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<pubnumber>2300586010</pubnumber>
<title>Greenhouse Effect Sea Level Rise And Salinity In The Delaware Estuary</title>
<pages>97</pages>
<pubyear>1986</pubyear>
<provider>NEPIS</provider>
<access>online</access>
<operator>LAI</operator>
<scandate>20060520</scandate>
<origin>hardcopy</origin>
<type>single page tiff</type>
<keyword>sea level salinity rise delaware estuary river water drbc aquifer basin drought new jersey greenhouse figure tidal intrusion magothy chloride</keyword>
<author>Hull, C. H. J.; Titus, J. G.; Lennon, G. P.; Thatcher, M. L.; Tortoriello, R. C. Hull, C. H. J. ; Titus, James G. Environmental Protection Agency, Washington, DC. ;Delaware River Basin Commission, West Trenton, NJ. ;Lehigh Univ., Bethlehem, PA. ;ICF, Inc., Washington, DC. United States. Environmental Protection Agency. ; Delaware River Basin Commission.</author>
<publisher>United States Environmental Protection Agency ;</publisher>
<subject>Greenhouse effect; Sea level; Salinity; Water quality; Earth atmosphere; Climate; Precipitation(Meteorology); Droughts; Estuaries; Aquifers; Temperature; Atmospheric physics; Delaware River Estuary Region Sea level--Delaware River Estuary ; Salinity--Delaware River Estuary ; Greenhouse effect, Atmospheric--Delaware River Estuary Region (N.Y.-Del. and N.J.) ; Groundwater--New Jersey--Quality ; Delaware River Estuary Region</subject>
<abstract>In the coming decades, increasing concentrations of carbon dioxide and other greenhouse gases will warm the earth's atmosphere. This could mean both an increase in global sea level and changes in precipitation patterns. A joint report by the EPA and the Delaware River Basin Commission examines the implications of a repeat of the 1960's drought combined with both a 21 inch and a 7 foot scenario of sea level rise. Planning should not wait until uncertainties about sea level rise are eliminated.  </abstract>

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

 image: 








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

Biblliography:
   1. Sea Level—Delaware River Estuary (N.Y.-Del.-Penn. and N.J.)
2. Salinity—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. I.  Hull, C.H.J.  II. Titus, James G.
GC89.G75  1986    363.7'394      86-11454
 image: 








       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

                   Richard C. Tortoriello
               Delaware River Basin Commission

                     Gary M. Wisniewski
                      Lehigh University

                      Gary A. Yoshioka
                      ICF Incorporated
                                      Protection Agency
                           5,  L.!bra-,',i  (E'L-_,/;)
                    £wO £. Dearborn t:ruet,  Boom 1670
                    Chicago,  11  60504
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
recommendation for use.  Please  send comments to James G.
Titus (PM-220), Strategic  Studies Staff, U.S. Environmental
Protection Agency,  Washington, B.C.  20460.
 image: 








                                      11
                                  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 "greenhouse 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 resolved 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 today'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 be an
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.
The Environmental Protection Agency has initiated studies on the impacts of
sea level rise and climate change on erosion, flooding, and wetland
protection, but has not previously 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.
 image: 








                                     ill
    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.
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                          TABLE  OF CONTENTS

                                                                         Page

I.     INTRODUCTION 	      1

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
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                                     vi
                          LIST OF FIGURES
Figure 1    Global  Temperatures and Sea Level Rise in the Last

Figure 2
Figure 3

Figure 4
Figure 5
Figure 6
Figure 7
Figure 8

Figure 9
Figure 10

Figure 11
Figure 12

Figure 13

Figure 14

Figure 15

Figure 16
Century 	
Concentrations of Selected Greenhouse Gases Over Time 	
Estimated Global Warming Due to a Doubling of Greenhouse
Gases 	
Global Sea Level Rise Scenarios 	
General Location of the Delaware Basin 	
The Delaware Estuary 	
Change in Yearly Mean Sea Level at Philadelphia 	
Chlorinity Response of Delaware Estuary to Projected
35-Year Rise in Sea Level, 1965-2000 	
Chloride Concentrations vs . River Mile 	
Percent of Tidal Cycles in Which Specified Concentration
is Exceeded at Torresdale for Three Sea Level Scenarios . . .
Saltwater Intrusion in a Coastal Aquifer 	
Modeled Area Showing Outcrop Area and River Reaches of the
Potomac-Raritan-Magothy Aquifer System 	
Potentiometric Surface of the Potomac-Raritan-Magothy
Aquifer System, November -December 1973 	
Potentiometric Surface of the Potomac-Raritan-Magothy
Aquifer System at Year 2000 	
Chloride Concentrations at Wells in the Camden City
Vicinity 	
Injection-Type Seawater Intrusion Barrier 	
5
7

10
13
18
19
29

31
35

37
42

44

46

47

48
62
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                                     Vll
                            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
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                                   -1-
                           I.   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
 image: 








                                   -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 8.2-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 of 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.
 image: 








                                   -3-
          II.   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 (Bonn, 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
 image: 








                                   -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 Philadelphia.)




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 warming of 0.4°C 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 possible acceleration in the rate  of sea level rise stems




from measurements showing that concentrations of carbon dioxide (CCO,




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"
 image: 








                                 -5-
                               FIGURE 1

                 GLOBAL TEMPERATURES AND SEA LEVEL
                      RISE IN THE LAST CENTURY
              0.2 .
   Temperature  o
             -0.2
               10
   Sea Level
      (cm)
               -5
                1880
  i
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
          level curve adapted from:  GORNITZ, V., S. LEBEDEFF, and J. HANSEN,
          1982.  Global Sea Level Trend in the Past Century.
          215:1611-1614.
                       Science
 image: 








                                   -6-
(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,  CCL, 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 33°C




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




effect per se 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 C02 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 CCL  alone.
 image: 








                                                -7-
                                             FIGURE 2

     CONCENTRATION OF SELECTED GREENHOUSE GASES OVER TIME
§ 340
5  «°
e
e
«  32S
O"
«  »»
      1
        Carbon Dioxide
        Concentrations
                        l»70    l»'5     l»«    IMS
                                                      308
                                                    O. 3°2
                                                    Q.
                                                     i 300
                                                      298
2. Nitrous Oxide
   Concentrations  «
                                                                                              300
                                                                                              29«
                                                                                              299
                                                                  1877     1878
                                                                                 1878
                                                                                        1880
  200 -
           I	1	1	1       i
       3.CFC11 Concentrations
                                                    360
                                                   S.32Q
                                                   Q.
                                                   $280
                                                   »-
                                                   z
                                                    240
                                                    200
                                                        -  4. CFC12 Concentrations
                                                                           rfJl'lH
                                                         1976    1977    1978     1979    I960    1981
                             • . '  i ' i ' i ' i ' i ' i  ' i ' i ' r
                             5.  Methane Concentrations
                            3000  2000
                                      1000 700 500   300  20O
                                             Timt (yrj 8 P )
    1. C.D. Keeling, R.B.  Bacastow, and T.P. Whorf, 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
      and Application to Three years of CFCL3 Data." Journal of Geophysical Research, 88(C13):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(C13):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.
 image: 








                                   -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

CO  emissions remain in the atmosphere (Nordhaus and Yohe 1983).   The

Academy estimated a 98 percent probability that CO  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 CO  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 , the NAS analysis implies that the "effective doubling" of all

greenhouse gases has a 98 percent chance of occurring by 2050.l  An

international 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 C0_.  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.
     1 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.
 image: 








                                   -9-
    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 1°C 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.  These indirect 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 1.5° and 4.5°C (3°-8°F).




    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
 image: 








                                  -10-
                                FIGURE 3

             ESTIMATED GLOBAL WARMING DUE  TO A  DOUBLING
              OF GREENHOUSE  GASES:   DIRECT  EFFECTS AND
                        CLIMATIC FEEDBACKS
   O
   o
   >*f
   03
   D
   •**
   CO
   i_
   <D
   a.
   E
   <D
0
                               I
    Direct Effect
      of CO2
      and Other
     Greenhouse
       Gases
 Water
 Vapor
Feedback
Decreased
Reflectivity
  Due to
Retreat of
  Ice and
   Snow
Cloud
Height
I
Cloud
Cover
NOTE:    Although Hansen et al. estimate  a  positive feedback from the clouds,  a
        negative feedback cannot be ruled  out.
Sources:   Adapted  from:  HANSEN7, 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.  Earth  and J.G. Titus.
          Nostrand Reinhold, p. 62.
                                               New York:  Van
 image: 








                                   -11-
that Greenland's glacier meltwater will raise the sea another twelve




centimeters in the next century, while Bindschadler (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 level.




    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 Projecting




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 NAS estimate of 1.5°-4.5°C); 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
 image: 








                                   -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.
    2 Computer printout underlying calculations from Seidel and Keyes  1983.
 image: 








                                       -13-
                                     FIGURE 4

                       GLOBAL SEA  LEVEL  RISE SCENARIOS:
                 LOW, MID-RANGE LOW, MID-RANGE HIGH,  AND HIGH
       Inch**
        100
LEVEL
 RISE
         50-
         25
          0-
 CMS
250-
                200_
                1 SO
                100
                 50-
                                                                           HIGH
                                                            MID-RANGE
                                                               HIQH


                                                            MID-RANGE
                                                               LOW
                                                                 • MAS

                                                            LOW
                                                                         2075
     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, B.C.:  National Academy
              Press (Revelle estimate does not include Antarctica).
 image: 








                                  -14-
                              TABLE 1

           SCENARIOS OF GLOBAL SEA LEVEL RISE:   1980-2100
                              (centimeters)
Current Trends
  2000

2.0-3.0
  2025

4.5-6.8
  2050

7.0-10.5
  2075

9.5-14.3
 2080

10-15
  2100

12.0-18.0
EPA Scenarios
     High             17.1      54.9     116.7      211.5
     Mid-range high   13.2      39.3      78.9      136.8
     Mid-range low     8.8      26.2      52.6       91.2
     Low               4.8      13.0      23.0       38.0
NAS Estimate-
                                         70.0
                                                  345.0
                                                  216.6
                                                  144.4
                                                   56.2
     SCENARIOS OF SEA  LEVEL  RISE AT LEWES,  DELAWARE:  1965-2100
                               (centimeters)
Current Trends
  2000

   13
  2025

   22
  2050

   31
  2075

   41
 2080

  43
  2100

   50
EPA Scenarios
     High             27.7       71.7      140.0      290.8
     Mid-range high   23.7       56.1      102.0      166.1
     Mid-range low    19.3       43.0       76.7      120.5
     Low              15.3       29.8       46.0       67.3
NAS Estimate*
                                         100.6
                                                  380.6
                                                  251.5
                                                  180.0
                                                   91.8
    * Excluding Antarctic contribution.

Sources:  HOFFMAN7, 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 (does not include Antarctica);  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.
 image: 








                                   -15-
               III.   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 (Earth 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
 image: 








                                   -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 (Bonn, 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). 3  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
    3 Louisiana is also experiencing salinity increases from sea level rise
 (Haydl 1984).
 image: 








                                   -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 of 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
 image: 








                  -18-



               FIGURE 5

GENERAL LOCATION OF THE  DELAWARE BASIN
                                         NEW
                                        JERSEY
                                    LAWARE
 90 Miles
 image: 








                          -19-



                        FIGURE 6

                THE DELAWARE ESTUARY
   PENNSYLVANIA
                                    rlv«r mil* 120/
                           Torresdale

                         rlv«r mil* 100
                    Philadelphia
                                                Burlington
             Chester
       Marcus Hook

/   Wilmington
Reedy Island
  DELAWARE

         N
         A
                                                     Trenton
                                                 Atlantic Ocean
                           Cape Henlopen
 image: 








                                   -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).
 image: 








                                   -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/1 and 100 mg/1,  respectively.
 image: 








                                   -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 mg/1.  Moreover, the Philadelphia water intake




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




concentrations less than 30 mg/1.




    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
 image: 








                                   -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 consumptive uses 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 decree--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
 image: 








                     TABLE  2

EXISTING AND SCHEDULED RESERVOIRS  THAT  CAN  CONTROL
       SALINITY IN  THE DELAWARE  ESTUARY a/

Name of Facility or Project
( 1)
Ex i st i ng

Cannonsville Reservoir


Pepacton Reservoir


Lake Wai lenpaupack e_/


Mongaup River System e/


Neve rs ink Reservoir

Francis E. Walter Reservoir f/


Beltzville Reservoir


Nockamixon Reservoir


Blue Marsh Reservoir

Scheduled

Cannonsville Reservoir
Mod if icat ion h/


Prompton Reservoir
Mod i f icat ion J_/


Merri 1 1 Creek
Reserve! r j/

Francis E. Wa 1 ter h/
Reservoir Modification
87
Trexler Reservoir J./


Location of dam, stream
( River-mi le q/)
(2)


W. Br. Delaware River
(330.71 - 18.0)

E. Br. Delaware River
(330.7 - 33.3)
.
Wa I lenpaupack ureek D/
(277.7 - 16.4 - 1.4)

M o n C| 3 u p Rivsr
(261 . 1 - 12.0)

Neve rs ink River
(253.64 - 41 .9)
Lehigh River
( 183.66 - 77.8)

Pohopoco Creek c/
( 183.66 -41.5- 5.2)

Tohickon Creek
( 157.0 - 1 1 .0)

Tulpehocken Creek d/
(92.47 - 76.8 - 6.5)


West Branch,
De 1 awa re R i ve r
(330.7 - 18.0)

West Branch
Lackawaxen River
(277.7 - 27.1 - 4.9)

Merri I I Creek
(177.4 - 7.8 - 3.8)

Lehigh River
(183.7 - 77.8)

Jordan Creek
(183.7 - 36.3 - 4.6)
Lonq-Term Ac
I
Cubic Meters
(3)

6
373 x 10

6
560 x 10

0 /
	 e/

	 0 /
e/

6
I35 x 10

0 f/

6
49 x 10

6
49 x 10

6
18 x 10


6
49 x 10


6
38 x 10


6
57 x 10

6
86 x 10

6
49 x 10

tive Storage (
Bill ions
of Ga I I ons
(4)


98


I 48

...... 0 /
G/

„ /
H/


36

0 f/


13


13


4.8



13



10



15


23


13

Capacity a/
Ac re- Feet
(5)


302,000


454,000

_______ 0 /
	 H/


_______ QI


109,200

0 f /


39,830


39,815


14,620



39,800



30,900



46,000


70,000


40,000

 image: 








                                       TABLE 2 (continued)
                                            FOOTNOTES
    a/ 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.
    b/ Tributary of the Lackawaxen River.
    c/ Tributary of the Lehigh River.
    d/ Tributary of the Schuylkill River.
    e/ Privately owned hydroelectric  power system.   Storage  available  for salinity control  only
after DRBC declares a drougtit emergency.
    £/ Federal  flood-control  reservoir.   Storage  capacity  available for salinity control  only
after DRBC declares a drought emergency.
    g/ 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.
    h/ 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  I95U.
    ±/ Scheduled  for completion in 1995.
    j/ Construction began in 1985.  Planned  completion date  is 1988.
 i
N>
 image: 








                                   -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 1981).  Under its emergency powers, the

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

emergency was in effect for many months.  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

water 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 production was subject to

abnormal stresses related to the high salinities.

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

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

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

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








                                   -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




(133-mile) 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 to take




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 aspect of the problem would be useful for more accurate projections of




the impact of a large rise in sea level.




    The DRBC (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.
 image: 








                                   -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 easy interpolation between locations.
 image: 








                                 -29-
                              FIGURE 7

             CHANGE IN YEARLY MEAN SEA LEVEL FROM 1923
                      TO 1980 AT PHILADELPHIA
    24 r
     18
(0
S
ULJ


I
O

!
12
     6
                  I
                            I
                                      I
                                                I
                                                      I
                                 I
                1930
                     1940
1950

YEAR
1960
1970
1980
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.
 image: 








                                   -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/1.  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
 image: 








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                             INCREASE  IN MAXIMUM 60-DAY CHLORIDE

                                       CONCENTRATION, mg/l
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 image: 








                                   -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.
 image: 








                                   -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/1 to 305 mg/1.  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-centimeter 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-centimeter rise would result in exceedance of that
 image: 








                                  -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                    605                   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
  123.9                13                     13                      55
    &/ DRBC salinity-control  point, where objective is to prevent 30-day
average chloride concentration  from exceeding 180 mg/1.

    b/ Interpolated value.

    Note:  Model inputs are based  on  observed tides during calendar year 1965.
 image: 








                           -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
14
13
12
11
10 I 9
8
7
6
5
4
3
2
                                       (MILE 98--DRBC SALINITY
                                        CONTROL POINT.)
55  60   65   70
80
86  90   95

 RIVER MILE
                                      100  105  110  115  120 125  130
 image: 








                                   -36-
chlorinity about 15 percent of the cycles.   The base case (1965 sea level)




never showed chloride concentrations in excess of 78 mg/1;  the maximum




calculated chlorinity at Torresdale was 62  mg/1.  Similarly,  the calculated




chloride concentration exceeded 250 mg/1 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/1.









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
 image: 








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                                   -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




(Raskin 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 sea 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 bay's 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
 image: 








                                   -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 lower 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 species of birds and fish, are partially protected from




current human interference by federal and state laws.   Although these




ecosystems could migrate landward with rising sea level, such migration would




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




bulkheads,  levees, and other structures; there are currently no environmental




programs to ensure that development and other human activities permit this




migration in the future (Titus, 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.
 image: 








                                   -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
 image: 








                                   -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
 image: 








                                 -42-
                              FIGURE 11

             SALTWATER  INTRUSION  IN A COASTAL AQUIFER
                                                            Ground
                                                            Surface
Note:  H = 40 x h
 image: 








                                   -43-
layer, and has a poor hydraulic connection 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 reaches shown in Figure 12 using a groundwater model developed by Luzier




(1980) for 1973 and 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 rise 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
 image: 








                                       -44-
                                    FIGURE 72
Source;

        «« ^sey: U^CeS^^^
 image: 








                                   -45-
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/1 from background levels (5 to 10 mg/1)

(Camp Dresser and McKee 1982).  Elevated chloride levels persisted more than
    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.
 image: 








                                     -46-
                                  F1GURE 13


       POTENTIOMETRIC SURFACE OF THE POTOMAC-RARITAN-MAGOTHY
                 AQUIFER SYSTEM,  NOVEMBER-DECEMBER 1973
      Contour show* altitude of the
      aquifer's water surface In feet
      (1 foot » .305 meters).
      Datum Is NQVD (sea level) of
      1929. Contour Interval variable.
              •n

       Location and number of
       observation wells.
                                                                     MILES

                                                                     KILOMETERS
                     New jersey

                     Pennsylvania
                RM 110
                Torresdale
                RM 98
                RM 69-
                                                                    ATLANTIC OCEAN
                     Cone of Depression
                     at canter Exceeds
                     -SO Feet NQVD
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.
 image: 








                                       -47-
                                    FIGURE 14


        POTENTIOMETRIC SURFACE OF THE  POTOMAC-RARITAN-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
      (1 foot * .305 meters).
      Datum Is NQVD (sea level) of
      1929. Contour Interval 20 ft.

              •n

      Location and number of
      observation wells.

     --— 250 mg/L     -»

       Chloride concentration near
       bottom of aquifer system
       In milligrams per liter.

     saiBMSVi 2SO mg/L   •••••
     Chloride concentration near
     top of aquifer system In
     milligrams per liter.
                      New Jersey

                      Pennsylvania
                RM 110
                Torresdale
                RM 98
                RM 69-
                                                                MILES

                                                                KILOMETERS
                                                                      ATLANTIC OCEAN
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.
 image: 








                                       -48-
                                    FIGURE 15

    CHLORIDE CONCENTRATIONS  AT WELLS IN THE CAMDEN CITY VICINITY
        LEGEND

Oalalr 3  	Wall Nama
      R.M. 104.6	Rlvar Miles from
                  Mouth of
                  Dalawara Bay

          t-%1     Indicates tha flva
          b*ul     yaara of drought
                  (1961-1966)
k
hlorlde Concentration (mg/llter)
-» r» w 4
o o o o <
| 1
•Camden C
•R.M. 97.5







•g=












•—— <




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                                                   ^Camden City 7, 11

                                                   y^X
                                                  /(     ^-^•^-S
                                                   I j Dalawara Rlvar

                                                        LOCATION MAP
                                                           -Dalalr 2
                                                           -R.M.  104.6
     0   '30 '40  '60  '60  '70 1980 '30  '40   '60  '60  '70 1980 '30  '40 '80  '60  '70  1980
                                40
                                  -Puchack 2
                                  -R.M. 104.7
                                30
                                20
                                10
                                                         10
         30   '40  '60  '60  '70 1980 '30  '40  '60  '60  '70 1980 '30 '40  '60  '60  '70  1980
hlorlde Concentration (mg/llter)
10 u> t
o o o o e


* Puchack 4
- R.M. 104.











—••^M












— -"























vXv







•'•II-'
•il-l:
l^^*"H_
: '-'^^^
.•'.•'.:•



















                                40r
                                  -Morris I
                                  -R.M. 106. 1
                                30
                                20
                                10
        '30  '40  '60  '60  '70 1980 '30  '40  '60 '60  '70 1980  '30 '40 '50  '60  '70  1980
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.
 image: 








                                                   TABLE  4

                 RECHARGE OF DELAWARE  RIVER WATER  INTO  POTOMAC-RARITAN-MAGOTHY AQUIFER  SYSTEM
                                   AND MAXIMUM  SALINITY LEVELS  OF RECHARGE
River Reach
1
2
3
4
5
6
1
8
9
10
1 1
12
13
14
Length of
Reach
(Mi les)
8.0
6.2
5.0
2.5
2.7
2.9
2.8
2.8
2.8
4.5
2.5
6.5
5.4
5. U
River Mi le
123 - 131
117 - 123
1 12 - 1 17
109.5 - 1 12
106.5 - 109.5
104 - 106.5
101 - I0t
98 - 101
95.5 - 98
91 - 95.5
88.5 - 91
82 - 88.5
76.5 - 82
71 - 76.5
Est ima ted
Reach Recharge
to Aquifer
System
(cfs)**

2. 1
6.6
1 .3
4.0
23.0
19. 1
9.4
4.9
13. 1
1 1 .9
1 1 .8
1.4
5. 1
Percent of
Total River
Recharge to
Aquifer System

2. 1
6. 1
1 .3
3.5
20.0
16.6
8.2
4.2
\ 1 .14
10.4
10.5
1 .3
4.6
Maximum 30-Day Average
Chloride Concentration img/l)
No Rise*
-
-
-
-
50
50
100
100
150
250
350
600
1 100
2250
73-cm Rise*



50
50
100
200
250
350
450
700
1050
1650
2950
250-cm Rise*
100
200
350
500
650
900
1200
1450
1700
2000
2500
3050
3950
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).
 image: 








                                   -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/1, 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 95.5) with chloride concentrations




in the estuary in excess of 50 mg/1 extending up into reach 5 (river mile
 image: 








                                   -51-
106.5 to 109.5).   Although the 250-rag/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/1 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/1 (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/1 within a very short distance of the




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




be below 250 mg/1.  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/1.  Sodium concentrations




greater than 50 mg/1 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
 image: 








                                                 TABLE  5

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





R i ve r
Reach
1
2
3
4
5
6
7
8
	
9
10
1 1
12
13
14


Est imated
( 1978)
Ground-Water
Velocity Range
(meters/year)
0-90
0-90
90-150
30-60
90-180
270-580
460-550
240-370
120-150
180-400
300-370
90-150
0-30
60-90
Time that 30-Day Average
Chloride Concentration
Exceeded 78 mg/ 1 and
250 mg/l (days)

78 mq/l

BASE


-
-
-
60
1 10
140
160
170
180
190
200
230

250 mq/

73 cm BASE



30
100
130
150
160
170
180
190
200
210
250







100
120
140
160
180

73 cm
,






100
120
140
160
180
200
220

250 cm


120
130
140
150
160
170
180
190
200
400
400
400
Maximum Aquifer Penetration
Distance for Duration of
Contact Time
meters)

78 mq/l

BASE
-
-
-
-
-
95
165
140
65
185
180
80
15
55

73 cm



5
50
205
225
160
70
195
190
80
15
60
250 mq/

BASE
-
-
-
-
-
-
-
-
-
1 10
120
60
15
45

73 cm
-
-
-
-
-
-
-
100
50
150
160
75
15
55


250 cm


50
20
70
240
240
170
75
205
200
165
35
too
                                                                                                                     Ui
                                                                                                                     N3
                                                                                                                      I
Note:    A chloride concentration of 78  mg/l  corresponds to a  sodium concentration of 50 mg/l, the New
        Jersey drinking water standard.
 image: 








                                   -53-
from the river with thirty-day chloride concentrations in excess of 250 mg/1.




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




dispersing to insignificant background levels.




    In summary, a recurrence of the 1960s1 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 from alternate




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
 image: 








                                   -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.
 image: 








                                   -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 such an 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
 image: 








                                             TABLE  6

                       UNSCHEDULED RESERVOIRS IN  DRBC'S  PLAN  THAT  COULD  BE
                  USED TO OFFSET  SALINITY  INCREASES IN THE  DELAWARE  ESTUARY  a/
Name of Project
( 1)
Tocks Island Reservoir
Aquash ico 1 a Reserve I r
Maiden Creek Reservoir
Evansburg Reservoir
Newark Reservoir
Icedale Reservoir
Tota 1
Location b/
(2)
Delaware River
(217.2)
Aquashicola Creek
(183.66 - 36.3 - 4.6)
Ma iden Creek
(92.5 - 86.7 - 9.6)
Skippack Creek
(92.47 - 32.3 - 3.0 -
1.0)
White Clay Creek
(70.7 - 10.0 - 12.0)
W. Branch Brandywine Cr.
(70.73 - 1.5 - 20.0 -
25.6)

Increment of Long-Term Storage Capacity
Cubic Meters
(mill ions )
(3)
525
30
91
29
37
18
730
Bill ions
of Ga I Ions
(4)
139
8
24
8
10
5
194
Ac re -Feet
( thousands)
(5)
425.6
24
74
23.5
30
14.6
592
    a/ These multipurpose projects  are  currently  (1985)  in  the  DRBC'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
deauthorizat ion of some of these  projects.   They  are generally  in reserve  status—for development
after year 2000,  if needed.

    b/ 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.
                                                                                                                i
                                                                                                               Ul
                                                                                                               o\
 image: 








                                   -57-
level rise and increased water consumption well inuo 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.
 image: 








                                   -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 depletive uses.   In 1983, the DRBC (1983b,




1983c) adopted regulations that automatically cut  back consumption within the




basin and diversions out of the basin during droughts.




    Decreasing depletive uses of water has been one of the DRBC's 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 New York City and other areas




may impose increasing hardships on these areas as  alternate supplies 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:  Surfacewater  Users




    If measures are not undertaken to prevent a salinity increase, 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




as a temporary measure during the 1960s1 drought,  when the Torresdale 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
 image: 








                                   -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.
 image: 








                                   -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.
 image: 








                                   -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 reduce 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




"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
 image: 








                                  -62-
                               FIGURE  16

             INJECTION-TYPE SEAWATER  INTRUSION  BARRIER
  wEW MEAN
  SEA LEVEL
PIEZOMETRIC SURFACE

 INJECTION BARRIER
      WELL
                                                       IMPERVIOUS BED
                                               WATER SUPPLY
                                                  WELL
                                                           AQUIFER
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.
 image: 








                                   -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 it 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 on 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.
 image: 








                                   -64-
                           VI.  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 regions, 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,., 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
 image: 








                                   -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.
 image: 








                                   -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.
 image: 








                                   -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.
 image: 








                                  -68-
                             APPENDIX A

                 TECHNICAL DESCRIPTION OF DELAWARE
                      ESTUARY SALINITY MODEL
Governing Equations:  Knowns and Unknowns

    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:

                            9h    3Q

                          bi7 + 7T-q = 0


Longitudinal momentum equation:


       3Q    3(QU)        3h      Adc  3        Q|Q|               (a-2)
       	 + —	  + gA	 + g	—^  + g	1—  = 0
        3t       3x         3x        p  3x      AC2Rh
 image: 








                                   -69-
Salt balance equation:




                  a(Ats)    a(QS)       a             as

                 	^-   + 	  =  	   (A* E	)              (a-3)

                    3t         3x       3x       l   9x



Equation of state (relation between density, salinity,  and temperature):




                                 P  = <*T  +  PTs                          O-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
                                                        c


the water surface to the centroid of the cross section; p = mass density of



water; R,  = hydraulic radius of core area; C = Chezy coefficient;  A  =  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 ay and &j



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 /p) 3p/3x, couples the  two hydraulic equations  to the
               C


salt balance equation through the equation of state (a-4).
 image: 








                                   -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 Harleman (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
E(x,t)   =  K
               1 9x
                                                  mET                    (a_5)
in which K is a stratification parameter that depends on the degree of
                                                   o
vertical stratification in the estuary.  The value s is defined by the


relation s = s/so , s0 being the maximum salinity at the ocean boundary.


The value x is defined by the relation x = x/L, L being the length of the


estuary from the ocean boundary to the head of tide, and E-j- is the


Taylor-type dispersion coefficient applicable in the upstream freshwater


portion of the estuary where 3s/3x = 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
 image: 








                                   -71-
                              ET=  77UnRh5/6                         (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,

!2/t.  The stratification 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
                                         P  FF
                                         M^D
                                                                          (a-7)
in which P  is the tidal prism, calculated by integrating the flow at the

ocean boundary during the flood portion of the tidal cycle; Qf is the

freshwater inflow upstream of the salt front; and T is the duration of the

tidal period.   The densimetric Froude number, fF-, is defined by
                              FD=     	—                         (a-8)
 image: 








                                   -72-
in which Ap  represents the density difference between fresh water and




ocean water; p the ocean density,  and U  and h  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/(U L), and the estuary number, as




shown in Figure A-l.   The densimetric estuary numbers, tEn, 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/(U L) 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,
 image: 








                              -73-
                          FIGURE A-l

                CORRELATION OF  STRATIFICATION
                PARAMETER WITH  ESTUARY NUMBER
  -2
 10  -
                                                  "i	'—I—i  i i i u
103
u L
 o
             ROTTERDAM
                                       HUDSON
                                O WES 10
                                   A DELAWARE 3


                                   l***"-^4_
                                 DELAWARE 2*

                                        DELAWARE 1
id4
J	1 I  I I I I	I    I  I  I  I I I I I
    0.1
                                            10
                                                                100
 image: 








                                   -74-
                                 At <  .
                                        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 32s/3x2,

which means 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 L) vs. E  relationship  (Figure A-l) 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
 image: 








                              -75-
                          FIGURE A-2

            CALIBRATION DISTRIBUTION  OF MANNING'S "nf
Manning's
    n
           .05
           .04
.03
           .02
            .01
                         50          100        150         200

                        Distance from ocean, meters X  10~3
 image: 








                                   -76-
of a three-month calculated set of salinities  with  observed  values  provided




calibration values of
                           	  =  0.0015
                           U0L
                                  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 Commission 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.
 image: 








                                   -77-
                              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-l.  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
 image: 








              -78-








          FIGURE B-1




ESTUARINE GEOMETRY SCHEMATIZATION
 image: 








                          -79-
                     FIGURE B-2

      TYPICAL ESTUARY CROSS SECTION SHOWING INCREASE
         IN WIDTH  RESULTING FROM SEA LEVEL RISE
ELEVATION
OF INUNDATION
                              W
                                                              core
                     FIGURE B-3

         TYPICAL ESTUARY CROSS SECTION SHOWING
    ADDITIONAL CROSS-SECTIONAL AREA (RIGHT-HAND SIDE)
             RESULTING  FROM SEA LEVEL RISE
ELEVATION OF INUNDATIONy
                                   Awfi
 image: 








                                   -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
                           A A   I AW
                           AA =   	
where, AA  = the sum of left-hand area AAy  and right-hand area AAR,



       AW  = the sum of left-hand width AW,  and right-hand width AW-,
                                          ii                       K


       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*=     Acore  +  *A    =  w + _ AA _        (b.2)


                  dcore  +  Az                dcore  +  Az
where, A     and d     are the area and depth of the core.
        core      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
 image: 








                                   -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.
 image: 








                                   -82-
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                                   -86-
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