Greenhouse Effect, Sea Level Rise, and Salinity in the Delaware Estuary
A Joint Assessment by EPA and the Delaware River Basin Commission of
what must be done to protect water supplies and wildlife
TABLE OF CONTENTS
LIBRARY OF CONGRESS CATALOGING INFORMATION
THE BASIS FOR EXPECTING A RISE IN SEA LEVEL (omitted--obsolete)
SALINITY IN THE DELAWARE ESTUARY
--The Delaware Estuary
--Saltwater Intrusion and the DRBC
--Estimating Impacts of Sea Level Rise on Salinity
IMPACT OF INCREASED RIVER SALINITY ON NEW JERSEY AQUIFERS
RESPONSES TO SALINITY INCREASES
TABLE OF S INCLUDED ON THIS WEBSITE
Figure 9--Change in Estuary Salinity During Drought As
Sea Level Rises
Figure 12--Areas where Aquifer is Connected to the River
Figure 14--The Estuary Recharges Aquifer because Aquifer
is Pumped Well Below Sea Level
Figure 15--The Lasting Impact of the 1960s Drought on
Figure 16--Illustration of
Groundwater Salt Intrusion Barrier
The standard way of citing this
article is: Hull, C.H.J. and J.G.Titus (eds). 1986. Greenhouse Effect, Sea Level Rise, and Salinity in the
Delaware Estuary.. Washington, D.C.: U.S. Environmental Protection Agency
and Delaware River Basin Commission.
This web page provides the final
text as approved by EPA and DRBC for publication, with the following exceptions:
First, the section on global warming and sea level rise is obsolete and hence is
omitted. Second, the appendices of the report are also omitted. In addition,
some of the figures and tables are omitted. Because I did the rewriting and
typing of the original report, I still had alot of the files. The appendices
were done by Lou Thatcher and Tony Creamer; some of the tables were done by Jack
Hull; and I have not seen any of the three in ages. Note that Jack Hull drafted
the section on the Delaware Estuary, Gerry Lennon drafted the section on the
Aquifer, and I drafted the Summary, Introduction, Responses, and Next Steps
Sections. Lou Thatcher and Jack Tortorielly did the model runs estimating
salinity changes, while Tony Creamer obtained the topographic sheets and made
the calculations of how the width of the estuary would change as sea level
rises, which had to be fed into the model. I can not remember what the other
We have omitted some of the
figures where it just did not seem worth the storage. If you need those missing
items, you can find the report in any government depository library that takes
EPA publications, and maybe NTIS. If you plan to quote this verbatim, it would
be a good idea to look at the original also, because I can not be absolutely
sure that a few cosmetic changes were not made after I handed over my text files
to the contractor who did the page layout. Any text in red signifies changes
that I would make if the article were submitted in 1997 (e.g., downard revisions
on how rapidly sea level will rise).
The following information is from the inside cover of
the report. The front cover is a picture of the Delaware Memorial Bridge.
Congress Cataloging-in-Publication Data
effect, sea level rise, and salinity in the Delaware Estuary
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
(NY-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 RR_11J
Back to Cost of Holding Back the Sea
See also More Sea Level Rise Reports
C . H .J . Hull
Delaware River Basin Commission
James G. Titus
Gerard P. Lennon
Cooper Union College
Richard C. Tortoriello
Delaware River Basin Commission
Gary M. Wisniewski
Gary A. Yoshioka
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, D.C. 20460.
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. Unfortunately, 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 ll feet. I left the preceeding statement in for color. That range
would now be more applicable to the year 2200. See chapter 8 in The
Probability of Sea Level Rise
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 implications 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. This is the
last time I am going to remind you that those scenarios are obsolete. For a
discussion of local sea level scenarios, go to chapter 9 in "The
Probability of Sea Level Rise" which suggests that the low scenario has
about a 20% chance by 2100 and over a 50% chance by 2150. The high scneario has
a 10 percent chance by 2200. 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.
1. Sea level rise could
substantially increase the salinity of the Delaware estuary in the next century.
If no countermeasures are taken, a repeat of the 1960s' drought with a 2.4-foot
rise would send the salt front upstream to river-mile 100, compared with mile 93
for current sea level. Moreover, the chloride concentration at mile 98, the DRBC
salinity control point, would increase from 136 parts per million (ppm) to 305
ppm. An 8.2-foot rise would send the salt front upstream to mile 117 and would
increase salinity to 1560 ppm at the salinity control point.
2. Accelerated sea level rise
could cause excessive salinity concentrations 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.
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.
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.
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
at the time, that study
did not consider the implications of an acceleration of the current rate of sea
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
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
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
THE BASIS FOR EXPECTING A RISE IN SEA LEVEL(omitted)
SALINITY IN THE DELAWARE ESTUARY
A rise in sea level of even thirty centimeters (one foot)
would have major impacts on coastal erosion, flooding, and saltwater intrusion.
Until this effort, no one had estimated the saltwater intrusion expected to
result from an accelerating rise in sea level due to the greenhouse effect.
However, previous EPA studies have examined the impacts of erosion and flooding,
as well as possible responses (Barth and Titus 1984). Ongoing EPA studies are
investigating the potential impacts on coastal sewerage systems, wetlands and
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.
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
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.
rise in sea level generally results in increased salinity, assuming other
factors remain constant. In this respect the impact of sea level rise is similar
to the impact of reduced flows during a drought. The former increases the
saltwater force, whereas the latter decreases the freshwater force. Salinity
levels generally respond to changes in tide and river flow within a matter of
minutes or hours.
In the past
eighteen thousand years, sea level has risen one hundred meters (three hundred
feet), converting freshwater rivers into brackish estuaries (Donn, Farrand, and
Ewing 1962). Chesapeake Bay and the Delaware estuary are examples of such
drowned river valleys. The Delaware estuary is probably the first estuary for
which the salinity effects of future sea level rise have been studied (Hull and
Tortoriello 1979) 1 . 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
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 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 watershed
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
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
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 lOO mgd),
respectively (Supreme Court 1954). Basin-wide consumption is projected to rise
to 52.2 cubic meters per second (l,l91 mgd) by the year 2000 (DRBC 1981).
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/l). 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
DRBC seeks to attain
its salinity goals by keeping the chloride and sodium concentrations at river
mile 98 below 180 mg/l and lOO mg/l, respectivelv. 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/l. 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 saltiness 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 slreamflow.
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 these other reservoirs
were designed for local community water supplies, they sometimes augment
freshwater flows into the estuary, incidentally, during critical low-flow
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 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), 2 relates freshwater inflows, tides, and ocean
salinities to chloride distribution in the estuary. (Technical details of the model are presented in Appendix A of the
published report, omitted from this web page.
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.
(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
Estimating Impacts of Sea Level Rise on
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 location.
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.
maximum sixty-day average chlorinities for 1965 and 2000 were compared to show
the effect of the thirty-five-year sea level rise. Figure 8 shows the increase
in the maximum sixty-day average chlorinities as a function of river miles. The
chlorinity increase due to the simulated sea level rise was most pronounced at
river mile 60, where the sixty-day average increased by about 210 mg/l. The
average position of the salt front moved two to four kilometers (one to two
miles) upstream. The salinity impact of the projected sea level change decreased
with distance seaward and landward of river mile 60, with no measurable 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 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 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 estuary. For sea level increases of
60 centimeters (2 feet) and more, not only would the depth of the estuary
increase, but the width would also increase. The techniques used in these
model-geometry modifications are described in Appendix B.
Table 3 and Figure 9 compare the maximum
thirty-day average chloride levels at different river miles for a recurrence of
the 1964-65 drought at the 1965 sea level and rises of 73 and 250 centimeters
over that level. We estimated that a 73-centimeter rise would increase the
maximum thirty-day chlorinity at river mile 98 from approximately 135 mg/l to
305 mg/l. The thirty-day average location of the salt front would advance to
mile 100, compared with mile 93 for such a drought occurring in 1965. Although
the salt front would be well below Philadelphia's Torresdale intake on average,
the 78-mg/1 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/1 chloride value to be exceeded during more than 50 percent of the
cycles, while a 73-centimeter rise would result in exceedance of the chlorinity
about 15 percent of the cycles. The base case (1965 sea level) never showed
chloride concentrations in excess of 78 mg/l; the maximum calculated chlorinity
at Torresdale was 62 mg/l. Similarly, the calculated chloride concentration
exceeded 250 mg/l about 42 percent of the tidal cycles for the 250-centimeter
rise, but did not reach the 250-mg/1 level for the 73-centimeter rise, which
resulted in a maximum chlorinity of about 129 mg/l.
A rise in sea level of several feet would substantially
exacerbate today' 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
Oysters . In the upper, narrow reach of Delaware Bay
are found natural
which are managed by the oyster industry with supervision by the State of New
Jersey to provide seed oysters for planting in leased growing areas in seaward,
more saline areas of the bay. Because of their location in less saline water,
the natural seed-oyster beds provide havens for the young oysters from some of
their natural enemies that require higher salinities for survival. Oyster
biologists believe that increased salinities over the natural beds at critical
periods in the annual life cycle of oyster predators and competitors would
afford an advantage to these oyster enemies (Corps of Engineers 1982). Although
the highest salinities generally occur during summer droughts, experts have
expressed concern that the increases in springtime bay salinities resulting from
increased depletive use of fresh water, or from storage of springtime runoff in
reservoirs, would harm the natural beds and deprive the bay's oyster industry of
its seed-oyster source (Haskin 1954; Gunter 1974).
Hull and Tortoriello (1979) presented evidence that for the
historical period of decline in oyster production in Delaware Bay, the observed
gradual rise in 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.
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 increase 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
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.
IMPACT OF INCREASED RIVER SALINITY
ON NEW JERSEY AQUIFERS
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
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 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 to 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 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 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 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). 3
During the 1961-66 drought, the salt front moved up the
Delaware estuary and allowed salt water to recharge the Potomac-Raritan-Magothy
aquifer system. Increased salinity was observed in many wells adjacent to the
Delaware River (Figure 15). In Camden County wells, for example
chloride concentrations increased 10 to 70 mg/l from background levels (5 to 10
(Camp Dresser and McKee 1982). Elevated chloride
levels persisted more than ten years; once introduced into the aquifer salinity
contamination tends to remain (Camp Dresser and McKee 1982).
From such observed data, aquifer
salinity distributions can be generated. Simulating the salinity distribution in
the aquifer for the sea level scenarios requires a predictive numerical model.
However, a first-order approximation can be deduced by considering (1) the
estuary's salinity distributions for selected sea level rise scenarios (see . Figure 9);
and (2) the distribution of inflow into the aquifer (see Table 4).
Table 5 shows the penetration
distances during the time that chloride concentrations exceed 250 and 78 mg/l,
respectively, for the fifteen-month drought simulation. Although we simulated
only fifteen months of the five-year 1961-1966 drought, these fifteen months
were the worst part of that drought, with the lowest river flows and the highest
estuarine salinities. Therefore, the computed chloride concentrations of
recharge water would be no greater if we simulated the entire five-year drought.
The estimates in Table 5 are based on groundwater velocities near the advancing
edge of the saltwater front, estimated for each river reach based on 1978 water
levels from Walker (1983) and aquifer properties affecting water velocities from
Luzier (1980). The inflow rate obtained by Vowinkel and Foster (1981) was
divided by the available cross-sectional area and porosity, providing an
alternative method of computing groundwater velocities The velocity ranges were
extended to include both these estimates.
For the baseline scenario (recurrence of the 1964-65
drought flows with no sea level rise), the thirty-day average 250-mg/1 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/l extending up into reach 5
(river mile 106.5 to 109.5). Although the 250-mg/l line would not penetrate to
reach 8, penetration distances of over ninety meters (three hundred feet) are
predicted for the 78-mg/l line in reaches 6, 7, and 8 (Table 5) If in subsequent
years the salinity in the recharge water decreased again to normal levels, the
slug of high-salinity water would continue to move toward the area of lower
water levels, that is, toward the center of the major cone of depression in
Camden County (see 1973 water levels in Figure 13). As this slug slowly moves,
however, the chloride concentration would decrease because of diffusion,
dilution by lower salinity recharge water (including precipitation), and
withdrawal from the aquifer. Nevertheless, levels in excess of the New Jersey
drinking water standard (50 mg/l sodium, corresponding to 78 mg/l chloride)
could occur for several years in areas within a mile or two of the river.
For the 73-centimeter sea level
rise scenario, water with chloride concentrations slightly in excess of 250 mg/l
(corresponding to a sodium concentration of 145 mg/l) would begin to recharge
the aquifer system in the vicinity of reach 8 (river mile 98 to lOl). The
dilution and diffusion of the salt water as it moves through the aquifer would
undoubtedly reduce the chloride concentration below 250 mg/l within a very short
distance of the Delaware River. Above reach 8, the chloride concentrations are
predicted to be below 250 mg/l. Thus, like the baseline case, no significant
region of the aquifer adjacent to the Delaware River above river mile 98 should
experience sustained chloride concentrations above 250 mg/l. Sodium
concentrations greater than 50 mg/l would be present in the recharge water as
far as reach 4 and would penetrate several hundred feet in reaches 6, 7, and
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 from the river with thirty-day
chloride concentrations in excess of 250 mg/l. The slug of high-salinity water
would move significant distances before dispersing to insignificant background
In summary, a
recurrence of the 1960s' drought with a higher sea level would cause increased
sodium and chloride levels in parts of the Potomac-Raritan-Magothy aquifer.
These increased levels would persist for long periods--probably several
decades--as the high-chloride water dispersed and propagated toward pumping
wells. For many years, some wells would experience elevated sodium levels that
could make the water unfit for many purposes, including human consumption, in
which case, water from alternate sources could be required.
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
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.
RESPONSES TO SALINITY
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.
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
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.
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 level rise and increased water
consumption well into 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.
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
uses of water has been one of the DRBC's tools for combating 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 1960s' 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
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.
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, 4 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 other liquids, including hazardous waste
materials. It is also possible to inject materials that form a zone of low
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
Modified pumping patterns. For aquifers where moderate
occurs and the effecl 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 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
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 C02, 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
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 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, waler 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.
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.
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 l990s or later.
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
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.
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.
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.
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1983. Global Sea Level: Estimating and Explaining Apparent Changes. In Coastal
Zone 83, edited by O.T. Magoon, 2777-2795. New York: American Society of Civil
BARTH, M.C., and
J.G. TITUS, eds., 1984. Greenhouse Effect and Sea Level Rise: A challenge for
This Generation. New York: Van Nostrand Reinhold.
BAUERSFELD, W.R., E.W. MOSHINSKY, E.A. PUSTAY, and F.L.
SCHAEFER, 1985. Water Resources Data -- New Jersey -- Water Year 1984. Volume 2.
Delaware River Basin and Tributaries to Delaware Bay. U.S. Geological Survey
Water-Data Report NJ-84-2, Trenton, New Jersey, 184 pp.
BELLA, D.A., and W.J. GRENNEY,
1970. Finite-Difference Convection Errors, Journal of the Sanitary Engineering
Division, ASCE, Vol. 96, No. SA6.
BENTLEY, L., 1983. The West Antarctic Ice Sheet: Diagnosis
and Prognosis. In Proceedings: Carbon Dioxide Research Conference: Carbon
Dioxide, Science, and Consensus, DOE Conference 820970. Washington, D.C.:
Department of enemy.
BINDSCHADLER, R., 1985. Contribution of the Greenland Ice
Cap to Changing Sea Level. In M.F. Meier, 1985. Glaciers Ice Sheets and Sea
Level. Washington, D.C.: National Academy Press.
BRAUN, P., and A.A. FLORIN, 1963 Drinking Water and
Congestive Heart Failure--Sodium Concentration of Selected New Jersey Water
Supplies. Journal Medical Society of New Jersey 60:504-509.
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.
CHARNEY, J., Chairman, Climate
Research Board, 1979. Carbon Dioxide and Climate: A Scientific Assessment.
Washington, D.C.: NAS Press.
CHEN, R.S., E. BOULDING and S.H. SCHNEIDER (eds.), 1983.
Social Science Research and Climate Change: An Interdisciplinary Appraisal.
Boston: D. Reidel Publishers.
CORPS OF ENGINEERS, 1982. Delaware Estuary Salinity
Intrusion Study. Philadelphia District, Philadelphia: Pennsylvania: U.S. Army
Corps of Engineers, 71 pp., appendices.
DELAWARE RIVER BASIN COMMISSION (DRBC), 1981. The Delaware
River Basin Comprehensive (Level B) Study--Final Report and Environmental Impact
Statement. West Trenton, New Jersey, 140 pp.
DELAWARE RIVER BASIN COMMISSION (DRBC), 1983a. Resolution
No. 83-12, A RESOLUTION to amend the Comprehensive Plan by establishing the
policy that the drought of record will be used as the basis for determination
and planning of dependable water supply. Adopted June 29, 1983, West Trenton,
New Jersey, 2 pp.
RIVER BASIN COMMISSION (DRBC), 1983b. Resolution 83-13, A RESOLUTION to amend
the Comprehensive Plan relating to criteria for defining drought warning and
drought conditions, and to a schedule of phased reductions in diversions,
releases and flow objectives during such periods. Adopted lane 29, 1983, West
Trenton, New Jersey, 9 pp.
DELAWARE RIVER BASIN COMMISSION (DRBC), 1983c. Resolution
83-14, A RESOLUTION to amend the Comprehensive Plan by the addition of policy on
the conservation of water. Adopted June 29, 1983, West Trenton, New Jersey, 2
ELLIOT, A.J., 1978.
Observations of the Meteorologically Induced Circulation in the Potomac Estuary,
Estuaries and Coastal Marine Science, 6:285-299.
GORNITZ, V., S. LEBEDEFF, and J. HANSEN, 1982. Global Sea
Level Trend in the Past Century. Science 215:1611-1614.
G., 1974. An Example of Oyster Production Decline with a Change in the Salinity
Characteristics of an Estuary--Delaware Bay--1800-1973 (Abstract). Proceedings
National Shellfish Association. 65:3.
HANSEN, J.E., A. LACIS, D. RIND, and G. RUSSELL, 1984.
Climate Sensitivity to Increasing Greenhouse Gases. In Greenhouse Effect and Sea
Level Rise: A Challenge for This Generation, edited by M.C. Barth and J.G.
Titus. sow York Van Nostrand Reinhold, p. 62.
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.
HARBAUGH, A.W., J.E. LUZIER, and F. STELLERINE, 1980
Computer-Model Analysis of the Use of Delaware River Water to Supplement Water
from the Potomac-Raritan-Magothy Aquifer System in Southern New Jersey,
Delaware. U.S. Geological Survey Water Resources investigation, 80-31.
HARLEMAN, D.R.F., and C.H. LEE,
1969. The Computation of Tides and Currents in Estuaries and Canals, Technical
Bulletin No. 16, Committee on Tidal Hydraulics, United States Army Corps of
HASKIN, H.H., 1954.
Testimony in Delaware River Case, New Jersey v. New York et al. Supreme Court of
the United States, No. 5, Original, New Jersey Testimony, Vol. III, pp.
HAYDL, N.C., 1984.
Louisiana Coastal Area, Louisiana: Water Supply, Initial Evaluation Study. New
Orleans: U.S. Army Corps of Engineers.
HAYS, J.P., and W.C. PITMAN III, 1973. Lithospheric Plate
Motion, Sea Level Changes, and Climatic and Ecological Consequences. Nature
HICKS, S.D., 1978.
An Average Geopotential Sea Level Series for the United States. Journal of
Geophysical Research 83(C3):1377-1379.
HICKS, S.D., H.A. DeBAUGH, and L.E. HICKMAN, 1983. Sea
Level Variation for the United States 1855-1980. Rockville MD: National Ocean
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
HOGARTY, R.A., 1970. The Delaware
River Drought Emergency, Inter-University Case Program #107. New York:
Bobbs-Merrill Company, Inc.
HOLLEY, E.R., JR., and D.R.F. HARLEMAN, 1965. Dispersion of
Pollutants in Estuary Type Flows, Report No. 74, Hydrodynamics Laboratory,
Department of Civil Engineering, Massachusetts Institute of Technology,
HUGHES, T., 1983. The Stability of the West Antarctic Ice
Sheet: What Has Happened and What Will Happen. In Proceedings: Carbon Dioxide
Research Conference: Carbon Dioxide, Science, and Consensus, DOE Conference
820970. Washington, D.C.: Department of Energy.
HULL, C.H.J., and R.C. TORTORIELLO, 1979. Sea-Level Trend
and Salinity in the Delaware Estuary. Staff Report. West Trenton, New Jersey:
Delaware River Basin Commission
KEELING, C.D., R.B. BACASTOW, and T.P. WHORF, 1982.
Measurements of the Concentration of Carbon Dioxide at Mauna Loa, Hawaii. Carbon
Dioxide Review 1982, edited by W. Clark. New York: Oxford University Press,
377-382. Unpublished data from NOAA after 1981.
KONIKOW, L.F., and J.D. BREDEHOEFT, 1978. Computer Model of
Two-Dimensional Solute Transport and Dispersion in Ground Water. Techniques of
Water Resources Investigations of the U.S. Geological Survey. Ch. C2.
KORCH, G., R. RAMAPRASAD, and L.
ZISKIN, 1984. Analysis of Sodium Content of Community Water Supplies. Journal
Medical Society of New Jersey 80:12:1007-1009. (Reprinted in New Jersey
Effluents, [Spring Issue 1984] 18(1)12-13, 25).
LACIS, A., J.E. HANSEN, P. LEE, T. MITCHELL, and S.
LEBEDEFF, 1981. Greenhouse Effect of Trace Gases, 1970-80. Geophysical Research
Letters 8(10). 1035-1038.
LUZIER, J.E., 1980. Digital-Simulation and Projection of
Head Changes in the Potomac-Raritan-Magothy Aquifer System, Coastal Plain, New
Water Resources Investigations, 80-11.
MEIER, M.F., 1984. Contribution of Small Glaciers to Global
Sea Level. Science, 226:4681, 1418-21.
MEIER, M.F. et al., 1985. Glaciers, Ice Sheets and Sea
Level: Effect of a CO2-Induced Climatic Change. Washington, D.C.: National
P.P. LEAHY, and L.L. KNOBEL, 1984. Effect of Eustatic Sea-Level Changes on
Saltwater-Freshwater Relations in the Northern Atlantic Coastal Plain. U.S.
Geological Survey Water-Supply Paper 2255, U.S. Government Printing Office,
Washington, D.C., 28 pp.
MERCER, J.H., 1970. Antarctic Ice and Interglacial High Sea
Levels. Science 168:1605-1606.
NAJARIAN, T.D., M.L. THATCHER, and D.R.F. HARLEMAN, 1983.
The Effect of Sub-Tidal Variations on Long-Term Water Quality Trends. ASCE
Specialty Conference on Environmental Engineering, Boulder. Colorado.
NORDHAUS, W.D., and G.W. YOHE,
1983. Future Carbon Dioxide Emissions from
Fossil Fuels. In Changing Climate. Washington, D.C.:
National Academy Press
A., 1964. Pollutant in University of
Describing the Diffusion of an Introduced One-Dimensional Estuary, Studies in
Oceanography, Tokyo Press, Tokyo, Japan, pp. 216-226.
RAMANATHAN, V., H.B. SINGH, R.J. CICERONE, and J.T. KIEHL,
1985. Trace Gas Trends and Their Potential Role in Climate Change. Journal of
Geophysical Research (August).
RASMUSSEN, R.A., and M.A.K. KHALIL, 1984. Atmospheric
Methane in the Recent and Ancient Atmospheres: Concentrations, Trends, and
Interhemispheric Gradient, Journal of Geophysical Research. 89(D7):
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
and S. LEBEDEFF, 1984. Potential Climatic Impacts of Increasing Atmospheric CO
with Emphasis on Water Availability and Hydrology in 2 the United States. NASA
Goddard Space Flight Center. Washington, D.C.: Government Printing Office.
SCHAEFER, F.L., 1983. Distribution
of Chloride Concentrations in the Principal Aquifers of the New Jersey Coastal
Plain, 1977-81. U.S. Geological Survey Water Resources Investigations Report
SCHAEFER, H.F., 1931.
"A Review of Problems in Maryland, Created by the Drought of 1930." Prepared for
Maryland State Department of Health, Baltimore, Maryland. Proceedings of the
Fifth Annual Maryland-Delaware Water and Sewerage Association, Wilmington,
Delaware, May 5 and 6, 1931, pp. 38-69.
SEIDEL, H.F., 1985. Water Utility Operating Data: An
Analysis. Journal American Water Works Association, 77(5):34-41.
SEIDEL, S., and D. KEYES, 1983.
Can We Delay a Greenhouse Warming? Washington, D.C.: Government Printing
Chairman, Climate Research Board, 1982. Carbon Dioxide: A Second Assessment.
Washington, D.C.: NAS Press.
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.
STONE, H.L., and P.L.T. BRIAN,
1963. Numerical Solution of Convective Transport Problems, Journal of the
American Institute of Chemical Engineers, Vol. 9, No. 5.
STONE, L., 1978. An Assessment of
Alternate Seawater Intrusion Control Strategies for the Oxnard Plain of Ventura
County, California. Report submitted in partial satisfaction of the requirements
for the degree of Doctor of Environmental Science and Engineering, Berkeley:
University of California.
SUPREME COURT, 1954. "Decree of the U.S. Supreme Court in
the Case of N.J. vs. N.Y. et al., Delaware River." N.J. vs. N.Y., 347 U.S. 995
SUSQUEHANNA RIVER BASIN
COMMISSION, 1973. Comprehensive Plan for Management and Development of the Water
Resources of the Susquehanna River Basin.
TAYLOR, G.I., 1954. The Dispersion of Matter in Turbulent
Flow Through a Pipe, Proceedings, Royal Society of London, Series A,
and D.R.F. HARLEMAN, 1972. Mathematical Model for the Prediction of Unsteady
Salinity Intrusion in Estuaries, Technical Report No. 144, R.M. Parsons
Laboratory for Water Resources and Hydrodynamics, Department of Civil
Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts.
THATCHER, M.L., and D.R.F.
HARLEMAN, 1978. Development and Application of a Deterministic Time-Varying
Salinity Intrusion Model for the Delaware Estuary (MIT-TSIM). Prepared for
Delaware River Basin Commission, Trenton, New Jersey, Volume l--Main Report, 170
pp.; Volume 2--Appendices; 159 pp.
THATCHER, M.L., and D.R.F. HARLEMAN, 1981. Long-Term
Salinity Calculation in Delaware Estuary. Journal of the Environmental
Engineering Division, Proceedings Paper 16011. 107(EEl):11-27. (See also
discussions by Fischer, H.B., in August 1981, by Hull, C.H.J., in December 1981
and closure in February 1983.)
THOMAS, R.H., 1985. Responses of the Polar Ice Sheets to
Climatic Warming. In M.F. Meier, 1985. Glaciers, Ice Sheets and Sea Level.
Washington, D.C.: National Academy Press.
TITUS, J.G., T.R. HENDERSON, and J.M. TEAL, 1984. Sea Level
Rise and Wetlands Loss in the United States. National Wetlands Newsletter, Vol.
6, No. 5. Washington, D.C.: Environmental Law Institute.
TITUS, J.G., 1985. Sea Level Rise
and Wetlands Loss in Coastal Zone '85 edited by O.T. Magoon, H. Converse, D.
Miner, D. Clark and L.T. Tobin. New York: American Society of Civil
ENVIRONMENT PROGRAM AND WORLD METEROLOGICAL ORGANIZATION (UNEP), 1985.
International Assessment of the Role of Carbon Dioxide and of Other Greenhouse
Gases in Climate Variations and Associated Impacts. Conference Statement.
Geneva: United Nations Environment Program.
UNTERSTEINER, N., 1975. Sea Ice and Ice Sheets: Role in
Climatic Variations. Physical Basis of Climate Modeling (April), Series
VOWINKLE, E.F., and
W.K. FOSTER, 1981. Hydrogeologic Conditions in the Coastal Plain of New Jersey,
Open-File Report 81-405. Trenton, New Jersey: U.S. Geological Survey, 39 pp.
WALKER, R.L., 1983. Evaluation of
Water Levels in Major Aquifers of the New Jersey Coastal Plain, 1978. U.S.
Geological Survey Water Resources Investigations Report 82-4077.
WEISS, R.F., 1981. "The Temporal
and Spatial Distribution of Tropospheric Nitrous Oxide." Journal of Geophysical
WUEBBLES, D.J., M.C. MacCRACKEN, and F.W. LUTHER, 1984. A
Proposed Reference Set of Scenarios for Radiatively Active Atmospheric
Constituents. Carbon Dioxide Research Division, U.S. Department of Energy:
1983. Evaluation of Water Levels in Major Aquifers of the New Jersey Coastal
Plain, 1978. U.S. Geological Survey Water Resources Investigations Report
WEISS, R.F., 1981.
"The Temporal and Spatial Distribution of Tropospheric Nitrous Oxide." Journal
of Geophysical Research, 86(C8):7185-95.
1. Louisiana is also
experiencing salinity increases from sea level rise (Haydl 1984).
2. 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 wellmixed 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...[remainder of note garbled]
3. There are
practical limits to the control of salinity in the Delaware estuary by reservoir
regulaton. 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 mlle 98, does
provide some control of salinity throughout the estuary.
4. 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.
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