Greenhouse effect, sea level rise, and salinity in the Delaware Estuary

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

United States Delaware May 1986
Environmental Protection River Basin EPA 230-05-86-010
Agency Commission
co E PA Greenhouse Effect, Sea Level
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Rise, and Salinity in the Delaware
Estuary

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Library of Congress Cataloging-in-Publication Data
Greenhouse effect, sea level rise, and salinity In the Delaware Estuary,

Biblilography:
1. Sea Level--Delaware River Estuary (N.Y. -Del. -Penn. and N.J.)
2. Sallnlty--Delaware River Estuary (N.Y.-Del.-Penn. and N.J.)
3. Greenhouse effect, Atmospheric--Delaware River Estuary Region
(N.Y. -Del. -Penn. and N.J.) 4. Delaware River Estuary Region
(N.Y.-Del.- Penn. and N.J.)--Climate 5. Water, Underground---
New Jersey--Quality. 1. Hull, C.H.J. 11. Titus, James G.
GC89.G75 1986 363.7'394 86-11454

GREENHOUSE EFFECT, SEA LEVEL RISE, AND
SALINITY IN THE DELAWARE ESTUARY

Edited'by

C.H.J. Hull
Delaware River Basin Commission

James G. Titus
Environmental, Protection Agency

Other Contributors:

Gerard P. Lennon
Lehigh University

M. Llewellyn Thatcher
Cooper Union College

R.ichard C. Tortoriello
Delaware River Basin Commission

Gary M. Wisniewski
Lehigh University

Gary A. Yoshioka
ICF Incorporated proporty c6c

U DEPARTMENT OF COMMERCE NOAA
COASTAL SERVICES CENTER
2234 SOUTH HOBSON AVENUE
CHARLESTON SC 29.405-2413.

This document has been reviewed in accordance with the U.S.
Environmental Protection Agency and Delaware River Basin
Commission peer and administrative review policies and
approved for publication. Mention of trade names or
commercial products does not constitute endorsement or
C-1 recommendation for use. Please send comments to James G.
Titus (PM-220), Strategic Studies Staff, U.S. Environmental
.Protection Agency, Washington, D.C. 20460.

CC),
C31i

SUMMARY

Increasing atmospheric concentrations of carbon dioxide and other gases
are expected to warm the earth a few degrees (C) in the next century by a
mechanism commonly known as the "greenhous-e effect." Such a warming could
alter precipitation patterns-and raise sea level. Although it is not yet
possible to predict whether particular areas.will receive more or less
rainfall,there is a general agreement that sea level will rise. Unfortu-
nately, estimates for the,year 2025 range -from 5 to 21 inches above current
sea level, while estimates of the rise by 2100 range from 2 to 11 feet.

Several issues must be resolv@d for society to rationally address the
possibility of significant changes,in climate and sea level. Officials'making
decisions about near-term projects with long lifetimes must examine the
potential consequences and determine whether these risks justify a shift to
strategies that are less vulnerable to changes in sea level or the frequency
or severity of droughts. Research officials must assess the opportunities for
improving predictions and decide whether the need for these improvements
justifies accelerating the necessary research. Decision makers must decide
whether.to base policies on toddy's inadequate knowledge or ignore the
implications until they are more certain.

One potential impact of a global warming and rise in sea level would bean
increase in the salinity of estuaries, which might threaten drinking water and
aquatic ecosystems. The Delaware River Basin Commission (DRBC) has long
considered the implications of droughts on management of water resources in
the Delaware estuary; since 1979, it has also considered the implications of
recent sea level trends. However, the DRBC has not previously focused on the
possibility that the "greenhouse warming" could exacerbate salinity problems.
nvironmental Protection Agency has initiated studies on the impacts of
sea @"teVeP@'i,'-Is&can(:@flimate change on erosion, flooding, and wetland
protection, but As -n`ot?-' eviously examined the impacts on salinity.

This joint report by the Environmental Protection Agency and the Delaware
River Basin Commission examines the implications of the greenhouse warming for
salinity control in the Delaware estuary. The study focuses on the implica-
tions of (1) a 21-inch rise in global sea level expected by 2050, which would
imply a rise of 2.4 feet in the Delaware estuary; and (2) a 7-foot global rise
by 2100, which would imply an 8.2-foot rise in the Delaware estuary. The
authors estimate the increase in estuary salinity, estimate the possible
increase in salinity of the Potomac-Raritan-Magothy aquifer system, discuss
the implications, and examine possible responses. Potential changes in
precipitation are not evaluated.

CONCLUSIONS

1. Sea level rise could substantially increase the salinity of the
Delaware estuary in the next century. If no countermeasures are taken, a
repeat,of the 1960s' drought with a 2.4-foot rise would send the salt front
upstream to river-mile 100, compared with mile 93 for current sea level.
Moreover, the chloride concentration at mile 98, the DRBC salinity control
point, would increase from 136 parts per million (ppm) to 305 ppm. An
8.2-foot rise would send the salt front upstream to mile 117 and would
increase salinity to 1560 ppm at the salinity control point.

2. Accelerated sea level rise could cause excessive salinity concentra-
tions at Philadelphia's Torresdale intake if no countermeasures are taken.
For a 2.4-foot rise, sodium concentrations would exceed 50 ppm (the New Jersey
drinking water standard) during 15 percent of the tidal cycles during a
recurrence of the 1960s drought. For an 8.2-foot rise, sodium concentrations
would exceed 50 ppm during 50 percent of the tidal cycles.

3. Accelerated sea level rise could threaten the New Jersey aquifers
recharged by the Delaware River. During the 1960s drought, river water with
chloride concentrations as high as 150 ppm recharged the Potomac-Raritan-
Magothy aquifer in the vicinity of Camden, raising chloride concentrations of
some wells from 20 ppm to 80 ppm. A repeat of the 1960s' drought with a
2.4-foot rise in sea level would result in river water with concentrations as
high as 350 ppm recharging the aquifer in this area. During the worst month
of the drought, over one-half of the river water recharging the aquifer would
have chloride concentrations in excess of 250 ppm. With'-an 8.2-foot rise, 98
percent of the recharge during the worst month of the drought would have
chloride concentrations greater than 250 ppm, and 75 percent of the recharge
would be greater than 1000 ppm. (The EPA drinking water standard is 250 ppm,
and water with chloride concentrations greater than 78 ppm generally exceeds
the 50-ppm sodium standard.)

4. Planned but unscheduled reservoirs could offset salinity increases
expected in the next forty years. Salinity increases resulting from a one
foot rise in sea level expected in the next forty years would require
increased reservoir capacity of at least 110 thousand acre-feet. However,
reservoirs planned by the DRBC but not yet scheduled would have a combined
capacity of 592 thousand acre feet.

5. Possible shifts in precipitation resulting from the greenhouse warming
could overwhelm salinity increases caused by sea level rise. Excessive
salinity has been a problem only during droughts. Unfortunately, it is not
possible to determine whether the Delaware River Basin will receive more or
less rainfall in the future. A recent study by NASA suggested that a tenfold
increase in drought frequency cannot be ruled out. On the other hand, some
researchers have suggested that most coastal areas will experience a 10
percent increase in precipitation.

6. Uncertainties regarding future climate change do_not necessarily imply
that waiting for better predictions is the most prudent strategy. There is
no guarantee that accurate climate projections will be possible when they are
needed. Moreover, some measures may have potential benefits so far in excess
of their costs as to be warranted in spite of current uncertainties. For
example, identifying potential reservoir sites long before they are necessary
and not developing them for other uses can ensure that they are available if
and when they are needed, without imposing substantial costs. Waiting until
they are needed could result in no satisfactory sites being available.

7. A regional study should be initiated that examines the potential
impacts of precipitation changes as well as sea level rise for the Delaware
estuary and adjacent river basins. A thorough understanding of the water
resource challenges faced by the Delaware River Basin is not possible without
considering the needs of New York City and other areas outside the Basin that
depend on the Delaware for water supply.

TABLE OF CONTENTS

Page

I. INTRODUCTION ................................................... I

II. THE BASIS FOR EXPECTING A RISE IN SEA LEVEL
By James G. Titus .............................................. 3

Past Changes in Climate and Sea Level ...................... 3
The Greenhouse Effect ...................................... 4

III. SALINITY IN THE DELAWARE ESTUARY
By C.H.J. Hull, M. Llewellyn Thatcher, and
Richard C. Tortoriello ...................................... 15

Saltwater Intrusion ........................................ 15
The Delaware Estuary ....................................... 16
Saltwater Intrusion and the DRBC ........................... 21
Estimating Impacts of Sea Level Rise on Salinity ........... 28
Implications ............................................... 36

IV. IMPACT OF INCREASED RIVER SALINITY ON NEW JERSEY AQUIFERS
By Gerard P. Lennon, Gary M. Wisniewski, and Gary A. Yoshioka 40

The Relationship Between Sea Level and Aquifer Salinity .... 40
The Potomac-Raritan-Magothy Aquifer System ................. 41
Impact of a Drought on the Aquifers--Current and Future
Sea Level .............................................. 45
Improved Estimates ......................................... . 53

V. RESPONSES TO SALINITY INCREASES
By C.H.J. Hull and James G. Titus ...... ; ....................... 55

Preventing Salinity Increases .............................. 55
Adapting to Increased River Salinity: Surfacewater
Users .................................................. 58
Adapting to Increased River Salinity: Groundwater
Users .................................................. 60

VI. NEXT STEPS
By C.H.J. Hull and James G. Titus .............................. 64

Considering Climate Change ................................. 64
Necessary Research ......................................... 66
Conclusion .................................................. 67

APPENDIX A: TECHNICAL DESCRIPTION OF DELAWARE ESTUARY SALINITY MODEL
By M. Llewellyn Thatcher ................................. 68

APPENDIX B: MODIFICATION OF SALINITY-MODEL GEOMETRY FOR LARGE
RISES OF SEA LEVEL
By M. Llewellyn Thatcher ................................ 77

REFERENCES ........................................................... 82

LIST OF FIGURES

Page

Figure I Global Temperatures and Sea Level Rise in the Last
Century ................................................... 5

Figure 2 Concentrations of Selected Greenhouse Gases Over Time ..... 7

Figure 3 Estimated Global Warming Due to a Doubling of Greenhouse
Gases ..................................................... 10

Figure 4 Global Sea Level Rise Scenarios ........................... 13

Figure 5 General Location of the Delaware Basin .................... 18

Figure 6 The Delaware Estuary ...................................... 19

Figure 7 Change in Yearly Mean Sea Level at Philadelphia ........... 29

Figure 8 Chlorinity Response of Delaware Estuary to Projected
35-Yeai@ Rise in Sea Level, 1965-2000 ...................... 31

Figure 9 Chloride Concentrations vs. River Mile .................... . 35

Figure 10 Percent of Tidal Cycles in Which Specified Concentration
is 'Exceeded at Torresdale for Three Sea Level Scenarios 37

Figure 11 Saltwater Intrusion in a Coastal Aquifer .................. 42

Figure 12 Modeled Area Showing Outcrop Area and River Reaches of the
Potomac-Raritan-Magothy Aquifer System .................... 44

Figure 13 Potentiometric Surface of the Potomac-Raritan-Magothy
Aquifer System, November-December 1973 .................... 46

Figure 14 Potentiometric Surface of the Potomac-Raritan-Magothy
Aquifer System at Year 2000 ............................... 47

Figure 15 Chloride Concentrations at Wells in the Camden City
Vicinity .................................................. 48

Figure 16 Injection-Type Seawater Intrusion Barrier ................. 62

vii

LIST OF TABLES

Page

Table 1 Scenarios of Future-Sea Level Rise .......................... 14

Table 2 Existing and Scheduled Reservoirs That Can Control
Salinity in the Delaware Estuary ............................ 24

Table 3 Maximum 30-Day Chloride Concentration at Different River
Miles ....................................................... 34

Table 4 Recharge of Delaware River Water into Potomac-Raritan-
Magothy Aquifer System ...................................... 49

Table 5 Velocities, Contact Times, and Penetration Distances for
Ground Water with Elevated Chloride Concentration ........... 52

Table 6 Unscheduled Reservoirs in DRBC's Plan That Could Be Used
to Offset Increases in the Delaware Estuary ................. 56

1. INTRODUCTION

Increasing atmospheric concentrations of carbon dioxide, methane,

chlorofluorocarbons, and other gases are expected to raise the earth's average

surface temperature several degrees in the next century by a mechanism

commonly known as the "greenhouse effect." Such a global warming would

probably raise sea level and substantially change precipitation patterns

worldwide, altering water quality and availability and upsetting wetland and

aquatic ecosystems. Scientific understanding is not yet sufficient to

estimate the impacts accurately, but it is sufficient to expect that the

changes will be substantial.

Although it is not yet possible to project future climate change for

specific regions, there is a consensus on the probable increase in average

temperatures, Because sea level depends mostly on the global average

temperature, it is possible to estimate the likely range of its rise. Recent

reports by the National Academy of Sciences and the Environmental Protection

Agency project a worldwide rise in sea level of sixty to one hundred fifty

centimeters (two to five feet) in the next century. Such a rise would be a

substantial acceleration over the rise of thirty centimeters (one foot) that

has taken place along the Atlantic coast in the last century.

One of the impacts of a rise in sea level is an increase in the salinity

of estuaries and aquifers. In 1979, the Delaware River Basin Commission

(DRBC) investigated the impact of recent sea level trends on salinity in the

estuary and determined the measures that would be necessary by the year 2000

to counteract the increased salinity caused by droughts and sea level rise.

Because no projections on the impact of the greenhouse effect were available

-2-

at the time, that study did not consider the implications of an acceleration

of the current rate of sea level rise.

This report examines the potential impacts of accelerated sea level rise

on salinity in the Delaware estuary and adjacent aquifers in New Jersey.

Although the impacts we examine are uncertain and contingent upon particular

rates of sea level rise occurring in the future, this type of analysis is

useful because it may be possible to identify cost-effective opportunities to

prevent or mitigate possible consequences that warrant consideration even

today. We hope that this report stimulates interest in the long-term planning

necessary for management of the Delaware estuary to meet successfully the

challenge of a rise in sea level.

This report first describes the basis for expecting a rise in sea level.

It then explains how droughts and rising sea level increase the salinity of an

estuary, describes the impact of droughts on salinity that would result from a

73- and 250-centimeter (2.4- and 81.2-foot) rise in sea level, and discusses

some of the consequences. Section 4 discusses the impact of increased river

salinity on the adjacent Potomac-Raritan-Magothy aquifer system in New

Jersey. Section 5 provides a qualitative.discussion of possible responses,

including ways of preventing salinity increases in the estuary and the

aquifer, and ways of adjusting to the increases.

The report concludes by outlining the next steps that should be taken to

determine the best responses to the greenhouse effect. Problems with

increased salinity generally occur during droughts, the frequency o f which may

be different in the future. Although this effort is limited to sea level

rise, a more in-depth assessment must also consider possible changes in

precipitation.

-3-

11. THE BASIS FOR EXPECTING A RISE IN SEA LEVEL

Past Changes in Climate and Sea Level

Throughout geologic history, sea level has risen and fallen by over three

hundred meters (one thousand feet). Although changes in the size and shape of

the oceans' basins have played a role over very long periods of time (Hays and

Pitman 1973), the most important changes in sea level have been caused by

changes in climate. During the last ice age (18,000 years ago), for example,

the earth was about five degrees celsius colder than today, glaciers covered

most of the northern hemisphere, and sea level was one hundred meters (three

hundred feet) lower than today (Donn, Farrand, and Ewing 1962).

Although most-of the glaciers have melted since the last ice age, polar

glaciers in Greenland and Antarctica still contain enough water to raise sea

level more than seventy meters (over two hundred feet) (Untersteiner 1975). A

complete melting of these glaciers has not occurred in the last two million

years, and would take tens of thousands of years even if the earth warmed

substantially. However, unlike the other glaciers, which rest on land, the

west antarctic ice sheet is marine-based and more vulnerable to temperature

increases. Warmer ocean water would be more effective than warmer air at

melting glaciers, causing West Antarctica to melt. Mercer (1970) suggests

that the West Antarctic Ice Sheet completely disappeared during the last

interglacial period (which was one or two degrees warmer than today and

occurred 100,000 years ago), at which time sea level was five to seven meters

(about twenty feet) above its present level.

Over relatively short periods of time, climate can influence sea level by

heating and thereby expanding (or cooling and contracting) sea water. In the

-4-

last century, tidal gauges have been available to measure relative sea level

in particular locations. Along the Atlantic Coast, sea level has risen about

30 centimeters (one foot) in the last century (Hicks, Debaugh, and Hickman

1983). (Figure 7 shows the rise that has taken place at,Phi-ladelphia.)

Studies combining all the measurements have concluded that average worldwide

sea level has risen ten to fifteen centimeters (four to six inches) in the

last one hundred years (Barnett 1983; Gornitz, Lebedeff, 'and Hansen 1982). At

least part of this rise can be explained by the thermal expansion of the upper

layers of the oceans resulting from the observed wa.rming of 0.40C in the last

century (Gornitz, Lebedeff, and Hansen 1982). Meltwater from mountain

glaciers has also contributed to sea level rise (Meier 1984). Figure 1 shows

that global temperature and sea level have been rising in the last century.

Nevertheless, questions remain over the magnitude and causes of sea level rise

in the last century.

The Greenhouse Effect

Concern about a possibl6accelerat ion in the rate of sea level rise stems

from measurements showing that concentrations of-carbon dioxide (CO 2),

methane, chlorofluorocarbons, and other gases,released by human activities are

increasing. Because these gases absorb infrared radiation (heat), scientists

generally expect the earth to warm substantially. Although some people have

suggested that unknown or unpredictable factors could offset this warming, the

National Academy of Sciences (NAS) has twice reviewed all the evidence and

found that the warming will take place. In 1979, the Academy concluded: "We

have tried but have been unable to find any overlooked physical effect that

could reduce the currently estimated global warming to negligible proportions"

FIGURE 1

GLOBAL TEMPERATURES AND SEA LEVEL
RISE IN THE LAST CENTURY

0.2

Temperature o
(00

-0.2

Sea Level
(Cm)

1880 1920 1960
Year

Sources: Temperature curve from: HANSEN, J.E., D. JOHNSON, A. LACIS, S.
LEBEDEFF, D. RIND, AND G. RUSSELL, 1981. Climate Impact of
Increasing Atmospheric Carbon Dioxide, Science 213:957-966. Sea
lwv-@ 11 rllrlll@@

level curve adapted from: GORNITZ, V., S. LEBEDEFF, and J. HANSEN,
1982. Global Sea Level Trend in the Past Century. Science
215:1611-1614.

(Charney 1979). In 1982, the NAS confirmed the 1979 assessment (Smagorinsky

1982).

A planet's temperature is determined primarily by the amount of sunlight

it receives, the amount of sunlight it reflects, and the extent to which its

atmosphere retains heat. When sunlight strikes the earth, it warms the

surface, which then reradiates the heat as infrared radiation. However, water

vapor, CO 25 and other gases in the atmosphere absorb some of the energy

rather than allowing it to pass undeterred through the atmosphere to space.

Because the atmosphere traps heat and warms the earth in a manner somewhat

analogous to the glass panels of a greenhouse, this phenomenon is generally

known as the "greenhouse effect." Without the greenhouse effect of the gases

that occur in the atmosphere naturally, the earth would be approximately 330C

(60'F) colder than it is currently (Hansen et al. 1984). Thus, the greenhouse

effect per @@e is not just something that will happen in the future; it is an

existing natural characteristic of the atmosphere.

In recent decades, the concentrations of these "greenhouse gases" have

been increasing. Since the industrial revolution, the combustion of fossil

fuels, deforestation, and cement manufacture have released enough CO 2 into

the atmosphere to raise the atmospheric concentration of carbon dioxide by 20

percent. As Figure 2 shows, the concentration has increased 8 percent since

1958 (Keeling, Bacastow, and Whorf 1982). Recently, the concentrations of

methane, nitrous oxide, chlorofluorocarbons, and some other trace gases that

also absorb infrared radiation have also been increasing (Lacis et al. 1981).

Ramanthan et al. (1985) estimate that these gases will warm the earth as much

as CO2 alone.

-7-
FIGURE 2

CONCENTRATION OF SELECTED GREENHOUSE GASES OVER TIME
360
345 1.Carbon Dioxide ao6. 2.Nitrous Oxide 30e
concentrations Co
E ncentratione if
0
340 304 00 0 0 090. 304
Or 0 0 0 0 0
- 0 0 00
=6 302 0
302
0 0% 00 0
C 0 a
0, 330 0 (%0 - 00 0
Cc C! 300 0 000 d9 300
z 0 00 800 0 0
325 CP 00 808
C4 0-0 (to 0 0 - 0 0
0 .0 069 0 (9
298 .0 C8 0 298
0 0(b 4 0 80 0CO
315 296 296
3101 197d 1077 197a 1972 1080
195s 1940 1966 1970 1975 19ao 1985
350
-3. C@Cll Concentrations 4. CFC12 Concentrations
200

0320

260

160 Lj
W P1
Is
240

140

f 200
1976 1977 J978 J979 1980 1981 1976 1977 1978 1979 1980 1981

4?bo
5. Methane Concentrations
........ 71,
37
U

1000 -

U &
750
A A

boo
3000 2C 00 100a Too 500 15. .0
Timt (yrs 8 P)

1. C.D. Keeling, R.B. Bacastow, and T.P. Whdrf, 1982. "Measurements of the Concentration of
Carbon Dioxide at Mauna Loa, Hawaii." In Carbon Dioxide Review 1982, edited by W. Clark.
New York: Oxford University Press, 377-382. Unpublished'data from NOAA after 1981.

2. R.F. Weiss, 1981. "The Temporal and Spatial Distribution of Tropospheric Nitrous Oxide."
Journal of Geophysical Research, 86(C8):7185-7195.
3. D.M. Cunnold et al., 1983. "The Atmospheric Lifetime Experiment. 3. Lifetime Methodology
0 0
0 00:b '0

POO
0. 0 C1 0.
8-0 0 0 j 808
.69 .00-r. '9
2 - @C-o

and Application to Three years of CFCL3 Data." Journal of Geophysical Research, 88(Cl3):8379-8400.
4. D.M. Cunnold et al., 1983. "The Atmospheric Lifetime Experiment. 4. Results for CF2CL2 Based
on Three Years' Data." Journal of Geophysical Research, 88(Cl3):8401-8414.
5. R.A. Rasmussen and M.A.K. Khalil, 1984. "Atmospheric Methane in the Recent and Ancient Atmos-
pheres: Concentrations, Trends, and Interhemispheric-Gradient." Journal of Geophysical
Research, 89(D7):11599-11605.

-8-

Although there is no doubt that the concentration of greenhouse gases is

increasing, the future rate of that increase is uncertain. A recent report by

the National Academy of Sciences (NAS) examined numerous uncertainties

regarding future energy use patterns, economic growth, and the extent to which

CO2 emissions remain in the atmosphere (Nordhaus and Yohe 1983). The
Academy estimated a 98 percent probability that CO2 concentrations will be

at least 450 parts per million (1.5 times the year-1900 level) by 2050 and a

55 percent chance that the concentration will be 550 parts per million. The

Academy estimated that the probability of a doubling of CO2 concentrations

by 2100 is 75 percent. Other investigators have estimated that a doubling is

likely by 2050 (Wuebbles, MacCracken, and Luther'1984).

If the impact of the trace gases continues to be equal to the impact of
Co 23 the NAS analysis implies that the "effective doubling" of all
greenhouse gases has a 98 percent chance of occurring by 2050.1 An

internation al conference of scientists recently estimated that an effective

doubling by 2030 is likely (UNEP 1985). However, uncertainties regarding the

emissions of trace gases are greater than those for CO 2* Although the

sources of chlorofluorocarbon emissions are well documented, regulatory

uncertainties related to their possible impact on stratospheric ozone

depletion make their growth rate--currently about 5 percent--difficult to

forecast. The current sources of methane, nitrous oxide, and other trace

gases have not yet been fully catalogued.

Studies on the greenhouse effect generally discuss the impacts of a
carbon dioxide doubling. By "effective doubling of all greenhouse gases" we
refer to any combination of increases in the concentration of the various
gases that causes a warming equal to the warming of a doubling of carbon
dioxide alone. If the other gases contribute as much warming as carbon
dioxide, the effective doubling would occur when carbon dioxide concentrations
have reached 450 ppm, 1.5 times the year-1900 level.

Considerable uncertainty also exists regarding the impact of a doubling of

greenhouse gases. Physicists and,climatologists generally agree that a

doubling would directly raise the earth's average temperature by about 10C if

nothing else changed. However, if the earth warmed, many other aspects of

climate would be likely to change, probably amplifying the direct effect of

the greenhouse gases. Theseindirect impacts are known as "climatic

feedbacks."

Figure 3 shows estimates by Hansen et al. (1984) of the most important

known feedbacks. A warmer atmosphere would retain more water vapor, which is

also a greenhouse gas, warming the earth more. Snow and floating ice would

melt, decreasing the amount of sunlight reflected to space, causing additional

warming. Although the estimates of other researchers differ slightly from

those of Hansen et al., climatologists agree that these two feedbacks would

increase the expected global warming. However, the impact of clouds is far

less certain. Although recent investigations have estimated that changes in

cloud height and cloud cover would add to the warming, the possibility that

changes in cloud cover would offset part of the warming cannot be ruled out.

After evaluating the evidence, two panels of the National Academy of Sciences

concluded that the eventual warming from a doubling of greenhouse gases would

be between 1.50 and 4.50C (30-80F).

A global warming of a few degrees could be expected to raise sea level in

the future, as it has in the past. The best understood mechanism is the

warming and resulting expansion of sea water, which could raise sea level

one-half meter in the next century (Hoffman, Keyes, and Titus 1983). Mountain

glaciers could melt and release enough water to raise sea level ten to thirty

centimeters (four to twelve inches) (Meier 1984). Revelle (1983) estimates

-10-

FIGURE 3

ESTIMATED GLOBAL WARMING DUE TO A DOUBLING
OF GREENHOUSE GASES: DIRECT EFFECTS AND
CLIMATIC FEEDBACKS

CL
E 0-
4) Direct Effect Water Decreased Cloud Cloud
Of C02 Vapor Ref lectivity Height Cover
and Other Feedback Due to
Greenhouse Retreat of
Gases Ice and
Snow

NOTE: Although Hansen et al. estimate a positive feedback from the clouds, a
negative feedback cannot be ruled out.

Sources: Adapted from: HANSEN, J.E., A. LACIS, D. RIND, and G. RUSSELL,
1984. Climate Sensitivity to Increasing Greenhouse Gases. In
Greenhouse Effect and Sea Level Rise: A Challenge for This
Generation, edited by M.C. Barth and J.G. Titus. New York: Van
Nostrand Reinhold, p. 62.

that Greenland's glacier meltwater will raise the sea another twelve

centimeters in the next century, while Bindscha.dler (1985) estimates the

impact to be between ten and twenty-five centimeters. Antarctica could

contribute to sea level rise either by meltwater running off or by glaciers

sliding into the oceans. Although no one has estimated the impact of melting,

Thomas (1985) estimates that Antarctic ice discharges are likely to add

another twenty-four centimeters to worldwide sea leve 1.

In 1983, two independent reports estimated future sea level rise. In the

National Academy of Sciences report Changing Climate, Revelle (1983)

estimated that the combined impacts of thermal expansion, the Greenland

icesheet, and mountain glaciers could raise sea level seventy centimeters (two

and one-third feet) in the next century. Although he also stated that

Antarctica could contribute two meters per century to sea level starting

around 2050, Revelle did not add this contribution to his estimate.

In a report by the Environmental Protection Agency entitled Projectin

Future Sea Level Rise, Hoffman, Keyes, and Titus (1983) stated that the

uncertainties regarding the factors that could influence sea level are so

numerous that a single estimate of future sea level rise is not practical.

Instead, they consulted the literature to specify high, medium, and low

estimates for all the major uncertainties, including fossil fuel use; the

absorption of carbon dioxide through natural processes; future emissions of

trace gases; the global warming that would result from a doubling of

greenhouse gases (the NA S estimate of 1.50-4.50C); the diffusion of heat into

the oceans; and the impact of ice and snow. They estimated that if all of the

low assumptions prove to be correct, the sea will rise 13 cm (5 in) by 2025

and 38 cm (15 in) by 2075 over the 1980 level. If all of the high assumptions

-12-

are correct, the sea will rise 55 cm (2 ft) by 2025 and 211 cm (7 ft) by

2075. However, because it is very unlikely that either all the high or all

the low assumptions will prove to be correct, the authors concluded that the

rise in sea level is likely to be between two mid-range scenarios of 26 to 39

cm (11 to 15 in) by 2025 and 91 to 136 cm (3 to 4-1/2 ft) by 2075. Figure 4

and Table 1 illustrate the EPA and NAS estimates. Although neither of these

studies examined options to limit the rise in sea level by curtailing

emissions, Seidel and Keyes (1983) estimated that even a ban on coal, shale

oil, and synfuels would only delay the rise in sea level expected through 2050

by twelve years.2

Recent analysis by the Polar Research Board of the National Academy of

Sciences indicates that glaciers in Greenland and East Antarctica, as well as

those in West Antarctica, could eventually release enough ice into the oceans

to raise sea level two or three centimeters (about one inch) per year (Meier

et al. 1985). However, current thinking holds that such a rapid rise is at

least one hundred years away. Moreover, a complete disintegration of the West

Antarctic Ice Sheet--and the resulting six-meter (twenty-foot) rise in sea

level--would take several centuries (Bentley 1983; Hughes 1983). It is

possible that snowfall accumulation could partially offset the effect of

melting ice.

The East Coast of the United States is slowly sinking (Hoffman, Keyes, and

Titus 1983). Thus relative sea level rise along the Delaware estuary will be

twenty-five to thirty centimeters (ten to twelve inches) per century greater

than global sea level rise, as shown in Table 1.

Computer printout underlying calculations from Seidel and Keyes 1983.

-13-

FIGURE 4

GLOBAL SEA LEVEL RISE SCENARIOS:
LOW, MID-RANGE LOW, MID-RANGE HIGH, AND HIGH

CM3
Inahe*
250-
100

200-
SEA
LEVEL
RISE 150-
MIO-RANGE
Go- HIGH
100 - MID-RANGE
LOW

0 NAS

25- 50- LOW

0i 0jw
2000 2025 2050 20TS

YEAR

Sources: HOFFMAN, J.S., D. KEYES, and J.G. TITUS, 1983. Projecting Future
Sea Level Rise. U.S. GPO #055-000-0236-3. Washington, D.C.:
Government Printing Office; REVELLE, R., 1983. Probable Future
Changes in Sea Level Resulting From Increased Atmospheric Carbon
Dioxide. In Changing Climate. Washington, D.C.: National Academy
Press (Revelle estimate does not include Antarctica).

-14-

TABLE I

SCENARIOS OF GLOBAL SEA LEVEL RISE: 1980-2100
(centimeters)

2000 2025 2050 2075 2080 2100

Current Trends 2.0-3.0 4.5-6.8 7.0-10.5 9.5-14.3 10-15 12.0-18.0

EPA Scenarios

High 17.1 54.9 116.7 211.5 - 345.0
Mid-range high 13.2 39.3 78.9 136.8 - 216.6
Mid-range low 8.8 26.2 52.6 91.2 - 144.4
Low 4.8 13.0 23.0 38.0 - 56.2

NAS Estimate* - - - - 70.0 -

SCENARIOS OF SEA LEVEL RISE AT LEWES, DELAWARE: 1965-2100
(centimeters)

2000 2025 2050 2075 2080 2100

Current Trends 13 22 31 41 43 50

EPA Scenarios

High 27.7 71.7 140.0 290.8 - 380.6
Mid-range high 23.7 56.1 102.0 166.1 - 251.5
Mid-range low 19.3 43.0 76.7 120.5 - 180.0
Low 15.3 29.8 46.0 67.3 - 91.8

NAS Estimate* - - - - 100.6 -

* Excluding Antarctic contribution.

-15-

111. SALINITY IN THE DELAWARE ESTUARY

A rise in sea level of even thirty centimeters (one foot) would have major

impacts on coastal erosion, flooding, and saltwater intrusion. Until this

effort, no one had estimated the saltwater intrusion expected to result from

an accelerating rise in sea level due to the greenhouse effect. However,

previous EPA studies have examined the impacts of erosion and flooding, as

well as possible responses (Barth and Titus 1984). Ongoing EPA studies are

investigating the potential impacts on coastal sewerage systems, wetlands, and

seawalls.

The Delaware River Basin Commission (DRBC) has considered the implications

of recent sea level trends in its policy making since the late 1970s.

Accordingly, the DRBC already had the necessary model and data for assessing

accelerated sea level rise. This section provides background information on

the Delaware estuary, and presents estimates of saltwater intrusion likely to

result from sea level rise in the next century due to the expected global

warming.

Saltwater Intrusion

Salinity in an estuary ranges from that of sea water (at the mouth) to

that,of fresh water (near the head of tide). The salinity at a particular

point varies over the course of a year, depending primarily on the amount of

fresh water flowing into the estuary. Mixing and advection caused by tidal

currents and wind can also change the salinity at a particular point.

In the Delaware estuary, tidal, effects extend as far upstream as Trenton,

where the tidal range is more than twice that of the ocean boundary. Although

-16-

the net flow of the estuary tends to carry salt water toward the ocean, tidal

currents carry salt water upstream, where it mixes with fresh water.

Differences in the densities of salt water and fresh water also contribute to

saltwater intrusion; heavy salt water on the bottom tends to move upstream

when adjacent to lighter fresh water, forming a wedge.

A rise in sea level generally results in increased salinity, assuming

other factors remain constant. In this respect the impact of sea level rise

is similar to the impact of reduced flows during a drought. The former

increases the saltwater force, whereas the latter decreases the freshwater

force. Salinity levels generally respond to changes in tide and river flow

within a matter of minutes or hours.

In the past eighteen thousand years, sea level has risen one hundred

meters (three hundred feet), converting freshwater rivers into brackish

estuaries (Donn, Farrand, and Ewing 1962). Chesapeake Bay and the Delaware

estuary are examples of such drowned river valleys. The Delaware estuary is

probably the first estuary for which the salinity effects of future sea level

rise have been studied (Hull and Tortoriello 1979).' The salinity of this

estuary, as affected by the impacts of river diversion and flow regulation

projects, has been the subject of study--and litigation--since the early 1930s.

The Delaware Estuary

The Delaware River Basin covers an area of thirteen thousand square miles

in New York, Pennsylvania, New Jersey, and Delaware. It is located in the

heart of the megalopolis that stretches from Boston to Washington, D.C., on

3Louisiana is also experiencing salinity increases from sea levellrise
(Haydl 1984).

-17-

the eastern seaboard of the United-States. The Delaware River reaches from

the Catskill Mountains of southern New York to the head of Delaware Bay. The

river is tidal from Trenton, New Jersey, to the bay; the tidal river and bay

form the Delaware estuary, which is 215 kilometers (133 miles) long. The

boundary between the estuary and the ocean is a line between Cape May, New

Jersey, and Cape Henlopen, Delaware. Major cities on the estuary include

Trenton and Camden, New Jersey, Philadelphia, Pennsylvania, and Wilmington,

Delaware. The lower reach of the tidal river is physically connected with the

northern part of Chesapeake Bay by the Chesapeake and Delaware Canal, which

runs from Delaware City, Delaware, westward about twenty-seven kilometers

(seventeen miles) to the Elk River in Maryland. Figure 5 shows the general

location of the Delaware Basin; Figure 6 is a map of the estuary.

The Delaware estuary is one of the most extensively used tidal waterways

in the world. From the ocean, past Philadelphia and almost to Trenton, the

estuary has a navigable depth of at least twelve meters (forty feet) and is a

major port for ships of all nations. Sport and commercial fishing are

important uses of Delaware Bay, where oysters are the major shellfish

harvested. Many industries along the banks o f the estuary use fresh or

brackish water for cooling and other processes. The estuary also serves the

region by assimilating or transporting to the sea the residual wastes

discharged from its tributaries as well as from about one hundred municipal

and industrial wastewater treatment plants located along the estuary.

Based on data published by the U.S. Geological Survey (Bauersfeld et al.

1985), we estimate that the average flow of fresh water into the Delaware

estuary from its tributaries is 609 cubic meters per second (21,500 cubic feet

per second). The nontidal Delaware River,@ which drains about half the

-18-

FIGURE 5

GENERAL LOCATION OF THE DELAWARE BASIN

NEW YORK

1�R

PENNSYLVANNIA

NEW
MARYLAND JERSEY

D AWARE

90 Miles

-19-

FIGURE 6

THE DELAWARE ESTUARY

Trenton

PENNSYLVANIA river milt 120
Torresdals, Burlington

river mile 100
Philadelphia

Camden

Chester
Warcus Hook

river mile 80
Wilmington

NEW JERSEY
river mile 60

Reedy Island

0 4 10 Miles

Kilofflotoro

DELAWARE

N
Delaware Bay

Ca pe
May

Atlantic Ocean

Cape Henlopen

-20-

basin, has an average flow rate of 332 cubic meters per second. The

Schuylkill River drains about 15 percent of the Basin and conveys an average

flow of 84 cubic meters per second. The Christina, which drains 5 percent of

the Basin, has an average flow of 24 cubic meters per second. Smaller -

tributaries provide most of the remaining freshwater input, with smaller

contributions from aquifers and direct rainfall onto the estuary.

The waters of the tidal river at Philadelphia and northward are normally

fresh, and several municipalities, including Philadelphia, obtain portions of

their public water supplies directly from this part of the river. Other

cities take ground water from aquifers that are recharged in part by the tidal

portion of the river.

The many consumptive uses of water throughout the Delaware Basin reduce

the flow of fresh water into the estuary. Basin-wide withdrawal of.fresh

water is estimated at 351 cubic meters per second (8 billion gallons per day),

of which 24.9 cubic meters per second (568 mgd) is used consumptively (i.e.

evaporated or otherwise removed from the Basin instead of draining back into

the estuary). Community water systems withdraw approximately 51.7 cubic

meters per second (1,180 mgd), of which approximately 10 percent is consumed.

The average daily per capita water use in the Basin is 0.617 cubic meters per

day (163 gpd), compared with the mean rate of 0.606 cubic meters per day (160

gpd) for the United States (Seidel 1985). In addition, diversion of Delaware

River water to New York and northeastern New Jersey are authorized up to 35

and 4.4 cubic meters per second (800 and 100 mgd), respectively (Supreme Court

1954). Basin-wide consumption is projected to rise to 52.2 cubic meters per

second (1,191 mgd) by the year 2000 (DRBC 1981).

-21-

Saltwater Intrusion and the DRBC

,The water resources of the Delaware River Basin are under the regulatory

control of the Delaware River Basin Commission (DRBC), a regional

federal-interstate compact agency established in 1961 to represent the.federal

government and the states that share the Basin. The five commission members

are the U.S. Secretary of the Interior and the Governors of Delaware, New

Jersey, New York, and Pennsylvania. The DRBC cooperates with state and

federal agencies to ensure that the water resources of the Basin are protected

and developed to meet the growing demands for all reasonable uses.

One-of the most.important responsibilities of the DRBC is to monitor and

control salinity in the estuary. Excessive concentrations of ocean salts at

water intakes would create public health risks, increase the cost of water

treatment, and damage.plumbing and machinery. High salinity could also upset

the ecology of the estuary.

The DRBC tracks the levels of both sodium and.chloride ions in the

estuary. To protect public health, the Commission attempts to control

salinity so that sodium levels of potable supplies do not exceed 50 milligrams

per liter, based in part on-New Jersey's 50-mg/l drinking water standard. For

a variety.of purposes, the DRBC also tracks the 250-mg/l isochlor (the line

across the estuary where chloride concentrations equal 250 mg/1). Although

this isochlor represents more than detectable levels of sea salts, it is

commonly known as the "salt front." This level also represents the EPA

drinking water standard for chlorides and the concentration at which water

tastes salty to many people.

DRBC seeks to attain its salinity goals by keeping the chloride and sodium

concentrations at river mile 98 below 180 mg/l and 100 mg/l, respectively.

-22-

These limits were designed primarily to protect the public groundwater

supplies pumped from aquifers upstream of mile 98, which have a good hydraulic

connection with the estuary. Over one-half of the water entering these

aquifers is supplied by the estuary. DRBC has estimated that as long as the

river mile 98 objective is met, sodium levels in most wells tapping the

aquifers will remain below 50 mg1l. Moreover, the Philadelphia water intake

at Torresdale-(river mile 110.4) will be supplied with water with sodium

concentrations less than 30 mg1l.

Because the flow of fresh water opposes salt water migrating upstream, the

highest salinities in the estuary occur during droughts. Thus, the DRBC keeps

salinity from reaching unacceptable levels both by limiting consumptive uses

of water and by releasing water from various reservoirs during periods of low

streamflow.

When reservoir releases are needed for salinity control in the estuary,

the DRBC directs the U.S. Army Corps of Engineers to release water from

DRBC-financed impoundments operated by the Corps. Table 2 lists reservoirs on

which the DRBC currently relies, and scheduled increases in reservoir

capacity. The Corps has constructed two multipurpose impoundments in the

Basin: Beltsville Reservoir on a tributary of the Lehigh River, and Blue

Marsh Reservoir on a tributary of the Schuylkill River. Two reservoirs

originally designed for flood control (Francis E. Walter Reservoir on the

Lehigh River and Prompton Reservoir on the Lackawaxen River) have also been

operated for salinity control during drought emergencies. The U.S. Congress

has authorized modifications of these facilities for water storage purposes;

the DRBC plans to fund these modifications. Augmentation of low flows is also

provided by many small reservoirs that are not listed in Table 2. Although

-23-

these other reservoirs were designed for local community water supplies, they

sometimes augment freshwater flows into the estuary, incidentally, during

critical low-flow periods.

. Efforts to decrease consumptiveuse@, of water require the Commission-to

address both the diversion of water to other basins and consumptive uses of

water in the Delaware River Basin. The City of New York diverts fresh water

from the upper part of the Basin, as authorized by the U.S. Supreme Court in

1954. The court decreed that the City release water from its reservoirs

during low-flow periods to compensate downstream interests for the water that

is diverted or stored at other times. The current (1986) Basin Comprehensive

Plan incorporates an agreement among the parties to the 1954 decre6--New York

City and the Four Basin States--calling for special drought operation of the

City's Delaware River Basin reservoirs to meet downstream needs for salinity

control while conserving and storing water against the possibility of an

extended drought. Water is also diverted through the Delaware and Raritan

Canal to northeastern New Jersey, with similar provisions to curtail diversion

during droughts.

Some of the most important consumptive users of water in the Basin are

steam-electric power plants. Because scheduled publicly owned reservoir

capacity in the Basin will not be sufficient to meet increased consumption of

water projected to the year 2000 (the DRBC's current planning horizon), the

DRBC has required these utilities to develop storage capacity to provide

freshwater flows into the estuary to offset their consumption.

The most severe drought of record in the Delaware River Basin was that of

the 1960s. For a four-month period the average flow at Trenton was only one

quarter the long-term average flow, and during the worst month the flow was

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TABLE 2 (continued)

FOOTNOTES

g/ These reservoirs are operated or designed to serve multiple purposes, including salinity
control, or will tend to provide salinity control as an incidental benefit when operated for other
purposes. Only part of the storage capacity in these impoundments will be available for salinity
control. The operating plan for these reservoirs is based in part on offsetting the projected
rise in sea level to the year 2000 based on the recent trend, but does not take into account any
future acceleration of that trend related to the greenhouse effect.

t!/ Tributary of the Lackawaxen River.

q/ Tributary of the Lehigh River.

!1/ Tributary of the Schuylkill River.

g/ Privately owned hydroelectric power system. Storage available for salinity control only
after DRBC declares a drought emergency.

f/ Federal flood-control reservoir. Storage capacity available for salinity control only
after DRBC declares a drought emergency.

_q/ Statute miles, measured along the axis of Delaware Bay and River from the Mouth of the
bay. Second and third mileages indicate distances above the Mouths of tributaries.

!2/ Scheduled for completion in 1990; designed primarily to maintain conservation releases in
upper Delaware River, with secondary use to support downstream flow objectives and diversions to
New York City within limits Of U.S. Supreme Court decree of 1954.

l/ Scheduled for completion in 1995.

I/ Construction began in 1985. Planned completion date is 1988.

-26-'

only 13 percent of the average. In late 1964, the salt front advanced up-the

estuary As far as river mile 102, just above the Benjamin Franklin Bridge in.

Philadelphia. (The salt front's average location is'near-river mile 69.) The

drought continued through 1966. Because of the threat to water systems

depending on the estuary, the DRBC declared an emergency, as authorized by the

Delaware River Basin Compact -(DRBC 19 81). Under its@emergency powers, the

;.DRBC regulated the river flows to control salinity and conserve water. The -

emergency was in effect for many I mon.ths. Several impoundments in the Basin in

1965 made it possible for the DRBC-to call for water,releases at strategic

times to control salinity in the estuary, thereby preventing major harm to

wate r users that draw upon the estuary for their supplies.- However,

significant economic damages associated with the higher salinities were

reported by some water users. Some industries in the reach below Philadelphia

were forced to switch temporarily to a municipal system that imports-water

from the Susquehanna River Basin. Shellfish-productibn was subject to

abnormal stresses related to the high sali nities.

The DRBC'uses-a mathematical model to study salinity changes. The

Delaware estuary salinity model, developed for the DRBC by Thatcher -and

Harleman (1978),4 relates freshwater inflows, tides, and ocean salinities to

chloride distribution in the estuary. (Technical details of the model are

4 The model is a deterministic, one-dimensional time-varying model that
simulates saltwater intrusion in the tidal system extending from the head of
tide at Trenton to the Atlantic Ocean:' A one-dimensional model was developed
because the Delaware estuary is well mixed vertically, especially in the tidal
river above Delaware Bay, and even the bay is vertically homogeneous during' '
low-flow periods when salinity intrusion is likely to be a problem. The well-
mixed-character of this estuary is related to strong tidal currents and
shallow average depth. The normal range of tides at the mouth of the bay
varies from 3.95 feet in December to 4.3 feet in.August. 'At the head of the'
tidal river at Trenton, the tidal range varies from 7.6 feet in January to
8.55 feet in June.

-27-

explained in Appendix A.) The dynamic nature of the estuary is reflected in

the model outputs, which can show the average chloride concentration every few

minutes at one hundred equally spaced cross sections along the 214-kilometer

(1337mile) estuary. Typical simulations have produced.maximum and minimum

chlorinity readings at key locations for each tidal cycle over a period of a

year or more (Thatcher and Harleman 1981). These simulations have been used

to analyze the effects of various methods of reservoir operation on year-round

salinity distribution in the estuary. The model has also been used to predict

the effects of rising sea level on estuarine salinity, as discussed next.

The salinity distribution of an estuary'affects sedimentation and

shoaling. Thus, changes in salinity could change the geometry of the

estuary. Although maintenance dredging for navigation would tend to maintain

the present dimensions of the main channel in the tidal Delaware River and

Bay, changes in salinity-related sedimentation and shoaling outside the

channel accompanying a very large rise in sea level might alter the geometry

and thus the dispersion,characteristics of the estuary. In modeling the

changes in sea level and salinity intrusion, we have not attempted totake

into account possible changes in shoaling characteristics. This is not a

serious modeling flaw for a rise less than one meter. Additional research in

this aspept of the problem would be useful for more accurate projections of

the impact of a large rise in sea level.

The DkBC (1983a) uses the 1961-1966 drought as the basis for planning a

dependable water supply. Thus, for assessing most salinity problems, the

model is calibrated for the drought conditions of 1965, the driest year of

record in the Delaware Basin. The model is adjusted to reflect post-1965

changes in reservoir capacity, depletive uses of water, and sea level.

.-28-

Estimating Impacts of Sea Level Rise on Salinity

Current Sea Level Trends., Although worldwide sea level has been rising 1

to 1.5 millimeters per year (4 to 6 inches per century), the measured rise

along the east coast has been greater, because of local subsidence. Hicks

(1978) reported an average rise of 3.7 millimeters per year at Lewes,

Delaware, for the period 1921 through 1975. Hicks, DeBaugh, and Hickman

(1983) report a rise of 2.6 millimeters per year at Philadelphia, as shown in

Figure 7.

The DRBC was the first government agency to investigate the potential

effects of recent sea level trends on salinity in a particular estuary (Hull

and Tortoriello 1979). In 1979, the current DRBC planning horizon was the

year 2000, and the DRBC wished to know what estuarine salinity changes would

.result from the projected change in sea level from 1965 to 2000. Considering

only historical trends, not accelerated sea level rise from the greenhouse

effect, Hull and Tortoriello (1979) estimated a 35-year rise of 13 centimeters

(0.42 feet), and analyzed this rise with the Delaware estuary salinity model.

The model was first exercised for 1964-1965 drought conditions, including

observed sea level, but with flow of the Delaware River at Trenton regulated

by reservoirs to maintain an average flow of three thousand cubic feet per

second for the low-flow season. A fifteen-month period (1 October 1964

through 31 December 1965) was simulated. The minimum, mean, and maximum

chlorinities for each tidal cycle, as well as the running sixty-day averages,

were simulated over the fifteen-month period. These data were produced for

locations spaced along the axis of the estuary, with spacing close enough to

allow easv interpolation between locations.

-29-

FIGURE 7.

CHANGE IN YEARLY MEAN SEA LEVEL FROM 1923
TO 1980 AT PHILADELPHIA

z 12
Uj

1930 1940 1950 1960 1970 1980

YEAR

Source: HICKS, S.D., H.A. DeBAUGH, and L.E. HICKMAN, 1983. Sea Level
Variation for the United States 1855-1980. Rockville, MD: National
Ocean Service.

-30-

Next, a model simulation was carried out for year-2000 conditions,

assuming a recurrence of the 1964-1965 drought flows but with sea level

adjusted upward by 13 centimeters (0.42 feet) to reflect the projected sea

level rise. Other model inputs were held at the values used for 1965.

The maximum sixty-day average chlorinities for 1965 and 2000 were compared

to show the effect of the thirty-five-year sea level rise. Figure 8 shows the

increase in the maximum sixty-day average chlorinities as a function of river

miles. The chlorinity increase due to the simulated sea level rise was most

pronounced at river mile 60, where the sixty-day average increased by about

210 mg/l. The average position of the salt front moved two to four kilometers

(one to two miles) upstream. The salinity impact of the projected sea level

change decreased with distance seaward and landward of river mile 60, with no

measureable effect above mile 120.

Using a series of year-2000 simulations with various degrees of streamflow

regulation, Hull and Tortoriello (1979) found that the salinity increase

caused by the projected thirty-five-year rise in sea level could be offset by

a level of year-round river-flow regulation that augmented the summer flow by

150 cfs. This augmentation could be provided by a moderately sized reservoir

(about fifty-seven million cubic meters, or forty-six thousand acre-feet) in

the Delaware Basin. These findings have been used in the formulation of plans

for water resources development for the Basin (DRBC 1981).

Accelerated sea level rise. Because of limited resources, we investigated

only two scenarios of accelerated sea level rise. Because the magnitude of

the future rise is uncertain, a conservative approach is to pick a wide range

so that our results are most likely to encompass the actual situation. We

finally settled on 73- and 250-centimeter (2.4- and 8.2-foot) rises over 1965

-31-

FIGURE 8

CHLORINITY RESPONSE OF DELAWARE ESTUARY TO PROJECTED
35-YEAR RISE IN SEA LEVEL, 1965 TO 2000

240 -

W 220 -

0 200 -
_j
ISO -

E 160 -
2F
2 140
c'c 120 -

z
< Uj 100 -
Q
z
z 0 so -
LU
co
< 60
Uj
cc
0 40
z

0
20 40 60 so 100 120 140
RIVER MILE

Source: HULL, C.H.J., and R.C. TORTORIELLO, 1979. Sea-Level Trend and
Salinity in the Delaware Estuar . Staff Report. West Trenton, New
Jersey: Delaware River Basin Commission.

-32-

levels at Lewes, Delaware. (For drought conditions the DRBC Salinity Model

requires inputs relative to 1965 sea level, which was 6 centimeters lower than

1980 sea level.)

We hope that the reader will not attribute excessive significance to these

scenarios. Nevertheless, it is useful to understand when a 73- or 250-

centimeter rise is likely to take place. Because relative sea level at Lewes

is rising about 2.5 millimeters per year more rapidly than the global average,

these estimates do not correspond directly to published estimates of worldwide

sea level rise. The 73-centimeter scenario is consistent with the National

Academy of Sciences estimate for 2050, while the 250-centimeter case is

consistent with the NAS projection for 2125.5 The 73-centimeter scenario is

also consistent with the EPA's mid-range low estimate for 2050, as well as

EPA's high estimate for 2025.. The 250-centimeter scenario is consistent with

the EPA mid-range high estimate for 2100 and the EPA high estimate for 2075.

Although our understanding of future sea level rise is incomplete, the

73-centimeter scenario appears to be a more realistic near-term possibility

than the 250-centimeter scenario. Nevertheless, when considering responses to

sea level rise in the next fifty to seventy-five years, one should not

completely ignore the rise that may occur in subsequent years.

The earlier DRBC simulations (Hull and Tortoriello 1979) involved only a

relatively minor change in mean sea level, 13 centimeters (0.42 feet), which

did not require any modification of the salinity model. However, in the study

reported here, it was necessary to consider changes in the geometry of the

estuary itself, as well as in the mathematical representation (model) of the

5 Revelle estimates 70 centimeters per century due to factors other than
Antarctica and 2 meters per century after 2050 due to Antarctic deglaciation.

-33-

estuary. For sea level increases of 60 centimeters (2 feet) and more, not

only would the depth of the estuary increase, but the width would also

increase.-- The techniques used in these model-geometry modifications are

described in Appendix B.

Table 3 and Figure 9 compare the maximum thirty-day average chloride

levels at different river miles for a recurrence of the 1964-65 drought at the

1965 sea level and rises of 73 and 250 centimeters over that level. We

estimated that a 73-centimeter rise would increase the maximum thirty-day

chlorinity at river mile 98 from approximately 135 mg/l to 305 mg/l. The

thirty-day average location of the salt front would advance to mile 100,

compared with mile 93 for such a drought occurring in 1965. Although the salt

front would be well below Philadelphia's Torresdale intake on average, the

78-mg/l isochlor would be at river mile 109, just below the intake at mile

110.4. A 250-tentimeter rise would bring the salt front up to river mile 117,

well above Torresdale.

Further analysis of the simulations of saltwater intrusion using the

modified geometry yielded statistical information for comparing the numbers of

tidal cycles during which chloride levels exceeded a particular value. Figure

10 presents these comparisons for river mile 110.4, Torresdale. This figure

shows the effects of post-1965 sea level rises of 73 and 250 centimeters in

terms of-the percent of tidal cycles during which a given chloride

concentration would be exceeded by the maximum and minimum concentrations

calculated for every tidal cycle (total of 705 cycles in the simulation

period). For example, a sea level rise of 250 centimeters would cause the

78-mg/l chloride value to be exceeded during more than 50 percent of the

cycles, while a 73-centimete r rise would result in exceedance of that

-34-

TABLE 3

MAXIMUM 30-DAY CHLORIDE CONCENTRATION (MG/L)
AT DIFFERENT RIVER MILES FOR A, RECURRENCE
OF THE 1960s' DROUGHT

1965 Sea Level
River Mile Base Case 73-Centimeter Rise 250-Centimeter Rise

61.9 4,660 5,357 7,726
64.6 4,010 4,718 7,127
67.3 3,358 4,084 6,571
70.0 2,760 3,474 5,943
72.7 2,243 2,928 5,373
75.4 1,778 2,427 4,873
78.1 1,390 1,998 4,398
80.8 1,065 1,619 3,914
83.5 800 1,295 3,426
86.2 588' 1,021 3,021
88.9 431 804 2,652
91.6 301 60@ 2,289
94.3 210 450 1,967
96.9 151 335 1,655
98.0 a/ 136 b/ 305 b/ 1,560 b/
99.6 114 262 1,421
102.3 82 193 1,211
105.0 57 135 1,001
107.7 38 89 789
110.4 26 56 608
113.1 19 35 437
115.8 15 23 301
118.5 14 17 196
121.2 13 14 110
1231.9 13 13 55

a/ DRBC salinity-control point, where objective is to prevent 30-day
average chloride concentration from exceeding 180 mg1l.

b/ Interpolated value.

Note: Model inputs are based on observe d tides during calendar year 1965.

-35-

FIGURE 9

MAXIMUM 30-DAY CHLORINITY VS. RIVER MILE FOR A
RECURRENCE OF 1960s' DROUGHT:
(a) 1965 SEA LEVEL; (b) 73-CENTIMETER RISE;
(c) 250-CENTIMETER RISE

RIVER REACH
8000
7000 14 13 12 11 10 9 8 1 7 101 5 14 1 3 1 2

8000- 250-CM RISE
.j

0
5000.

z
0 4000- (MILE, 98--DRSC SALINITY
a CONTROL POINT.)
Lu 73-CM RISE
3000-
0 BASE

2000-

1000-

0-F
55 so 6'5 ;0 ;5 ;o ;5 @o 95 100 106 110 1;6 120 125 130
RIVER MILE

-36-

chlorinity about 15 percent of the cycles. The base case (1965 sea level)

never showed chloride concentrations in excess of 78 mg/l; the maximum

calculated chlorinity at Torresdale was 62 mg/l. Similarly, the calculated

chloride concentration exceeded 250 mg/l about.42 percent of the tidal cycles

for the 250-centimeter rise, but did not reach the 250-mg/l level for the

73-centimeter rise, which resulted in a maximum chlorinity of about 129 mg/l.

Implications

A rise in sea level of several feet would substantially exacerbate today',s

salinity problems in the Delaware estuary. The upper estuary above the

Schuylkill.River in Philadelphia, now a source of fresh water for both

municipalities and industries, would become too salty for most uses,

necessitating a switch to alternative supplies--at great expense.

Philadelphia's water supply intake at Torresdale, now in the freshwater reach

of the estuary, would be subject to occasional invasions of sea salts, which

would sometimes leave the water unacceptable for the City's many water

customers. Industries now using fresh water from the upper estuary would,

after the sea level rise, find brackish water at their intakes during dry

periods. Those industries now using brackish water from the middle and lower

reaches of the estuary would experience much higher salinities than those for

which their systems were designed, which would damage pipes, tanks, and

machinery and increase water-treatment costs. In some cases these industries

would have to shift permanently to alternative.water supplies.

Oysters. In the upper, narrow reach of Delaware Bay are found natural

oyster beds, which are managed by the oyster industry with supervision by the

State of New Jersey to provide seed oysters for planting in leased growing

-37-

FIGURE 10

PERCENT OF TIDAL CYCLES IN WHICH SPECIFIED CONCENTRATION
IS EXCEEDED AT TORRESDALE DURING A RECURRENCE
OF THE 1960s' DROUGHT FOR THREE
SEA LEVEL SCENARIOS

w
a
1.1.1100 -
w
X 78 mg CI/I
Uj 90- 50 mg Na/I 250 mg CI/I
co

z
.0 80-

z 70- maximum Concentration
w I For Tidal Cycle
z Minimum Concentration
0 60- For Tidal Cycle

so-

z
40-
w
250-CENTIMETER RISE
>- 30-

20-

LL
0 73-CENTIMETER RISE
10
... . . ............ ..
z
w
0-
LU -T'
CL 100 200 300 400 500 600 700

BASE CASE
CHLORIDE CONCENTRATION (mg1I)

-38-

areas in seaward, more saline areas of the bay. Because of their location in

less saline water, the natural seed-oyster beds provide havens for the young

oysters from some of their natural enemies that require higher salinities for

survival. Oyster biologists believe that increased salinities over the

natural beds at critical periods in the annual life cycle of oyster predators

and competitors would afford an advantage to these oyster enemies (Corps of

Engineers 1982). Although the highest salinities generally occur during

summer droughts, experts have expressed concern'that the increases in

springtime bay salinities resulting from increased depletive use of fresh

water, or from storage of springtime runoff in reservoirs, would harm the

natural beds and deprive the bay's oyster industry of its seed-oyster source

(Haskin 1954; Gunter 1974).

Hull and Tortoriello (1979) presented evidence that for the historical

period of decline in oyster production in Delaware Bay, the observed gradual

rise in see level was a more likely cause of increasing bay salinities than

depletive use or storage of fresh water. If the relatively small rise in sea

level--less than thirty centimeters (one foot)--during the period for which

observations are available could damage oyster beds significantly, the much
greater rise considered herein could severely threaten the bayots oyster

industry. The 'natural seed oyster beds near the head of Delaware Bay would

tend to shift up the estuary. Such a shift would reduce yields both because

the estuary is much narrower above the bay and because shifting upstream 'would

bring the oyster beds closer to upstream sources of pollution.

General ecological impacts. Potential impacts of increasing salinities

on other estuarine plants and animals have been matters of concern expressed

by ecologists (Corps of Engineers 1982). The magnitude of salinity increases

-39-

found-in the DRBC model simulations of postulated accelerated rises in sea

level would be expected to produce major changes in the ecology of the

Delaware estuary. There would be an up-estuary advance of marine and

estuarine species and a retreat of freshwater. species. Some species now

thriving in the relatively clean waters of the,louier estuary would migrate

into the more polluted areas of the.upper estuary,.closer to wastewater

outfalls and other hazards. Water craft using.the now freshwater. reaches of

the upper.estuary would be subject to,problems...caused by marine fouling

organisms. These marine.organisms would also infest water systems that take

water from.the tidal river in reaches now free of this problem.

Although this report focuses on salinity, other environmental impacts of

rising sea level may be important and should be investigated. Higher water

levels could drown much of the approximately 830 square kilometers (320-square

miles),of wetlands along the estuary. These wetlands., which provide critical,

habitats.for many.spe.cies of birds and fish,,are partially protected from

current human interference by federal and state laws. Although these

ecosystems could migrate landward with risingsea level, such migration would

be inhibited if development just inland of.the marsh is protected by

bulkheads, levees, and other.,structu.res;.there are currently no envi ronmental.

programs to ensure that development and other,human activities permit this

migration in the. future,(Titus,j.,Henderson, and.Teal 1984; Titus 1985). By

removing one of nature's cleansing mechanisms,:a loss of wetlands could

increase pollution loadings in.the estuary., Although long-term management of

the estuary will have to consider,.these impacts, they.are.beyond.the scope of

this report..

-40-

IV. IMPACT OF INCREASED RIVER SALINITY
ON NEW JERSEY AQUIFERS

Perhaps the most serious potential implication of increased river salinity

would be saltwater contamination of adjacent aquifers. Many water users in

the lower Delaware River Basin adjacent to the estuary depend on groundwater

supplies, which are recharged in part by the river. Some New Jersey wells

used for public water supply have already been shown to produce water with

high concentrations of sodium, which, according to the State Health

Department, represent a public health hazard (Braun and Florin 1963; Korch,

Ramaprasad, and Ziskin 1984). The increasing salinities in the Delaware

estuary that would accompany a large rise in sea level would severely

aggravate the existing saltwater intrusion problems of aquifers in the

Delaware Basin, primarily in New Jersey and Delaware. Some aquifers now

heavily used would probably become too salty for drinking water and would have

to be abandoned or limited to agricultural and industrial uses.

This section focuses on the impact of increased estuary salinity on the

Potomac-Raritan-Magothy aquifer system, which supplies much of the water used

in southern New Jersey. Although other aquifers are hydraulically connected

to the estuary, this aquifer is the only major system with a connection to the

part of the estuary likely to become salty as a result of future droughts or

sea level rise.

The Relationship Between Sea Level and Aquifer Salinity

The only portion of an aquifer likely to be salty is the part below sea

level. In coastal aquifers, a layer of fresh water floats on top of the

heavier salt water. The salt water generally forms an intrusion wedge such

-41-

that the farther inland (the higher the water table), the farther below sea

level is the boundary between fresh and salt water, as shown in Figure 11.

According to the simplistic Ghyben-Herzberg relation, for aquifers where the

water table slopes toward the ocean, this boundary is forty meters below.sea

level for every meter above sea level the freshwater level in the aquifer

lies. As sea level rises, the freshwater/saltwater boundary shifts inland and

upward, with a time lag depending on how far that boundary is from the coast.

Pumping wells cause water levels to fall below sea level, and if the

withdrawal rate is too high, the equilibrium saltwater line will move far

inland. The time lag is the major reason that many heavily pumped coastal

aquifers are not yet salty.

Many aquifers such as those in the Potomac-Raritan-Magothy aquifer system

release water into rivers in their natural state. If such an aquifer is

pumped so that groundwater levels fall below mean sea level, it will be

recharged by nearby rivers. As discussed in Section 3, estuary salinity could

respond to sea level rise or changes in precipitation quite rapidly. Thus,

should the river become salty even temporarily, salt could infiltrate into

such an aquifer and persist for a long time. The Potomac-Raritan-Magothy

aquifer system is both a coastal aquifer and an aquifer recharged by a river.

The Potomac- Raritan-Magothy Aquifer System,

The Potomac-Raritan-Magothy aquifer system is the principal source of

water for the population and industrial centers in the coastal plain of

southern New Jersey (Luzier 1980). The aquifer extends along the coast from

North Carolina to Long Island. In New Jersey, the Potomac-Raritan-Magothy

lies directly on top of bedrock, is confined above by a relatively tight clay

-42-

FIGURE 1.1

SALTWATER INTRUSION IN A COASTAL AQUIFER

Ground
Surfaco

Water Table v

IN
7 ----------- ----------

Ocean
Fresh
Salt Water m
Water

Note: H 40 x h
,,,,,@water Tabi,

-43-

layer, and has a poor hydraulic connectiofi to other aquifers far offshore.

The Delaware River flows along the outcrop of the Potomac-Raritan-Magothy from

Trenton, New Jersey, to Wilmington, Delaware (Figure.12), and there is a good

hydraulic connection between the river and aquifer system, especially above

river mile 98 (Camp Dresser and McKee 1982).

Vowinkle and Foster (1981) calculated the inflow into the aquifer for the

river teaches shown in Figure 12 using a groundwater model developed by Luzier

(1980) for 1973and 1978 groundwater levels. The data showed that the

greatest inflow occurs between river miles 101 and 106.5--adjacent to wells in

the vicinity of Camden City--where water levels are significantly below mean

sea level.

Even without a iise in sea level due to the greenhouse warming, saltwater

intrusion into the aquifer will worsen in the future. The existing saltwater

boundary to the south of Camden (Fig. 14) reflects a sea level that was

fifteen to thirty meters (fifty to one hundred feet) lower than the present

sea level, implying an ongoing adjustment to the one hundred meter rise that

has taken place over the last eighteen thousand years (Meisler, Leahy, and

Knobel 1984). As ground water is removed and the aquifer approaches

equilibrium with current sea level, the salt front will move farther inland

from the Atlantic Ocean.

Figure 13 illustrates the water levels in the Potomac-Raritan-Magothy

aquifer system based on 1973 field data. Figure 14 illustrates a prediction

@that water levels will be more than 37 meters (120 feet) below mean sea level

in Camden County by the year 2000, if the rate of groundwater withdrawal

increases by 1.7 percent per year. As a result of deep saltwater movement

from offshore, the saltwater line in the aquifer will advance to the location

-44-

FIGURE 12

MODELED AREA SHOWING OUTCROP AREA AND R.IVER REACHES
OF THE POTOMAC- RAR I TAN -MAGOTHY AQUI-FER SYSTEM

2 R

BURLINGTON
4

VIP
7 M
CAMDEN
'4 CAMDEN
NO,

.. ........ ..........
10
0 .40 GLOUCESTER
To 11

13 EXPLANATION

0
utcrop area of Potomac
Group and
Raritan and
14 Magothy Formation*

Reach Segments
SALEM -Is-

J s. V
DELAWARE

10 MILES
SALEM CITY 0 5

0 5 10 KILOMETERS

Source: VOWINKLE, E.F., and W.K. FOSTER, 1981. Hydrogeologic Conditions in
o
-405.
the Coastal Plain of New Jersey, Open-File Report 81 Trent n,
New Jersey: U.S. Geological Survey, 39 pp.

shown in Figure 14, far enough inland to render the Potomac-Raritan-Magothy

ground'water in Atlantic, Cape May, and Cumberland Counties brackish or salty.

Impact of a Drought on the Aquifers- -Current and Future Sea Level

Salinity levels in the ground water are monitored at selected locations by

the United States Geological Survey and other agencies (see, for example,

Schaefer 1983). Low salinity levels are normally found in the Potomac-Raritan-

Magothy aquifer system adjacent to the Delaware River above river mile 98

because of freshwater inflows. However, when the salt front moves up the

estuary during droughts, the high-salinity recharge water from the Delaware

River increases salinity in the ground water, as shown in Figure 15.

Table 4 shows the maximum thirty-day average chloride concentrations at

the center of each reach for each of the three sea level scenarios for a

recurrence of the 1964-65 drought. Because the DRBC is primarily concerned

with protecting the Potomac-Raritan-Magothy aquifer system above river mile

98, we focus on reaches 1 through 8,(river mile 98 through 131).6

During the 1961-66 drought, the salt front moved up the Delaware estuary

and allowed salt water to recharge the Potomac-Raritan-Magothy aquifer

system. Increased salinity was observed in many wells adjacent to the

Delaware River (Figure 15). In Camden County wells, for example, chloride

concentrations increased 10 to 70 mg/l from background levels-(5 to 10 mg/1)
(Camp Dresser and McKee 1982). Elevated chloride levels--"ersisted more than
P

6 There are practical limits to the control of salinity in the Delaware
estuary by reservoir regulation. Although it is recognized that some recharge
of aquifers by the estuary takes place seaward of mile 98--some as far,down as
the Delaware Memorial Bridge--it is not practical to control salinity to
provide drinking-water quality at all points along the estuary where recharge
occurs. On the other hand, regulation at any point on the estuary, say at
mile 98, does provide some control of salinity throughout the estuary.

-46-

FIGURE 13

POTENTIOMETRIC SURFACE OF THE POTOMAC- RAR ITAN-MAGOTHY
AQUIFER SYSTEM, NOVEMBER-DECEMBER 1973

10 0 4 8
MILES
KILOMETERS
Contour shows altitudo of the 0 4 8 12
aqulfer's water surface In toot 40
g
toot a .305 motors).
atum is NGVD (sea level) of A.
1929. Contour Interval variable. q.

Location and number of x MOMMOUT14
observation wells. W -0-sbcou"
.W1

0z
UJO OCEAN COUNTY

Now J9rSsY
******" oil X
Pennsylvania

0
te BURLINGTON C U14TY
RM 110 ............ ...... C@0
Torresdale
AMDEN OLNTY411
ATLANTIC COUNTY
olq
ATLANTIC OCEAN
0
Uck)TER COUNTY
L
RM 98 .......... ....... d-
%-
CAPE MAY
COUNTY
...........
Dela@are SALE COUNTY' I
Delawar, 0
N A UMBEALAND COUNTY
Bridge _'C
RM 69-11111 Memorial I

Cone of DepreflsdlOn
Novo "A
E.ce.
0.
F* I

Source: LUZIER, J.E., 1980. Digital-Simulation and Projection of Head
Changes in the Potomac-Raritan-Magothy Aquifer System, Coastal
Plain, New Jerse . U.S. Geological Survey Water Resources
Investigations, 80-11.

-47-

FIGURE 14

POTENTIOMETRIC SURFACE OF THE POTOMAC- RAR ITAN-MAGOTHY
AQUIFER SYSTEM AT YEAR 2000 WITH.
.ANNUAL EXTRACTION GROWTH RATE OF 1.7 PERCENT

contour shows altitude of the
aquifer's water surface In feet
9
loot a .305 mWers).
.tum Is NOVO (**a level) of
1929. contour interval 20 ft. 0 4
on ?MILES
KILOMETERS
Lo ation and number of 7 0 4 a 2
observation wells.
250mg/L
Miog@N@Mou N .@b
W C
0
Chloride concentration near
bottom of aquifer system
in milligrams per liter.

ammme 250 mg/L IMMME %
A

Chloride concentration near
ImW .
top of aquifer 9 stem In In I-r 1.
milligrams per lyler. 0z
S! I
two OCEAN COUNTO
w
0

Now Jar SOY
Pennsylvania....

A4W
U TON COUNTY 4P
RM 110 ......
Torreadaie

C OUNTY
0 ATLANTIC COUN
t. a ATLANTIC OCEAN
a CEO NTY
10 NIP
RM 98 . .................

MAY
CAPE
...... COUNTY
............
Dela@are IM COU<4--40
osiawar a I @A
RM 69-11111 memorl 4b CUMBERLAND COUNTY
arlda: aO

.0 2

...................
Re
00.

Source: LUZIER, J.E., 1980. Digital-Simulation and Projection of Head
Changes in the Potomac-Raritan-Magothy Aquifer System, Coastal
Plain, New Jersey. U.S. Geological Survey Water Resources
Investigations, 80-11.

-48-

FIGURE 15

CHLORIDE CONCENTRATIONS AT WELLS IN THE CAMDEN CITY VICINITY

LEGEND :O__ Morris 1.
Delair 3 - well Name *lair 2:'3
*Puchack 2.'
A.M. 104.8-River Miles from 70==
Mouth Of Camden City 7. 11
Delaware Say
60
a the five I I I I
Indicate Delaware River
years of drought
61-1989)
LOCATION MAP

40 40- 11 1
-Camden Oily -Camden Cli-j- Delilr 2
Z -A.M. 97.6- -R.M..97.6. _R.M 104.5
E 30 1 3 30_
It
C if
11 ILA IF
A
2
C
r
10== 10
to-
X-X

0 0
30 '40 '50 0 '70 1080 '30 '40 '50 '60 '70 1980 '30 '40 150 160 '70 1980

-40 140 140
OsIa'Ir 3 -Puch@ack 2' -Puch'ack 3
-R.M. 104.8 -R. M. 104.7 -A.M. 104.7
E 30 3

20
20= 20-

IAX- I
0 10 10 10

0 0 0
'30 '40 '50 160 170 580 '3 0 '40 '50 '00 '70 1980 '30 '40 '60 '60 '70 1980

40 4 40
-Puchack 4 -Morris I -Morris 6
Z A.M., 104.7 -R.M. 108.1 -R.M. 104.9 7-
" 30
E 30 30

20 20- 20
C

'0
0 10 10
z Oi 0 - OR;
Q '30 '40 '60 '60 '70 1980 '30 '40 '50 '60 '70 1930 '30 '40 '50 so 170 1980
'@% @3c

Source: CAMP DRESSER and McKEE, INC., 1982. Groundwater Management Plan for
Study Area 1: Coastal Plain Formations. Prepared for Delaware River
Basin Commission, West Trenton, New Jersey.

TABLE 4

RECHARGE OF DELAWARE RIVER WATER INTO POTOMAC-RARITAN-MAGOTHY AQUIFER SYSTEM
AND MAXIMUM SALINITY LEVELS OF RECHARGE

Estimated
Reach Recharge Percent of
Length of to Aquifer Total River Maximum 30-Day Average
Reach System Recharge to Chloride Concentration (9!gLl)
River Reach (Miles) River Mile (cfs)** Aquifer System I No Rise*j 73-cm Rise* 250-cm Rise*

1 8.0 123 - 131 100

2 6.2 117 - 123 2.1 2.1 200

3 5.0 112 - 117 6.6 6.1 350

4 1 2.5 1 109.5 - 112 1 1.3 1.3 50 500
5 2.7 (06.5 - t09.5 4.0 3.5 50 50 650

6 2.9 104 - 106.5 23.0 20.0 50 100 900

7 2.8 101 - 104 19.1 16.6 100 200 1200

8 2.8 98 - 101 9.4 8.2 100 1 250 1450

9 2.8 95.5 - 98 4.9 4.2 150 350 1700

10 4.5 91 - 95.5 13.1 11.4 250 450 2000

11 2.5 88.5 - 91 11.9 10.4 350 700 2500

12 6.5 82 - 88.5 11.8 10.5 600 1050 3050

13 5.4 76.5 - 82 1.4 1.3 1100 1650 3950

14 5.4 71 - 76.5 5.1 4.6 2250 2950 5400

Post-1965 rise in sea level superimposed upon a recurrence of the 1964-65 drought flows.
Total 1978 river recharge was approximately 43% of total water entering the aquifer system (Luzier 1980).

-50-

ten years; once introduced into the aquifer salinity contamination tends to

remain (Camp Dresser and McKee 1982).

From such observed data, aquifer salinity distributions can be generated.

Simulating the salinity distribution in the aquifer for the sea level

scenarios requires a predictive numerical model. However, a first-order

approximation can be deduced by considering (1) the estuary's salinity

distributions for selected sea level rise scenarios (see Figure 9); and (2)

the distribution of inflow into the aquifer (see Table 4). '

Table 5 shows the penetration distances during the time that chloride

concentrations exceed 250 and 78 mg/l, respectively, for the fifteen-month

drought simulation. Although we simulated only fifteen months of the

five-year 1961-1966 drought, these fifteen months were the worst part of that

drought, with the lowest river flows and the highest estuarine salinities.

Therefore, the computed chloride concentrations of recharge water would be no

greater if we simulated the entire five-year drought. The estimates in Table

5 are based on groundwater velocities near the advancing edge of the saltwater

front, estimated for each river reach based on 1978 water levels from Walker

(1983) and aquifer properties affecting water velocities from Luzier (1980).

The inflow rate obtained by Vowinkel and Foster (1981) was divided by the

available cross-sectional area and porosity, providing an alternative method

of computing groundwater velocities. The velocity ranges were extended to

include both these estimates.

For the baseline scenario (recurrence of the 1964-65 drought flows with no

sea level rise), the thirty-day average 250-mg/l isochlor in the estuary

penetrates into reach 10 (river mile 91.0 to 95.@) with chloride concentrations

in the estuary in excess of 50 mg/l extending up into reach 5 (river mile

-51-

106.5 to 109.5). Although the 250-mg/l line would not penetrate to reach 8,

penetration distances of over ninety meters (three hundred feet) are predicted

for the 78-mg/l line in reaches 6, 7, and 8 (Table 5). If in subsequent years

the salinity in the recharge water decreased again to normal levels, the slug

of high-salinity water would continue to move toward the area of lower water

levels, that is, toward the center of the major cone of depression in Camden

County (see 1973 water levels in Figure 13). As this slug slowly moves,

however, the chloride concentration would decrease because of diffusion,

dilution by lower salinity recharge water (including precipitation), and

withdrawal from the aquifer. Nevertheless, levels in excess of the New Jersey

drinking water standard (50 mg/l sodium, corresponding to 78 mg/1 chloride)

could occur for several years in areas within a mile or two of the river.

For the 73-centimeter sea level rise scenario, water with chloride

concentrations slightly in excess of 250 mg/l (corresponding to a sodium.

concentration of 145 mg/1) would begin to recharge the aquifer system in the

vicinity of reach 8 (river mile 98 to 101). The dilution and diffusion of the

salt water as it moves through the aquifer would undoubtedly reduce the

chloride concentration below 250 mg/l within a very short distance of the

Delaware River. Above reach 8, the chloride concentrations are predicted to

be below 250 mg/l. Thus, like the baseline case, no significant region of the

aquifer adjacent to the Delaware River above river mile 98 should experience

sustained chloride concentrations above 250 mg/l. Sodium concentrations

greater than 50 mg/l would be present in the recharge water as far as reach 4

and would penetrate several hundred feet in reaches 6, 7, and 8.

For the more severe 250-centimeter sea level rise scenario, a significant

zone (reach 3 and seaward) of the aquifer system would be recharged by water

TABLE 5

VELOCITIES, CONTACT TIMES, AND PENETRATION DISTANCES FOR
GROUND WATER WITH ELEVATED CHLORIDE CONCENTRATIONS

Time that 30-Day Average
Chloride Concentration Maximum Aquifer Penetration
Exceeded 78 mg/1 and Distance for Duration of
Estimated 250 mg/I (days) Contact Time (meters)
(1978)
Ground-Water 1 78 mg/I 250 mg/I 78 ff!q/ I
River Velocity Range I I I I I
Reach (mete rs/yea r) BASE 73 cm BASE 73 cm 250 cm BASE 73 cm BASE 1 73 cm 1 250 cm I

1 0-90

2 0-90

3 90-150 120 50

4 30-60 30 130 5 20 Ln

5 90-180 100 - 1 140 1 - 50 1 1 70 1

6 270-580 1 60 1 130 1 1 - 150 95 205 240

7 460-550 110 150 160 165 225 240

8 240-370, 140 160 100 170 140 160 100 170
------- I ---------------- ------ ------- ------ ------- -------- ------ ------- ------ ------- --------
9 120-150 160 170 120 180 65 70 50 75

10 180-400 170 180 100 140 190 185 1 195 1 110 1 150 1 205

11 300-370 180 190 120 160 200 180 190 120 160 200

12 90-150 190 200 140 180 400 80 80 60 75 165

13 0-30 200 210 160 200 400 15 15 15 15 1 35 1

14 60-90 230 250 180 220 400 55 60 45 55 100 1

Note: A chloride concentration of 78 mg/1 corresponds to a sodium concentration of 50 mg/l, the New
Jersey drinking water standard.

-53-

from the river with thirty-day chloride concentrations in excess of 250 mg/l.

The slug of high-salinity water would move significant distances before

dispersing to insignificant background levels.

In summary, a recurrence of the 1960s' drought with a higher sea level

would cause increased sodium and chloride levels in parts of the

Potomac-Raritan-Magothy aquifer. These increased levels would persist for

long periods--probably several decades--as the high-chloride water dispersed

and propagated toward pumping wells. For many years, some wells would

experience elevated sodium levels that could make the water unfit for many

purposes, including human consumption, in which case, water fromalternate

sources could be required.

Improved Estimates

Although we used the DRBC salinity model to estimate surfacewater impacts,

no similar model was available for assessing groundwater impacts without an

investment of resources exceeding what was available for this study. To more

adequately evaluate the impact of the estuary salinity distributions on the

groundwater system will require a solute transport and dispersion model, such

as the one presented by Konikow and Bredehoeft (1978). A significant field

investigation should be conducted, including an in-depth review of existing

field data. Because of the complex hydrogeology, a numerical model is

required. The model must contain such features as salinity concentration at

the boundaries, which can vary in time and space. Although a two-dimensional

representation may prove adequate, a three-dimensional model may be

necessary. During drought conditions, high-chloride water will recharge the

aquifer far up the estuary for a limited period of time. The output of a

-54-

numerical model will allow tracking of the slug of high-chloride water as it

propagates and moves through the aquifer in the down-gradient direction.

-55-

V. RESPONSES TO SALINITY @INCREASES

In spite of the severity of projected salinity increases, the major

impacts are far enough in the future to be incorporated into planning by the

DRBC, state governments, and the private sector. The options fall primarily

into two categories: preventing increased salinity or adapting to it. This

section briefly discusses such options. A determination of the most

appropriate responses to be undertaken is outside the scope of this report.

Preventing Salinity Increases

Increasing river flow can offset salinity increases. The DRBC currently

maintains capacity to release fresh water from reservoirs and has regulatory

authority to decrease consumptive use of water during droughts.

Hull and Tortoriello (1979) determined that the thirteen-centimeter

(five-inch) rise in sea level expected for the period 1965-2000 (based on

recent trends) would require an increase in reservoir capacity of fifty-seven

million cubic meters (forty-six thousand acre feet). The DRBC's comprehensive

plan provides for suchan increase in capacity.

A conservatively low extrapolation of the results from Hull and

Tortoriello (1979) implies that for the thirty-centimeter (one-foot) rise in

sea level expected through 2025, the required additional reservoir capacity

would be approximately 140 million cubic meters (110 thousand acre feet),

about one fourth the capacity that would be provided by the proposed Tocks

.Island reservoir. Table 6 lists reservoirs that are currently in the DRBC's

long-range comprehensive plan, with a combined reservoir capacity of 730

million cubic meters (592 thousand acre-feet). These reservoirs would augment

streamflow during droughts enough to offset salinity increases caused by sea

TABLE 6

UNSCHEDULED RESERVOIRS IN DRBC'S PLAN THAT COULD BE
USED TO OFFSET SALINITY INCREASES IN THE DELAWARE ESTUARY a/

Increment of Long-Term Storage Capacit
Cubic Meters Billions Acre-Feet
Name of ProJect Location b/ (millions) of Gallons (thousands)
(2) (3)

Tocks Island Reservoir Delaware River 525 139 425.6
(217.2)

AqUashlcola Reservoir Aquashicola Creek 30 8 24
(183.66 - 36.3 - 4.6)

Maiden Creek Reservoir Maiden Creek 91 24 74
(92.5 - 86.7 - 9.6)

Evansburg Reservoir Skippack Creek 29 8 23.5
(92.47 - 32.3 - 3.0
1.0)

Newark Reservoir White clay Creek 37 10 30
(70.7 - 10.0 - 12.0)

Icedale Reservoir W. Branch Brandywine Cr. 1 18 5 14.6
(70.73 - 1.5 - 20.0
25.6)

Total 730 194 592

A/ These Multipurpose projects are currently (1985) in the DRBG's Comprehensive Plan, but
this does not guarantee ultimate construction, which will.depend on further analysis of water
demand, environmental impact, and financial feasibility. Such analysis may result in
deauthorization of some of these projects. They are generally in reserve status--for development
after year 2000, if needed.
statute miles, measured along the axis of Delaware Bay and River from the mouth of the
bay. Second and subsequent mileages indicate distances above the mouths of tributaries.

-57-

level rise and increased water consumption well [email protected] the 21st century.

However, most of these dams have not yet been scheduled for construction.

Although reservoirs are generally not built before-they are needed,

incorporating future reservoirs into the Comprehensive Plan long before

construction can help to limit eventual costs. Otherwise, the best sites may

be developed for other uses, increasing the cost of purchasing the land,

perhaps to the point where a dam at that site becomes economically infeasible,

which could necessitate selection of an alternative reservoir site that is

less environmentally or economically attractive.

The advantage of adding reservoir capacity is that such an approach fits

within the current policy framework. The limitations, however, must also be

considered. Although dams can mitigate environmental disruption caused by

consumption of water, environmental disruption can result from the dams

themselves, a factor of no small importance in the opposition to the proposed

Tocks Island Lake, the consideration of which has been deferred until after

the year 2000. Moreover, the capacity of reservoirs must keep pace with

increased consumptive use of water, as well as sea level rise. Finally, each

additional dam tends to cost more than the previous one, as the least costly

sites are usually developed first. Thus, even ignoring environmental

questions, there is a limit to the ability of reservoirs to counteract

saltwater intrusion in a cost-effective manner.

Increased private storage capacity could augment public reservoirs. As

mentioned in Section 3, electric utility companies in the Delaware Basin are

already required to develop enough storage capacity to offset their new

consumptive uses during low-flow conditions. Actions could be taken to

encourage other users to develop storage or decrease consumption.

-58-

Decreasing the depletive use of water from the river would also prevent

salinity from increasing*. The DRBC has used its special powers during,several

drought emergencies since 1965 to curtail diversions to New-York City and '-

northeastern New Jersey and other depletivd uses. -In 1983, the bRBC (1983b,

1983c) adopted regulations that automatically cutback consu#ti6n withih@the

basin and diversions out of the basin during-droughts.

Decreasing depletive uses of water has been one of the DRBVs tools-for

combatting saltwater intrusion. Nevertheless, there are practical and

physical limits on the ability to-offset salinity increases caused by a large

rise in sea level. Although conservation has been exploited to a high degree.

within the basin, consumptive use is*expected to grow with population.

Curtailing*diversions of Delaware River water to N6w,York City and other areas

may impose increasing hardships on these areas as alternate supplie's such as,,

the Hudson River also become saltier. Moreover, even if all depletive uses of

water were-eliminated, a substantial rise in sea level would eventually.

increase salinity in the estuary, as it has since the last ice age.

Adapting to Increased River Salinity: Surfaciewater Userg

If measures ake not undertaken to prevent a salinity'indiease, water.-users

will-have to adapt to it. The City of Philadelphia could adapt to,increased

salinity by moving its intake upstream. This approach was actively considered

a.s a temporary measure during the,1960s' drought, when the Torr6sdale intake

was threatened-by saltwater intrusion (Hogarty 1970).

.Although Philadelphia will almost certainly continue to rely on the

Delaware River for part of its water supply, other users may be able'to shift

to alternative supplies. The Chester (Pennsylvania) Municipal Authority has

already done so. Formerly taking its water supply from the tidal Delaware

-59-

River below Philadelphia, the Authority was forced to abandon this source in

1951 because of frequent high salinities related to low river flows. The

Authority now obtains its water supply from the Susquehanna River Basin.

However, the Susquehanna River flows cannot be reduced without limit to help

Delaware Basin@water users avoid increasing salinity; the Susquehanna has its.

own problems, including the need to maintain adequate low flows for salinity

control in upper Chesapeake Bay (Schaefer 1931; Susquehanna River Basin

Commission 1973).

Some industries along the Delaware estuary may,eventually find it

impossible to obtain adequate freshwater supplies. Such industries may be

forced to relocate to areas where fresh water is available. Others may be

able to survive at their present locations by shutting down river pumps during

periods of high salinity and switching to municipal water distribution systems

with access to fresher sources. This has happened in past droughts in the

area along the Delaware estuary served by the Chester Municipal Authority.

However, alternative sources may be prohibitively expensive.

Although water conservation measures could make only a limited

contribution toward preventing salinity increases, they could also play a role

in adapting to decreased availability of fresh water. Nevertheless, they

would face institutional barriers that could substantially delay an effective

response. Additional regulations of water use would require identification of

additional activities to be controlled. Although higher prices could

theoretically induce an economizing shift toward conservation, public agencies

would find it difficult to raise water prices, particularly for those whose

water is supplied by wells on their own property.

-60-

Finally, companies and individuals may adapt@by using water with higher

salinity. Companies that use water for cooling may experience increased

corrosion of pipes and machinery, or may invest resources in

corrosion-resistant materials. Some individuals may shift to bottled water

during droughts,7 while others may choose to drink water with elevated salt

content rather than go to the expense of distilling water. Health-conscious

people may respond to salt-laden drinking water by reducing salt intake from

other sources. Nevertheless, the health hazard of elevated sodium in water

ingested by persons subject to hypertension and other diseases requiring

low-sodium diets is an argument for avoiding high salt content in public

drinking-water supplies, so that susceptible persons will not be forced to

save money by sacrificing health.

Adapting to Increased River Salinity: Groundwater Users

Groundwater users can adapt to increased salinity in ground water by many

of the same methods by which surfacewater users can respond. In addition,

efforts may be undertaken to prevent the river from recharging the aquifers

with salt water. The methods include physical barriers, extraction barriers,

freshwater injection barriers, and increased recharge from sources other than

the estuary. Modified pumping patterns could also be employed.

Physical barriers. Subsurface physical barriers, such as sheet pile

cutoff walls, clay slurry trenches under earth dams, and impermeable clay

walls, are routinely used by engineers to control the movement of water and

7 A large fraction of citizens in New Orleans use bottled water or
purchase home distillers; the salt-intrusion problem in Louisiana probably
will continue to be more severe than that in the Delaware River Basin.

-61-

other liquids, including hazardous waste materials. It is also possible to

inject materials that form a zone of low permeability.

Extraction barriers. Extraction barriers consisting of a line of pumping

wells parallel to shore have been used in various locations in order to

prevent or.redtce saltwater intrusion (Stone 1978). Extraction barriers may

withdraw:some-fresh water'that would'otherwise be useful and thus may not be a

viable option where water supplies are scarce.

Freshwater injection barriers. 'Figure 16 illustrates a typical injection

barrier'in operation to control the saltwater intrusion for cases where the

sea level is in excess of freshwater levels. In contrast to the extraction

barrier, with an injection barrier, fresh water is injected into the aquifer

through a line of wells along the shoreline. The higher groundwater levels

along the injection barrier prevent saltwater intrusion.

Increased recharge. In many coastal locations in the United States,

sufficient amounts of fresh water are available for recharge during periods of

high precipitation. @Although some water is captured during these periods and

stored in surface reservoirs, very little water is artificially recharged to

groundwater reservoirs for use during droughts. This extra water, which.is

ft wasted" to the ocean, could be used to replenish the aquifer, build up

groundwater levels, and slow or stop saltwater intrusion.

Modified pumping patterns. For aquifers where moderate pumpage already

occurs and the effect of a sea level rise is projected to be important, a

phased shutdown of wells can be designed as the monitored saltwater intrusion,

progresses. Instead of a disorganized search for alternate water as the

chloride concentrations increase, logical permitting of new wells or new

economical surfacewater distribution schemes can be implemented. Because a

-62-

FIGURE 16

INJECTION-TYPE SEAWATER INTRUSION BARRIER

PIEZOMETRIC SURFACE IMPERVIOUS BED
WATER SUPPLY
INJECTION BARRIER WELL
mEW MEAN WELL
SEA LEVEL

*w. 71
4.0

'N X:

FRESH WATER AQUIFER
SEA WATER

Source: SORENSEN, R.M., R.N. WEISMAN, and G.P. LENNON, 1984. Control of
Erosion, Inundation and Salinity Intrusion Caused by Sea Level Rise.
In Greenhouse Effect and Sea Level Rise: A Challenge for This
Generation, edited by M.C. Barth and J.G. Titus. New York: Van
Nostrand Reinhold.

-63-

saltwater slug will pass through the aquifer even when the drought that caused

the high river salinity has passed, the well could be reopened after the

aquifer has become fresh again. However, such natural purging of a

contaminated aquifer may require decades, if not centuries.

Although i-t is technically possible to use physical, extraction, or

@injection barriers to prevent saltwater intrusion in the Potomac-Raritan-.

Magothy aquifer system, the large expense probably would not be justified.

Harbaugh, Luzier, and Stellerine.(1980) present technical information ori..how

an injection barrier could be employed in the aquifer system to reduce the

existing saltwater intrusion. However, Camp Dresser and McKee (1982) provide

cost estimates showing that the implementation of such a groundwater barrier

is not feasible because of the large area needing protection. Although these

types of barriers may be considered, they probably cannot be justified

economically.

Increased recharge in the aquifer's outcrop could be employed at a

reasonable cost, as could modified pumping patterns, which would shift the

pumping away from the critical areas. The State of New Jersey is currently

studying alternative water systems for the critical area of excessive drawdown

in Camden County. Among alternatives being considered is the improvement of

the water distribution system, which would transfer water to the area of heavy

drawdown from other sources, thus relieving pumping stress in the critical

area.

-64-

V1. NEXT STEPS

Considering Climate Change,

Although this paper focuses on the impact of sea level rise on salinity,

other consequences of the greenhouse effect may accelerate or delay the

consequences of sea level rise. For example, if droughts become more severe

in the future, the resulting reduction in river flow would also allow salinity

to increase. Although projections of drought conditions cannot currently be

made for specific regiorfs, general circulation models suggest that drought

frequencies may change substantially.

Rind and Lebedeff (1984) examined model calculations of the change in

drought frequency, caused by a doubling of atmospheric CO 21 for four regions

of the continental United States, one of which included the Delaware River

Basin. Two of the regions would change slightly, one would experience half as

many droughts, while the other would experience ten times as many. Although

the Delaware River Basin is largely in the latter region, the authors strongly

warn that their model does not accurately project climate for particular

regions.

This report focuses on rising sea level because our ability to project it

is far superior to our ability to predict future precipitation change.

Nevertheless, planning for hydrologic shifts may be more important than

planning for sea level rise. It is possible to plan around a gradual rise in

sea level; even waiting until the 1990s for a confirmation of the predicted

global warming would allow time to prepare for the most severe consequences.

By contrast, a drought can occur suddenly, and several droughts may have to

occur before people know that their area is more prone to drought than it was

-65-

in the past. Thus, successful planning for changes in the hydrologic cycle

will probably have to start before those shifts are well understood.

Chen, Boulding, and Schneider (1983) have thus argued that in this

situation, water resource officials should rely on "robust" strategies--

policies that are less vulnerable to large changes in conditions and can

accommodate a shift in either direction. In the case of the Delaware River

Basin, two types of policies readily come to mind. Reservoirs provide more

water storage for increased drought frequency, but they can also be used to

prevent flooding that would occur from an increased frequency of extremely wet

periods. Market mechanisms can also help for shifts in either direction

because they encourage individuals to.adapt quickly to new information rather

than to wait for the government to formulate its response.

Although policies have been identified that would reduce the vulnerability

of the water supply in the Delaware River Basin to future climate change, it

would be infeasible and unwise to implement these policies until a

comprehensive assessment of the likely impacts and possible solutions has been

undertaken.

The DRBC's long-range comprehensive plan includes numerous measures that

would reduce the vulnerability of the region's water supply to salinity

increases resulting from rising sea level or changes in climate.

Comprehensive assessments of the likely impacts and possible solutions should

be undertaken to provide adequate lead time for implementing these measures if

and when they become necessary.

-66-

Necessary Research

The highest priority is to determine the impact of various climate change

scenarios on river salinity and the streamflow modification required to

maintain acceptable salinity levels in the face of climate change. An

examination of the costs and benefits of various response options should then

be undertaken for each of these scenarios. By examining each option for a

variety of possible sea level and precipitation changes, it may be possible to

identify which solutions are likely to be robust and which are likely to be

clearly inferior. A particularly important question for such an analysis is

what amount of resources could be saved by planning in the 1980s, compared

with delaying the planning until the 1990s or later.

A second research priority that concerns other parts of the nation as well

as the Delaware River Basin is to develop better estimates of future sea level

rise and climate change. In addition to undertaking the research, it is

essential that the results be made available to decision makers and the public

at large. For the private sector to make locational and design decisions that

are consistent with expected water availability, people must become informed

about future conditions.

Improvements in the models for estimating salinity changes will also be

necessary. The model used in this report to estimate river salinity would

benefit from a more in-depth assessment of the impact of sea level rise on

shoaling and the estuary's width and cross-sectional geometry. Increasing

salinity of the Potomac-Raritan-Magothy aquifer system is already a research

priority of the U.S. Geological Survey. Current efforts should be

supplemented with analysis of the implications of rising sea level on that

system.

-67-

Conclusion

The expected rise in sea level and climate changes caused by the

greenhouse effect are likely to have profound impacts on the quality and

availability of water in the Delaware River Basin. Although the greatest

impacts are decades in the future and cannot be predicted precisely,

assessments of how to respond should start now. Public officials responsible

for water quality will have to decide whether to adapt to salinity changes or

attempt-to prevent them. Such assessments may require lengthy public debates,

after which planning, design, and implementation may take decades.

Furthermore, even current trends may necessitate management changes by the

year 2000.

An important impediment to implementing the farsighted policies that will

be necessary is the relatively short planning horizon of 15-20 years generally

used by the DRBC, as well as other agencies. This time horizon has been

appropriate in the past because decisions have involved such phenomena-as

economic growth and technology that did not require.a longer lead time. But

given the longer-term impacts of climate change and sea level rise, the longer

lead time required to prepare for the consequences, and the potential

magnitude of the impacts, a longer time horizon is warranted.

We cannot rule out the possibility that our current understanding

overlooks factors that will substantially reduce the saltwater intrusion

expected from the greenhouse effect. Perhaps the Delaware River Basin will be

one of the regions that experience fewer droughts in the future. Should one

conclude that preparations are not necessary? Can we afford to gamble with

our water supplies on the hope that problems will not emerge in the future?

Such issues are outside the scope of a technical report and must be addressed

by policy makers and the public at large.

-68-

APPENDIX A

TECHNICAL DESCRIPTION OF DELAWARE
ESTUARY SALINITY MODEL

Governing Equations: Knowns and Unknowns

I The model is based on the general, one-dimensional equations of open

channel hydraulics and conservation of salt as coupled through an equation of

state that relates density to salinity and to temperature. The unknowns of

these equations are the surface elevation, the velocity (discharge divided by

area), and the salt concentration. Known quantities are the geometry, the

time-varying tributary inflows and tributary salinities, the temperature, and

the tidal elevations at the ocean boundary throughout the period being

modeled. The time scale of calculation is sub-tidal so as to properly account

for the estuarine dynamic response to the driving force of the ocean tidal

oscillation and to ensure that the mixing can be represented as accurately as

'possible. The use of such a small time-scale is essential, as sub-tidal

variations play an important role in long-term and short-term salinity

concentrations (Najarian et al. 1983; Elliot 1978). The equations on which

this model is based are as follows.

Continuity equation:
b ah aQ
a t a X

Longitudinal momentum equation:
aQ + a (QU) + gA ah + g Adc a P QIQL 0 (a-2)
2
t X X P a X AC R h

-69-

Salt balance equation:
(At s) a (Qs)
t + X 8 X (At E ax (a-3)

Equation of state (relation between density, salinity, and temperature):
P T + OTS (a-4)

In the above equations: b = total surface width;.h = depth from water surface

to horizontal datum; Q cross-sectional discharge; q = lateral inflow per

unit length; U = longitudinal velocity averaged over the cross section of the

core area; A = core area; g.= acceleration of gravity; d,.= distance from

the water surface to the centroid of the cross section; p = mass density of

water; Rh = hydraulic radius of core area; C = Chezy coefficient; At the

total area of the cross section', including that of storage areas; s salinity

averaged over the total cross section;*and E = the longitudinal dispersion

coefficient. All of the aforementioned quantities (except g) are functions of

longitudinal location (x), and time (t). The coefficients aT and OT

depend only on temperature.

The continuity equation (a-1) and the momentum equation (a-2) are

essentially in the form used by Harleman and Lee (1969) to describe the

unsteady tidal hydraulics of estuaries and canals. Thatcher and Harleman

(1972) incorporated an additional term into the momentum equation that

includes the effect of the longitudinal density gradient due to salinity.

This term, gA(d C/P) Wax, couples the two hydraulic equations to the

salt balance equation through the equation of state (a-4).

-70-

The one-dimensional salt balance equation (a-3) can be obtained by

spatially integrating the three-dimensional convective-diffusion equation for

turbulent flow, as demonstrated by Okubo (1964) and Holley and Harlemian (1965).

Longitudinal Dispersion Relationship

The longitudinal dispersion coefficient, E, represents the combined effect

of internal circulation induced-by saline density gradients and mixing due to

boundary shear. The boundary shear effect is assumed to be represented by a

dispersion relation similar to that formulated by Taylor (1954). The density

gradient effect is assumed to be proportional to the absolute value of the

local, longitudinal salinity gradient. This assumption implies that

density-induced circulation is greatest in the region in which the

longitudinal salinity gradient is largest. This relationship, assumed by

Thatcher and Harleman (1972), is

30S
E (x,t) K o + ME T (a-5)
;3 X I
in which K is a stratification parameter that depends on the degree of
vertical stratification in the estuary. Th e value 9 is defined by the
relation so = s/s.2 so being the maximum salinity at the ocean boundary.
The value X0 is defined by the relation X0 = x/L, L being the length of the

estuary from the ocean boundary to the head of tide, and ET is the

Taylor-type dispersion coefficient applicable in the upstream freshwater
portion of the estuary where aso/axo = 0. The coefficient m is used to

account for channel irregularities and other effects not caused by

density-induced circulation. The coefficient ET is defined for free surface

flow by

-71-

5/6
ET 77 UnRh (a-6)
(where n is Manning's n)

The local salinity gradient is expressed in dimensionless form and the

stratification parameter, K, has the dimensions of a dispersion coefficient,

12/t The stratificat Iion parameter, K, is assumed to be independent of

distance and time within a particular:tidal period. However, K may vary from

one tidal period to the next, depending on the degree of stratification. In

order to make the model more predictive, it is necessary to relate this

stratification parameter to the gross estuary properties that determine the

degree of stratification. This is done by a correlation between K. and a

densimetric estuary number as defined by

PtFF2
ED D (a-7)
QfT

in which,Pt is the tidal prism, calculated by integrating the flow at the
ocean boundary during the flood portion of the tidal cycle; Q f is the

freshwater inflow upstream of the salt front; and.T is the duration of the
tidal period. Thed:ensimetric,Froude number,T D' is defined by:

UO
JF D = ;--- -- (a-1)
g @ Po
__ho
P

-72-

in which Ap0represents the density difference between fresh water and
ocean water; p the ocean density, and U0and h0 are the maximum tidal

velocity and the depth, respectively, at the ocean boundary.

By using salinity data from laboratory flumes, estuary models, and field

studies, Thatcher and Harleman (1972)-found a correlation between the

normalized stratification parameter, K/(U0L), and the estuary number, as
shown in Figure A-1. The densimetric estuary numbers, E W extend over two

orders of magnitude ranging from relatively stratified conditions in the

Rotterdam Waterway to fairly well-mixed conditions in the Delaware estuary.

Within this range, the ratio K/(U0L) varies only by a factor of 5. The

longitudinal dispersion coefficient is thus determined by equations (a-5) and

(a-6) as a function of local parameters and global estuary parameters.

Numerical Solution of Governing Equations

Initial conditions and boundary conditions being specified, equations

(a-1) through (a-4) can be solved by numerical techniques for the dependent

variables, elevation, h; discharge, Q; and salinity, s; as functions of

distance, x; and time, t. The finite difference scheme used to solve the

tidal-dynamic equations is similar to that of Harleman and Lee (1969), and is

a staggered explicit scheme wherein surface elevations and discharges are

calculated at alternative locations in the space and time mesh. This scheme

has been shown to be efficient in calculation, but the choice of Ax and At

must be made in a manner that does not violate the approximate stability

criterion,

-73-

FIGURE A-1

CORRELATION OF STRATIFICATION
PARAMETER WITH ESTUARY NUMBER

-2 t I I I I I I
10

OWES 2
ROTTERDAM WES 11 WES 10
POTOMAC
,a3 &DELAWARE 3
+ OWES 1 4,
k HUDSON OE W A R E 72
u L
0 OWES 10 DELAWARE

1641
0.1 10 100

-74-

A X
A t <
U + C (a-9)

where, Ax and At are the longitudinal distance and time increments of

calculation, U is the average cross-sectional velocity, and c
/gh is the wave

speed at the same location as U.

The finite-difference scheme employed for solution of the salt-balance

equation (a-3) is a six-point implicit scheme based on the minimum-error

investigation of Stone and Brian (1963). This scheme has a truncation error.

with terms proportional to (AX)2 and (At)2 and thus is of second

order. The truncation error contains no term proportional to a2S/aX2,

whichmeans it has no numerical dispersion term as found in some first-order

schemes (Bella and Grenney 1970).

Calibration Parameters

Three parameters are treated as calibration coefficients for this model.

The first is the friction parameter used to determine the Chezy coefficient.

This is achieved through a Manning's "n" distribution for the estuary. Using

observed values of high and low tidal elevations throughout the estuary, the

calibration distribution of Manning's "n" was determined. This distribution

(Figure A-2) was then used in all subsequent calculations.

The second and third parameters relate to the longitudinal dispersion

relationship of equation a-5, specifically to the determination of parameters
K and m. The slope of the K/(U 0L) VS. E D relationship (Figure A-1) was

assumed to be that shown, e.g., -(1/4). The intercept of this relationship

was treated as a calibration parameter. Sensitivity analyses and comparison

-75-

FIGURE A-2

CALIBRATION DISTRIBUTION OF MANNING'S "n"

.05

.04

Manning's .03
n

.02

.01

50 100 150 200
01stance from ocean, meters X 10-3

-76-

of a three-month calculated set of salinities with observed values provided

calibration values of

K 0.0015 E_ 1/4
UoL D (a-10)
m = 35

Additional Sources of Information

Further details about the model's development and application can be found

in the two-volume report made to the Delaware River Basin Cdmmission by

Thatcher and Harleman (1978). This report includes data sources for

calibration and verification as well as the results of sensitivity studies.

Further applications by the Commission have been documented in DRBC reports.

Thatcher and Harleman (1981) have presented some of the model results in a

paper published in the Journal of the Environmental Engineering Division of

the American Society of Civil Engineers. This paper was discussed by Fischer,

August 1981, and by Hull, December 1981. The authors' closing response can be

found in the February 1983 issue of that journal.

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APPENDIX B

MODIFICATION OF SALINITY-MODEL GEOMETRY
FOR LARGE RISES OF SEA LEVEL

The salinity model represents estuarine geometry by a schematization to a

double rectangular section as shown in Figure B-1. The flow-carrying

rectangle is referred to as the core area and the adjoining rectangle (if any)

represents the storage area. The schematization in use by the Delaware River

Basin Commission is based on the U.S. Army Corps of Engineers "Table of

Mid-Tide'Volumes." This source of geometry is accurate, but is limited to

near present.conditions of sea level because of the rectangular schematization

in terms of a constant width. As shown in Figure B-2, to schematize a

significant rise in sea level, Az, would require new widths, whereas the

schematization based on the Table of Mid-Tide Volumes can accommodate only new

depths. A procedure for modifying this rectangular schematization for a sea

level rise of approximately seven or eight feet is presented as follows.

Figure B-3 shows the basic relationships leading to a second rectangular

schematization of a typical estuary cross section that would be.filled to the

elevation of inundation. To.create a rectangle whose width is the distance

between contours of inundation, and whose area is the sum of the present core

area plus the additional inundated area, would result in a new depth that

would be very shallow in comparison with reality. This is because the shallow

inundated region can be very wide compared to the present width of the

estuary. To use such a shallow depth would distort the model calculations

because the speed of propagation of the tidal wave is primarily dependent upon

-78-

FIGURE B-1
ESTUARINE GEOMETRY SCHEMATIZATION

,Lx

STORAGE

CORE
AREA

_79-

FIGURE B-2

TYPICAL ESTUARY CROSS SECTION SHOWING INCREASE
IN WIDTH RESULTING FROM SEA LEVEL RISE

AZ
MSL
ELEVATION
OF INUNDATION dcore
-7
w

FIGURE B-3

TYPICAL ESTUARY CROSS SECTION SHOWING
ADDITIONAL CROSS-SECTIONAL AREA (RIGHT-HAND SIDE)
RESULTING FROM SEA LEVEL RISE

AWR
ELEVATION OF INUNDATION

AR
Az,

mmw
--------------- L &z

_80-

the depth. To maintain this most important parameter, depth, a second

approach is presented.

The bottom elevation of the core area (sometimes called "conveyance area")

will be maintained. Outside the core area, the additional cross-sectional

area of inundation, AA, will be calculated in terms of the newly inundated

width, AW, by assuming triangular cross sections adjacent to the rectangular

core area. With reference to Figure B-3, this area is

AA AW ) (A Z (b-1)
AZ, 2

where, AA = the sum of left-hand area AA and right-hand area AA
L R
AW = thesum of left-hand width AW L and right-hand width AW R$

Az = elevation of inundation - mean sea level, and

Az' = elevation of inundation - mean high water.

Note that the change in width, AW, was from mean high water to the

elevation of inundation. These parameters come from topographical data

related to mean high water. A linear slope was assumed, and this slope was

utilized to calculate the additional area for a prescribed sea level rise.

These calculations yielded a new Effective Width, W*

W*= A core + AA AA (b-2)
- = W +
d core + AZ d core + A Z

where, Acore and dcore are the area, and depth of the core.

The storage widths of the original schematization are maintained. As the

measurement of width between contours of inundation was along the main stem of

-81-

the estuary, this assumption is conservative. It is conservative because it

is probable that new, significant storage areas would be opened up adjacent to

the main stem under the sea level rise condition.

-82-

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