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




       SLOPE STABILIZATION

      AND EROSION CONTROL

          USING VEGETATION



                            A
                        MANUAL
                     OF PRACTICE
                    FOR COASTAL
                       PROPERTY
                        OWNERS





                        Property of csc Library





      Sponsored by.                                   Prepared by:
SHORELANDS & COASTAL ZONE                             Mguerm
 MANAGEMENT PROGRAM       W K  I I N G T 0 N S T A T E  BloddynamIlr Inc.
Washington Department of Ecology  D E F RI I   T  fMB
       :Olympia.          E C 0 L 0 G Y         Geotechnical & Biotechnical Engineers
                                             Bainbridge Island, Washington
                      PUBLICATION NO. 93-30
                          MAY, 1993












                         ACKNOWLEDGMENTS
    The preparation of this manual was made financially possible using funds
    appropriated and administered by the Washington State Department
    of Ecology Shorelands and Coastal Zone Management Program and
    secured through the National Oceanic and Atmospheric Administration.
    The authors would like to gratefully acknowledge the numerous technical
    individuals who provided editorial comments on the manual. We would
    also like to acknowledge James Scott and Douglas Canning of the
    Washington Department of Ecology whose shared vision made this
    manual possible.


                          IMPORTANT NOTICE
     The contents of this publication are for general information and applica-
     tionsonlyandshould notbeconstrued as asubstituteforsite specificdesign
     and installation recommendations from professionals expert in geotechnical,
     coastal and/or biotechnical engineering practices. Accordingly, Washing-
     ton Department of Ecology and the preparers of this manual make no
     representation or warranty of any kind, whether expressed or implied,
     concerning the accuracy, completeness, suitability, or utility of any infor-
     mation, apparatus, product, vegetation, or technique presented in this
     publication and assume no liability.

                  Manual Development: Rian Myers, Myers Biodynamics, Inc.
                        Graphic Design: Rachel Ruud
                           Illustrations: Randy Benedict
                       Contract Officer: James Scott
                                       Shorelands and Coastal Zone Management
                                       Washington Department of Ecology
                                       P.O. Box 47600
                                       Olympia, Washington 98504-7600


                                    A

 This manual is funded in part by the National Oceanic and Atmospheric Administration. The views
expressed herein are those of the author and do not necessarily reflect the views of NOAA or any of its
                                    sub-agencies.
The recommended bibliographic citation for this publication is: Myers, Rian D. 1993. Slope Stabilization
and Erosion Control Using Vegetation: A Manual of Practicefor Coastal Property Owners. Shorelands and
       Coastal Zone Management Program, Washington Department of Ecology. Olympia.
                                  Publication 93-30.






INTRODUCTION


   Puget Sound and its associated coastal waters have
      created a dramatic system of coastal landforms along
which have developed the population centers of Western
Washington. It is the natural beauty of this coastal system
that continues to place residential pressures on coastlines.
Construction practices on and around coastal slopes, in
combination with the increasing stormwater runoff from
developing properties around Puget Sound, contribute to
the acceleration of slope erosion and landslide activity along
coastal waterways.
Too often, well intended erosion control and slope stabiliza-
tion programs do not recognize and incorporate vegetation
as a legitimate design tool to address these slope processes.
Primarily, these oversights are because the use of vegetation
alone (soil bioengineering) or together with other slope
stability structures (biotechnical engineering) for slope
protection is poorly understood. Therefore, the value of
vegetation along a slope is either under-estimated or ignored
during the important project planning, design, and agency
permitting periods.
When properly installed and maintained, vegetation can
protect slopes by reducing erosion, strengthening soil, and
inhibiting landslides which increase general slope stability.
The use of vegetation to manage erosion and protect slopes
is relatively inexpensive, does not require heavy machinery
on the slope, establishes wildlife habitat, and can improve
the aesthetic quality of the property. This publication intro-
duces general soil bioengineering practices to coastal property
owners so that they may realize the practical and financial
benefits of using vegetation to control erosion and help
stabilize slopes. u




 How to Use ThisManual

  USING THIS PUBLICATION


                                   Slope Stabilization and Erosion       and library systems. For many
                                   Control Using Vegetation provides     situations, professional design
                                   coastal landowners and govern-        assistance should be sought. The
                                   ment officials with basic informa-    information provided in this
                                   tion concerning the nature and        publication provides the basic
                                   use of slope planting techniques      information necessary to make
                                   to manage soil erosion and            general planning decisions and
                                   shallow seated land movements.        simple installations on slopes.
                                   Information is introduced on site     The manual is not intended as
                                   evaluation, planning, vegetation      a substitute for professional
                                   systems, materials, planting          geotechnical/biotechnical engi-
                                   techniques, and general compat-       neering design or site-specific
                                   ibility of the installation with      consultation.
                                   traditional property owner use.
                                   This publication is a companion       AGENC              PERMI
                                   document to another Washington        Readers working for government
                                   State Department of Ecology           agencies, whose responsibilities
                                   publication entitled Vegetation       may involve policy creation,
                                   Management  A Guidef or Puget         geologically hazardous areas, and
                                   Sound BluffProperty Owners.           development/permit application
                                   The publications should be used       reviews, can use this manual to
                                   together to foster a better under-    help them determine whether
                                        standing and appreciation for    help them determine whether
                                   standing and appreciation for         projects address vegetative systems
                                                    the r ole and maintenance oas a viable component of slope
                                   vegetation along the coastal zone     stability maintenance. Permitting
                                   of Puget Sound. The following         agencies will find this publication
                                   sections present an idealized         useful in suggesting alternative
                                   scheme of how these publications      slope maintenance practices to
                                   might be used by landowners           coastal land owners who are
                                   and local government.                 unfamiliar with the advantages of
                                   COASTAL LAND OWNERS                   slope planting techniques. This
                                   Readers who own coastal property    publication may also allow agency
                                   and who are concerned about soil      personnel to better understand the
                                   erosion control and shallow land      cause and effect relationship of
                                   movement prevention can use           shoreline development and the
                                   this and other Washington             continuing maintenance of slope
                                   Department of Ecology publica-        stability and erosion control.
                                   tions to select and employ general
                                   slope protection practices which
                                   may be applicable to their
                                   property. Additionally, readers
                                   can access a wealth of information
                                   available through public agencies


2




                                                                                         How to Use This Manual U

SELECTING A SLOPE MAINTENANCE PROGRAM


The coasts of Puget Sound contain
a variety of landforms which can
vary greatly in their composition            r.
and historical use. This makes it
difficult to cover all of the prob-
lems landowners may encounter
on their properties in this general                                                                 A
publication. Nevertheless, this                                                                     B
manual will introduce some gen-             A) Backshore Berm
eral planting techniques that may           B) Low Bank
be used alone or in combination             c) High Bank                                            C
with other revegetation programs            0) Bluff/Cliff
and existing natural areas to
protect coastal slopes.
It is important for you, the
property owner, to understand          Figure 1. Typical Puget Sound Coastal Slope Profiles.
your site characteristics, and the
erosion and land movement              which slope planting techniques
processes which may effect it.         m
Only then can you begin to select        ay proble selution I
                                      identified problems. Use Table 1
appropriate protection measures        as general guide to the appropri-
to reduce potential slope erosion      ate slope protection measures for
and land movements.                    your site. The sections on the
The first step in the development      role of vegetation in slope
of a slope maintenance program         stabilization and erosion control
is to gather basic site information    and vegetative planting tech-
so that you may better identify niques should be reviewed to
and select suitable vegetative         determine the specific goals and
treatments for problem slope           limitations of each technique.
areas. The checklist on page 1         This publication addresses only
will help you identify and             the unconsolidated soil portions
organize your slope's key features     of coastal zone slopes. Bedrock
and characteristics. The back-
                                      exposures forming the cliffs of
ground information needed to
         groun  infomatio  needd to   the Puget Sound coastal zone are
fill out the checklist is generally      t P uget in as tal in are
contained in the section - Under-   no        tis     cuse in   vegeta-
standing Your Property. Use the        tic        ation beca ues a-
         checklst asa sumary o yourtion installation techniques are
checklisteas valsummarion your         not applicable to these areas. The
                                      general shapes of Puget Sound
Once you have generally charac-        coastal slopes are illustrated in
terized the existing conditions        Figure 1. Use Figure 1 to recog-
and uses of your slope, the next       nize some of the slope shapes that
practical step is to determine         are familiar to you. When you




* How to Use This Manual



      RATING   KEY TO APPLICABILITY AND COMPATIBILITY GRAPHICS
      SYSTEM          Use the key provided to review the slope management techniques introduced later
                      in this publication and determine which alternatives may be suitable for a general
        ao            slope configuration.
         Excellent    APPLICABILITY                        COMPATIBILITY



          Good             ..



                      FaIr                                                     CONTROL         SE.
          FPor







       Recommended    =     L                                  GEOTECHNICAL                    VIEW


    compatibility of management techniques with existing or future coastline resource uses. The degree of general applicability
    or compatibility ranges from Not Recommended E) to Excellent 0 and is indicated accordingly in the graphics window.

                                    identify your general slope            combination of geologic and
                                    shape(s), you can begin to under-      environmental influences.
                                    stand the behavior of your             Additionally, the placement of
                                    property and start to account for      vegetative components into
                                    erosion and landslide processes        actively failing slope areas such
                                    which may act upon your slope.         as landslides or earth flows can
                                    You then can implement a               not be expected to have any
                                    number of vegetative slope             short-term stabilization benefits
                                    protection measures discussed          until these movements are
                                    later in this manual,                  arrested and the sources of the
                                    The placement and maintenance          problem are eliminated.
                                    of vegetation on a slope is            In cases where the toe of a coastal
                                    important to a slope protection        slope is exposed to all but the
                                    program. However, there are            smallest of Puget Sound wave
                                    limits to the stabilization role       energies, you must recognize that
                                    that vegetation can perform            vegetation alone will not stop
                                    which must be recognized at the        long-term erosion. However, it
                                    onset of the planning process.         may reduce the rate at which a
                                    First, vegetation alone can not        slope toe is eroded to a potentially
                                    control deep seated earth move-        acceptable level.
                                    ments that may result from a


4




                                                                                      Unnderanding Your Property ï¿½

UNDERSTANDING YOUR PROPERTY














                   BedrTill
                   Till 
                   Areas covered by

                   Drift deposits
                   proglacia Iakes  ?    3               !7 ff



                                                               Lmil of g acialion
               T85h       OUtwash In


Figure 3. Glacial Sediments in the Puget Lowlands (from Downing, 1983. Used with
permission of the Washington Sea Grant Program).

The locations of Puget Sound           beaches which have varying slope
coastlines were established by the     heights and beach widths. The
retreat of the last period of          glacial deposits which define the
glaciation in the Puget Sound          general geologic composition of
lowlands. Coastlines are continu-      coastal slopes are illustrated in
ally modified by coastal marine        Figure 3. Glacial till is typically
processes and by the gradual           the most common geologic unit
natural rise in the sea level.         along Puget Sound coastlines
Today, Puget Sound coastlines          and contributes heavily to the
boast a range of shore forms           sands and gravels deposited on
which include high bluffs and          beaches. The effect of the slow
rock cliffs, tidal mud flats, and      rise in sea level over time in the
sand and gravel beaches. You are       Puget Sound area can be seen
probably most familiar with the        on Figure 4.
common Puget Sound bluffs and
their associated sand and gravel





                                                                                                          5






 *Understanding Your Prop ery



                                                                  a

                                      ~~~~~~~~Ya r b e f ~ Yore present







                                                      Yearsbeoepe,,






                                                                    Mines sanO'Oiredsandng~a















                                      C             ~~~~1000

                                                       Years before present













                                      0  -     /    ~~~Present







                                           /      ~~~~~-Meaflseatm





                                  ALongsthnre transport                                         v Shoreline    v Coastline

                             Figure 4. Coastal Bluff Development. Left: Evolution of a gravel and cobble beach. The longshore
                             transport diagrams illustrate the direction of material movement along the beach. Right: Sea level since
                             the last glaciation (from Downing, 1983. Used with permission of the Washington Sea Grant Program).




6




                                                                                        Understanding Your Property U

THE ART OF SITE                        * SLOPE ANGLE AND HEIGHT
EVALUATION                             To determine the angle
Selection of a successful vegeta-      of your slope, an easy
tion program requires that the         method is illustrated in
landowner spend time under-            Figure 5. It is a simple                       2. Read slope angle directly
                                                                             standing waihpeat the point where string
standing what is happening device which can be itret h otatr
                                                                                  ~ .~intersects the portractor.
around their slope. This means         constructed with a
that you need to start keeping a       protractor and a
mental list of your observations       yardstick. The protrac-
on the behavior of your slope and      tor is fastened securely
note deviations from that typical      to a yardstick with a       3. Convert slope angle to  1. Hold device
behavior. Observations made            string and weight             horizontal:vertical ratio. parallel to the
during periods of heavy precipita-     attached as shown.                 =3:1                  slope lace
tion, strong winds, freeze-thaw,        When the yardstick is          3o = 1.5:1
heavy wave action, or other local      held up and aligned             4Sï¿½ = 1:1
slope movements are extremely          with what appears to       Figure 5. Slope Angle Determination.
important and empowers you to          be the average slope of
help provide solutions to your         the land, the slope angle can be
situation. The Ecology publica-        read directly from the protractor.
don - Vegetation Management: A         This slope angle can then be
Guide jor Puget Sound Bluff            converted to the appropriate
Property Owners will also be           horizontal/vertical ratio as shown.
helpful to you in performing your
site evaluation - particularly as i      he quickest way for you to
relates to existing vegetation.        estimate slope height is to visually
                                       estimate the height of some
Your site observations should be       nearby vertical structure on the
grouped into the following             slope (i.e. tree or bluff face) and
general categories: (1) the nature     then estimate how many tree
of the slope toe, face, and crest -    heights would equal the overall
noting the existing slope soil and     slope height.
vegetation conditions; (2) identify
known slope problems or poten-            SOIL
tial hazardous areas; and (3) note     Site specific information noting
factors you feel contribute to         soil types, thicknesses, and
slope erosion and stability            moisture conditions is very
problems.                              helpful to you when you select
The Coastal Pro both plant species and planting
               The  oastlPrperty Owner  techniques to be used in your
Checklist provided in this manual      program. Observing the types of
will allow you to start organizing     vegetation already living on the
your observations. Additional          slope is a good due to slope soil
information about your slope site      conditions. The County Soil
should also be added to the            Conservation Service, Soil Con-
checklist as necessary. The            servation Districts and Coopera-
following discussion will aid you      dye Extension Agents are good
in completing your checklist. sources of information and
                                       expertise on soil characteristics.

                                                                                                             7




*Undmionnding Your Property

                                  *MICROCLIMATE                        *VEGETATION
                                 Puget Sound coastal weather is        Evaluation of the existing slope
                                 strongly influenced by changing       vegetation is the key final
                                 topographic and atmospheric           observation of the slope because
                                 conditions. The degree of             it should confirm your previous
                                 precipitation, available sunlight,    observations. Use the presence
                                 temperatures, and wind can            of vegetation (or lack of it) to
                                 change radically from one coast-      confirm or modifyr your site
                                 line sector to another and            evaluation. Vegetation will exist
                                 consequently from site to site.       in areas which favor its establish-
                                 These factors should be recog-        ment. As you identifyr specific
                                 nized in your site evaluations and    types of vegetation on your slope,
                                 planning effort which includes        you can consult other references
                                 both planting and drainage            (see recommended reading
                                 control elements.                     section) to determine the range
                                          8 DRAINAGE ~~~~of environmental conditions
                                 Wae DRin andontesoeih (i.e. soils type and moisture,
                                 most common agent causing lgtpeeecs t. hc h
                                 erosion and slope instability and    observed plants tolerate. You
                                 should be adequately examined         should then be able to confirm
                                 during the site evaluation and        your original observations. If
                                 planning effort. Observations of      your observations indicate that
                                 your slope's drainage conditions      these species should not typically
                                 should include a careful search       grow on your slope, you may
                                 for seepage from the slope face. w    antoprrmyuevlais
                                 Surface water runoff should also    again or investigate whether the
                                 be investigated and is best           site has recently been disturbed
                                 observed during periods of heavy      or modified.
                                 rainfall. Pipe discharges and
                                 uncontrolled drainages across
                                 poorly vegetated surface soil are
                                 typical slope erosion problems.
                                 Visual observation of surface
                                 water runoff problems indlude
                                 watching for thin layers of water
                                 flowing across the slope face.
                                 Surface water runoff contained in
                                 channels usually starts in small
                                 rills in the upper soil horizon and4
                                 then through time erodes into
                                 gullies which downcut into the
                                 slope. Runoff which concentrates
                                 into channels creates greater
                                 problems for slope stabilization
                                 programs because of the magni-
                                 tude of erosive forces.





                                                                                       Undertanding Your Property U


SLOPE  EROSION                         (e.g. soil type, slope length and
Loss of your slope's surface soil      steepness, ground roughness, type
layers by the action of wind,          of vegetation covering the slope,
water, and ice are what is referred    and exposure to winds). A typical
to as soil erosion processes.          formation of rills and gullies is
Rainfall is the major factor along     shown schematically on Figure 6
Puget Sound coastlines. However,       Wind and frost wedging erosion
wind and frost wedging do act          can be reduced by allowing plant
upon some exposed slopes. The          foliage to cover exposed slope
rates of erosion can be controlled     areas. The foliage creates a
by reducing the sources of runoff      physical and thermal barrier
to the slope and/or by modifyring      which protects the surface soils.
the nature of the site conditions
which influence runoff rates


  PUGET SOUND COASTAL SLOPE PROCESSES

    SOIL - MASS MOVEMENT




                      **-., ~ ~     ~       ~       ~       l.,"'I 





    Rotation                                           Fl


    SOIL - EROSION                                                               ROCK - EROSION











    Rills/                   Seepage/ Wave Action                                    Rock Fall
    Gullies                  Frost Wedging

Figure 6. Typical Puget Sound Coastal Slope Processes.

                                                                                                            9




* Undentanding YourPropemy


                                    SOIL MASS MOVEMENT                     SPECIAL NEEDS AREAS
                                   When a downward movement of            Should you recognize or suspect
                                    relatively intact masses of slope      that your property or adjacent
                                    material occurs, it is called a mass   properties contain any of the
                                    movement (instead of erosion).         following landforms or slope
                                    Mass movements can take the            conditions, you should contact
                                    form of landslides, earth/debris       the appropriate government
                                    flows and slumps, and rock falls/      agencies to acquire assistance in
                                    earth topples. Figure 6illustrates     these technical areas. You may
                                    these basic soil movement              also want to have consultations
                                    processes. These events have been      with technical experts in these
                                    lumped together by planning            areas:
                                    agencies and the pubic and are           1) Historical or Recent Land
                                    generally called landslides. For            slides/Areas designated as
                                    simplicity, mass movements will             Geologically Hazardous
                                    be referred to as landslides in this        Geologically Hazardous
                                                                                Areas [A, F]
                                    manual. Recognition of active or
                                    historical landslide areas is            2) Unstable Slope Fills [A, F]
                                    important. Should you believe            3) Planting Vegetation on
                                    landsliding has occured or that             Slopes Steeper than 1.5
                                    there is the potential for land-            Horizontal to 1 Vertical
                                             sliding on or adjacent to          (33 degrees) [F]
                                             your property, it would
                                             Iybeu prudent to secure the     4) Coastal Marine Erosion
                                             assistance of a profes-            [A, B, D, 
                                             sional geotechnical              5) Wetlands [A, B, C, HI
                                             engineer prior to the site      6) Habitat for Endangered,
                                             planning process. It is            Threatened, Rare Animal
                                             important to reiterate             Species (e.g. bald eagle or
                                             that vegetation can be             osprey nests/alternate nests/
                                            used to control shallow              perch trees) [E]
                                             seated landsliding which
                                             is common along coastal
                                             slopes. However, it does        A - County Planning Office Dept.
                                             not address deep seated             of Community Development
                                             landslide events. Vegeta-        B - Washington Dept. of Ecology
                                             tion can also be a              C - Army Corps of Engineers
                                             valuable component of
                                             biotechnical engineering        D -Washington Dept. of Fisheries
                                                                              E- Washington Dept. of Wildlife
                                             design solutions to these
                                                                              F - Geotechnical/Biotechnical
     Initial shallow-seated landsliding.     deep seated potential               Professional
                                             landslide conditions.
                                    Consult a geotechnical/                  G - Coastal Engineering
                                    biotechnical engineer for design                 Professional
                                    input on stabilization alternatives.      H -Weand Professional



10




                                                                                          UndeMnding Your Prope  ï¿½

COASTAL PROPERTY OWNER CHECKLIST


WHAT LANDFORM(S) ARE LOCATED                               * GROUNDWATER
ON  MY PROPERTY?  (check glossary definitions)               Is there evidence of groundwater in the slope?
  H  Low Bluff (for this publication, < 10 feet)             1]  Seepage or damp surfaces seen on the slope face
  a  High Bluff (for this publication, > 10 feet)            ]  Active or historical landslides
  H  Low Cliff (not generally applicable to this publication)  What are your contributions to groundwater
  H  High Cliff (not generally applicable to this publication)  in the slope?
  H  Low Bank (for this publication, < 10 feet)              H  Water infiltration areas (roof and curtain drains)
  [1 High Bank (for this publication, > 10 feet)             H  Septic system
  El Beach with Backshore Berms of                           H  Irrigation systems
     Sand/Gravel/Cobbles (marine/estuarine)
  H  Wetlands (check with the County Planning Office)        VEGETATION
                                                         - Is there vegetation on or adjacent to the slope?
PROPERTY DESCRIPTION AND                                   If yes, where is it and what are the species.
OBSERVATIONS
     What is the elevation of the house above the
     high tide water surface?                             If no, is there evidence of past vegetation?
     What is the average angle of the slope face?         What happened to it and what were the species?
     Do waves reach the toe of the slope?                 (check other properties)
     What are the diameters of beach sediments
     around the slope toe? (e.g. sand/gravel/cobbles)
     Has the slope face been recontoured or filled?
                                                             _ Is there evidence of vegetation movement
     What is soil material type(s) of the slope? down the  slope?

FACTORS INFLUENCING SLOPE EROSION   ï¿½ MARINE WATERS
AND STABILITY                                              _      Is there a noticeable beach width above the high
* SURFACE WATER RUNOFF, WIND                                     water line?
  AND FROST WEDGING                                       -         Are wave energies eroding the toe of the slope?
  Can the effects of surface water runoff be                    Are there coastal erosion control
  visually identified?                                          structures along the beach of your or
  H  Rainfall impact erosion                                     neighboring properties? (e.g. bulkheads)
  H  Soil rills and gullies                                      If yes, are these structures causing erosion?
  H  Winter freeze-thaw evidence                                 Is your property flood prone?
  H Wind erosion
                                                         * SLOPE USE
  [1 Pipe discharge erosion                                * SLOPE USE
                                                           How do you use the slope?
  What does your property contribute to runoff?               ] Access to the beach (raillroadstairs/other)
  [  Significant upland impervious surface                   [  Vegetation removal for view maintenance
  H1  Drainage pipe discharge onto slope                     a  Horticultural/garden areas
  [  Sprinkling/irrigation/hot tub releases                    H Waste/debris fills
  H  Other                                                   H  Natural greenbelt induding slope crest





 Understanding Your Property



GENERAL APPLICABILITY








  ADVANTAGES/                                 SEEDING    CONTAINER                     LIVE            CONTOUR               BRUSH
  DISADVANTAGES                          (MIXED SPECIES) BARE ROOT    STAKING    WATTLING    LAYERING

   Rainfall Erosion: Foliage
   Intercepts railndrops                           ï¿½ 

   Runoff Erosion Control: Roots
   bind surface soil particles  0                                                           

   Wind  Erosion Control: Plants
   reduce wind exposure                                                                                                        * 

   Frost Action Erosion Control: 
   Roots restrain soil movement            ï¿½

   Slope Stabilizatlon: Reintorce soil
   & resists shallow seated landsliding                                                     

   Slope Stabilization: 
   Plants help dewater slope 

   Runoff Erosion Control: Plants                                                                                              *
   filter soil particles from runoff

   Immediate Erosion
   Control/Slope Stabilization

   Slope Stabilization: Resistance
  to deep seated landsilding

   Low Initial malntenance 


   Low long-term maintenance                                                                                                   *


   Low Impact construction                                                                  

   Plants prevent slope undercutting
   by waves

   Relative low-cost construction                                                                              

   Plants combine with other
   structuralfeatures                                                                                          

   Aesthetic/wildllfe benefits                                                                                 


 Table 1. General Applicability of Slope Protection Plant Techniques.




                                                                                                      The Role ofVegewtaon 

THE ROLE OF VEGETATION


To comprehend the benefits and                  mechanisms are those processes
contributions of how vegetation                 of water use and movement in the
influences soil erosion and slope               slope when living plant materials
stability, you may think of its role            exist in the soil. The general roles
as either hydrological or mechani-              that vegetation plays in slope
cal in nature. The mechanical                   maintenance and reinforcement
contributions arise from the                    are summarized in Table 2. The
physical interactions of either the             net effect of vegetation is usually
foliage or root system of the plant             beneficial to slope stability.
with the slope. The hydrological


  VEGETATION AND SLOPE STABILITY
   Legend: (+) Beneficial to stability  (-) Adverse to stability

  MECHANISM                                                                                       INFLUENCE

     Hydrological Mechanisms

     Foliage intercepts rainfall, causing absorptive and evaporative losses
    that reduce rainfall available for infiltration.                                                       (+)

     Roots and stems increase the roughness of the ground surface and
    the permeability of the soil, leading to increased infiltration capacity.  -

     Roots extract moisture from the soil which is lost to the atmosphere
    via transpiration, leading to lower pore-water pressure.                                               (+)

    Depletion of soil moisture may accentuate desiccation cracking
    in the soil resulting in higher infiltration capacity (uncommon around Puget Sound).  -

     Mechanical Mechanisms

    Roots reinforce the soil, increasing soil shear strength.                                             (+)

    Tres roots may anchor into firm strata, providing support to the upslope soil mainly through
    buttressing and arching.(+

    Weight of trees surcharges the slope, increasing normal and downhill force components.'

    Vegetation exposed to the wind which transmits forces into the slope. (Degree of adverse
    effect Is dependent upon exposure and health of vegetation. Typically a minor consider-                (-)
    atlon for Puget Sound Inland Waterways.)

    Roots bind soil particles at the ground surface, reducing their
    susceptibility to erosion. (

Table 2. Vegetation and Slope Stability (Source: Modified from Greenway, 1987).
* Tree weight in some situations is benefical to slope stability. Trees should not be arbitrarily cut to "unweight" slopes.


                                                                                                                      13




* The Roe of Vegeation


                                                                       AN OUNCE OF
                                                                       PREVENTION
                                                                       No amount of slope disturbance
                                                                       followed by replanting should
                                                                       replace rational site planning
                                                                       when it comes to avoiding slope
                                                                       disturbances. Should you have
                                                                       the option, maintain all the native
                       ' .r  z                                           vegetation you can and potentially
            9<'* . ï¿½E~F ï¿½~,~cS~-                                         accept the natural retreat of the
                                 ï¿½ï¿½ï¿½I~~~~~~~t~~~ 4eslope crest. Accordingly, you
                 .... W  _  B y itshould plan the location of your
                                                                       residence carefully. Maintaining a
                                                                       greenbelt along slope crests is
                                                                       good practice. Do not assume
                                                                       cutting trees to "unweight" your
                                                                       slope is benefical to slope stability
                                                                       - often it is not. Also, remember
                                                                       as a general rule, do not introduce
                                                                       water onto or into your slope.
                                                                       PLANNING AND
                                                                       INSTALLATION GOALS
                                                                       Since you have now spent time
                                                     failure planes    observing your slope features and
                                                     Xfailure plans    have begun to understand what is
                                                                       happening around your slope, you
        Figure 7. Root Reinforcement of a Slope.                         should be able to establish some
                                                                       basic planning and planting goals
                                  The protection of the slope            which address the problems you
                                  against shallow seated landsliding     have noted. You should divide
                                  is a key benefit of a revegetation     the slope into different areas if
                                  or existing vegetation mainte-         this makes sense based on your
                                  nance program. The function that    observations. This may allow you
                                  mixed vegetation provides by           to accomplish different goals in
                                  increasing the apparent cohesion       those areas. Now is the time for
                                  of the surface soil structure of a     you to consider any drainage
                                  slope is illustrated in Figure 7.      improvements to your slope (see
                                  The different types of root            For More Information). These
                                  systems that plants provide can        improvements should be compat-
                                  strengthen potential shallow-          ible with your planting program.
                                  seated failure planes on your slope
                                  by both fiber reinforcement of the    Typically, the slope can be
                                  near surface soil and binding soil     separated into at least three areas:
                                  structure together into a larger       the crest, face, and toe. Planting
                                  unit through tap or lateral root       objectives are usually slightly
                                  networks,                              different in these zones. At the


14




                                                                                            The Role ofVegetation ï¿½

slope toe, you may be concerned        PLANT SPECIES
with providing plants which resist     SELECTION
down-slope soil movements, are        An effective method to properly
tolerant to wet soils or occasional    select plant species involves
saltwater spray, and can handle        coordinating your site conditions
changes to coastal marine deposi-      and planting objectives with the
tion or erosion processes. On the      recommendations of local nursery
slope face you may decide to           publications and qualified native
select plants and planting tech-       plant professionals. Plant material
niques which tolerate a range of       can be both purchased or gathered
soil and light conditions, can         depending upon your own situa-
handle some soil movements, can        tion or plant availabilities. Your
resist shallow seated landsliding,     local native plant nurseries and
manage surface runoff, and are         state agencies involved in revegeta-
compatible with other slope uses.      tion programs should be able to
Along the slope crest you may          assist you in locating appropriate
want to revegetate a buffer area       planting materials. The Hortus
to strenghten soils and reduce        Northwest Journal to native plant
erosion. Pulling these objectives     sources is a valuable resource or
together is an important mile-        you can contact DNR and SCS
stone in your planting effort.         for potential plant sources. You
Obtain assistance if you find the      should use Table 3 in this manual
planning process is complicated        as a starting point for your plant
for your situation.                   selections. There are still many
                                       other species from which to
SLOPE PREPARATION                     choose. It is generally not desirable
                                      to select ivy, Scot's broom or other
The first task of your planting        ornamental exotic plants. Select-
program will be to prepare the         ing native plants will usually
planting area just prior to plant-      ng nauve plants wi  usually
ing, avoiding and protecting           increase the success of the planting
against wet weather conditions.        program and reduce your long-
This task requires that soil areas     term maintenance requirements.
be prepared keeping disturbance        Seeding and planting of vegetation
to a minimum according to the         should be done carefully. In many
requirements of each planting          cases, grass and legume seed
technique. Once the slope has          mixtures will have to be seeded
been prepared, you should mark         by hand scattering along the face
the positions or alignments of         of the slope. The seed should then
your planned plantings. Excava-        be covered with an appropriate
tions should be performed              mulch material. For large scale
concurrently with plant installa-      planting on hard-to-reach areas,
tions. This will allow installations   machines called hydroseeders
to proceed effectively and reduce     which spray mixtures of seed,
your total time on the slope.          water, and mulch materials are
                                      recommended. These applications
                                      are commonly used by the Soil          Continued on page 24...




* The Role of Vegetation



  PLANT SELECTION GUIDE*



                                                                                            WATER1               LIGHT2
    NAME                               FORM & HABIT                      MATURE SIZE    REQUIREMENTS  REQUIREMENTS 

    Red Alder                          Deciduous tree; seeds             Height: 80'+          Moist                 Full Sun
     (Alnus rubra)                     prolifically on bare soil         Spread: 40'           conditions,                               ,
                                                                                            No data




    Pacific Willow                     Deciduous multi-stemmed           Height: 40'+         Wet conditions,        Full Sun
     (Salix lasiandra)                 tree; does not spread             Spread: 25'           Usage high?







    Scouler Willow                    Deciduous tree or shrub;           Height: 30'           Dry-Moist             Full Sun
     (Salix scouleriana)               does not spread                   Spread: 15'           conditions,
                                                                                            Usage high?




    Sitka Willow                       Deciduous tree or shrub;          Height: 30'           Moist                 Full Sun
     (Salix sitchensis)                does not spread                   Spread: 25'            conditions,
                                                                                            Usage high?




     Douglas Fir                       Coniferous tree;                   Height: 200'+         Dry-Moist             Full Sun
     (Pseudotsuga menziesii)           does not spread                    Spread: 50'          conditions,
                                                                                            Usage moderate










   Table 3. Plant Selection Guide (Partial listing of appropriate native plants for erosion control and slope stabilization).

16




                                                                                                                 TheRok ofVegeration ï¿½







SOIL                  ROOTING3                  RECOMMENDED              PLANTING4
REQUIREMENTS   CHARACTERISTICS   SPACING                                 CONDITION                COMMENTS5

Any soil              Fibrous,                  10'+                     Bareroot seedlings        Fast grower in poor mineral
                      Moderately deep                                    up to 3' tall; larger    soils; typical 40-50 year
                                                                         plants in containers     lifespan; large limbs become
                                                                                                  brittle; provides food
                                                                                                  for birds


Any soil -            Fibrous,                  6'+ for rooted plants;   Rooted plants to          Fast grower in saturated or
tolerates shallow     Moderately deep           2' for whips or          10' tall in containers;    shallowly flooded areas; 25
flooding during       and widespread            cuttings                 cuttings 18"-24";        year lifespan -  large limbs
the growing                                                              whips 4'                 become brittle, tend to break
season                                                                                            off; stumps produce long,
                                                                                                  fast-growing whips; easily
                                                                                                  rooted


Any soil              Fibrous,                  6' for rooted plants;    Rooted plants to          Of the willows listed
                      Moderately deep           2' for whips or          10' tall in containers;    here, this species tolerates
                      and widespread            cuttings                 cuttings 18"-24";        the driest conditions
                                                                         whips 4'; whips not
                                                                         recommended


Any soil              Fibrous,                  6' for rooted plants;    Rooted plants to          Fast grower in moist to
                      Moderately deep           2' for whips or          10' tall in containers;    saturated soils; widely used
                      and widespread            cuttings                 cuttings 18"-24";        for streambank stabilization
                                                                         whips 4'; whips not
                                                                         recommended


Any soil              Tap - Modified            10'+                     12"-18" bareroot          Generally not considered
                      Tap, Shallow to                                    seedlings; larger        a primary species for slope
                      deep and                                           plants in containers     face stabilization; high root
                      widespread                                                                  strength but typical shallow
                                                                                                  rooting characteristics in
                                                                                                  thin coastal soils; can be
                                                                                                  planted in stands in slope
                                                                                                  crest greenbelts; good eagle
                                                                                                  and osprey perch and nest
                                                                                                  trees; potential for wind
                                                                                                  throw in thin or disturbed
                                                                                                  soils




                                                                                                                                  17




* The Role of Vegetation


  PLANT SELECTION GUIDE (CONT.)

                                                                                          WATER'               LIGHT2
    NAME                             FORM & HABIT                     MATURE SIZE    REQUIREMENTS  REQUIREMENTS

    Northern Black                   Deciduous;                       Height: 100'+        Moist                 Full Sun
    Cottonwood                       does not spread                  Spread: 40'          conditions,
    (Populus trichocarpa)                                                                  Usage high




    Red-Osier Dogwood                Deciduous shrub;                 Height: 20'          Moist-Wet,            Full Sun
    (Cornus stolonifera              does not spread                  Spread: 20'          No data              Sun/Shade
    or Cornus sericea)




    Black Twinberry                  Deciduous shrub;                 Height: 10'          Moist,                Full Sun
    (Lonicera involucrata)           does not spread                  Spread: 8'           No data




    Ninebark                         Deciduous shrub;                 Height: 15'          Moist,                Full Sun
    (Physocarpus capitatus)          does not spread                  Spread: 10'          No data              Sun/Shade



    Cascara                          Deciduous tree/shrub;            Height: 25'          Moist,                Full Sun
    (Rhamnuspurshiana)               does not spread                  Spread: 15'          No data



    Salmonberry                       Deciduous shrub;                Height: 8'           Moist,                Sun/Shade
    (Rubus spectabilis)              spreads by underground           Spread: 6'           No data               Full Shade
                                     runners to form thickets



    Hooker Willow                    Deciduous shrub;                 Height: 20'          Moist-Wet,            Full Sun
    (Salix hookeriana)               does not spread                  Spread: 15'          No data






    Red Elderberry                   Deciduous shrub;                 Height: 15'           Moist,               Full Sun
    (Sambucus racemosa)              does not spread                  Spread: 10'          No data              Sun/Shade
                                                                                                               Full Shade



18




                                                                                                                 The Role of Vegetation ï¿½



SOIL                  ROOTING3                  RECOMMENDED              PLANTING4
REQUIREMENTS   CHARACTERISTICS   SPACING                                 CONDITION                COMMENTS'

Any soil -            Fibrous,                  6'+ for rooted plants;   Rooted plants to          Fast grower in moist to
tolerates shallow     Shallow to deep           2' for whips or          10' tall in containers;    saturated soils; also widely
flooding during       and widespread,           cuttings                 cuttings 18"-24";        used for streambank
the growing           extensive                                          whips 4' tall            stabilization; potential for
season                                                                                            wind throw


Any soil -            Fibrous,                  3'+ for rooted plants;   Rooted plants to         Attractive shrub that
tolerates shallow     Shallow                   2' for cuttings          6' tall in containers;   produces bright red stems
flooding during                                                          bareroot & cuttings
the growing                                                              18"-24" tall
season


Any soil              Fibrous,                  4'+                      Rooted plants to          Produces yellow twin flowers
                      Shallow                                           6' tall in containers;    and black twin-berries; some
                                                                         bareroot 18"-24" tall    success reported from
                                                                                                  cuttings


Any soil              Fibrous,                   4'+                     Rooted plants to          Produces masses of tiny
                      Shallow                                           6' tall in containers;    white flowers which change
                                                                         bareroot 18"-24" tall    to reddish seed clumps


Any soil              Tap,                      4'+                      Rooted plants to          Shiny, black berries are
                      Moderately deep                                   6' tall in containers;    favored by Cedar Waxwings
                                                                         bareroot 18"-24" tall


Any soil              Fibrous,                  4'+                      Rooted plants to          Spreads quickly once
                      Shallow                                           4' tall in containers;    established; berries provide
                                                                         bareroot 6"-8" tall;     food for a variety of
                                                                         cuttings 18"-24"         songbirds


Any soil              Fibrous,                  3'+ for rooted plants;   Rooted plants to 6'       A horticultural variety,
                      Moderately deep           2' for cuttings          tall in containers;      "Clatsop," has been developed
                                                                         bareroot & cuttings      by the Soil Conservation
                                                                         18"-24" tall; whips      Service for its vigor, disease
                                                                         4'; whips not            resistance & attractive foliage;
                                                                         recommended              salt spray tolerant

Any soil              Fibrous,                  4'+                      Rooted plants to          Produces red, non-edible
                      Shallow                                            6' tall in containers;   berries; some success reported
                                                                         bareroot 18"-24" tall    from woody cuttings



                                                                                                                                  19




* The Role of Vegetation


   PLANT SELECTION GUIDE (CONT.)
                                                                                          WATER'               LIGHT2
     NAME                             FORM & HABIT                     MATURE SIZE    REQUIREMENTS  REQUIREMENTS

    Douglas' Spiraea                 Shrub;                           Height: 8'           Moist-Wet            Full Sun
     (Spiraea douglasii)              spreads by seed &                Spread: 6"           conditions,
                                     underground runners                                   No data
                                     to form seed


    Snowberry                        Deciduous shrub;                 Height: 4'           Dry-Moist             Full Sun
     (Symphoricarpos albus)           spreads by underground           Spread: 3'           conditions,          Sun/Shade
                                     runners to form thickets                              No data              Full Shade



    Salal                            Evergreen shrub;                 Height: 3'           Dry-Moist             Sun/Shade
     (Gaultheria shallon)             spreads by underground           Spread: 3'           conditions,          Full Shade
                                     runners to form thicket                               No data



    Ocean Spray                      Deciduous shrub;                 Height: 10'+         Dry-Moist             Full Sun
     (Holodiscus discolor)            does not always spread           Spread: 6'           conditions,          Sun/Shade
                                     aggressively                                         No data



    Vine Maple                       Deciduous shrub;                 Height: 15'+         Moist                 Sun/Shade
     (Acer circinatum)                does not always spread           Spread: 10'          conditions,          Full Shade
                                     aggressively                                          No data



    Kinnickinick                     Low-growing shrub;               Height 8"            Dry conditions,       Full Sun
     (Arctostaphylos Uva-ursi)        spreads to form a dense,         Spread: 6"           No data
                                     evergreen carpet


    Thimbleberry                     Deciduous shrub;                 Height: 4'            Moist                Full Sun
     (Rubus parviflorus)              spreads by underground           Spread: 4'           conditions,          Sun/Shade
                                     runners to form thickets                              No data


    Indian Plum                      Deciduous shrub;                 Height: 10'           Moist                Full Sun
    (Oemleria cerasiformis)          spreads by underground           Spread: 6'           conditions,           Sun/Shade
                                     stems to form open stands                             No data              Full Shade



    Evergreen Huckleberry            Evergreen shrub;                 Height: 6'           Dry-Moist             Sun/Shade
    (Vaccinium ovatum)               does not spread                  Spread: 3'           conditions,          Full Shade
                                                                                          No data


20




                                                                                                                   TheRoleofVegeration ï¿½


SOIL                   ROOTING3                   RECOMMENDED              PLANTING4
REQUIREMENTS   CHARACTERISTICS   SPACING                                   CONDITION                COMMENTSS

Any soil - tolerates    Fibrous,                  3' for rooted plants;    Rooted plants to          Spreads quickly &
shallow flooding       Shallow                    2' for cuttings          6' tall in containers;    aggressively in most sites
during the                                                                 bareroot & cuttings
growing season                                                             18"-24" tall


Any soil - tolerates    Fibrous,                  2'+                      Rooted plants to          Tolerates high winds and
shallow flooding       Shallow                                             24" tall; bareroot        often grows on vegetated
during the                                                                 6"-18" tall               slopes overlooking salt water
growing season


Any soil - tolerates    Fibrous,                  2'+                      Rooted plants 4" to       Widely available; difficult to
shallow flooding       Shallow                                             12" tall                  establish; slow growing;
during the                                                                                           tolerates salt spray
growing season


Any soil - tolerates    Fibrous,                  4'+                      Rooted plants to          Produces attractive sprays of
shallow flooding       Moderate                                            2' tall in containers;   creamy-white flowers; will
during the                                                                 bareroot 6"-12" tall     root spread
growing season


Any soil - tolerates    Fibrous,                  8'+                      Rooted plants to 4'       Large specimens widely
shallow flooding       Moderate                                            tall in containers;       available; spreads by root
during the                                                                 balled & burlapped       and seed
growing season                                                             plants to 10' tall


Any slightly           Fibrous,                   2'                       Rooted plants in          Widely available evergreen
acid soil              Shallow                                             containers               ground cover; tolerates salt
                                                                                                    spray


Any soil               Fibrous,                   3'                       Rooted plants in          May be difficult to find in
                       Shallow                                             containers               some native plant nurseries



Any soil               Fibrous w/horizontal,    4'+                        Rooted plants to 4'       Male and female flowers are
                       underground runners,                                in containers;           on separate plants; only
                       Shallow                                             bareroot 6'-8' tall      female flowers produce the
                                                                                                   attractive "plums"

Slightly acid          Fibrous,                   3'+                      Rooted plants to         Attractive, but slow growing;
                       Shallow                                             2' tall in containers    difficult to establish; tolerates
                                                                                                   salt spray


                                                                                                                                    21




* The Role of Vegetation


  PLANT SELECTION GUIDE (CONT.)
                                                                                          WATER'               LIGHT2
    NAME                             FORM & HABIT                     MATURE SIZE   REQUIREMENTS  REQUIREMENTS

    Nootka Rose                      Deciduous shrub;                 Height: 6'            Moist                Full Sun
    (Rosa nutkana)                   spreads by underground           Spread: 3'           conditions,
                                     runners to form thickets                              No data




    Red Currant                      Deciduous shrub;                 Height: 8'            Dry-Moist            Full Sun
     (Ribes sanquineum)               does not spread                  Spread: 6'           conditions,           Sun/Shade
                                                                                          No data


    Wax Myrtle                       Evergreen shrub;                 Height: 15'           Dry-moist            Full Sun
     (Myrica californica)             does not spread                  Spread: 8'           conditions,          Sun/Shade
                                                                                          No data


     Native Plant                     Annual and perennial grass       Height: 1'-2'        Dry-Wet               Species/mix
     Seed Mixes                       and forb mixes available         Spread: varied       conditions,           dependent
                                                                                           Medium - high








   *Table 3 based on information from: Myers Biodynamics staff experience; Binns, 1980; Stevens & Vanbianchi, 1993; Kruckeberg, 1982.


   FOOTNOTES
   'WATER REQUIREMENTS                        2LIGHT REQUIREMENTS                         3ROOTING CHARACTERISTICS
     Dry   - Once established, tolerates dry    Full Sun    - Requires sun throughout       Fibrous - Lacks a central root; root
              soil conditions during the                      the day                                  mass composed of fibrous
              growing season                    Sun/Shade - Requires shade for about                  lateral roots
     Moist  - Requires moist soil throughout                  1/2 the day                   Tap    - With a stout, central main
              the growing season                Full Shade - Requires shade                           root
     Wet   - Tolerates saturated soil                         throughout the day          Shallow, Moderate, Deep refers to relative
              year-round                                                                  rooting depth (influenced by soil and
     Usage - Relative water uptake by plant                                              groundwater conditions)
              [e.g., high or no data]











22




                                                                                                                    TheRoleofVegetation U



SOIL                   ROOTINGs                   RECOMMENDED               PLANTING4
REQUIREMENTS   CHARACTERISTICS   SPACING                                    CONDITION                 COMMENTS,

Any soil,              Fibrous,                   3'                        Rooted plants to           Thickets of spring stems
prefers rich soils     Shallow                                              2' tall in containers;    create a formidable barrier;
                       (not extensive)                                     bareroot to 18" tall;      produces attractive, pink
                                                                           cuttings 12"-18"          flowers followed by large,
                                                                                                     red hips; tolerates salt spray


Any soil               Fibrous,                   6'+                       Rooted plants to 4'        One of our finest ornamental
                       Shallow                                             tall in containers;        natives; produces clusters of
                       (not extensive)                                     bareroot to 18" tall       white to red flowers


Slightly acid,         Fibrous,                   10'+                      Rooted plants to 10'    Tolerates salt spray; high
with organic           Moderate                                                                        wildlife usage
matter


Species/mix            Fibrous,                   Apply as                  Seed                       Woody plant seeds also
dependent              Shallow                    recommended                                          available (success typically
                                                                                                     low); very slow to establish;
                                                                                                     avoid exotic commercial
                                                                                                     mixes; seed mixes typically
                                                                                                     used in conjunction with
                                                                                                     other vegetation plantings;
                                                                                                     typically short-term erosion
                                                                                                     control technique





4PLANTING CONDITION                           SCOMMENTS
Sizes given are those that are generally      Growth rate; ornamental & wildlife value;
found in nurseries; other sizes may also      wind/salt spray tolerance; maintenance;
be available                                  average life span

















                                                                                                                                      23




* The Role of Vegetation

        Continued from page 15.    Conservation Service and other       to slope plantings. Mulch protects
                                   agencies.                            against rain and wind while seeds
                                  Where broadcast seedngs are          are germinating and plants pro-
                                   made, time of seeding for grasses    pogating. It also reduces loss of
                                   and legumes is very important.       soil moisture during extended dry
                                   Seeding should be avoided in         periods. Because of the severe
                                  July, August, and September           nature of most coastal slope areas,
                                  wherever possible as extensive       a mulch cover addition is neces-
                                   drought periods can occur.           sary if vegetation is to be estab-
                                   Legumne-based mixtures should be    lished from seed.
                                  seeded as early as possible but no   A wide variety of mulches can be
                                   later than mid-June. Grass-based      used. These range from scattered
                                   mixtures can be seeded before and    straw to sprayed fiber. More
                                  after July through September. It     common materials and methods
                                   should be realized that healthy,     may include: hay or straw (1V/2-
                                   herbaceous ground covers may         2 tons/acre), jute netting, plastic
                                   require an initial fertilizer applica-    netting (not recommended),
                                   tion to achieve higher successes.    manure or compost (not recoin-
                                  Select native species and use a      mended), wood fiber, or fiber
                                   slow-release formulation (do not      matting. Check with your local
                                   over fertilize).                     Soil Conservation Service office,
                                  Woody plant materials should         nursery people, or garden and
                                   come from plant stock which is       farm centers to get more informa-
                                   dormant and should be planted        tion on local availability or
                                   immediately. Materials can be        suitability for your situation.
                                   installed up to 48 hours after        One other short-term anchoring
                                   cutting if they are kept cool and    method which has helped to
                                   moist by covering cuttings with      stabilize slopes during vegetation
                                  moist mulch.                          establishment in some areas sus-
                                  Willow, cottonwood, and dog-          ceptible to shallow soil move-
                                  wood can be planted as cuttings       ments involves "naiing down" a
                                   or saplings and are particularly     slope face with 5 foot metal fence
                                  good for seep zones and other wet     posts. The posts are driven
                                  areas of slope faces. However,       perpendicularly into the slope face
                                  avoid planting willows near artifi-    in a grid pattern with 10- 15 feet
                                   cial drains because their roots seek    spacings between them. The posts
                                  water and may eventually dog or      are cross-connected with heavy
                                         disrpt   he  rais. henplanting    wire or cable which has the effect
                                   other shrubs and trees on slope o yn h niesoefc
                                  areas, consult qualified nursery      together from top to bottom and
                                  people to determine appropriate       side to side. The posts should be
                                  species for your conditions.          driven in almost all the way into
                                                                         the ground, wired, and then the
                                   MULCHING                             slope should be planted and
                                  Mulching of seeded or planted        mulched.
                                  areas is of particular importance

24




                                                                                              Planting Program U

PLANTING PROGRAM


PLANTING ZONES                         edge is currently cleared, a strip
Without using more advanced            may be left undisturbed and a
stabilization techniques, the          revegetation program imple-
maximum slope to be considered         mented.
for vegetative stabilization is        0SOEFC
(i.5Hi. ThoriotloIvearticany           Vegetation should be established
god  plant IV) Ther foremany           on patchy and barren slope faces
     good pl~~ants minthformo or terraces to reduce erosion.
grasses, vines, shrubs, admnrPlanting practicality depends
trees that can be used for slopegralontecrcerfth
stabilization projects. Plant    s     loeatlnd patiecularacte of the
selection is dependent upon the        slope, angl.d slperiual of t.he I
goals of your erosion control          slopdeagrees) sholdope ofns.5HiV
program and site conditions.           the dividing linel  betcosierend
Typically, effective programs          manageablen slope bewend aslp
incorporate structural diversity       manaeabep enough tand veeaslope
in plant selections (trees/shrubs      stepeouldhb dificut orgtaimossbl
with goun spcovers).ns                 to establish without employing
         mix   o f  species. ~~other reinforcement techniques.
* SLOPE CREST                          If room exists at the top of a
The vegetation along the edge          slope, low slopes can be graded
of the top of the slope serves as      back to a gentler configuration.
a protective buffer for the slope      3H:1IV or flatter slopes are ideal
face. If possible, you should bcueteesoe a epe
maintain or reestablish a greenbelt    paedndpanted wthwesesloed  a   epe
         whichwouldprovie a bffervehicles. However, in most coastal
between the slope face and resi-       areas, slopes are too steep or too
dential structures. This is particu-   high for mechanical planting
larly important in areas where         techniques. Slope regrading may
slopes are too steep and too high      be neither economically feasible
for economically feasible stabiliza-    nor technically desirable for the
tion methods. For example, some idvda rpryonr
coastal high bluffs in residential     idvda   rpryonr
arma along Seattle, Tacoma,            Various species and mixtures of
Edmonds, and Port Townsend             species can be planted on slope
waterways may be too severe to         faces and expected to succeed in
attempt stabilization. In cases like   this rather severe environment.
these, you may choose to main-         These include seed mixtures of
tain a strip of dense natural          grasses and legumes and a range
vegetation along the bluff edge.       of shrubs and minor trees.
The roots of the vegetation can        Large trees should be used on the
strengthen a bluffs resistance to      face of slopes sparingly and with
slumping or sliding. If the bluff      caution. Should these trees


                                                                                                          25




* P4neing Pogam

                                   collapse because of undermining        dynamic changes in the coastal
                                   of the root system by erosion or      shore system. Vegetation at the
                                   by windthrow, large volumes of         slope toe can sometimes help
                                   earth can be disturbed by the         reduce marine erosion to
                                   tree roots when they pull from the    manageable levels.
                                   slope. The resulting large, bare
                                   areas are opened to further            PATN    IE
                                   arerosinwhc  mare oenedanger           Late fall and early spring are
                                   erosiontwhich mayendandeget ,         usually the best times for slope
                                   Newadjacentre  should and       vion .  installations. During these periods
                                   generally be established on the        pat  r  eidrat   h
                                             New maor tres shoud notplants are semi-dormant, the
                                   face of coastal slopes. Existhe        slope soils are easiest to work, and
                                   faejof coastre  slouldsbe Existi g     vegetative cover is at a minimum.
                                   mjoritoredeforsins shofuldbercly If slope moisture is an installation
                                   ting and toppling. If the trees        polm   aluulypoie  h
                                             monitred or sins o undecut-problem, fall usually provides the
                                   become unstable, they should be         slope
                                   cut before they fall. Root systems
                                   should be left intact to bind the      MAINTENANCE
                                   soil for a short period of time        Use the Ecology publication -
                                   while new live, well-rooted vege-      Vegetation Management: A Guide
                                   tation establishes itself. Establish-    for Puget Sound BluffProperty
                                   ing new vegetation prior to felling    Owners to plan for a range
                                   a tree would be advantageous to        maintenance considerations in
                                   the slope protection program.         your erosion control program.
                                     * SLOPE TOE                          Most programs do not have
                                   In those situations where the         significant long-term maintenance
                                   bottom of your slope is suscep-        requirements.
                                   tible to frequent or periodic wave
                                   attack, vegetation alone will not
                                   be adequate as an erosion control
                                   tool. In such cases a form of
                                   structural toe protection may also
                                   be required. If the toe is not
                                   subject to coastal marine erosive
                                   forces, trees and woody shrubs
                                   can be useful in resisting upland
                                   landsliding and tolerating the










26




                                                                                      Planting Techniquesfl

PLANTING TECHNIQUES


When you review the following           It is always advisable to consult
planting techniques remember            additional resources prior to
that the descriptions are meant to      undertaking your site work.
introduce general slope planting        Additionally, these and other
techniques to coastal landowners. techniques may be combined with
As a result, a technique may not        structural/mechanical slope
be adequately discussed to the          stabilization designs (biotechnical
level of detail required for your       engineering) which are also
unique property characteristics. beyond the scope of this manual.



   Six GENERAL PLANTING TECHNIQUES









             SEEDING                                                         LIVE STAKING
         (MIXED SPECIES)




                                        CONTAINER OR
                                         BARE ROOT








             CONTOUR                                                              BRUSH
            WATTLING                                                           LAYERING




                                    AVOIDANCE/RETREAT
                                              OR
                                  BiOTECHNICAL SOLUTIONS





                                                                                                   27




* Planting Techniques


    SEEDING


                                   * DESCRIPTION AND                      * PLANNING
                                     FUNCTIONS                              CONSIDERATIONS
                                   Seeding involves the application       Drilling soil holes into the slope
                                   of grass, forb, and woody plant        area can reduce the seed quantities
                                   seed mixes to slope areas. Seeds       required. Practically, this method
                                   may be applied to slopes by            is best used on mild slopes, in
                                   broadcasting seed mixes onto the       smaller prescription areas, and for
                                   slope by hand or by placing seed       woody plant seed stock which is
                                   into small holes placed into the       more expensive that grass seed
                                   slope. Hydroseeding is also            mixes. Typically, a 3-inch
                                   another option used for hard to        diameter by a 4-inch deep hole is
                                   access locations. Seeding creates      a good size for the planting hole.
                                   a shallow fibrous rooting zone in      Make sure surrounding soil is
                                   the upper foot or so of the surface    loosened around the hole so that
                                   profile which binds near-surface       future root systems can develop.
                                   soils and protect soil surfaces        Drop a slow release fertilizer
                                   from surface water runoff, wind,       capsule to the bottom of the hole
                                   and freeze-thaw erosive forces.        and cover with about 31/2 inches
                                   Seeding is usually applied in          of soil. Then place about 20 seeds
                                   combination with other planting        into the hole and cover the seed
                                   techniques to address most             as directed by the seed supplier.
                                   erosion control issues.                Broadcast seeding is the most
                                                                          common application method
                                                                          employed in projects. Seeds are
                                                                          scattered uniformly by hand
                                                                          onto the slope. If the application
                                                                          area soil has been roughened
                                                                          slightly, seed germination will be
                                                                          more successful. It is also impor-
                                                                          tant to make sure precipitation
                                                                          does not wash seeds down the
                                                                          slope. Mulch seed immediately
                                                                          to keep seeds from being blown
                                                                          and washed away, or eaten by
                                                                          wildlife, and to keep the surface
                                                                          soils moist. Fertilize areas as
                                                                          required by mix directions.
                                                                          Hydroseeding is another applica-
                                                                          tion method that uses seed mixed
         Figure 8. Seeding (grasses shown here) with erosion control mulch. with water, fertilizer, and some-
                                                                          times mulches to spray apply the
                                                                          mixture onto expansive or hard
                                                                          to reach slope areas.


28




                                                                                              Planting Techniques 


* LIMITATIONS                          APPLICABILITY               COMPATIBILITY
Good for mild erosion problems
or in combination with other           L.            X*

rooting systems of grasses and
               techniques~~~~~~~~~~~~~~~~~~~~~~~~. Th  shallow....-.. .'..v
forbs do not significantly increase       BLUFF    srzK               AEUDAWS
the shear strength of the surface     LUFF         .CRU
soil profile and limit landsliding.
Woody plants seeded into slopes                                                 [ _
need five to ten years to begin to           A      \
develop extensive rooting net-                         AR,              TEI                     IE
works. Woody plant roots do a           jLOW  MARIN ES
better job providing root rein-
forcement of the surface soils but
are   le       s         s effective  th    an native grass
mixes at reducing  erosion  at the
soil surface. Seed  germination
for all species require that soils
to be kept moist. Seeding should
include mulching to achieve
adequate erosion control. Seed
nixes using combinations of wild
strawberry, wild ginger, oxalis,=:>                                         ,2
sword fern and bracken fern have       -:
been reported to be more success-
ful than grass-based mixes for
some sites.
a ADVANTAGES AND
  DISADVANTAGES
Advantages: Seeding can be
quickly applied to slopes,
materials are inexpensive, and
technique is compatible with
many slope situations.
Disadvantage: Seeding does not
readily self-repair eroding slope     Slope seeding with long straw mulch and juts matting.
areas. Seeding is not adequate to
be used alone for highly eroded
areas or for shallow seated
landslide stabilization.







                                                                                                             29




P Planting Techniques


    CONTAINER OR BARE ROOT PLANTING

                                                                         * PLANNING
                                        Space as recommended.              CONSIDERATIONS
                                        Spacin and   sonpeantl.          Use rooted pant materials when
                                                                         you need a fast action program
                                                                         for specific slope areas. This
                                                                         allows you to avoid the critical
                                                                         germination period for seeding
                                                                         programs or root development
                                                                         period for cuttings. Place material
                                                                         into positions on the slope during
                                                                         the fall or spring. When placing
                                                                         material in holes make sure you
                                                                         loosen the root ball or in the case
                                                                         of base root plants, make sure
                                                                         roots are not bound or bent
                                                                          upwards in the holes. Install
         Figure 9. Container/bare root planting (single or bunch planting).  according to the specific require-
                                                                         ments of each plant or plant
                                   a DESCRIPTION AND                     grouping. It is common practice
                                     FUNCTION                             to prune the plants after installa-
                                   Container and bare root planting      tion which will allow a greater
                                   involves placing single or bunches     percentage of available plant
                                   of rooted plants into excavated        energy to be used for developing
                                   holes on the slope. This method        healthy rooting systems.
                                   can be used for woody plants or        Because the immediate slope
                                   for non-woody plants which will        stabilization expectations of using
                                   eventually spread into a uniform       rooted materials are often too
                                   root coverage. Container and           high, it is a good idea to use plant
                                   bare root plant material can be        groupings or bunch plantings.
                                   purchased directly from nurseries     This method allows you to
                                   or gathered from other sites and       place plants which have slightly
                                   propagated by the landowner.           different rooting and foliage
                                   Transplants from nearby areas          characteristics which may
                                   (away from the slope) can also be     strengthen the overall reinforce-
                                   used. Rooted plant materials offer    ment program. Bunch planting
                                   the property owner the most           also allows the plants best suited
                                   immediate solution to developing       for the slope environment to
                                   an erosion control and slope           eventually dominate the plant
                                   stabilization program that can
                                   secure a slope.






30




                                                                                            Planting Techniques 


community. Finally, in cases            APPLICABILITY                COMPATIBILITY
where one species used is not                                                                  .: 1 L i
healthy or has been recently           -.i
plninhuereous speciesus dino    {_.. [........_ _. . . ~....... F4ii...._
stressed, you have provided some    :\
safety factor in your planning by                                           . 
planting numerous species. 01  lei BLI
Mulching around the plants is                                                    L             .   L
recommended as a minimum.                   A                                    i J ] 
* LIMITATIONS                                         [ h i
Container planting does not            "     '..'t s,
address gully erosion control              -                                T
                                             i~~l Lo.~..~ ~~~        CIE,.''ElOICHNIC'L    WIIOIF Vt%'~, IEW g'~"'
problems. Landowner must
identify available plant sources
ahead of time to have the  
quantity, species, and rooted
condition necessary for the
progra      m.           Container plants can
be relatively expensive,
- ADVANTAGES AND
 DISADVANTAGES
Advantages: Well developed
rooted plant materials installed
for faster slope stabilization,
typically higher plant success,
minimal slope disturbance using
planting holes.
Disadvantages: Relative cost
of materials, hard to install into
some mulching systems, initial
watering requirements.                  Container plants (Red-osier dogwood and Salal shown).

















                                                                                                          31




* Planting Techniques


    LIVE STAKING


                                   * DESCRIPTION AND                      * PLANTING
                                     FUNCTION                               CONSIDERATIONS
                                   Live stakes are sections of woody      Woody plants which have good
                                   plants that are cut into lengths       rooting characteristics make good
                                   and placed into the slope. The         staking plant stock. Stakes are
                                   plant material is installed during     generally 2 to 3 feet long and 1/2
                                   the fall or spring when the            to 1112 inches in diameter and can
                                   original plant (and consequently       be collected from sections or
                                   cuttings from it) are dormant.         branches of plants from donor
                                   The plant materials used for           sites. Stakes should be flat cut on
                                   stakes are usually hardy species       the top and diagonal cut on the
                                   which root easily and eventually       bottom so they will be installed
                                   grow into mature woody shrubs          correctly.
                                   that reinforce the soil structure of   Stakin  can be used alone and
                                   the slope. (See Table 3 for some     w    h  g
                                   cutting species alternatives.)              ohrpatn  ehius
                                                                          Typically, if stakes are used alone
                                                                           on the slope they will be spaced
                                                                           across the slope as recommended
                                                                           for each species and slope
                                                                           situation. Each row should have
                                             Space as recommended.
                                             Spacin dependedl             the same spacing but should
                                        Spacing dependent on plant
                                             selection and slope angle.    alternate stake positions so that
                                                                           if you look down or up slope no
                                                                           two consecutive rows should have
                                                                           stakes directly above or below
                                                                           one another (a diamond pattern).
                                                                           Stake rooting will be most
                                                                           effective if the stake is not posi-
                                                                           tioned vertically but positioned
                                                                           at an angle off horizontal so that
                                                                           rooting can occur more effectively
                                                                           along the entire below ground
                                                                           length as shown on Figure 9.
                                                        Length =2-3  ft.Stakes are typically be placed into
                                                                           predrilled holes using rebar
                                                                           sections which are slightly smaller
                                                                           than the diameter of the stakes.
                                                                           Gently tap stakes into holes with
                                                                          soft mallets or other instruments.
                                                                           Remove the top section of the
                                                                          stakes that get damaged during
                                                                          installation. It is good practice to



32




                                                                                                Plandng Techniquesfl

mulch the staked area after the          APPLICABILITY                 COMPATIBILITY
installation is completed.
Live staking is also used with
contour wattling to secure wattles
             stake installation is the same as    __S~~~~~~~~~~~~~~~~~~~~~~."'......'3...._..:.___:.
along a contour. The method of
stake installation is the same as     HI       G   . . . .. A~l....                  .                U ^c"~ o~L ~   ,pELF
described for independent stakes.
L liMiTATiONS                                1                                         E
Used on slopes of 1.5 horizontal
to 1 vertical or flatter. The best                    c/':'.--..?A
                                                                     '1    * OEOTECSNICAL WU.DUFE
time for staking installation is fall JJ LoWN ï¿½          1 GN ..
                           installation is             ~~~~~~ES'iUARINE  $TERUC'1JRES  EORE8OWS
and spring which requires careful
planning to perform slope work
in this time period. Often the
planting period for many projects
is planned for the summer and
early fall and this typically results
in low propagation of the cuttings
and ultimately poor slope
protection performance of the
vegetation system. Live staking
does not provide an immediate
solution to slope stabilization.
 ADVANTAGES AND
  DISADVANTAGES
Advantages: Stake sources are
plentiful and inexpensive, can be
planted with minimal surface
preparation/disturbance, can be
placed into irregular (but stable)
slope surfaces, helps reduce slope
soil moisture.
Disadvantages: Does not solve
existing erosion problems
(excluding benefits from associ-
ated mulch), staking is not a
short-term solution to slope
instabilities.
                                        Live stake installaton.








                                                                                                              33





* Planting Techniques


    CONTOUR WATTLING


                                                                          ï¿½ PLANNING
                                                    Spacing varies from    CONSIDERATIONS
                                                    4-10 feet depending  Woody plants which are particular-
    1) Excavate email trench along slope                                 ly suitable to contour wattling are
             1)~~~~~~ Ecvtsmltrnhaong slp  oite dogodandion
      contour. Place live stakes along                x                  willow, red-osier dogwood, and
      trench edge on 3-foot centers
                       trench edge on 3-fooll cent ers                  ~snowberry. Wattling is generally
      (see section on live stakes).
                                                                          considered good for slopes of
    2) Placewattlesintotrench with  .                                     1.5H:1V or less. The installation
      ends overlapping. Secure dead
      stakes through middle of wattles of wattles along slopes requires a
      at 2-3 foot centers.            Sr                                 greater degree of planning prior to
    3) Pull excavated soil down into                                      installation. Generally, wattles are
       and around wattles leaving
       approximately 20% of wattle                                                 area placed horizontally in shallow
       located above slope surface yet in                                 trenches along preselected align-
       contact with soil. Walk on wattles
      to compact and achieve good        3                               ments on the slope at a single
       soil-wattle contact.                                               contour elevation. The wattles are
    4) Move upslope to next trench                                        placed into the trenches and
       alignment and repeat processa                                      partially covered creating what
                                                                          appear like slope terraces. Wat-
  Figure 10. Contour wattling                                            tling installation along a slope face
                                                                          should progress from the slope toe
                                     * DESCRIPTION AND                    upslope to the crest until planting
                                     FUNCTION                             is complete.
                                   Contour wattling is an erosion        Wattles are created by laying plant
                                   control planting method which          materials length wise between two
                                   can also be used to stabilize very    bucking horses (or modified saw-
                                   shallow soil structure against         horses). Plant materials should be
                                   landsliding. The method involves       about ]/2 - 1P/2 inches in diameter
                                   packing lengths of woody plant         and about 4 to 8 feet in length.
                                   material into cables or bundles        Butt ends and top ends are usually
                                   (sometimes called live fascines)      laid alternately until a bundle has
                                   about 8 to 10 inches in diameter. been created that looks like an 8
   Wattle (yive fascines)          The bundles are laid continuously    to 10 inch wide cigar. Bundles are
              Dead stake           along slope contours as shown in       then tied together using untreated
                  /Live stake
                  Lie/tk           Figure 10. The cabling effect          lengths of twine. This process is
                      Minimum      along the slope helps to intercept     repeated until you fabricated the
                           angle io surface water runoff and route it     length of wattling necessary to
                                   laterally before it creates erosion    finish a contour length. Next you
                                   problems. The wattles help trap        live stake the downslope side of
                                   sediment by creating barriers          the trenches to hold the wattles in
                                   (living fences) to protect down        the trench overlapping the ends of
                         Fgndetail.  slope areas against material falls   bundles slightly. Place dead stakes
                                   or erosion.                            (2 foot long section of a 2 x 4 stud
                                                                          cut diagonally) through the wattles


34




                                                                                                Planting Techniquesf

every two feet. Finally, pull the      APPLICABILITY               COMcPATIBILITY
soil from the trench excavation                                                  F
down into the wattles and com -nI K
pact into the trench by walking
on the bundles. Make sure there
is good soil-plant contact aroundBLF
and in the wattle.                                                 0I ...IJi   I   E  OR Ll
About 80 percent of the wattleL                1                     WJI
should be buried below the exist-                    t       H/1
ing soil surface as shown in Figure
11. Leave the remaining area                            AO~EXCL                    WlLF
above the existing soil surface       [ESKI~NE                         TRUA~RIEA
then cover with soil to intercept
water and create mild slope
terraces. At this time it is good to
excavate the next upsiope trench
and then repeat the process. It is
important to get the plant
materials into the trenches before
they have a chance to lose critical
stem moisture. Seeding and
mulching should follow immedi-
ately after installation.
* LIMITATIONS
There is a significant quantity of
plant material required for this
technique. Installation is best per-
formed with a labor crew of 3 to 4
people. The technique is time
consuming if quality work is
performed. For dry sites, summer
watering maybe initially necessary.
*ADVANTAGES AND
  DISADVANTAGES:
Advantages: Good erosion control
technique, can be used to manage
mild gully erosion, can serve as       Wattle construction,
slope drains when wattle cables
are angled slightly.                                      MK of species or speciessore
Disadvantages: On steep or long
slope lengths, high runoff
velocities can undermine wattling
near drainage channels, can dry                                          Untreated twine ties
out if not property installed,Fi u e1.Wtldta.
covered, or maintained.Fire1.Wtldta.


                                                                                                              35





P Planting Techniques


    BRUSH LAYERS


                                                       Spacing varies from     Layering provides the best tech-
                                                       4-10 feet depending      nique to achieve soil reinforce-
    I) Excavate trench so that                           on site conditions       ment to resist potential shallow-
       approximately 1/4 of average                       7                       seated landsliding events. Brush
       brush length extends beyond
       slope face. Do not over excat layers act as live fences to capture
    2) Lay an appropriate mix of Zsh                         A                    debris moving down the slope.
       species and/or brush species  ' L 'N'IN
       from different sources along
       trench sidewall.                                                             CONSIDERATIONS
    3) Pull excavated soil down into                                              This technique can be very dis-
       trench and compact soil into     2         ~          ri~0,                ruptive to native soils and can
       the original slope configuration.                                          trigger      movements
       Slightly mound soil behinduring
       brush layers.                                                              installation. It is important to
    4) Move upslope to next trench                                                perform installation in phases and
       alignment and repeat process.                                              not to excavate more area than is
                                                                              necessary to install plant materials.
                                                                              If there are large quantities of
  Figure 13. Brush layering.                                                      loosened soils on the slope,
                                       * DESCRIPTION AND                        layering is a good slope stabiliza-
                                       FUNCTION                                 tion approach. Also, if imported
                                     Brush layer planting consists of           soil material will be used to restore
                                     live woody plant material placed           eroded areas, brush layering
                                     into the slope face along trenches         should be considered. It is best to
                                     excavated along slope contours             install materials into the imported
                                     as shown in Figure 13. This                fill area and avoid disturbing
                                     technique is most applicable to            existing soil structures. Use brush
                                     areas subjected to cut or fill             layering on slopes up to 1.5H:iV
                                     operations or areas that are               or in highly eroded gully areas.
                                     highly disturbed and/or eroded.            Plant material should be prepared


     Spacing 4-10 feet.
                                        Flow direction                    Spacing dependent
                                                            rw~ ~~~~~o f_-ieldl conditions.

               Minimum
               angle = 101

               -9    ~~~~11 14L



                                                                                      Gully section looking up-slope.
                  Length = 2-6 ft.

  Figure 14. Brush layering detail.    Figure 15. Brush layering for gullies.


36




                                                                                                Planting Techniques 


as described under contour             APPLICABILITY               COMPATIBILITY
wattling except for the length of
the collected material.                            ....
 ('LIMITATIONS                                   '1!..~~....?}~...i..
Not good for dense, stiff soil                       :      .
structures. Not recommended as   -]                                E01 A]                      'I ."
a solution to gully erosion control                            ....
unless technique shown on Figure
15 is used to rehabilitate gullies.                *: 
  ADVANTAGES AND, :.... .                                ...:.....:..
  DISADVANTAGES:                       W| LOWEINK     CAR
Advantages: Good immediate soil
reinforcement and slope dewater-
ing function, good erosion







                                                              ~IE
control capabilities for dry debris.
Disadvantages: Labor  intensive
procedur e, technique is intoler    ant
to development of water channels
(rill    s an d gullies). Therefore , use
technique for appropriate site
conditions.




                                        Brush layering in fill unit.



  AVOIDANCE/RETREAT OR BIOTECHNICAL SOLUTIONS

Although avoidance is not truly a      If structures can be  relocated,
planting procedure, it should b     e greenbelts   and low-impact slope
discussed as a viable technique to    planting may proceed with less
weigh when it comes to slope           ris k t o    structures.



          restoration ~ ~      ~       rstraio usin getechica
resto    ration using geotechnical Biotechnical engineering solutions
engineering design tabil    ity        use  both vegetation  and inert
construction. For some sites it       structural designs to address steep
will be more economical for            slopes greater than 1.5H: IV,
home-owners to relocate struc-        known landslide areas, compli-
tures away from slope crests than     cated drainage issues, and slope
to mobilize construction crews to     restoration programs.
perform traditional advanced
geotechnical slope stabilization.

                                                                                                               37




* For More InJermation

  FOR MORE INFORMATION


  Elizabeth C. Miller Library            Planning and
  Center for Urban Horticulture          Engineering Departments:
  3501 NE 41st Street                    Washington Department of
  Seattle, WA 98195                        Ecology (WDOE)
  206/543-8616
  Continuing Education
  Continuing Education                   Washington Sea Grant Program
  206/685-8033                           Environmental Protection Agency
                                          (EPA)
                                       National Oceanic and
  International Society of                 Atmospheric Adminstration
  Arboriculture, Pacific NW Chapter        (NOAA)
  P.O. Box 15729
  Seate, WA 981157                       U.S. Army Corp of Engineers
  Seattle, WA 98115
  206/365-3901                           U.S.DA. Soil Conservation
                                          Service District Offices
                                       Washington State University
  Plant Amnesty                            Extension Offices
  906 NW 87th Street                     Washington State Department
  Seattle, WA 98117                        of Fisheries (W.D.F.)
  206/783-9813
           ~206/783-9813    ~Washington State Department
                                          of Wildlife (W.D.W.)
  Puget Sound Water
  Quality Authority
  P.O. Box 40900
                                       Washington D.O.E.
  Olympia, WA 98504                      Shorelands Publications:
  Olympia, WA 98504
  8001547-6863                           Vegetation Management A Guide
                                         for Puget Sound Bluff Property
                                          Owners
  Washington Native Plant Society        Marine Shoreline Erosion:
  P.O. Box 576 W 987Structural Property Protection
  Woodinville, WA 98072                    Methods

                                        Shoreline Bluff and Slope Stability:
                                          Management Options











  Note: This section and the glossary developed jointly with the Department of Ecology - Shorelands and with Elliott Menashe, 1993.

38





                                                                                                               Glossay ï¿½

GLOSSARY


APPARENT COHESION                         BLUFF                                    enough to transmit the thrust of
The resistance to soil particles          An unvegetated high bank                 flooding by lateral compression
separating from one another which         composed largely of unconsolidated       and capable of sustaining the weight
is independent of soil particle           deposits with a near-vertical face       of overlying strata or man-made
forces.                                   overlooking a body of water.             structures without losing its
BANK                                      BLUFF CREST                              structural integrity when arched
BANK                                      BLUFF CREST
The rising ground bordering the           Upper edge or margin of a                or exposed to loading.
sea, a river, or lake. Also see           shoreline bluff.                          DECIDUOUS
BLUFF and CLIFF                                                                    Losing leaves or needles in the fall.
                                         BLUFF FACE
BEACH                                    The sloping portion of a high bank.       DRAINAGE  (SOIL)
The zone of unconsolidated                                                         The rapidity and extent of the
material that extends landward            BLUFFTOE                                 removal of water from the soil
from the low water line to the place      The base of a bluffwhere it meets        by surface runoff and by down-draw
where there is marked change in           the beacflow through the soil. Also, the
material or physiographic form, or        BUFFER                                   natural and artificial means for
to the line of permanent vegetation       A protective strip of vegetated land.     improving this removal by a system
(usually                                                                           of surface and subsurface conduits.
the effective limit of storm waves).      CLEAR-CUT
The seaward limit of a beach is the       A timber harvest method which             EARTHQUAKE
extreme low water line. A beach           removes all the trees on an area         A sudden motion or trembling
includes FORESHORE and                    in one operation.                        in the Earth caused by the abrupt
BACKSHORE.                                CLIFF                                    release of slowly accumulated strain
                                                   ~~~~~~CLIFF         .          (by faulting or by volcanic activity).
BEARING CAPACITY                         A high, very steep to perpen-dicular
The load per unit area which              or overhanging face of rock rising        EROSION
the ground can safely support             above the shore.                         The wearing away of rock or soil
without excessive deformation.                                                     and the movement of the resulting
                                         COASTAL ZONE                    .        particles by wind, water, ice, or
BEDROCK                                   The sea-land fringe area bordering       gravity, but usually excluding
                                                                                 gravity, but usually excluding
A general term for the rock, usually      the SHORELINE where to coastal            Mass Movements.
solid, that underlies soil                waters and adjacent lands exert a
or other unconsolidated, surficial        measurable influence on each other.    EVERGREEN
material.                                 COHESION                                 A plant which retains its needles or
                                                                    of mdi-      leaves for more than one growing
BIOENGINEERING                           The internal resistance ofindi-           season.
In soil applications, refers to the       vidual soil particles to separate
use of live plants and plant parts to     from one another.                         EXTREME HIGH WATER
reinforce soil, serve as water drains,                                              (EHW)
                                         COMPETENCE                               The average height of the highest
act as erosion prevention barriers,       (1) In hydrology the ability of a        tidal waters reached during the year
land promte denwernowar ,o ,              current of water or wind to              over a 19-year period.
                                         transport particles, emphasizing
 BIOTECHNICAL                             the particle size rather than the         FEEDER BLUFF
In slope stability engineering,           amount, measured as the diameter         An eroding shoreline bluff which
 refers to the use of both live plant      of the largest particle transported.     supplies material to accreting
 material and inert structures to          (2) In structural geology a sediment     shorelines.
stabilize and reinforce slopes.           or rock layer, rigid and strong


                                                                                                                       39





* Glossary


  FLOW                                      INTER-DEPENDENT                           OVERSTORY
  A MASS MOVEMENT involving                 A group of plants which growing           The portion of a forest that
  rapid flowage of wet soil, rock,          together protect each individual          forms the upper crown cover.
  and displaced vegetation as a             from disturbance by wind, erosion
  VISCOUS mass down a slope or              or other natural processes. Often         PERCENT SLOPE
  a channel; including mudflow,             shallow rooted trees will remained by 100)
  debris flow, and earthflow.               windfirm because they form a wide,        between the vertical and the
                                                                                   horizontal distance for a given
                                           spreading root mat.
  FORMATION - (GEOLOGIC)                                                              slope; e.g., a 3-foot rise in a 10-foot
  The ordinary unit of geologic map-        INTERSTICES                               horizontal distance would be a 30
  ping recognized by field criteria         Openings or spaces in rock or soil        percent slope.
  consisting of a larger, persistent,       that are not occupied by solid
  and mappable strata of predomi-           matter.                                   POORLY SORTED
                               na.ndy~ one.kindof~ rock~ or .Unconsolidated deposits that
  nasediment type.                          INTERSTICES OR FRACTURES                  consist of particles of many sizes
                                           The flow of rain water into soil          mixed together in an unsystematic
  GEOTECHNICAL                              material.                                 manner so that no one size fraction
  Refers to the application of civil                                                  predominates.
                                           JOINT
  engineering technology to some
  engin eering  technology to some          A crack (parting or fracture)             RILL
  aspect of the earth     .                 formed in rock by movements               A tiny drainage channel cut in a
   GEOTECHNICAL STRUCTURES                   normal to the cracks and without          slope by the flow of water. Can
  Along coastal slopes, refers to slope     shear movements (by displacement)         develop into a gully with continu-
   protection designs such as retaining      of the rock on either side of the         ing erosion.
  wall, revetments, and designed            crack.
                                                                                    RUNOFF
   slope recontouring.                       LANDFILL                                  That part of the precipitation that
   GULLY                                     (1) The solid waste disposal process      appears in uncontrolled surface
   Large intermittent drainage chan-         using land as the final disposal site.    streams, drains, or sewers. It is
   nel developed from the erosion            (2) A fill area specifically for the      the same as streamflow unaffected
   forces of drainages occuring from         purpose of creating additional dry        by artificial diversion, imports,
   surface water runoff.                     land, usually accomplished by             storage, or other works of man
                                           covering a wet or swampy area or          in or on the stream channels.
   HARDPAN                                   slope face with sand or other
   A hard, impervious, often clayey          suitable material                         SATURATED
   layer of SOIL lying just below the                                                  A condition in which the INTER-
   surface. Sometimes synonymous             MASS MOVEMENT                             STICES of a material are filled with
   for TILL.                                 A unit movement of a portion of           a liquid, usually water.
                                            the land surface down a slope as a
   IMPERMEABLE                               SLIDE, a FLOW, or SOIL CREEP    SEISMIC
   Having a TEXTURE that does not            in which gravity is the main driving      Pertaining to earthquakes or earth
   permit fluids to move through it          force.                                    vibrations, including those that are
   freely.                                                                             man-made, e.g., explosions and
                                            NATURAL LANDSCAPE                        underground nuclear blasts.
   INFILTRATION                              ELEMENTS
   The movement of water or                  The natural watercourses, topogra-        SHEAR STRENGTH
   solutions into or through a rock or       phy, hydrology and vegetation             Resistance to lateral movement or
   soil through its INTERSTICES or           which comprise a particular site.         failure along a potential failure
   fractures; the flow of rain water                                                   surface.
   into soil material.




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                                                                                                                Glossary ï¿½


SHORELINE                                STRATIGRAPHIC SECTION                      UPLAND
The intersection of a specified          Any sequence of rock units found           A general term for elevated land
plane of water with the BEACH; it         in a given region (the oldest at the      above the beach which lies above
migrates with changes of the tide.        bottom and the youngest at the            the EXTREME HIGH WATER
SLIDE                                    top).                                      level.
A MASS MOVEMENT resulting    TABLELANDS                                             WETLANDS (BIOLOGICAL)
from failure of SOIL or rock along       The tops of bluff areas usually            Lands transitional between
a rotational or planar surface.           developed for homesites.                  terrestrial and aquatic systems
                                                                                  where the water table is usually
SLOPE                                    TENSILE STRENGTH                           at or near the surfaces or the land is
The inclination of the land surface       Resistance to rupture or failure due      covered by shallow water.
from the horizontal percentage of         to tensile forces or pulling.
slope is the vertical distance divided                                              WETLANDS
by the horizontal distance, then          THINNING                                  (JURISDICTIONAL)
multiplied by 100.                       Tree removal in a forest stand that        Land forms which support under
                                         reduces tree density and numbers in       normal conditions a predominance
SLUMP                                    a given area. Most discussions of          ofhydrophytic (wetland) vegeta-
A SLIDE characterized by a rotary         thinning stress increased growth          tion, hydric (wetland) soil types,
movement of a generally indepen-         and yield of timber.                       and wetland hydrology. Typically,
dent mass of rock or earth along a                                                  they are jurisdictionally defined as:
curved slip surface.                      TILL
                                         POORLY SORTED and generally               "Those areas that are inundated or
SOIL                                      unstratified sediments, deposited         saturated by surface or groundwater
In engineering work a soil is any         directly by and underneath a              at a frequency and duration
earthen material, excluding hard          glacier. Usually very hard and            sufficient to support, and that
bedrock, composed of 1) loosely          compact, with good bearing                 under normal circumstances do
bound mineral and organic                 capacity and low permeability.            support, a prevalence of vegetation
partides, 2) water, and 3) gases.                                                   typically adapted for life in
In agriculture, a soil is the loose      TOE OF SLOPE                               saturated soil conditions (Federal
surface material capable of               See BluffToe.                             Interagency Committee for
supporting plant growth, and              UNCONSOLIDATED                            Wetland Delineation, 1989)".
having properties resulting from          Said of sediment whose particles are      WINDTHROW
the integrated effect of climate and     loose and not cemented together.           Trees blown over by the wind.
living matter on the decomposition                                                  Usually caused by thinning or
of bedrock and surficial deposits.        UNDERCUTTING                              ad
                                        The removal of material at the base
SOIL ARCHING                             of a steep slope or cliff or other
A phenomena that transfers lateral        exposed rock by the erosive action
soil pressure to adjacent rigid           of waves, running water, or sand-
members (trees, piles, etc.)             laden wind.
anchored in an unmoving soil
or rock zone.                             UNDERSTORY
                                        Trees or other plants which tolerate
SOIL CREEP                                reduced-light conditions and
The gradual and steady downhill           normally grow beneath the forest
movement of soil and loose rock           canopy.
material on a slope.
STRATA
A layer of soil.



                                                                                                                       41






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