       3.0       ___      992       0.02
          Snowmelt                      -.2.7    361  0.01                             113    -.3.5                 950      0.02
          Maximur  _0`64                            0.2       0.1    26.4_ 0.04    _             0.3.    0.2_    77.4   _ 0.11
          Minimum      0.09                         -0.0-    0.0t    1.5       0.0   _           0.0       0.0       3.9       0.0
          Winter % of Total                                          52%                                            49%



























                                                             Page 2 of 4 





                                                          ANCHORAGE



                                                                      Commercial                       Pre-development
                                                     Area:          1 0 ac                        Area.           1 0Oac

                                    Assumed TSS
                           Snowmelt Snowmelt concentr                                    TSS
Assumed                    for      TSS cornc ation   Rainfall   Snowmelt        Runoff   concentra Rainfall   SnowmeII Runoff
Dav of Melt Date   Precip   imp=30  (mu/I)   ma/I   Runoff in Runoff   TSS lbs  cfs      lion ma/I Runoff in Runoff   CfS
       11  12-Jan              0.03      157    157               0.08       28     0.03      157               0.00    0.002
       12  13-Jan              0.03      151    151               0.08       27     0.03      151               0.00   0.002
       13  14-Jan              0.03      146    146               0.08-      26     0.03      146               0.00    0.002
          422-Feb.        _    0.03      195-  1-95.         _    0. 08 -    3-5    0.03- -_195                 0.00    0.002
        5 23-Feb               0.03      190-  190           - 0.08          34 --0.03.  ~190           -       0.00    0.002
        6  24-Feb     _        0.03      184    184               0.08       33      0.03i    184          - 0.00    0.002
        725-Feb                0.03      179    179               0 .08      32     0.03      179               0.00    0.002
          826-Feb              0.03      173    173               0.08 _     31      0.03      173              0.00    0.002
        1 10-Mar           0.04679      212    212                0 .12      60     0.05      212               0.01   0.003
        21 11-Mar_         0.02298       206    206               0.06       28      0.03-    206               0.00    0.002
        3_12-Mar          _0.04679      201    201                0.12   _56         0.05     201               00       .0
        413-Mar            0.03002       195 __195                0.08       35      0.03     195               0.00    0.002
          514-Mar         -0.01-96-7     190    190o               0.05.     22   _0.02_  190                   0.00   -0.001
        6  15-Mar          0.01967       184    184          _   0.05        22 .  0.02       184               0.00    0.001
        7  16-Mar           0.01967      179    179               0.05       21      0.02     179               0.00    0.001
        8 17-Mar           0.01967       173    173          __0.05          20      0.02     173               0.00    0.001
         918-Mar            0.0352,    168    168            _    0.09       35     0.04      168               0.01    0.002
       10  19-Mar          0.04037       162    162         _     0.11       39     0.04   _162                 0.01    0.003
       11 20-Mar          -0.04058       157    157               0.11       38     0.05      157               0.01    0.003
       12  21-Mar      -     --0.0383    151    1I5 1     _       0.10       315    0.04.    151                0.01    0.003
       13 22-Mar   _       0.03023       146    146               0.08       26      0.03     146               0.00    0.002
       14  23-Mar            0.0383      14 0    140       __ 0.10 -           3 2   0.0 4 _    140            -0.01 _  0.003
       15  24-Mar          0.32          135 _135                 0.10__s 304 667    0.0      135'              0.01    0.003
       16 -25-Mar          0,02588.    129_  12 9                 0.07      .20.   0.03       129               0.00    0.002
       17  26-Mar            0.0383      124 -124                 0.1I0   _29        0.04     124               0.0 1    0.003
       -18  27-Mar          0.03106      11 8    118      ___0.08            22      0.03 _ 118                 0.00    0.002
       19  28- Mar         0.03002       113  _113          _     0.08       20     0.03       113              0.00    0.002
       2-0  29-Mar          0.02588    -107    107 ___            0.07        17     0.03      107              0.00    0.002
       21I 30-Mar_          0.04017      102    102               0.11       25      0.04.     102              0.01 __0.003
       22__31-Mar           0.04617       96      960.12                     27      0.05~   96                 0.01-  0.003
                 23   1-Apr  0.04617   __ 91    ~~~~~9-1-         0.-12      25     0.5.       911              0.01    0.003
      24    -pr0.06336_   8 5   _85'                              017        33   __0.07 -     85               0.0 1 _ 0.004

        26___4Ap 0.0354                   75      75              0.09       16;    0.041       75              0.0 1    0.002
      2 7   5-Apr _____0.04679           69__69           _      0.12       19      0.05       69       _      0.01-  0.003
      28   6-Apr           0.05_176      64      64     _____   0.14        20      0.6        64              0.01    0.003
      29   7-Apr    _      0.05176       58      58               0.14       18     0.06   _58                  0.01    0.003
      30   8-Apr.          0.03894       53      5 3      ____     - 0.1     12     0.04.      53              0.01    0.003
      31   9-Apr,          0.05073       47      47 --0.13-   14   -0.06                       47               0.01.  0.003
      32  10-Apr           0.06522 _     42 - 42           _ -   -0.1-7-  -1-6   --0.07        42               0.01    0.004
      33  1 1-Apr .     _ 0.051-76       36      3 6-             0. 14   II_    0.06         -3 6              0.01.  0.003
      34  12-Apr.          0.08157       31 - 31                 ... 0.22    1 5    0.09-      31               0..01 -0.005
   __ 35  13-Apr009                      25 __ 25  __             021-       12     0.09       25-              0.01    0.005
      36__14-Apr    _      0.087-58      20      2 0              0.2        10     0.10       20              -0.01__  0.006
            37  15-Apr_- - - -   0. 11346  14   ___I4     -       0.30       10      0.13       14             0.02 __ 0.0OB
          __2-M~y- 0f.09       ___167                    0.04'               19      0.02.    23-9    0.01I---          0.004
       2__4-May- O.09           ____            167     0.04'                19    0.02;   239.    0.01-                0.004
           --1-May_  0.15                        158     0.06                32      0.03'    226i   0.02              70.006
                 6un 0.14  ___1-59,   0.06.                                  30      0.02     227'   0.01--  _    0.006
           19-Jun    -0.16                ___17          0.07                34      0.03     224      0.02             0.007
           20-Jun     0.,26           __         149     0.12                55      0.05    _213 _ 0.03         _      0.012
           22-Jun   -0.1                         15      0.04        -      -22    0.02'    236  _0.01           _      0.004
           30-Jun     0.12         __        _162_  0.05                     26      0.02     231      0.01             0.005
             1--Jul-  -0.28                   1-4-8    0.12-         A       60      0.0-5    211      0,03.            0.013
             9-Jul    0.18            ----155            0.08           ___39    -0.03         221     0.02-             0.008
           13-Jul_  0.12         ___       __162        0.05    ______26            0.02      231     0.01              0.005
            I8-Jul    0.55                ___137         0.26               116  _0.11        196      0.06             0.027
                 24jl 0.0-9         _16                  0.04                 1 9      0.02-   -239,   0.01-           -0.004
           25-Jul    0.12         _162                   0.05                26     0.02_ _231        0.01              0.005
           3.-Au.  -_0. 15    _    _158                  0.06                32      0.03.    226      0.02             0.006
                 0.2c                        _ 153-   0.09                   43     0.04.-   219  --0.02    _           0.00
              I27AU9--     _    ___164                    .0                 24      0.02'    234_  -0.01   __          0.005
          13-Aua      0.3                       146     0.13s                64     0.06.     209     0.03              0.014




                                                           Page 3 of 4





                                                            ANCHORAGE



                                                                       Commercial                        Pre-development
                                                      Area    : 1    0ac                            Area:     I      O acI
                                                      0/oimp:        8 5                            % imp:  
                                     Assumed TSS
                            Snowmelt Snowmelt concentr                                     TSS
Day of Melt Date    Precip   imD=30  (mo/i)   m/Il   Runoff in Runoff   TSS lbs  efs l      ion mo/I Runoff in Runoff   cfssue  o  S  ocaln Rifl    nwet  uof cnetaRifl    nwetRnf 
           14-Aug     0.26                       149      0.12                55      0. 05     21-3    0.03              0.012
           16-Aug      0.1                        165     0.04                22      0 .02     236     0.01              0.004
           23-Aug     0.24                        150     0.11 -51                    0.04      214      0.03             0.011
            4-Sep.    0.16,                      157      0.07                34      0.03      224'   0.02               0.007
            6-Sep     0.17                       156      0.07                36.   0.03        223     0.02              01.007
            8P-Sep.   0.27                  -     148,   0~.12                 58     0.035     212.   0.03.              0.012
           11-Sep.   0.14                        159      0.06 -              30D  0.0O2_    22-7    0.01                 0.006
            _ 14Sep  0,16          _157  __0.07                               34     0.03      224      0.02             0.007
           15-Sep.    0.18         _155_  0.08                            _ 39        0.0-3     221 _    0.02             0.008
           17-Sep     0.51                       138      0.24               1 - -108    0.10 D-    1-97.    0,06         0.024
           18-Sep     0.12                       162      0.05                26      0.02      231-  0.01                0.005
           19Sp       0.64           I35                  0.31-              13-5    0.13-    192-   0.07                 0.031
           20-Seq.    0.14                        159     0.06                30      0.02-    227.   0.01.               0.006
           2_3-sep_   0.34                  -     144     0.1 5               72      0.06      206      0.04.            0.016
           26-Sep.   0.39                         142     0.18                83.   0.08        203.   0.04.              0.018
          _27-Sep.    0.4 7 _-                -- 1,39   _0.22.               100      0.09      -199     0,05            -0,022
                     29-Sep  0.3 4        ~       144     0.15                 72   _0.06       206:   0.04              -0.01_6
          *30-Sep_    0.29                       147      0.1 3               6       0.5       210 D   0.03          .p.1
            6-Oct     0.44                       140      0.21                93,  -0.09       201      0'05              0.021
           B -Oct     0.12                        162     0.05                26      0.02.    231.   0.01            .   0.005
           10-Oct     0.42                  -    141      0.19      ___- 89           COS8     202      0.05          _0.020
           13-O-ct.    0.09'                     167    -0.04                 1 9     0.02      239_  0.01          __ 0.004
           -24-Oct    0.14 -i                    159      0 6.06-- - _   __30'    0.02          227.   0.01           .0.006
         2625-DOt,    0.11                -       164     0.04                24      0.02      234 _   0.01              OPOS5
         211I-Nov_        _   -0.03.       75  75                   0.08       13     0.03    _75                 0.00    0-.002
             27  12-Nov        ~~~0.03    69       69              0.08        120.O03 _   69                     0.00    0.002
   __ 28  13-Nov                0.03       64      64              0.08        11     0.03       64               0.00-  0.002
      2 9-14-Nov               0.03-      58      58       -       0.08       10     0.03        58              0.00'   0.002
             30  15-Nov        ~~~0.03     53       30.08                       9     0.03       53               0.00    0.002
      30 15No                                                ___       _                                          __           5     3      I
      31  16-Nov_              0.03       47      47               0.08        9     0.03       47               0.00    0.002
      32  17-Nov-              0.03__     42      42__             0.08-_   8 __0.0-3           4 2_             0.00-   0.002
      33  18-Nov               0.03       36      36               0.08        7     0.03 ___36                  0.00'   0.002
      18 15-Dec                0.03   -118  -118                   0.08'     21      0.03      118               0.00,  0.002
      19  16-Dec              0.03       113     113               0.08       20O    0.03      1 1 3!            0.00    0.002
      20  17-Dec_              0.03      107     107               0.08'      19     0.03      107               0.00    0.002
         T-otal       -9.4-5-     __4-.2                            5.8    3322        4.2          0 687'    0.35         0.01
       Median Day    0.16          _             148       0.1      01- -a.9    _ 0.0          187
                an    9.45        _156 __                  3.6-             1734      0.03      223 .0.87             .    0.01
          Snowmelt         ___                    113'        _      5.8    1588      0.03      113               0.35.   0.00
         -Maximun-    0.64                                 0.3      0.3-  135.3.   0.13
          Minimum     0.0 9                                0.0      0.1       6.5 _ 0.0
         Winter % of Total                                                  48%                          .--        -
























                                                            Page 4 of 4





                                                                                 JUNEAU




                                                                        Residential                                           Industrial
                                                   Area      :        5ac                              -Area      ~       20 ac
                                                   % imp      : _    40         S                       %mp                50         S
                                                    CN ACIVI     I _83   __2.0                           CN AM It:         8 6   -   1.6
                                                    CN AMC III:      93        0.8                       CN AMC III:       9 4       0.6
                 1     2          3         4          6          7          8         9          10          1         12        1 3        I          1 5
                                        Snormel
Day0o           f            Snowmelt  TSS, cmo   Rainfall    Snownmell                       Concentral Rainfall    Snowniell                      Concenlrat
Melt    Date      PreciD    for mro=30 (moll I    Runoff in  Runoff    TSS lbs    Runofi els ton mowl   Runoff in  Runoff    TSS lbs    Runoff cis ion milo,
           1/5/87       0.13.                   0 In/a                  n/a       n/a         ni-a      nWa                   n/a        fl/a       n/a
           1/7/87       0.23-,                          0.01-                    1      000O       1~62-    -0.01-                    12       0.0O1.     181
           111/8/87      0.9.                           0. I11                  1 6 _0.02           124       0.14                    90       0.12       144
           1/9/8 7      0.52_                           0.12                    17._    0.0.3       123.      0.19                    97       0.13       14 3
         -1/15/87-     0.1I5-                     W          n/a - _n/a Wen/na n/a                                     -n/a -  fla       /a         na
         1/16/87-    0.98                              0.43               ,   93        0.09       108       0 49                   281       0.41        12 7
         1/178         0.4-6                            0.09                      I3.   0.0-2      1-27      0.11               - 76          0.1 0       147
    2 2   1/1  8/87               0.O03-    98.44 n/ae             0.04    _    4       0.01,        85,n/a             -0.0 5         0.     0. 01         0
    2 3, 1/19/87-       0.62-     0.03      90.96       0.18a      0.04    _  28__ 0.05 _   1-13              0.~211     0.09       1 54       0.22       1 29
          2/2/8 7      0.15        W        e       a                  n/a        n/a        n/a        n/a         W         /a        n/a        n/a

          2/4/8 7      0.1 3                      n/a      ___         n/ a       n la  - --n/a              0.00                     0-      0.00.      380
          2/15/847-    -0-.22                          0.0 1-     I    __       1       0.00-      166       0.01          I         10  __0.01  -.185

          2/18/87       0.16                      n/a      0            n/a( 246   __0 2/               n/0.na0 f                                 0a~~
         2/20/871a     0.352                           0.04            i        s       0.01       1372      0.06.          o        i-       0.09        1972
          2A/21/87      0.47                           -0.00                     09   0.00          2131    0.0              5         6       0.00         521
         2/29/8 7      0.29                       n/       W     e      n/a W     n      /a  - /        n/a   We n_ na                   n/a       n/
    2_ /169/87   O.15                             n/a                   n/a       n/a        n/a        n/a                   n/a    I /A           n/a
         3/262/87   O0.99                               0.13'                  18       0.03        1227      0.19G  12                        0.16       1397
         3292 /87  _ 0.217 -                            0.02-                   3- _ 0.00    2130            0.003         _         2    _  0.02   .   170
         2/208 --       0.29                      n/a                a1/a         n/a        n/a-      - -n/a                 n/a        n/a       a/al
          431 /8-7    O.8 -s                       n/a                n/a          na        nan/a                            n/a        n/         n/_
                                 4/9/87  0.18     n/a                  nia        n/a        n/a        n/a         _        n/a        n/a _      n/a~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-11a.9 A
         412 4/i8 7    0.21na                                  _        na         na        na                          n/a  n/a        n/ _       na
         4/16/87       0.99                             0.04                    6- 0.01.           -137      0.069                  41   22 0.069        1397

         4/139/87 _      02n/a                                          na        n/         na . We/eaW                      n/a        n/a       n/a
            4/20/7  _ 0.11.                       n/a                   n/a       n/a        n/a        n/a       W     e     n/         n/a        n/a
          4/27/87       0.12                      n/a                   n/a        nWa        n/a       n/a                   n/a        nla        n/va
          4/1418        0.211    We _         We                        na          /        n/a _      n/a                   n/a   _    /a         n/a

         5/12/87    O.1                           n/la                 n/a        n/a        n/a       n/a                   n/a        n/a        n/a
         9/2/8 7   We1                            n/a         e         /         n/a      W            na-n/a  0.00n/ 0                      0.0 - 27
          9 /4/8 7     0.15                       n/a                  n/a-  ae/a            n/a             0.00             11    We0                  243
          9/8/87.      0.13       _____           n/a                  n/a        -na        n/a             - 0.00-                   0   _0.00   238
         -5/23/87       0.5      3               -      0.00                    1I 0.00             16240.02            ..                    0.(01       178
     !5_ /2687_   0.28                            n/a                   n/a        n/a       Ala        Wea          I         /         n/a   24a
                0.5/271871  0.0-12  7 ___         n/a                  n/      I /       7 /           3      .00                             0.09   143
        __  6//8 7     0.134                      n/a                   n/a       We/a       n/               0.00                     0   -0.00   3 80
         65/2387        0.5                            0.00                     1I 0.00:           174'      0.02                    14.      0.01.      1 78
         516/1  /7     0.28                       n/a                   n/a        n/a       n/a        n/a       W      e      a        n/a        n/a
         6/127/87      0.15                        /                    n/a      -nta-  -We                   0.00                     I-     0.00        243
         6/513/67       0.4      .       .5            0.06                     1       00:        14                                 __        .1        17
                            state 7.  -0.9--            -0.09-   14~~~                  0.02 _   131 6        0.08                   58 7    _ 0.07 3     1.4 3
       _6/16/87        0.27                       n/a                  nla        l/ Ia   - -nra       -n/a                  nia        n/a        n/a
         6/I 2/87      0.96                             0.42                   52       W          W 0.09  I 09 0723                           0.40       128

        6/116/87-     0.31                             0.03                     9      0.01        14L2      0.04.                   30       0.03       163
        fill 9187     0.26                             0.01,                   2       0.00        1 53 -    002           i     s            0.02.      173
        6/21/87        0.75                            0.27                    34      0.06        114       0.31          I         8        0.2         133
        6/22/87       0.15   __                  n/a                   n~a        n/a       n/a              0.00          I                  0.00-      243
        6/24/-87      0.114.           We_       n/                    n/a        n/a        n/a .___        0.00                     0       0.00       273
        6/25187       0.54                             0.13                   1 8:     0.03        122       0 16                   1 04      0.14       1 42
        7/11/8167     0.36;                      n/a                   n/a        n/e        n/a             000-          I                  0.00       2-44-
        7/112/87'     0.13                       n/a                   n/a        n/a        n/a        __0.00                        0      0.00'       380
        7/113/8 7     0.26     1     ___               0.01'                   2.      0.00        1 53      0.02                    is      0.02:       1 73
        7/14/87   .0.611                               0.17                   2 3,     0.04        11 9      0.21                   130    _0.17         138S
        7/26/87--   0.14. ,_                     n/a    We____  /                 n/a    W /a   Wea               W     e    n          n/a        n/e
        7/27/87       0.26:                            0.01                    2       0.00       15 3       0.02'                   1 8     0.02        1 73
        7/28/87         0.2:     _____0.00                                     1I 0.00-   178                0.01                     6       0.01       -193
        7/29/87       0.52.                            0.12                   17       0.03        123       0.1 5                   97       0.13       1 43
         8/16/87     019,                        n/a                   n/a         /la      n/a        n/a                 We./a        n/a        n/a
        8/1 4/87,    0.1, 5                     n/a                   n/a        n/a       _n/!a      n/a                  -nia        nI/ a      -/a
        8/1 5/87      0.14                       n/a                   n/a        n/a    Ala                 0.00                     0       0.00       273
        8/16/87       0.17                             0.00                     0      -0.00       21 3      0.00.                    3       0.006      21 4
        all 7/87      0.29                             0.02.                    4      0.00        146       0.03                    25       0.03       166
        8/21/87.      0.24                       n/a                   n/e   Wea             n/e   We                        n/a ril n/a l n/
        8/26/8 7       1.11                            0.18              - 2 4         0.04.          118    0.26                   19 7      0.21   __136
    __    8/3087.      1.2-0.98:                                              89    .0.12          10 5 . 0.72              -       397   0.80            122
   ____8/31/8 7       0.41                             0.07                   10    -0.01-         13 1- 0 09-                      S 59      0.07'      151
             ___  9/2/87  0.21    __________          ~~~~~~~ ~~~~0.00'  -     -       0.0         17         .1                              .1'         8
         9/3/8 7      0.21      -_ __                  0.00i              I-10.00                  1 71     0.01                      8      0.OV    ISO
         9/4/8-7   -----0.74       __                  0.26'                 33        0.05        1 14      0.30                  1182,    0.25.        133
         9/.7/8 7      0.5-                            0.00          I                 0.0         174       0.02                    1 4     0.01        1 78
         9/9/87       0.34           ___               0.04.                   6       0.01        138       0.05                   38        0.04       159
               91/7   1.22           _ _               0.63                  74        0.13        1 04      0869                  384!,     0.58___  123

        9/1 1/87      0.44                             0.08                   12       0.02   I128   O.10                            69       0.08    I    ZS







             *                                                                  i~~~~~~~~~~~~4L





                                                                              JUNFAU






                                                 Area:          -     cArea:                                          2 O-ac
                                                 % imp     :      40          .                      %imp:            5O
                                                  CN AMC If:    a 63        2.0-                     CN ANII:    a 86           1 6
                                                  CN AMC III:      93 ~   0.8                         CN AMC III:      9 4      0.6
                   1  2         3         4          6         7          S         9         10        11         12   - 13            14    is
                                       Snowmell
Day of                      Snowmerl  TSS conc  Rainfall    Snowmnelt                      Concentrafl Rainfall    Snowmielt                   Concentrat        
Melt    Date      Precioto    IrMD=30 [Mo/I)     Runoff in  Runoff    TSS lbs  Runoff crs ion m/Il  Runoff in  FRunoff    TSS lbs   Runoff cis ion moail
         9112/9 7      0.17                           0.00          _        0.    0.00    _ 21 3         0.00                    3  _   0.00       21 4
         911418 7      0.t2                     In/a      -          11 niana             n/a    Ala             A    l    a        nWe    Ala
         9/1 618 7     0.14 6/                                        /          /         / 0.00                                 0      0k -  .00.  273
                          9/16/87  0.16               0.00                   0~~~~~~~~~~~~~~~~~~~'   0.00  24 6  0.00            2       0.00       226
         9/1 7/87.__ 0.43                             0.08         I         1       0.02       129       0.066   De0                               149
         9/1 -8/8-7    0 13     Me              _/9                  na   _ N/a           n/a             0.00         _          0      0.00       380
         9/119/ 87     0.45                           0.09.                  12.      _ 0.02    -127      0.11-                7 3       0.09       1 48
         9/21/I8 7     .0.-11-                   n/       __         n/a        n/a       n/Aa  -- n/a                   _ na       n/a       n/a
         9/2 7/ 87      0.3 --n/a _  __                              nia.  Ala            n/a    Ala           __        na         n/a       n/~a
                92/7   0.69                           0.23                  30       0.05       11 6      0.26                 1 62      0.22       135
         9-/2 9/87      .502 04.0                                                               11        02146                          0.20       137
         9/30/87       0.63                           0.19     S . __   25           0.04       11 8     0.22                  -138      0.19.      138
           10/1/87S     i 0.9                         0.37        _____47             0.08       11I0     09.42                 247       0.36       129
         110/2/87~  0.46.                             0.09                  12       0.02       1 27      0.11                  7 6      O.10o      14 7
                0._/35                                0.0                    6   _0.01X         1 37      D.06     ..41                  0.05       157
           104/87     0.69                           0.23-_ 30                       0.05       116       0.26        .        16T2 0.22            135
         10/5/87       0.53                           0.13                  18       0.03    .-122        0.16                 101  _ 0.1 3    _14 2
         10/6/67      01-9           .                 .00                           0.00       186       0.01                    5      0.00       199
         10/101/87     1.6        --                  0.16-                  2 1     0-.03      120       0.2                   12       0.9_        13
        10/1_1/187     0.67-                          0. 21I                28       0.04       1 116     0.25                  1 54     0.21       136
        10/28 0.1         8 i7   A                    0.00                    0      0.00       1 97      0.00                    4       0.003      206
         10/3/8        0.5004                                       _         6.      0.01      1 37      00                     410.05 s 17
         01014/87  _0.31                              0.35                           0.01       1 42      0,043                           .0A6
            10/15/87   ~~0.2                          0.00          I-0.00                      1 78      0~01          -         6      0.01.      193
        I10/1 7/8 70.04.                         Alna                n/a        n/a       n/a             0.00                           0.00       273
        10/18/987      0.29       __                  0.02-                   4      0.00       1 46      0.03'                  25       .03        166
                    iO/19!87  ~~~~~~~~~~~~~~0.5       014                    20       0.03       121       0.17                 112  ___5            141
        1 0/22/67      0.26                      n/-a             _n/a          n/a       Ala        Ala                -n/a        n/Aa  n/a
         10/23/87      05                             01                    20_  0Q.03_   120             0.18                  11 5     0.15 _      140
        1 0/24187 -    0.73     -           --        0.25                  33       0.05       11 4      0.29                  177      0.25       134
        1 0/26/87      0.56     ____0.14                                    2 0.     0.03       121'      0.17     ___          112.     0.15        141
        1 0/27/8 7   ~037                             0.05                    8      0.01       134!    0.07                     47      0.08         5
        10/28/87       0.31                           0.03                    5      0.01       142       0.04;                  -30      0.03.      163
        10/30/67' Al                             na          A    l    a        n/a    Ala    Ala             __ _        n/a       n/a    "Is
        1 0/31/67      0.19                           0.00                    0      0.00       1 86'     0.01'               _  5        0.00'      199
         11/1/87       0.46                           0.09         I         13      0.02       1 27      0.11                   76      0.10        147
         111/2/87      0.57                           0.19 5      _         20.      0.03       1201    0.18                    115      0.15        140
         11/3/87       0.17      C     I      A     O                         0      0.00       2133        0.00                         0.0_       214
         1115/87       0.53                           0.13      1_ 18                0.03       122       0.16                  101      0.13.       142
         11I/6/`87-    0.23-  0.01                                            1      0.00      __Lk2 L    0.01.           ___   12       0.01;       1I81
         11/8/87      0.38                            0.05          a                0.01       1 33      0.07                   5       0.6:       15
                 1//7   0.5                           0.1          I         1      I6 0.02      124:     0.14:         s     o           0.12       144
       -111/1 0/87    0.24                            0.01         _          2      0.00       159,    0.02.                    1 4.    0.01'      178
          _     _ _/1 8                                         _  _     _  _     _  _     _  _     _  _     _             A l a    _       A l a      Al nI eAa l 
           11/187      0,1                       n/a                   /A l na   A n/a               n/e    We_    Ala              n/a
               11D28  A~l                       na       _           r/         /          /         /                    /         /
        11/114/8-7     0.25_                          0.01         -          2.     0.00   --155         0.02                   16:    0.-02'       175
        I1tisis87                                          n/a       n/          na n/a   -/0i/                            /a       n/a  Al  na
        11/117/87-               A        l       a                  n/a        n/a       n/a    Ala         We           Ala    Ala           n/
    3 0 I11/18/87..       -      0.03      52.6 rA/a  . .       0.04          2      0.01l       46,n/a       ___0.05    _        0       0.01         0
         31  11/19/87  ~~0.11    0.03      471   /                .4          2       0.01        42fl/8             0.05         00 0.01 .            0
    .3 2 11/2 0/87               0.03      41.64 Ala             0.04         2       0.1          7n/      -        005_         0        .1_         0
        11/2 4187      0.47       ___                 0.00';                  0      0.00        lee      0.0~1                  10       0.01:      184
        11/2 5/87      0.18      .0.00:                                       Oi     0.00       246'      0.007                   2       0.00-     -226
        11/26/87       0.5            A     l      a         A    l    a        n/a        flS0.00,-1) .0                                             4
        11/27/8k7      0.52                           0.12                   1 7'    0.03       123'      0.15                   97       0.13       143
        11/28/8 7 __ 0.62                             0.18                   24      0.0         18       0.21                  134.     01          13
        111/29/8.7      0.5                           0.11         I         16'     0.02~   124i    G 01 4                      901    0.12'        144
       -1 2/2/87      0.24        W       e      /a                  n/a    "la    Ala    Ala                    A    l    a        Ala   _    l/a
         1 2/3/67      0.12           N          /O                   /A l   n/a    Ala    Ala                            n/a    Ala           fl/a__
    -_   1 2/4/87      0.19s                          0.000                   0       0.00   Iasi         0.01                    5   O.00    O199T!
        12/ 1 CIA87 _ 0.36        W       e       /                   n/a    A l/a MIE      /Aa            0.00         .         1I    0.001        244
        12/12/8 7  - 0.63                             0.19S                  25      0.04        118     S0.22                  138       0.1,9   I138 
       12/I 13/87'    0.6                             0.01                    2      0.00   I153          0.02                   1 8      0.02       1 73
        1 2/16/87         ____                   n/a   A              l/a   A l/a    Ala    Ala                ___        na    Ala    Ala
    26. 12/17/87       0.44       0.3     74.52      0.08'      0.04.       1 5      0.03       1 11;    0.10       0.05        85;      0.13       1 125
    2 7                0.211947   0.03_  69.04        0.01__  0.04'      5           0.01    8 7 0           0        .5         29        .-5        9 7
  -28 -12/20/87       0.27       0.03     63.56       0.2       04            6      001         8        0.03       0.0         34        .6        11
        12238 -       -. -1/                                         n/a       /af        n/a  We/a-                     n/a    Ala    Ala
        12124/87       1.13                           0.55                   66      0.12        1 06     0.81                  34.       0.51       124
        12/25/87       0.45        __                 0.09                   1 2      0.02       127      0.11                   73       0.09,      148

       Total  __      2.74                            9.46   D. 31        12835                          11.63      0.38      7351
       Medan Day      0.27                            0.06I      .4        8.69,     0.01       12 7      0.05.      .5       2.9.       00          1 57
       Rpain Ffpeb-C    38.54       __                6.591                 879      0.01        1 33     8.17                 5106,      0.03       1635
       Maximuam        1.2 se        _                0.63;     0.04,        74.     0.13   246.04        0.72:     0.05       397'      0610,  3.79.86
       Minimum          0 1                     ,     0.00      0.04          0      0.00      39.70      0.00.    0.05           0       0.00      0.01





                                                                                      JUNEAU




                                                                            -Commlercial --Pro-development
                                                              Are~ ~       ~~~~~a C  15_a                            Area :    20 ac- 
                                                         % imp              85         S.              Sonj ---1:1                 2      S
                                                            CN AMZII        94 _   0.6                             CN cAMCO      7 0 4.3
                                                            CN AMCIII      98.0       0.2_-                        CN ANCIII      85     1.8
                        1     2         3         4          -16         1 7       1 8       1 9      2 0      2       .1      2 2  2 23
                                              Snowmelt                                            Concentr          Rainfall Snownme
       Day of                       Snowmeil  'TSS Conc  Rainfall    Snowmeii             Runoff   ation             Runoff  it      Rlunoff
       Melt    Date      Precio    for imo=30 1Mo/II    Runoff in    Runoff    TSS lWS   CIS      MoI         i      n      Runoff  CIS
                  1/5/8 7     0 1 3                   0         0.00          .        0  -0.00        5 52          n/a            .0.00
                  117/87      0.23                              0.09                  6 8    0.06      21 8          n/a               0.00
                  1/8/8 7      0.9 --                           0.32            _    209     0.20      1 93             0.01           0.01
                  1/9/87      0.52                              0.34          .-     219     0.21_  19                  0.01            0.01
                 1/15/87      0 15.                             0.00                    1     0.00-   353            nWe                0.00
                 1/1 6/87     0.98.                             0.77  _    __        463      0.-49   I7  0i--.16-                      0.14-
                   I  78-7    0.4                               0.8 8-01                               195              0.01            0.01
            22 I1/1 8/87.  0.03                   96.44 n/a               0.08    __   0      0.02        0          n/a        0.00   0.00
            2 3, 1/l9987.      0.62     -0.03     90.98         0. 43     0.08 _      297.   0.32       1 72            0.04    0.00   0.03
                  2/28    a.15                                  0.00          I              -0.00    3153                              0.0
                  2/4/8 7 _     . 013_                          0.03                  23_  0.02        24 7          n/a                0.00
             V_25/87           0.22                             0.-08                 6 30.0 22   O-~    n/                             0.00
              __  2/8/87      ~~~~~0.16                         0.04                   35     0.03      235    W e          _           0.00
                 2~/8/7       0.5                               0.3                 225.   0.22  __191           _      0._02     _     __0.01
                  2/9/87        0.4                             0.23,                155S    0.14.    199.              0.00            0.0
                           .!1~~~~~/87   0.16   . ~~~~~~~~0.00                         2      0.00     32 8          nWe.               0.00
                2/119/87      0.15                             0.01                    5     0.00      289          n/a                0.00
                2!2 0/7       0.50.1I9D                                              128__  0 12_  203n/                  __ We    0.00
                2/21/87       0.17                             0.540                         0.3       22/a.0
                2/125/8 7     0.29          .0.03                                    27      0.02      242          n/a                0.00
                3/16/8 7      0.1I5                            0.001                         0.0       33na.0
                 3/2/8    _ .6 -0.00                                                    2     -0.00.    32           n/a               0c.00
                -3/28/187-    0.99--                            0.50                 311-  0.3-1   __184         -     0.00            0.00
                 3/29/87       0.27                             0.12          a    s          0.08     21 2          n/a                0.00
                3/30/87        0.1.                            0  .01. .      -       12     0.01_  265             na_                0.00

                 _--  _0                                                                        - 0. 8 --   _ _ _ _ _ _a                 _ _ _0

                                    4/3/8 7 ~ ~ ~      ~     ~      ~     ~     ~    ~    / 0/8                      n/a                0.00
                    -  _91 _   .1                              0.02                   15     0.01      298    W e a                    0.00
           4____511/87        0.1 -__                 ____      0.00                   27  0.02        3282  -      -n/a               0.0
                 4/12/87      0.35                              0.103'                297    0.02      2423          r/a                0.00
                 45 /3/87     0.23        ____                  0.09                  68     00 7 1                   /    _____00
                 54/2087      0.15                              0.0                   31     0.02      238    1      n/a         _ _    0.00
I                5/8/87~~~- -      0 13                         0.02                  235    0.021   -247           .n/a00
                5/23/87        0.12                     0l 14 -    W              e          0.09      20            n/a               0.00
                5/26/87       0.28                             -O__   .0              24      .0       245 8n/a                        00
                5/sile7----7  0.146                             0.03!                 27      0.02     242           n/a                0.00
                 5/2/8 7     0.14 -0.05                                              42  70.03         2421         n/a                0.00
                 65/817       0.23                             0.1;                  98.    0.0        210          n                  0.0
                                    6/11/87  0.16               0.00                   2     0.00      328.~~~~~~~~~~~~~~96   n/a  -~0.00
                      6/12/87  0.5     ___               __  0.04        ___          31    0.02      238           n/a                0.00

                 51618_        0.4                       _     0.315;    014                           198    DO__________
                                       0.31                    ~~~~~~~~~                     ~~~~~    ~~~~          ~~~0.27  1082  0.10  209n6,.0
             ___~~~~~~~~1  023                   D.11                                        0.0       24             /                 0.00
                       53/7   0.75                             0.85                  342     0.35      12               0.0            0.06
                        - -                                                             4002.145  _____a______
                6/25/87       0.54.      ___       _0.35                    _         3~ 02            1100'0.02
                57/1187       0.361.64 0.0.04                                                          227           n/a               0.00
                7/12/I8 7    0.1 f_ _ _ __ 0.03                                      23      0.03      24      3 1 /a                  0.00
                 7/15/87      0.26.                             0.141                 83'    0.07.     214'          n/a                0.0
                            7/14/87  ~~~~~~ ~~~~~~                                           ~~~~0.61'    2670  0.276  1 87  0.03      0.03
                7/26/87       0.14                             0.00           2              0.00.     328:          n/a               00
                 7/2/87'      0.26                             0.1                    83     0.0       214           f/ -0.00
                -7/ 287        0. -_ _                          0.075                 53   I0.04;      224           n/Ia               0.00-
                7/29/187   _  0.52- 4       ___         ___  0.234                   219     0.2--, 1  192a             0.001,         00
                 8/16/87-    0.15'    -                        -________0.03  2        2      0.00'     253'         n/a           .    0.00
               86/14/187     0.95                              0.00                    1    5 0.47     35           n/a                0.00
                 -8/15/870.14 I                   n        a                         2       0.I02      4'          n/a                00
                8/1 6/8 7.    0 0.        2           6           5          0.0.3!                    22             /                 0.00
                8/17/8 7      0.29                              0.04.                 98'    0.02      210'          n/a                00
                8/21/87       0.14_                            0.02                   15~    0.01i    259            n/a                0.00
                8/258/87.  0 .54                               0.60'                 367     0.22      191              0.012_          0. 02
       --_    ----7            .4                               0.04                 161      0.15'  227                0.00            0.00
                7912/87      0.21'a                            0.08'      2     3      :    0.05'      242     7     /a                0.00
            7/1 /3/87         0.26'                             0.08                  88'    0.078    2122           n/a                0.00
                9/4/1187     0.61                              0.54        2        337      0.264    183;             0.03            0.03
                97/2787       0.526                            0.14                  983    0.09       210,         n/a                0.00
              7129//8 7-  0.34                -    -0.18                            1243    0.011      2047         n/a                0.00
                9/10/87       1.522                            31.0 1                588     0.63'     1792             0.29'           0.24

                8/116/87:     0.4402617 0.17                                                           198 0.03022 n                    0.00



                                B-1 1.71 7---   0 2 9           0114                  9a, 0.09210                    n~a0.0


 I~ ~~~~~~~118                 .          4          0          .          2          15     00,       2      9     na      -00






                                                                            JUNEAU3




                                                     Area          C~~~~~ommerchil                             Pmif-development
                                                     Area-:. ~     I 5ac                                    Area:  -     20.ac
                                                 %im~p             85         S                             %imp          2       S:
                                                   CN AMACII       9 4       0. 6      _                  CINIAMiI   _  7 0     4.3

               1     2         3         4           1 6  I     17        18   _  19         20  2    _        21      2   .2  23

                                      Snowmeil                                            Concentr          Rainfall  Snowme
Day of                      Snowmlell  TSS conc  Rainfall     Snowmelf            Runoff   afion              Runoff  It     Runoff
           Melt Dte    preto   forimn=30Imall)  Runoff in    Runoff    TSS lbs  ci s    mo/I                in      Runoff  efs
         91 1218 7    0.17                              0,05                  4 0     0.03     232      F     i    l    e        .0
         9/114/87     0.12           -0.02                                    1-9    0.01      252           n/a        --      0.00
         9/15/8 7      0.14                          .0.03                    27      0.02     242           nla                0.00
         9/1 6187     0.186                             0.04                  3-5  -0-.03-    2-35           n/a                0.00
         9/-17/87      0.43                             0.26      _71                 06        197 "           0.00            0.00
         9/118/8 7     0 13    .                        0.03__                23  . 0.02        24 7         n/'a           - 0.00
         9/19/87       0.4                              0.27         '    AZ          0.17.    16                0.01           0.00
         9/211/87.     0.11                             0.02                   1 - . 50.01      258    W e a                    0.00
         9/2 7/87-      0.3.         .        _         0.04          _          30   0.02      239          n/a          _     0.00
         912 8187      0.89    0            ~        - ~.49.. -              31 0    0.31       184             0.05            0.05
         9/29/87      0.65                              0.4          _       28-9    0.29_   186          _     0.04     _ _    _0.04
         9M/30/7       0.6 3                            0.4 4                278      0.20      18 7            0.04            0.03
         1 0/1/97       0.8                             0.69           ___421         0.44-    178              0.13            0.11
         1-0/2/8-7    -0.46                             0.28                 187      0.18      195             0.01-           0.01
         1 0/3/87     0.35                              0 19                 1 29     0.12     203           nia                0.00
         1 0/5/87     0.53              O. 35                      2     _   25       0.22      1 91            0.02011
         0106/87      0.1I9.                            0.08                  49     0.04      227           n/a                0.00
                    10/10/87  1.06            ____    ~~~~~~~~~~~0.5         -4 _ 33  0.35      18               .10.01
         Oil/11/87     0.8C7-_                          0.48                 299      0.30      185             0.05            0.04
        10/l 1287     0.1I8                     _       0.06                  44      0.04     22 9          fl/f               0.00
        I10/ 1387.    03 5                              0. 19          __ 129         0.12      203          n/a                0.00
         10/1-4/8 7    0.31-                            01          1          0TO80.10 -20                   /                 0.00
        10/115/87       0.2                             0.753                         0.4       224           n/a                0.00
        I10/17/87      0.14                            -0.03                  -27_  0.02_  242               Wit                0.00
        10/18/87-    0.2j9                              091   .80 09                           210    O    - /a        -        0.00
        10/ 1987      0.56                             0.37     _   ___241           0.23      190o            0.02            0.02
        1 0/22-/877    0.2-6                           -0.02         I         19     0.01      251          nia                 0.00
        10/2 i3/87   E.5                                03-8  -_246                   __.24     1 89            0.02            0.02
        1 0/24/8 7    0)73                 0.53..                   -        331      0.34      18 3            0X.0        _   0.08
         01028/07     -0.56                             0.37                 241'    0.23   ISO                 0.0             0.02
    _   0102718 7      0.37                     __   0.20                     1 39    0.13      202             0.00   __       0.00
      _10/28/87       0.31-                            0.15         I        108     0.10      207      "la             -       0.00
        1 0/30/8 7      0.1,                            0.01                   1 2    0.01:    285.           n/a                0.00
      -10/31/187.     0.19                             0.06                   4 9'    0.04     227    W e a                     0.00
         11/11/87     0.48 6_   0.25                                         187      0.18      1 95            0.01            0.0
         11/2/87      0.57      _____                   0.38                 246      0.24      1 89            0.02            0.02
        -11/3/87      0.17                             0.05.-  40!    0.03                     232           n/a               -0.00
         111/5/87     0.53.                              .3                  225      0.22  Is81                0.02  -co-,1
         11/6/8 7     0.23                              0.09                   688    0.06     218:          n/a                0.00
         11/8/87      0.38      _____    __             0.21                  145,    0.13'     201,            0.00            0.00
         11/9/87        0.15,                           0.32   __209                  0.20~  1 93'              0.01            0.01
       I1I/l0/87.    -0.24                   -____01                          73     0.06      217    W e a                     0.00
               _          _     _                         _   _118 _     _1                     0_  _   _  0   2    _                             I~ .1 2 8Nt0
       11/112/87 _    0.11.                            0.02                   15.    0.01      258.    Wea                      0.00
                    11/14/87  0.25                     0.11         ~        ~~~    ~~~~~     ~~~ 78  0.07  21 5  fl/a    __ 0.00
                  I !~~~~~~~~~15!87  .   ..    . - ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~n/a  n/a  n/a  fl/a         n/a                00
       l11/1787-                               n/8                    n/a       n/a      n/a      W     e     a                0.00
   30-11/10887                  0.03       52.6 n/a- ____  0.08    a                 0.02        0           n/a        0.00   0.00
   3 1 11/1 9/8 7     0.11      0.03     47.12         0.02       0.08        28     0.06       85           nl/a       0.00   0.00
   32 11/20/67                  0.03     41.64 fl/a               0.08         0     0.02        0           Wea        0.00   0.00
       11/24/8 7      0.47                             0.12-        a          6     0.08      213           n/a                0.00
      11/- 25/87      0.Li     I__                      0.04       _____35'    0.03            238,          n/a       ,        0.00
       11/26/6 7      0. 15     _____0.04                                     31     0.02      238'          fl/a               0.00
       11/l27/87      0.52-  0.34                                            219i   0.21'      18921            0.01            0.01
       11/28/87       0.62,                             0.43                 273'    0.27      1871             0.04            0.03
       11/29/8 7       0.5'                             0.32'                209     0.20      193i             0.01            0.01
     ____  12/2/87'   ~~0.241                           0.02'                  1 5    0.01'    2591            /                 0.00
        1L2/3/87      0.12     _______0.02,                                   19     0.01      252'          n/a                0.00
      -12/4187    _0.19                                 0.06'                 4 9'    0.04,    227!   Wea                       0.00
               1/087  0.38'                             0.06                   48!   0.04       227'   We/                      0.00
     --1-2/12/87  .-0.83                ______   0.44.                        278     0.28      1 871            0.04.           0.03
               12138  02_6'                             0.11                   83'    0.07      21 4'        -na  -    -         0.600
                 12/18/87    ___________       ~~~~~~Noa               n/a       n/a      n/a       ,        n/a                0.00
   26_12/117/87       0.44'     0.03'    74.52          0.26      0.08'      1 97    0.22.    168:              0.00'   0.001  0.01
   2 7 12/119/87      0.24_   0.03   ..69.04            0.1I0     0.8         91     0.11      151'          n/a        0.00  Co0
   28a 12/2 0187      0.27~     0.03'    63.56 _        0.12      0.08'   I105        0.13     153'          n1/11      0.00'   0.00
           12/23/87   ~~0.2~                           0.01                    7     0.00      281'          n/a                0.00
      _12/24/87       1.1 3        ____0.92                                  541.    0.58   .173                0.24         -0.20
       12/25/8 7      0.45                              0.27                 182      0.17     1 96             0.01            0.00

       Totla         52.74                             27.02       0.84;   1782                                  2.05.  0.04'   -
      --efcafw lay_.  027'  -                           0.1I0     0.08.    70.12      0.08      214'    0.23'   0.02.   0.00   0.00
         Ran(Fe -C    38.5         4   19 .1             . 1               12544      0.05      222:             1 41.          0.00
           Maximum __    ~1.82           ______ 1.23'              0.08:      704!    0.77  552.07               0.29'   0.00   0.24
       Minimum          0.1                             0.00       0.08         0     0.00     0.01              0.00    0.00   0.00













                                                                44U




                                                           BETHEL



                                                                    Residential
                                                  Area:            5 ac                            Area:             1
                                                  % im           25         S:.                    % imp:_ .   40
                              TR 55 Factors:     CN-AMC 11       8 5      1.8                     CN-AMC 11        87
                                             AsmdCN-AMvC III     94       --0.6                   CN-AMC II I    95

    Assumed                   Snowmelt Snowmelt                                        TSS
    Day of                   for       TSS conc Rainfall   Snowmelt           Runoff    Concentrati Rainfall   Snowmelt
    melt     Date    Rain (in) irnp=30  (mg/I)   Runoff in Runoff in__TSS lbs ciofs_   on mngLl    Runoff in Runoff in
            8 19-Jan       _       0.03       8 7               0.03        3    0.005          8 87              0.04
            9  20-Jan   __         0.03       84      __        0.03   _   2    0.005  __      84                 0.04
           10  21 -Jan             0.03       81                0.03        2.   0.0.05    a 81                   0.04
           I11  22-Jan             0.03       78                0.03        2    0 .005         7 8               0.04
           12  23-Jan              0.03-      76                0.03        2    0.005   _      76                0.04
          -13  24-Jan       _    0.03-        73.-            -0.03.        2    0.005         73,               -0.04
           1 4. 25-Jan    _   _    0.03       70                0.03-- 2,_ 0.005.   _70                  ~        0.04
           1 5  26-Jan             0.03       67                0.03        2    0.005       _67                  0.04
                 42-Fb              .0        9                00 3 3  .___9_                                      00
            4 27-Feb               0.03       95                0.03        3    0.005         95                 0.04
            1  6-Mar               0.03.    1 06                0.03        3    0.005  __  106-           __   0.04
              1-21-Mar-          0-.047-    1-06               0.04        5-  0.008.         1-06                0.106
            2  23-Mar             0.023      1 03  -       - 0.02           2    0.004         1 03               0.03
            3  24-Mar  __ _ 0.047            100                0.04        5    0.008.        1 00               0.06
           -4  25-Mar            0.030       -98               0.03         3.   0.005         9_8                0.04
I        ~    ~~~5 26-Mar  _      0.020       95                0.02        2    0.004          95 __0.03
            6  27-Mar             0.020   9  92           _    0.02  __ 2    0.004   9    92                      0.03
            7  28-Mar             0.020'      89                0.02   _ 2    0.004             89 __    _        0.03
              29-Mar         _ 0.020          87      _        0.02         2    0.004  __      87          __    0.03
        9 30-Mar________  0.035               84   ___         0.03         3    0.006   _     8_4                0.05
           1 0  31 -Mar           0.040       81                0.03        3    0.007          81                 0.05
          IL1-1   P              0.041        78               0.03.        3    0.007         78    ___0.05
           12  _?_Apr              .3         76                0.03'       3    0 .007         76       _0.05
       -_    14   4-Apr          0.038        70       ~       0.03         3    0.007   _     70                 0.05.
           13   3_-Apr_           0.037        673              0.03:       2.   0.007    673                      0.04
             1   ' 6-Apr         0.026        65         0      .02______ 2 0.005               51           0     .0
          167                    0.038       62                0.03        2    0.007          62,_              0.05
          1 8   S-A r            0.031 __    59                0.03        2    0.006 _        59.                0.04
          1 9.__ 9-Apr     _    0.030    ----56                0.03-       2    -0.005-        56-               -0.0.4
                20  10-Apr    -~~  0.026      54               0.02         1    0.005 _       54                 0.03
          _21 _1-A__             0.040        5 1              0.03         2    0.007    _   51                  0.05
          __2_  12-AP~_           0.046       48                0.04        2    0.008 _        48-               0.06
       __ 23  13-Apr             0.046        45               0.04         2    0.008         45                 0.06
                24' 14-Apr'     ~~0.063       43.              0.05,        3    0.011         43!                0.08
          25, 15-Apr             0.050        40:              0.04.        2.   0.009         40        ~        0.06
          26'  16-Apr            0.035        37,              0.031        1'   0.006         37'                0.05
       __ 27' 17-Apr             0.047-       351              0.04!        2    0.00-8        35i                0.06
          28; 18-Apr             0.052'       32               0.04         2'   0.009         32'                0.07
                29: 19-Apr      ~~0.052       29               0.04'        1    0.009         29                 0.07
             2_7-MVay_  0. 17'                       0.00,                  0    0.000 n/a             0.00'
         28Ma            0.29                         0.03                  4    0.007        100      0.05
                6-Jun    0.22   _     __              0.00.                 0    0.0-00! n/a           0.00-
               15--Jun _0.22                  ____0.00                      0    0.000'n/a-            0.00-
               16-Jun    0.27                         0.03      _____3    0.005               103      0.04
               23-Jun    0.12          ___            0.00        ___       0    0.000in/a             00
               26-Jun    0.12                         0.00                  0    0.OO I n/a            0.00.
                15-Jul    0.31     ___                0.00i                 0    0.000'n/a       -     0.'
            ___17-Jul    0.23    __                  0.01                   2    0.003        109__ 0.02~
               24-Jul-  0.31                         0.00.                 0'   0.OO0in/a              0.00
               28-Jul   0.12                         0.00                  0'   0.000!n/a              0.00
                I-Auq     0.2                         0.00                  0    0.OOO1n/a              0.00



                                                          PagelIof 4




                                                       BETHEL



                                                                Residential
                                             Area:            5'ac                             Area:               1
                                             % imp:          25         S:                     % imp:            40
                          TR 55 Factors:     CN-AMC If        85       1.8                      ON-AMCII1         8 7
                                             ON-AMC III      94        0.6                     CN-AMC III         9 5
                                    AssumedI
Assumed                    Snowmelt Snowmelt                                          TSS
Day of                    for        TSS conc Rainfall   Snowmelt           Runoff    Concentrati Rainfall   Snowmelt
melt      Date    Rain (in)_imp=30   (mg/I)    Runoff in Runoff in TSS lbs  cfs   -on mg/I   Runoff in Runoff inI
          *8-Aug    0.11                           0.00      -0    0.000 n/a                         0.00
         _ 13--Aug.   0. 15S                      0.00                   0    0.000 n/a              0.00
          15-Aug_  0.52                           0.15                  1 5    0.031         8 6     0.18
             17-     Au                                0_2                                                  0I2200 4   700
          24-Aug    0.24                          0.02                   2    0.004         107      0.03
            -  7-S~~p-.1 1-                        0.00 0---    0.000-n/a                             0. 00.
                8-ep 0,15                         0.00.         O0  -0.0001                -146      0.00
           17-Sep    0.26                         0.00        -0    0.000 n/a                        0.00I
           18-Sep.   0.33                         0.05                   5    0.010          9 6     0.07
         -19-Sep.   0.14                          0.00                   0    0 .000        164      0.00
         *25-Sep    0.17                          0.00                   0    0.000 n/a        _     0.00
           30-Sep_- 0.13                          0.00                   0    0 .000_n/a             0.00
            1 -Oct O, 016                          0.00                  0    0.000         136       0.01
           2-Oct    0.31                          0.04                   5    0.009.         9 8     0.06
          -3-Oct    0.19                          0.01                   1    0.001         120      0.01
          28-Oct    0.18                   --    0.00    -0    0.000._n/a                      __    0.0-0
          2-9-IOct*    0.1                        0.00                   0    0. 000 n/a       __    0.00
          31 -Oct     0.3                         0.04       ___         4    0.008          99      0.05
      24  27-Nov       ___ 0.03            43                0.03         1    0.005      _43                    0.04
     25  28-Nov               0.03 _      40                0.03         1    0.005          40          ___ 0.04
     22  13-Dec        __     0.03        48                0.03         1    0.005          48         _       0.04
     23  14-Dec  ____         0.03        45                0.03         1    0.005   _      45                 0.04

       -Total       6.67'                                             140                 -    - 
      Median Day    0.20         __0.00                     0.03.       2      0.005         81      0.00       0.04
            Rain ___ 6.67                         0.39                  42    0.000        -107   0. 5
         Snowmelt                        ___ ____             1.3:      97'_  0.0 1    _ 72                     _2 .0
         Maximum Summer Day    _                  0.15      0.05    14.61 --0.031           164       0.18       00
        -Minimum Overall                          0.00      0.02      0.00      0.00         2 9      0.00       0.03
        TSS - Winter % of Total                                       70%3

























                                                     Page 2 of 4





                                                             BETHEL



                                                  Commercial                           Pre-Development
                                                   ac                              Area:            5 ac
                                                                 S:.             _~~% imp:          2        S:-
                                TR 55 Factors:            1.5                      CN-AMC 11       73       3.7
                                                          0.5                      CN-AMC III      8 7      1.5
       I                              ~~~~~~~~~~Assumed
      Assumed                   Snowmelt Snowmelt                       TSS
      Day of                   for       TSS conc                       Concentrati Rainfall   Snowmelt Runoff
      melt     Date    Rain (in) imp=30   (mg/I)   TSS lbs    Runoff cfs on mg/I   Runoff in Runoff in cfs
I         ~    ~~~~8 19-Jan         0.03       87                 0.002         -0 -0.00    0.001
             9 20-Jan               0.03       84          1      0.002         84               0.00-   0.001
            10  21 -Jan             0.03       8 1         1      0.002         81       I       0.00    0.001
U~~~~~~ _ 22Ja                                                                   __37 81  . 0       00     .
            12  22-Jan              0.03       78     6       I   0.002         78-              0.00,   0.001
            1 3  24-Jan             0.03       7 3         1      0. 002        7 3              0.00    0.001
            1 4  25-Jan             0.03 _    70  _ _1.   -0.002.               70.              0.00-  0.001
            1 5  26-Jan             0.03       6 7      _1 __0.002              67               0.00    0.001
             4  27-Feb              0.03       98          1      0.002         9 8              0.00    0.001
             5 28-Feb               0.03       95          1  _0.002            95               0.00    0.001
             1   6-Mar              0.03      106          1      0.002        1 06              0.00,   0.001-
               121-Mar*            0.047      1 06  I   _         0.003        1 06               0.01.  0.002
               223-Mar            0.023       103          1      0.001       103                0.00    0.001
             3  24-Mar             0.047      1 00         1      0.003        1 00              0.01.   0.002
             425-Mar               0.030    Ss             1      0.002         98               0.00    0.001
                        526-Ma r ~   ~     ~                         0        _2          9_1001 9500      .0
              626-Mar             0.020       92           1     0.001         92                0.00    0.001
             6727-Mar              0.020       692                 .0            200                       .0
                 7   8Mr.          0.2         8                  0.001.        89-              0.00.   0.001
             8 29-Mar              0.020       87          1      0.001 __      87               0..00-   0.001-
             9__30-Mar _003                    84.         1      0.002   __  84 _'_0.01    0. 0-01
            10  31-Mar             0.040       81  __      1      0,002         81                0.01    0 .001


               -1 ~   ~     _            2_ 7008 1               002-7-0.01,   0.001

          -1 55-___               0 .037   _ 67            1     0.002         67               -0.01    0.001
                 I ~~~0.026                   65          0~  0.001           _65.               0.00.   0 .00 1
            17_7-        ~        0.038     _62-           1     -0.002-       62-               0..0 1    0.001
           1 8   8_ Apr  .__     0.031       5-9         1_  0.002            59-               0.00    0.001
           19   9_Ir              0.030        56         0      0.002   -     56      -0.00    0.001
           20  10O-Apr      _     0.026        5 4         0     0.001         54'               0.00    0.001
           21 _  i ~~             0.040  _ 5I              1     0.002         51                -0.01-  0.001
           22. 12-Apr.            0.046- _   48           -1    0.003          48                0.01   _0.002
        __ 23' 13-Apr        __ 0.046         -4 5   __          0.003         45                0.0 1-  0.002
           24_ 14-Apr             0.063        43          1     0.003         43         ___  0.01    0.002
           25_ 15-Ap              0.050       40,          1     0.003.        40i               0.011  0.002
           26- 16-APF           __0.035__    37-           0     0.002 ~    37,                  0.01    0.001
           27'__17-Ap~__          0.047       35.         0      0.003         as       !        0.01    0.002
           2 8  1 8-Aqr           0.052       _32 _        0     0.003        .32                0.01    0.002
             2919--pr-            0.052       29          0      0.003         29                0.01    0.002
               Z7-May_..  0. 17  -0                              0.000in/a     __   _0.00                0.000
          2_ -Mav    0.29                        --1             0.002    .133         0.00               0.000
                 6-Junm  0,C.-2-2                  ___   0        0.000 n/a _    __ 0.00                  0.000
                15-Jun    0.22                             0      0.000:n/a             0.00              0.000
                16-Jun    0.27                             1      0.002        13       0.00              0.00 0
                23-Jun    0.12                             0      0.000,n/a             0.00              0.000
                26-Jun    0.12                    __       0      0.000 in/a     --     0.00    - --0
               1-A5-Jul.   0.31                            0     0.000        251      0.00              0.000
                17-Jul_  0.23                             1      0.001        142'    0.00               0.000
                24-Jul    0.31         ___                0      0.000        251      0.00              0,.000
                28-Jul___ 0.12                            0      0.000! n/a            0.00              0.000
                I1-Aun    0.2                             0      0.000,n/a             0.00              0.000



             U                                            ~~~~~~~~~~~~~~~~Page 3of 4





                                                        BEITIEL



                                             Commercial                            Pre-Development
                                              ac                               Area:             5 ac
                                                            S:                ~~~~%np           2        S:
                          TR 55 Factors:             1.5                       CN-AMCII1       73        3.7
                                                     0.5                      G N-AMC II I     87        1.5
                                    Assumed
Assumed                    Snowmelt Snowmelt                         TSS
Day of                    for       TSS conc                         Concentrati Rainfall   Snowmelt Runoff
melt     Date    Rain _(in) imp=30   (mg/I)   TSS lbs    Runoff cfs on mg/i   Runoff in Runoff in cfs
                 8-u 052                               0      0.008        116      0.00               0.000
            13-Aug    0.15                             0      0.000 n/a        -    0.00            -0.000
          I15-Aug     0.5                           _          .0 1                 0.03           ~0.006
           17-A~   0.24                                      0.001         14        .00.000
          24-Aug    0,54.               I                     0.001-  -  138        0.00.              0.000
          *7-Sej     0.11                              0      0.000~n/a          __0.00                0.000
            8-Sep    0.15                              0      0.000---..   172      0.0-0-             0.000
                17Se  .26                              0      0.000 n/a             0.00               0.000
           I1a-Sep    0.33                             2-   0.003-         1-28      0.00-             0.000
           I19-~p_ _0._1_4_                            0      0.000        lei       0.00              0.000
          25-Sep    0.17                              0      0.000~n/a        _     0.00          - 0.000
          30-Sep.   0.13'                             0,    0.000 n/a          _ 0.00                 0.000
            1 -Oct    0.16                             0  _0.000           166      0.00    -0.000
            2-Oct    0.31                              2      0.002        130       0.00          - 0.000
            3-Oct    0.1I9                             0      0.000      _153        0.00              0.000
              28-Oct  _.                                       __                                        __00  I/ .0  .
          28-Oct    0.18                              0      0.000 n/a              0.00           -~0.000
          31 -Oct     0.3                             2 0 .002             131      0.00              0.000
      24- 2-7-Nov.    __       0.03-       43          0      0.002         43                0.0      0.001
      25-28-Nov                0.-03       40          0      0.002         40                 0.00    0.001
      22  13-Dec               0.03        48          0      0.002         48                0.00    0.001
      23  14-Dec--             0.03        45          0      0.002         45                 0.00    0.001

         Total_      6.67                   ___       45                                     ____          0
       M~edian Day    0.20                             1      0.002         ----8 1  0.00.    0.00          0
         Rain    - 6.67        _                      16      0.000        140  _0.03.                     0
         Snowm-elt                                    29       0.00         70                -0.2 
         .Maximum S ummer D~ay  ---                 4.82      0.008        251.    0.03       0.01      0.01 
         Minimum Overall                            0.00       0.00          0      0.00      0 .00     0.00
         TSS - Winter % of Total                    64%                                                 89%3















                                                                         Page 4 of 4~~~~



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I                         Rainfall Runoff TR 55 CN Values for Juneau and Bethel

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   *MONTGOMERY WATSON 

BY          DATE __ __ CLIENT                          SHEET -__ OF
CHKD. BY    DESCRIPTION____                             JOB NO.










             ,.1~~~~~~~~~~~~~~~~~4


           ~~~~ ---~~~~~~~~4
             cow,                        TaL, .7                          *


  -~  _e -eL~M      'jt~pe . ï¿½oKd;F~Jj














                                        c~~~~~~~~~



     EN~L                              IS0/3
            In,         /~ JPP~-W*i  UMiC
                         ~~    -~~~-~~- w-- ~ ~ ~         C
          ~e    Ac.F~jQ Y P,,                                        U~ ~












              cSS'&~2 ~A3~i'C C     D c1                                    3 ru 
             unn'r~o   tAMC W~j 
                                             c~~~ ~~~7 ~






 EN iS I 1OI78) 




        Department of
           Aru Urban Hydrology

        Servicenean    for Small Watershed=
        Engineering
        Division
        Technical
        Release 55
        June 1986



I













                                    Table 2-2a.-Runoff curve numbers for urban areasl

                                                                                              Curve numbers for
                               Cover description                                             hydrologic soil group-

                                                            Average percent
          Cover type and hydrologic condition                impervious area2          A           B            C           D


Fully developed urban areas (vegetation established)

Open space (lawns, parks, golf courses, cemeteries,
  etc.)3:
    Poor condition (grass cover < 50%) .............. 68                                           79          86           89
    Fair condition (grass cover 50% to 75%) ........... 49                                         69          79           84
   Good condition (grass cover > 75%) .............. 39                                           61           74          80
Impervious areas:
  Paved parking lots, roofs, driveways, etc.
   (excluding right-of-way) .......................... 98                                         98           98          98
  Streets and roads:
    Paved: curbs and storm sewers (excluding
     right-of-way) .................................. 98 98 98 98
   Paved; open ditches (including right-of-way) ....... 83                                        89           92          93
   Gravel (including right-of-way) ................... 76                                         85           89          91
   Dirt (including right-of-way) ..................... 72                                         82           87          89
Western desert urban areas:
  Natural desert landscaping (pervious areas only)4...                                 63          77          85           88
  Artificial desert landscaping (impervious weed
   barrier, desert shrub with 1- to 2-inch sand
   or gravel mulch and basin borders) .............. 96                                           96           96          96
Urban districts:
 Commercial and business .......................... 85                                89          92           94          95
  Industrial ........................................ 72                               81          88           91          93
Residential districts by average lot size:
  1/8 acre or less (town houses) .......................65                             77          85           90          92
  1/4 acre ......................................... 38                                61          75           83          87
  1/3 acre ......................................... 30                                57          72           81          86
  1/2 acre ......................................... 25                                54          70           80          85
  1 acre ........................................... 20                                51          68           79          84
     2acres-12                                                                         46          65          77          82
 2 acres ..........................................                 12 46 65 77 82

Developing urban areas

Newly graded areas (pervious areas only,
 no vegetation)5.................................. 77                                              86          91          94
Idle lands (CN's are determined using cover types
 similar to those in table 2-2c).

'Average runoff condition. and I1, = 0.2S.
2The average percent impervious area shown was used to develop the composite CN's. Other assumptions are as follows: impervious areas
are directly connected to the drainage system. impervious areas have a CN of 98, and pervious areas are considered equivalent to open
space in good hydrologic condition. CN's for other combinations of conditions may be computed using figure 2-3 or 24.
3CN's shown are equivalent to those of pasture. Composite CN's may be computed for other combinations of open space cover type.
4Composite CN's for natural desert landscaping should be computed using figures 2-3 or 24 based on the impervious area percentage (CN
= 98) and the pervious area CN. The pervious area CN's are assumed equivalent to desert shrub in poor hydrologic condition.
Composite CN's to use for the design of temporary measures during grading and construction should be computed using figure 2-3 or 24.
based on the degree of development (impervious area percentage) and the CN's for the newly graded pervious areas.



                                          (210-VI-TR-55, Second Ed., June 1986)                                                2-5












                                    Table 2-2c.-Runoff curve numbers for other agricultural lands'

                                                                                                       Curve numbers for
                                      Cover description                                              hydrologic soil group-

                                                                       Hydrologic
                       Cover type                                      condition              A           B            C           D


     Pasture, grassland, or range-continuous                             Poor                68          79           86          89
       forage for grazing.2                                              Fair                49          69           79          84
                                                                         Good                39          61          74           80

     Meadow-continuous grass. protected from                                                 30          58           71          78
       grazing and generally mowed for hay.

     Brush-brush-weed-grass mixture with brush                           Poor                48          67           77          83
       the major element.3                                               Fair                35          56           70          77
                                                                         Good               430          48          65           73

     Woods-grass combination (orchard                                    Poor                57          73           82          86
       or tree farm).s                                                   Fair                43          65           76          82
                                                                         Good                32          58           72          79

     Woods.6                                                             Poor                45           66          77          83
                                                                          Fair               36           60          73           79
                                                                         Good               430          55           70          77

     Farmsteads-buildings, lanes, driveways,                                                 59          74           82          86
       and surrounding lots.

     'Average runoff condition. and I:, = o.2S.
      2'oo0:  <W50   ground cover or heavily grazed'with no mulch.
      Fair:   50 to 735, ground covet and not heavily graze(l.
      Good:  > 75% ground cover and lightly or only occasionally grazed.
     3ploor:  <50% ground cover.
      Fair:i  50 to 75% ground cover.
      Good:  > 75%c ground cover.
     4Actual curve number is less than 30: use CN  = 30 for runoff computations.
     sCN's shoun were computed for areas with 50ï¿½/ woods and 50'7 grass (pasture) cover. Other combinations of conditions may be computed
     from the CN's for %wood(s and pasture.
     61'oor: Forest litter,. small trees. and brush are destroye(l by heavy grazing or regulal burning.
     /a ir:  Woods are grazed but not burned. and some tlrest litter covers the soil.
     (;o1:  Woods are protected firom grazing, and litter andi brush adequately cover the soil.











I
                                                 (210-VI-TR-55, Second Ed., June 1986)                                                 2-7



United Statesional 
Department of         Nat i onal
Agriculture          Engineering
Conservation  I
                                                 l
Seï¿½rvi:ceï¿½    Handbook
                                                 I
                                                 I
Section 4            Hydrology                                   I
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                                                                          10.7

 Table 10.1.  Curve numbers (CN) and constants for the case I  = 0.2 S
  1      2    3       4        5            1      2    3       4        5
Cfor CN               S      Curve*       CN for    CN for      S      Curve*
condi-                       starts      condi-                        starts
 condi-  conditions values* starts       condi-  conditions values* starts
 tion                       where          tion                       where

                    (inches) (inches)                         (inches) (inches)
100    100   100    0          0            60    40    78    6.67       1.33
 99     97   100oo    .11       .02         59    39    77    6.95       1.39
 98     94    99      .204      .04         58    38    76    7.24       1.45
 97     91    99      .309      .06         57    37    75    7.54       1.51
 96     89    99      .417      .08         56    36    75    7.86       1.57
 95     87    98      .526      .11         55    35    74    8.18       1.64
 94     85    98      .638      .13         54    34    73    8.52       1.70
 93     83    98      .753      .15         53    33    72    8.87       1.77
 92     81    97      .870      .17         52    32    71    9.23       1.85
 91     80    97      .989      .20         51    31    70    9.61       1.92
 90     78    96    1.11        .22         50    31    70   10.0        2.00
 89     76    96    1.24        .25         49    30    69   10.4        2.08
 88     75    95    1.36        .27         48    29    68   10.8        2.16
 87     73    95    1.49        .30         47    28    67   11.3        2.26
 86     72    94    1.63        .33         46    27    66   11.7        2.34
 85     70    94    1.76        .35         45    26    65   12.2        2.44
 84     68    93    1.90        .38         44    25    64   12.7        2.54
 83     67    93    2.05        .41         43    25    63   13.2        2.64
 82     66    92    2.20        .44         42    24    62   13.8        2.76
 81     64    92    2.34        .47         41    23    61   14.4        2.88
 80     63    91    2.50        .50         40    22    60   15.0        3.00
 79     62    91    2.66        .53         39    21    59   15.6        3.12
 78     60    90    2.82        .56         38    21    58   16.3        3.26
 77     59    89    2.99        .60         37    20    57   17.0        3.40
 76     58    89    3.16        .63         36    19    56   17.8        3.56
 75     57    88    3.33        .67         35    18    55   18.6        3.72
 74     55    88    3.51        .70         34    18    54   19.4        3.88
 73     54    87    3.70        .74         33    17    53   20.3        4.06
 72     53    86    3.89        .78         32    16    52   21.2        4.24
 71     52    86    4.08        .82         31    16    51   22.2        4.44
 70     51    85    4.28        .86         30    15    50   23.3        4.66
 69     50    84    4.49        .90
 68     48    84    4.70        .94         25    12    43   30.0        6.oo
 67     47    83    4.92        .98         20      9    37   40.0       8.00
 66     46    82    5.15       1.03         15     6    30   56.7       11.34
 65     45    82    5.38       1.08         10     4    22   90.0       18.00
 64     44    81    5.62       1.12          5     2    13  190.0       38.00
 63     43    80    5.87       1.17          0     0      0 infinity infinity
 62     42    79    6.13       1.23
 61     41    78    6.39       1.28
*For CN in column 1.



                                                                             I
                                                                             I


Derivation of Snowmelt Runoff and TSS Loading from North Arctic/Orbit
  Data                                                                              I
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                           I                                                                                           ï¿½~~~~~~~~~~~~~


                                                                                           MARCH,  1988
 BASIN SNOW COVER/SNOW PACK
                 SOONh 0    05-I

 RESULTANT WIND      cm.                                                                .    L     ..        .

                                             lo~~~~~~~~~~~~~~~ph~~~~~~~I
                    4wr .as                                               t

 TEMPERATURE         if  .20 f

 oIScHARGE crs       ,o, *, 
 cu It/ see

                        .10I
                              ï¿½--~~~~~                   ~~~~~~ I `                              iA~
                                               .oa                                                                        p~~~~~~~~~~~~~~~~~~~~~~~~~~~~~E
  PRECIPITATION                                                          I-O                        L
  In        >.ot                      A                                                    i -
                                               r~~~~~~~~~~~~~~~~~
* WATER OUAUIY SAMPLE TAKEN    I..... *I
                                  S 0 IS  I      12  1 2         14 I          II      I?      II      Is   20

                                BREAKUP HYDROGRAPH                                                             FlGURE
                                                FOR 0
                                        ',ORBIT BASIN




                                           low. ~~~~~~~~~MARCH, 1988
 BASIN SNOW COVER/SNOW PACK                                                                        M

                      ronï¿½oeI                                                                                                      U
 RESULTANT WIND      c"L     L                          J                                                                           U

                 mom h0 J                  I                                I     I
                  lam,*                                                          I      A'       I
                   dq?                                                      ï¿½mLOAT Ur 4-/ 


 TEMPERATURE         jur .20  -./v  -            "-.-I -4                                   -.1L-                            I

OISCNAR E CFS       2? .15
      .11u              ~~.10 




                     C.A -
                                            1~~L~   ItrY I2'-7.   I01.ii                                         N~f    r
WATER QUAUTA SAMPLE TAKEN    'A     A J.                                   I
                        10       1                                              I P  I                r i~ j ,~,    m
                             20  2'     ~~22    22      24     25      26      27      It      2       20  MI

                               BREAKUP HYDROGRAPH    r

                                       ORBIT BASIN


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                             0oo0                                             IAPRIL,  1988 
     BASIN SNOW COVER/SNOW PACK                                                        


     RESULTANT WINO       CL            -                 -                -- 


                             I~mp             I
                    #01111H    ï¿½                iI I. B 

                      tur .25                        ,                                  r\ I\- i          I

     TEMPERATURE          Ilrl .2 0AL /1l

     OISCHARGE CFS         aOr  s      I        I        I             2              I

                          e1.     I       I\      1\       A                     I                        I

                         0.0I*       -               V15\                                          sOIt r 
     PRECIPITATION  I 
                         0.0'
                             I                                                               I  I 
   * WATER OUAUTY SAMPLE TAKEN     1m. I.ml                 I                I                                          I
                             11 3             2       &        *                        r el  ?  I

I                               ]I [ BREAKUP HYDROGRAPH                                                                           FIGURE

                                          ORBIT BASIN





                                                                                          APRIL.  1988
     EASIN SHOW COVnttSNOW PACK-                                     _-  1- - .J

                     I,
     RESULTANT WIND  CAM=




                     _ _  _                                                                       I                I 
                      A" .25 A0                                               7
                                            '-
     TEMPERATURE 'J .I --

    DISCHARGE CFS         20' .II
    cuit / mile                                                                               t             - I


                         o.0tI                                    C/                      J
    PRECIPITATION              S . j
    In                       e~T                   I    I        I            / - a M4 aL L . E W RT ,I                !

   * WATER OUAUTY SAMPLE TAKEN                                    ,I..   


                                 BREAKUP HYDROGRAPH                                                                        R
                                                FOR 
                                         ORBIT BASIN 









                                                                                  MARCH,  1988

                         Ji 001                               i~
   BASIN SNOW COVER/SNOW PACK
                 SOUTH a
                  IOm.A
   RESULTANT WIND  CAT" I                                                  W-HO ---

                 momT  0  .60

                   401  .30                                                                                 0

   TEMPERATURE      007 3 0           -.              -  -                          p4

   DISCHARGE CFS    2f .30                 M?
   cu it /          seeOMKA

       ""'"'           ..    Vh                   k-'--a .9
   PRECIPITATION        .
   In                 0.04  ~ ' ~.~kII ~t\
                                               ,,,_   LhlT~~~~~ ~~pr   L. -6     P~~~~~Il _   LLnt-
 * WATER OUAULT SAMPLE TAKEN    I .-. ..-
                                I 10    1I    12  i1   to        IS     I   is    Is               20            I
                              BREAKUP HYDROGRAPH                                                    ' URE
                                            FOR
                                NORTH ARCTIC BASIN




                                                                                  MARCH, 1988
   BASIN SNOW COVER/SNOW PACK


  RESULTANT WIND   c                             7-





  TEMPERATURE      I   .-   -A-                            --                      A
  DISCHARGE CIF                                                                                              ofl
  cu  / sees 
       Cul/n.                  I 
                             A
      ___  _         0oar.II-   /I    f'  A      nI      fmarae4\~           A 
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  in                  .0      rv
       _______    no                               'I---+ J" 

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                                                                             11           1 8~~~











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           BASIN SNOW COVER/SNOW PACK  APIL                                       198


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                           NOUNS             ,                                    19
                                   I- ~ ~  ~     ~     ~    ~     ~    I


           TEMPERATURE         3   4

           DISCHARGE CFS                            I\ So\ 






                                           II      FOR                             II~~~~~~~~~~~~~~~~~~~I~cm-

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Fig. 5.2 R values for areas east of1040. Because of irregular topographyi~l,,
United      S aecalculate R values in this region by using local rainfall data. R is In.
of 100 ft -tons/scre per in/hr. To convert R? to units of 10' J/ha per mm/hr, muiltiol
1.70. (20) Scale is in miles.





                                                   .a *---,   uIsit: pnecIse!50
tIr Kt is needed, other references (10, 20, 21) that explain how to calculate                                                                            Type                          I
individual storms and years from local data should be consulted.                                                                                        Type IA -
"isoerodlent" map, prepared by Wischmeier for the USDA (20) and shown                       40 -                                                        Type II -    
 5.2, is used to find the R value for sites east of the Rocky Mountains                 =  
,ximately 1040 west longitude). R can he interpolated for points between                X  I
,es. Contact local soil conservation service offices for more detailed infor-
I on R values in areas covered by this map. West of the 104th west merid- 30 -
regular topography makes use of a generalized map impractical. For the                   a                                  A 
In states, IH is calculated by using rainfall data. Results of investigations at   I 
                                                                                     o  20-



                                                                                         10 -


                                                                                         012
                                                                                                   3        6        9        12          1      18     21       24
                                                                                                                            Hours
                                                                                     Fig. 5.4 Time distribution of rainfall within storm types. Adapted from unpublished
                                                                                     data provided by Wendell Styner, U.S. Department of Agriculture, Soil Conservation
                                                                                     Service, West Technical Service Center, Portland, Oregon, October 28, 1981.



                                                                                     the Runoff and Soil Loss Data Center at Purdue University showed that R values
                                                                                     in the western states could be approximated with reasonable accuracy by using
                                                                                     2-year, 6-hr rainfall data. (20) Regression equations for three different storm
                                      3 Type IA                                       types (I, IA, and II) are used to calculate R values. Figure 5.3 shows the distrib-
                                       1ri Type I                                      ution of type I, IA, and II storms throughout the western states.
                                       0  Type 11                                         A storm type is distinguished by the rainfall distribution within the storm.
                                                                                     Figure 5.4 illustrates the time distributions of rainfall within the three types of
                                                                                     storms. A type 11 storm is characterized by gradually increasing rainfall followed
                                                                                     by a strong peak in rainfall intensity that tapers off to low-intensity rain. Type
                                                                                     II storms occur in the following areas:

                                                                                     * The eastern parts of Washington, Oregon, and California (east of the Sierra
                                                                                       Nevada)
                                                                                     ï¿½ All of Idaho, Montana, Nevada, Utah, Wyoming, Arizona, and New Mexico

                                                                                        Type I and IA storms occur in a maritime climate. Type I is typical of storms
                                                                                     that occur in southern and central California. These storms have a milder but
             Fig. 5.3 l)istribution of storm types in the                              definite peak similar to that of the type 11 storms. Type IA storms, which are
             western United States. (4) Type 11 storms                                 characteristic of storms in coastal areas of northern California, Oregon, Wash-
             occur in Arizona, Colorado, Idaho, Montana,
             Nevada, New Mexico, Iltah, slid Wyoming                                   ington, and the western slopes of the Sierra Nevada, have a low broad peak in
             also.                                                                    the rainfall distribution.



                                                                                                                                                                also.






                                                                                            Find:  The average annual R value for Sacramento, California.
                                                      __  _    .  g  4 f                    Given:  The 2-year, 6-hr rainfall is 1.2 in (30.5 mm).
                                                                                            Solution:  Sacramento is in the type I storm area. Thus

                                                                                                                     R = lf1.55p22   (0.0134 X (p, in mm)221
                                                                                                               where p - 1.2 in (30.5 mm)
                                                                                                                     R = 24.72, or 25

                                                                                               bThe rainfall erosion index does not account for erosion caused by snowmelt
                                                                                            runoff. In any area where snow accumulates and the soil freezes, snowmelt runoff
                                                                                            ,  increases erosion losses. Until researchers  develop a predictive method for this
                                              __ï¿½                     -                       > r eP f,.  _type of erosion, an addition component of the R value, termed R,, should he
                                                                                            added to the rainfall erosion index to determine a total R factor R,. R. is esti-
                    . /                                                                     mated by multiplying the average total winter precipitation (December through
                               . _,- /_             _                   _            .      March) in inches (mm/25.4) of water by 1.5 i(mm/25.4) X 1.5 = 0.059 X mmi.


5     1.0     1.5    2.0    2.5    3.0    3.5    4.0    4.5                                  EXAMPLE 5.2  Consider a site that has an R factor of 25 and receives 16 in (406 mm)
                             p = 2-year, 6-hr rain, in                                      of precipitation during the four winter months:

      ---4-   ~      507----`         5 --                              tR, =I 1.5(16 in) = 24    (0.059(406 mm) = 241
      25             50              75            100
                             o = 2-year. 6-hr rain, mm                                                            =    + R
                                                                                                                  = 25 + 24
.6  Relations between average annual erosion index and 2-year, 6-hr rainfall in                                    = 49
nia. (141

                                                                                               The R value is used to estimate the average annual soil loss. If erosion pro-
                                                                                            tection is required for less than one year, the soil loss for a portion of a year can
e differences in peak intensity are reflected in the coefficients of the equa-              be estimated by using a derivative of the R value. Since R is proportional to
 or the rainfall factor. Figure 5.5 is a graphical representation of the equa-               rainfall, the R value for a short time period can be calcula ted by mul tiplying the
 'I'he equations, also shown on the curves for each individual storm type,                  average rainfall during the shorter time period by the annual R value and divid-
                                                                                            ing the product by the average annual rainfall. For example, suppose you wish
                                                                                            to estimate soil loss in January. January rainfall averages 2 in (51 mm), and
                       R = 27p22         type II                                            annual rainfall averages 20 in (510 mm). Then
                       R =  16.55p22    type I
                       R = 10.2p2'2      type IA                                                                      2 in                 51mm
                                                                                                             Rj,, =  2]) in X R......lI    510 mm  X R .....

 p is the 2-year, 6-hr rainfall in inches. (If p is in millimeters, the equations
 ,.: R = 0.0219p22, type II; R = 0.0134p22, type I; JR = 0.00828p22, type                   EXAMPLE 5.3

  R ? valrue is rounded to the nearest whole number. When the rainfall time                 Given:  A site in California on the western slope of the Sierra Nevada where 2-year, 6-
  iR value is rou   5 anded to the nearesp      t whole number. When the rairall time       hr rainfall is 1.6 in (41 mm), December-March precipitation is 27.6 in (701 mm), and the
 ulion curves (Fig. 5.4) and the corresponding R value equations are com-                   storm type is IA.
 it is evident that the stronger the peak intensity of the typical storm, the
 the rainfall erosion index.                                                                Find:  , R., and R,.
                                                                                                                    Find: R, R,, and R,.~~~~~~~~~~~~~~~~~~~~~~1






           It = 1).2p?' = 28.7  
          It., = 1.5(27.6 in) = 41.4    10.059(701 mm) = 41.41                                                           o --
          R, = R, - R = 28.7 + 41.4= 70.1                                                                               /\    /\
                                                                                                                                        o,1 o, .(Example 5-4)

 Soil Erodibility Factor K                                                                                                        " 

,il erodibility factor K is a measure of the susceptibility of soil particles to                                         / 
Iment and transport by rainfall and runoff. Texture is the principal factor                                   60/ 
,ng K, but structure, organic matter, and permeability also contribute. K                                     o        , \        /          /           O
 range from 0.02 to 0.69.                                                                                          \A 
.'eral methods can be used to estimate a K value for a site, but a nomograph                               50          
,d using analyses of site soils is the most reliable. If a recent soil survey for                                                /
ea has been published and minimal soil disturbance is anticipated, the K           lo                                          * -                              a
listed in the survey of the soil series found on the site can be used.                                        / \   /       /

Agraph Method                                                                                                   .                                    \.  /   A  V
referred method for determining K values is the nomograph method. Use                           '   ,', :                                             ,'.
nomograph requires a particle size analysis to determine the percentages. ,j,,,,,, ,                                                     ,,- .               
I,I very fine sand, silt, and clay. The size range for each class is listed in                            ,,             ,,       ,      -  
 r:I.. ASTM D-422 (1) is a standard hydrometer analysis for particle size                                 ','  ,/,,;, ,,                               /    \ /
lution. (Specific particle sizes can be designated in the request for analysis.. ,......, ....                        i.                       ~/'' \v'
l ypically, values are reported for specified size intervals, such as every 5 or              %                                            '
. The fee for a particle size analysis is normally only a small fraction of the                                          Pcent srnd
ee for a geotechnical report.)                                                             Fig. 5.6  Triangular nomograph for estimating K value. (6) See Table 5.3 for adjust-
e determination of the K value should be based on the soil exposed during                  ments to K value under certain conditions.
itical rainfall months. Subsoils exposed during grading will have K values
tit from the topsoil K value. On large sites, several samples should be
 and analyzed separately to ensure that differences in soil texture are                    EXAMPLE 5.4
ed. If fill is imported, this material also should be characterized.                      Given:  A soil with the following particle size distribution.
X, more carefully the site soils are characterized, the more accurate the K
 will be. If analysis indicates significant variation in soil erodibility, it
 be advisable to use different K values for different parts of the site and to                          Component                Size, mm           Fraction, %

vative approach is to use the highest value obtained by analysis for all                                Very fne sand           0.1-0.05                10
,f the sitet since it may not be possible to know exactly what soils will he                           Silt                    0.05-0.002              20
'd or how varied the soils are.                                                                        Clay                  Less than 0.002            40
omograph developed by Erickson of the SCS-Utah office (6), based on the
Il nomograph provided by Wischmeier (21), is reproduced in Fig. 5.6. To
I nomograph, enter the triangle with any two of the particle size percents:                Find: Texture and K value.
;ind and silt; silt and clay; or clay and total sand. Use whole numbers.                  Solution:  Entering Fig. 5.1 with 40 percent total sand and 20 percent silt, the texture
 the dashed straight lines to their point of intersection. From that point,               is found to be on the border between clay and clay loam. Entering Fig. 5.6 with the same
 parallel to the dotted curves to the right side of the triangle, where the K              percents (see bold lines), the K value is found to be 0.19.
 are listed.                                                                                 Table 5.3 describes adjustments to the K factor. Adjustment I is a correction for very





    -II  -II -I -I -C -9   9 -9 -  -----








               ~         mm.~  ~             ~;' "' ...... IS vnlue9 for following slope lengths I, ft (m)
       ~
.,pe gradiet !0 20    30 40    50    60 70 80 90    100
                                                                          150  200  250 300 350 400   450  500
                                                                                                              600 700   800
dio 900 1000
     s,,';,  13.01   16.11    (9.11   112.2) 115.21   (18.31 121.31 (24.41   (27,41 13o.5)
                                                                         (46)   1611 (76) 1911   11071  1122)11371  11521
                                                                                                              11831 12131  (244) (2741
                                                                                                                                   1305)
      0.5    0.06 0,07 0.07 0.08   008   0.09 0.09 0,09 0.09 0.10
                                                                         0.10 0,11 0.11 0.12 0.12
                                                                                                0.13 0.13  0,13 0.14   0.14
~:1 0,14 0,15 0.15
      I 0.08 0.09 0,10 0.10 0.11 0,11 0.12 0.12 0.12 0.12
                                                                         0.14  0.14  0,15 0.16 0.16  0.16
                                                                                                     0.17 0.17 0.18   0.18 0.19
           11.10 0,19 0.20
                0.12 0.14 0,15   0.16 0.17 0,18   0,19 0.19 0.20
                                                                         0.23  0.25 0,26  0.28  0.29 0.30
                                                                                                     0.32 0.33   0.34 0.36 0.37
           0.14 0,39 0.40
                0,18 0.20 0.22   0,23   0.25 0.26   0.27 0.28 0.29
                                                                         0.32 0.35 0,38 0.40 0.42
                                                                                                0.43  0.45 0.46   0.49 0.51 0.54
           0.16                                                                                                                                                 0.55 0.57
                0,21 0.25   0,28 0.30   0.33   0.35   0.37 0.38 0.40
                                                                         0.47 0.53 0,58  0.62 0.66
                                                                                                0.70 0.73 0.76   0.82 0.87 0.92
                                                                                                                               0,96 1.00
~:! 5 0.17 0.24 0,29 034 0.38   0.41  0.45   0.48   0.51   0,53
                                                                         0.66  0.76 0.85 0.93 1.00  1.07
                                                                                                     !.13 1,20 1.31 1.42 !.51
           tl,21                                                                                                                                                1.60 !.69
                0.30 0.37 0.43   0.48   0.52 0.56 0.60   0.64 0.67
                                                                         0.82 0.95 1.06  1.16 !.26 1.34 1.43
                                                                                                         1,50 1.65 1,78   1,90 2,02
           11.26 2.13
                0.:17 045  0.52 0,58   0.64 0.69 0.74   0,78   0.82
                                                                         1.01 !.17 i.30  1.43  i.54 !.65  1.75
                                                                                                         1,84 2.02 2.18 2.33 2.47
:1 2,61
      8     0.31 0,44 (I.54 0.63   0.70   0.77 0.83   0.89 0.94 0,99
                                                                         1.21  1.40 !,57 1.72 1.85 1.98
                                                                                                     2.10 2.22 2.43   2.62 2.80
           0.37                                                                                                                                                 2.97 3.13
                0,52  0.64  0.74   0.83   0.91  0.98 !.05   I.!1   1.17
                                                                         1.44 1.66  1.85  2.03 2.19 2.35 2.49
                                                                                                         2.62   2.87 3.10 3.32 3.52
                                                                                                                                    3.71
,:1 !0        0.43  0.61  0.75   0.87 0.97 1.06   1.15   1.22 1.30   1.37
                                                                         1.68 1.94 2,16 2.37 2.56  2.74  2.90. 3.06
                                                                                                               3,35   3.62   3.87 4.11 4.33
     II     0,50  0.71  0.86   1.00 !.12 1.22 i,32 !.41 !.50   1.58
                                                                         1.93 2.23 2,50 2.74 2.95  3.16  3.35
                                                                                                         3.53   3.87 4.18 4.47 4.74
::1 4.99
     12.5    0.61  0.86  1.05   1,22 1.36   1,49 !,61 1.72   1.82 1.92
                                                                         2.35  2.72  3.04  3.33 3.59 3.84 4.08
                                                                                                         4.30 4.71 5.08   5.43 5.76
     15 6,08
           0.81 !.14 !.40 !.62 1.81 !.98   2.14 2.29 2.43   2.56
                                                                         3.13  3.62 4,05 4.43 4.79 5.12  5,43
                                                                                                         5.72   6.27 6.77 7.24 7.68
 :1                                                                                                                                                                       8.09
     16.7 0.96  1.36   1.67 1,92   2,15 2.36 2.54 2.72   2.88   3.04
                                                                         3.72 4.30  4.81 5.27 5.69 6.08  6.45
                                                                                                         6.80 7.45   8.04   8.60 9.12
                                                                                                                                    9.62
 :1 20         i.29 i.82  2.23  2.58 2.88 3.16 3.41 3.65 3.87 4.08
                                                                         5.00  5.77 6,45 7.06 7.63 8.16  8.65  9.12
                                                                                                              9.99 10.79 11.54 12.24 12.90
:1 22         1.51  2.13  2.61 3.02 3.37 3.69 3.99   4.27 4.53 4.77
                                                                         5.84  6,75 7.54 8.26  8.92 9.54 10.12 10.67
                                                                                                              11.68 12.62 13.49 14.31 15.08
~1 25 1.86  2.63 3.23   3.73 4.16 4.56 4.93   5.27 5,59 5.89
                                                                         7.21  8.33 9.31 10.20 il.02 !1,78 12.49 13.17  14.43
                                                                                                                   15.58  16.66  17.67 18.63
     30      2.51  3.56 4.36   5.03 5.62 6,16 6.65 7,11   7.54 7.95
                                                                         9.74 11.25 12.57 13.77 14.88 15.91 16,87 17.78 19,48 21.04
                                                                                                                        22.49 23.86  25.15
 I   3:1.3    2.98 4.22 5.17 5.96   6.67 7.30 7.89 8.43   8,95 9.43
                                                                        11.55 13.34 14.91 16.33 17,64 18.86 20.00 21.09
                                                                                                              23.10  24,95  26.67 28.29 29.82
     35      3.23 4.57 5.60   6.46 7,23 7.92 8.55 9.14 9.70 10.22
                                                                        12.52 14.46 16.16 17.70 19.12 20.44 21.68 22.86
                                                                                                              25.04 27.04 28.91 30.67 32.32
 I   40      4.0{!  5.66  6,9:1  800   8.95 9,80  10.59 !1.32  12.00  12.65
                                                                        15.50 17,89 20.01 21.91 23.67 25.30 26.84 28.29 30.99
                                                                                                                   33.48  35.79 37.96 40.01
     45 4.81  6.80 8.33 9,61 10.75  11.77 12.72 13.60 14.42 15.20
                                                                        18,62 21,50 24.03 26.33 28.44 30.40 32.24 33.99 37.23
                                                                                                                   40.22 42.99 45.60 48.07
 I   50      5,64 7,97 9.76 !1.27 12.60 13.81 14.91  15.94 16.91 17.82
                                                                        21.83 25,21 28.18 30.87 33.34 35.65 37,81 39.85 43.66
                                                                                                                   47.16 50.41 53.47 56.36
     55      6,48  9,16 il.22 12.96  14.48  15.87 17.14 18.32 19.43  20.48
                                                                        25.09 28.97 32.39 35.48 38.32 40.97 43,45 45.80
                                                                                                             50.18  54,20  57.94 61.45 64.78
 ! 57 6.82 9.64 il.80 13.63  15.24  ]6,69 18.03 19.28 20.45  21.55
                                                                        26.40 30.48 34.08 37.33 40.32 43.10 45,72 48. I9 52.79
                                                                                                                   57.02 60.96  64.66  68.15
     60 7.32 10.35 12.68  14.64 16,37 17.93  19.37 20.71 21.96  23.15
                                                                        28.35 32.74 36.60 40,10 43.31 46.30 49.11 51.77 56.71
                                                                                                                   61.25 65.48  69.45 73.21
 I 66,7 8.44 !!.93 14.61 16.88  18,87 20,67 22.32 23.87 25.31 26.68
                                                                        32,68 37.74 42.19 46.22 49.92 53.37 56.60 59.66 65.36
                                                                                                                   70.60 75.47 80.05 84.38
     70 8.98 12,70 15,55  17.96  20.08 21,99  23.75  25.39 26.93  28.39
                                                                        34.77 40.15 44.89 49.17 53.11 56.78 60,23 63.48 69.54
                                                                                                                   75.12 80.30  85.17 89.78
     75 9.78 13.83 16,94 19,56  21.87 23,95  25.87 27.66  29.34 30.92
                                                                        37.87 43,73 48.89 53.56 57.85 61.85 65,60 69.15
                                                                                                             75.75 81,82  87,46 92.77 97.79
 ! 80 10.55 14.93 18.28 21.11 23.60  25.85 27.93 29.85 31.66 33,38
                                                                        40.88 47.20 52.77 57.81 62.44 66.75 70,80 74.63 81.76
                                                                                                                   88.31 94.41 100.13 105.55
     85 11.30 15.98 19.58 22.61 25,27 27.69 29.90  31.97 33.91 35.74
                                                                        43.78 50.55 56,51 61.91 66.87 71,48 75,82 79.92  87,55 94.57
                                                                                                                       101.09 107.23 113.03
     90    12.02 17.00 20,82 24.04 26.88  29,44 31.80 34.00 3606 38.01
                                                                        46.55 53,76 60.10 65,84 71.11 76.02 80,63 84.99 93,11
                                                                                                                  100.57 107.51 !14.03 120.20
     95 12.71 17.97 22.01 25.41 28.41 31.12  33.62 35.94 38.12  40.18
                                                                        49.21 56.82 63.53 69.59 75.17 80.36 85.23 89.84 98,42
                                                                                                                  106.30 !!3.64 120.54 127.06
 I  100 13.36 18.89 23.14  26.72 29,87  32.72  35.34 37,78 40.08 42.24
                                                                        51.74 59,74 66.79 73.17 79.03 84.49 89.61 94.46 103,48 111.77
                                                                                                                       119.48 126.73 133.59
  ,,Inted from
              4.56Xs
  (65.4{ Xs'                     )( I )'
   l~ { !(I.(lO0 t ~'l~    t 0.065 1,5- topographic factor
                            7'~       { ,, slope length, ft Im X 0.3048!
                                    s ,, slope steepness,
                                   m = e~l~ment dependent upon slope ateepnm
                                       (0.2 for slopes < ! %. 0.3 fo! slopes ! 1o3~.
                                       0.4 for slopes 3.5 to 4.S%. nnd
                                       0.5 for slopes > 5~'I. )






                                                         1  1.9  2.8                               __JType lf cover                                 C factor      reduction, %
                                                                                             None                                                     1.0
effect of length is not as great as the effect of slope angle: LS increases 30               Native vegetation (undisturbedl                           001              99
percent for each doubling of length. For example, on a 2:1 slope, IS doubles                Temporary seedings:
* L is quadrupled:                                                    go90% cover, annual grasses, no mulch                                            0.1              90
                                                                                              Wood fiber mulch, g ton/acre (1.7 t/ha), with seedt    0.5              50
 Slope                  2:1             2:1               2:1                                Excelsior mat, jutet                                      0.3              70
 L.ength                30 ft (9.1 ml    60 ft (18.3 m)    120 ft (36.6 ml                   Straw mulcht
 I.S                    9.76            13.81             19.42                                1.5 tons/acre (3.4 t/ha), tacked down                  0.2               80
 Factor increase        1               1.4              2                                     4 tons/acre (9.0 t/ha), tacked down                    0.05              95
                                                                                            'Adspted from Refs. 11, 15, and 20
;, very long slopes and especially, long, steep slopes, should not be con-                   tForslpes ip to
ted. 'Those that already exisl should not be disturbed.
ope length can be shortened by installing midslope diversions. Local build-
odes often require terraces or drainage ditches at specified intervals. Chap-                if a complete cover of newly seeded annual grasses is well established before the
I of the Uniform Building Code specifies a 30-ft (9.1-m) interval. (9) Several              onset of rains.
,n control manuals recommend 15-ft (4.6-m) intervals between terraces. (2,                      In many areas, seed and wood fiber mulch are applied hydraulically shortly
'lecause these intervals are defined as vertical rise, the slope length would               before the rainy season. The early rains cause the seeds to germinate, but a com-
mewhat longer.                                                                              plete grass cover is not established until at least 4 weeks later. During the ger-
 -creasing steepness will require use of more land and so must be incorpo-                   mination and early growth period, the wood fiber mulch provides only marginal
 early in the project design. To ensure slope stability, a maximum gradient                 protection. A C value of 0.5 is an appropriate average representing little protec-
 Iuently recommended by the soils engineer.                                                  tion initially and more thorough protection when the grass is well established.
                                                                                              On bare soils mulch can provide immediate reduction in soil loss, and it per-
                                                                                            forms better than temporary seedings in some cases. Straw mulch is more effec-
                                                                                            tive than wood fiber mulch; it reduces loss about 80 percent (C value, 0.2) when
   Cover Factor C                                                                            it is applied at the rate of 3000 lb/acre (3.4 t/ha) and tacked down. Additional
 over factor C is defined as the ratio of soil loss from land under specified               reduction is obtained with 8000 Ih/acre (90 t/ha) of straw, but this rate may not
 or mulch conditions to the corresponding loss from tilled, bare soil. The C                be cost-effective.
  the same as the runoff coefficient C used in the rational method.                            Wood fiber mulch alone (without seed) provides very little soil loss reduction;
 I he [SIE, thie C factor reduces the soil loss estimate according to the effec-           it primarily helps seeds to become established so that the new grass can provide
 ss of vegetation and mulch at preventing detachment and transport of soil                   e erosion control. Other products, such as jute, excelsior, and paper matting,
 les. On construction sites, recommended control practices include the seed-                provide an intermediate level of protection; the C value equals approximately
 grasses and the use of mulches. These measures are often considered "tem-                 0.3. Test results of various mulch treatments are presented in Chap. 6.
  ,"-they are designed to control erosion primarily during the construction
   Permanent landscaping may be added later, or temporary erosion control
  may be left as a permanent cover. Any product that reduces the amount                    5.2f  Erosion Control Practice Factor P
  exposed to raindrop impact will reduce erosion. Table 5.6 lists C factors
  ious ground covers. The C values for vegetation were obtained from USDA                   The erosion control practice factor P is defined as the ratio of soil loss with a
   Itions (14, 20); those for mulch were obtained from Burgess Kay at the                   given surface condition to soil loss with up-and-down-hill plowing. Practices that
  sity of California, Davis, who tested materials on experimental plots                    reduce the velocity of runoff and the tendency of runoff to flow directly down-
  a rainfall simulator. (l 1)                                                              slope reduce the P factor. In agricultural uses of the USLE, P is used to describe
  en the soil surface is bare, C is 1.0. At the other end of the scale, undis-             plowing and tillage practices. In construction site applications, P reflects the
   native vegetation is assigned a value of 0.01; hence the advantage of                   roughening of the soil surface by tractor treads or by rough grading, raking, or
  ig as much existing vegetation as possible is clear. A C value of 0.1 is used            disking.







        -  -9 ms -eil -sl - IP -P m                                                                                                                     _ -                  _ _



I
I
I
I
I
I
I
I
I
I
I Appendix B


I
I
I
I



I






Appendix B


Algorithm for Determining Minimum Surface Area for Sedimentation Basin

Assumptions Made in Determining Inflow for Sedimentation Basin Sizing

Sedimentation Basin - Design and Quantities

Sedimentation Basin - Costs

Land Development Costs





































Stormwater Controls in Coastal Alaska .3 page B-I
June, 1995



                                                                       I
                                                                       I
                                                                       I
Algorithm for Determining Minimum Surface Area for Sedimentation BasinI

                                                                       I
                                                                       I

                                                                       I

                                                                       I
                                                                       I

                                                                       I
                                                                       I
                                                                      .I

                                                                       I
                                                                       I
                                                                       I
                                                                       I
                                                                       I
                                                                       I

                                                                       I








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                 ,yule .-i rartcle size Ulstribution Analyses for Suspended Sediment in Storm WaterStorm Water



       100%







        75%



 Percent

                                                                                                    /-./-E-  1(00th Ave. Grab, Q=0.3 cfs
                                                                                                    -- i/100th Ave. Grab, Q=0.6 cfs
Passing 50%                                                                                                           G     . 
 By Weight                       /-/-.- 100th Ave. Grab, Q=0.3 cfs
                                                                                                    ----- Basin Inlet Composite #1
                                                                                                    --E- Basin Inlet Composite #2




         25%






                                                                                                        Source: (JMM, 1992)
          0%
              0            10           20            30           40            50            60
                                           Particle Diameter, microns



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Sedimentation Basin -Design and QuantitiesI
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                                                         units                 Anchorage                          Juneau
                                                                  Residential    industrial   Commercial   Residential    Industrial
     Sedimentation Basin - Quantities

     Surface area required   IN                           sf          90            400         1600          450          2600

                              Iw =
     Dimensions of base pool  i max(3'd2,w=sqrt(A14))     ft          1 8     I      18          20            1 8          25
   I~~~~~~                                  ~           ~~~~~ 1--4w  It  72          72           80    72    102
     minimum pond surface   iApond                        ft         1296          1296          1600         1296         2600

Idepth (d)                     range: 3to 6ft      i        t     a                   3            3            3            3
     pond volume              VOLpond=.5'(Ab+A)'d         cf         1944           1944        2586          1944         4844
     depth from ground to top ofI
Ipond (do)                                            5   ft5                         5            5            5            5

     pond bottom area         Ab=(l-2d(3:1) x~ (w-2d(3:1))   SI        0             0           124            0           629

                              Ag=(i+2dg(4:1 ))'(w+2dg(4:,
a round surface area          Ii))                         sf        6496           646          7200         6496          9299 -

                              IVOLex=(.5'(A+Ag)+Apond)
I    excavation               !/27                         Cy         216           216          259           216          400

     Overall site length      I Ltot = (40+2'(5,4: 1)+I+5)  ft167                   167          175           16719
                              I Mot 
I    Overall site width   ~ (5+215,4:114w+20+5            ft           88            88           90           88            95  _
     area of site             I Atot = Ltot ' Wtot        sf            14,696       14,696       15,750        14,696       18,811
                              1 VOLlet=.5'(3+6)'(40+5(4:1
I    inlet/outlet             )+5)11.5                     CY          16            16           16            16           16

     Road Surface             Arced = 20'(Ltot-5)          sf            3,240        3,240'       3,400i        3,240        3,84

                              I SA = (Ltot'Wtot)-Aroad-
     landscaping             iApond                        sf           10,160       10,160        10,750       10,160       12,371

     Concrete on-grade broad crested weir
I    width of weir top        'T = .67                    ft          0.67          0.67         0.67         0.67          0.67
     Height of weir-fdn to top    H=7                      ft          7             7         __7              77
     width of weir at fdn I    b = T +2H(2:1)       I      t         28.67          28.67        28.67        28.67        28.67
     Length of weir structure    Lweir=w+2'(l(4:1)+3)     ft          32             32           34           32       39.4950976
                              Aweir=.51((b+T)H-(H-
     End area of weir        ..5)+(b+t-1))                sf         10.6           10.6         10.6         10.6          10.6 
                        forms~liweir                      If         192            192          204          192       236.970585
                         wwrn I Lweir '(2 '(sqrt(2'HA2)) + - sf       655           655          696           655          808
                     concrete ~Aweir'L weirl27            CY          13            13           13            13           115

     Cutlet Noe                                      1 5    if         15            15            15           1 5          1 5





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                                                   units                 Anichorage Jna

Ssdhem s sson BasIn - Costs 

from Mearis 1995 Heavy Construction Cost Dt

Anchioracoe City Cost Index
                all others                   1.37
                   forms                     1.24
                    wwrn                      1.44
                 concrete                     1.56I
        Juneau - use 105% of Anchrorage costs

Construsctiont Costs

Land mats                1 36 res. S5 Ind.Sl 2comn    $S/               6             5           12             6            5 

Land                                                   $            19.W4         16.20        40.800)       19,440       18.238

Excavation and Gradmo       UitCssfoMeng 
              mobidemtob                    370.00   S/ea       S IM                505           505          530           530I
          front Mid loader                    1.48   S/cy       4        737523                                459          84


               outlet Pipe                  25.50 I  SNl              522           52           522           58           5so

            fonnsain lace                     2.11    SM               501          501           532          526           649
                taint www                    35.00  VWca               331          331           351          347           429
            slab an grade            _     100.00   S/cv             1.951        1.951         2.073        2.048         2,528
InWetOultet Channel                          19.05   $/cV              423           423          423          444           444

Access (road)
           Pavement bass                      5.25   $/sv            2.580         2,580 .      2.707         2.709        3.210
          Prepare and roll                    1.26   Vsav             819,          619          650           650          770

Fancino
                  fencino                    12.35    SMt            8.260        8.260         8,597        8,673        10.000
                   Posts 89.00.  S/ea                                 486          486           4836         510           510
                    date                   925.00  S/orina          1.263         1.263         1,263        1.326         1.326
LandAcapnal
             rougoh grade                   18.55   SIMat             257           257          272          270           329
                   aeed-alooe mrs           ~~~~19.20   Whist         266           266          282           2834I

Subtotal                                               $            27.308        24,068        49.0836      27.701       28.195
25% Contingency                                        5              6,827        6.017        12.271        6.925 _       7.049
1 5% Engineering                                   ,                  4.096        3.610.        7.363        4.155     __4.229

TCC -Tota Capital Coat                                 5             38.231       33.695        68,720       38.782        39.4~72
Post Per unit volume of Pond                           5                 20           17            27           20 a

Annusiftod - IM%25yrs                                  5              4,212         3,712        7.571        4.273   __4.349
                   0.10 i rateI


Sits Maintenance

Frequent Site Mainteancpes                                                                                     _       
mowina-11Oxiy                                  1.68   S/inst            233          233           247          245           298
watonno -water 11 - x/vr                      11.80  SAWtBig     a le                81             66          859   I'M4
waterntla-no" set-upD-5WY                     2.78   S/AW               193          -9             0           202           246
lartilizet2xfvr                               2.76 1 S/mat               77           77            el     so__8               98
wowdcontrol 2xiyr                             0.28   S/msf                8            a                                       10
                         Subtotal                    51.328                       1.328        1.405      -1.395          1.698

Occasional basin cleanoultifevery 8 wa________
mnoi-demob                                     370   S/ea               505          505           505          530          -505
     .5 Pond11 volumne                                                  38            38           48            36      go
excavate @ .5 PMn  o                           1.48   S/cv               73            73           97            7            9
diaosoa- hault8hrs                             2.818   S/cv             142          142           188           149          370
reseed- .25 of landscaped
aite                                          19.20   S/mat               7             7            8             89
                         Subtotal                    5                763          763           846          799         1..165
      ________________   ~present value for 811h yr    54,736                      4,736         5.252        4.962         7.233
      ____________       ~~~present value for 1611, yr  S             7,708        7,708         8.547        8.075       11,771
                      ___present value fr2t  r        $9.572                      9.572    _10,615          10.028        14.619
                         annualize sum of 3 cleanou   5             2.425         2.425        2,690         2.541        3,704

Total O&M                       _____                                 3.754        -3.754        4.095         3.936        5.402
TAC -Total Annual Cost                                  5             7.966         7.466       11.666         8.208        9.751
TACcar developed acre                                   S             1.593           747         1.167        1.642          488a



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                                                          units    _ _           Anchorage       _      _             Juneau
                                                                   Residential     Industrial   Commercial   Residential   Industrial
       Land Use Development Costs

       Commercial and Industrial
                               . Development Area          acres
                               Development % Impervious    %  5 _                            10            10             5            20
                                                                            38   _       50            85            40            50

       buildingand site dev costs from Means          _$/sf                          _         50            64                         50
       Anchorage Cost Index:                         126.7    %
                                land cost                    $          1,306,800    2,178,000    5,227,200     1,306,800    4,138,200
                                bldg size  _ ___             sf           -      _     108,900    _ 123,420            _         217,800
                                bldg and site dev cost       $                        6,912,613    9,992,244                  14,516,487
       Total Site Development Cost                             $                       9,090,613   15,219,444                  18,654,687

       Annualization                            _              $                _._._1,001,495    1,676,697  _                  2,055,151
                            0.1 rate  _
                             25 period ___

       TCC as a Share of ProjectCost                 _%                                    0.371        0.452        .. 0.212
       TAC as Share of Annualized ProJect Cost                 %                            0.745        0.696  ___                  0.474

       Residential

       number of houses                                                          18                                       18
       median house price                                      $            109,700                                  113,500
       median annual mortgage _ .            . .               $              9,111                             ___    9,427
         15% down, 30 yrs, .08 rate + 10/0%insurance, taxes
       median household income                                 $             43,946                  __47924

       TCC per house/average house price                       %              1.936                              _ _ 1.898
       TCC/land price                    .                     %              2.926                                     2.968
       TAC per house/average house price ..         .     .                   4.857   .                                 4.838
       TAC per house/median household income               I  %               1.007                                     0.952






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