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Long Island-New Jersey (LINJ) Coastal Drainages Study

FY1998 Workplan—Background and Environmental Setting

November 4, 1997


The LINJ study area is in one of the more densely populated areas of the country. There is more than a century of a strong and prosperous industrial economy behind an industrial growth that was centered around the ports and metropolitan areas of New York City and Philadelphia, now considered the older urban portions of the study area. There also is a very productive agricultural heritage around the fringes of these metropolitan areas and in more rural areas of southern and northwestern NJ and eastern LI (figure 2). These areas, however, are rapidly becoming urban and suburban communities (figure 2b). Below is a basic description of the study setting and resources that contribute to the diversity and complexity upon which the LINJ stratification and water-quality issues are based.

Population and Land Use

The Long Island-New Jersey Coastal Drainages (LINJ) study unit covers more than 6,000 mi2 in New York and New Jersey. The study unit contains the metropolitan areas of New York City, Philadelphia, and the highly urbanized corridor in between. In 1990, the population of study unit was more than 10 million, concentrated mostly on Long Island and in northeastern New Jersey (figure 1). In 1973, the study area was 35% urban (28 percent urban residential and 7 percent urban nonresidential). We know that a significant increase (+9%) in urban land use and subsequent decrease in forest and agriculture land uses (-6%) has occurred between 1973 and 1990 in the study area. The large extent of urban area and continued growth in NJ and LI is the primary focus of this NAWQA study.

    Source of land use          Urban  Forest  Agriculture  Wetland  Misc
    1973 SU (GIRAS)             35%    34%     14%          9%       8%
    1990 SU (GIRAS/Census)      44%    30%     12%          8%       6%
    1973-1990 SU Change         +9%    -4%     -2%          -1%      -2%

    1973 ALL NJ (GIRAS)         24%    36%     25%          10%      5%
    1985 ALL NJ (GIRAS/TM)      32%    32%     22%          9%       5%
    1990 ALL NJ (GIRAS/Census)  29%    33%     23%          10%      5%
    1973-1990 NJ Change         +5%    -3%     -2%          0%       0%

    1973 LI (GIRAS)             62%    17%     9%           2%       10%
    1990 LI (GIRAS/Census)      66%    14%     8%           2%       10%
    1973-1990 LI Change         +4%    -3%     -1%          0%       0%
Stratification of the Study Area

Fortunately, there have been several significant efforts in NJ to develop an objective procedure for classifying or differentiating factors controlling both ground- and surface-water systems. Physiography plays a major role. An interagency ecomapping committee headed by the USFS is the most recent effort. Based on the ecoregion concept, they have defined subsections of NJ based on ecosystem differences within physiographic provinces (NJDEP 1994). This ecomapping fits well conceptually and practically with the stratification needs of the NAWQA study. It also works out well with Long Island; we simply treat LI as another subsection of the Coastal Plain. The result is a stratification of the LINJ into 6 ecoregion strata as shown in Figures a and b. We believe there is not enough differentiation between the inner and outer Coastal Plain subregions and so we lumped them as Coastal Plain-NJ. Furthermore, because land use plays such a dominate role in this study area, we believe that both SW and GW stratification can be simplified even further by combining similar ecoregion strata back to 3 primary SW strata and 4 primary GW strata. Land use then becomes the primary differentiating substrata within each of these primary strata.

Description of the Study Area

About two-thirds of the 6,000 square mile study area is Coastal Plain and characterized by flat to gently rolling topography of unconsolidated sedimentary (NJ and LI) and glacial (LI only) deposits. The other one-third is within the Piedmont and New England provinces (north of the Fall Line) and is characterized by rolling to hilly topography of weathered bedrock and glacial deposits in the northern half of each (figure 3).

Hydrogeologic characteristics of provinces north of the Fall Line differ greatly from those of the Coastal Plain. The New England province is underlain by igneous and metamorphic rocks, where as, the Piedmont province consists of layered shale, siltstone, and sandstone bedrock. Bedrock aquifers of these provinces are associated with water-bearing weathered joint and fracture systems typically within 300 feet of land surface. The top 100-150 feet is largely unconfined. Valleys in the glaciated northern half of each, however, are underlain by stratified drift and glacial till. These stratified drift aquifers are generally 30 to 40 feet thick, but may be 300 feet thick in some valleys.

Physiography--% SU       Coastal Plain--65%         Piedmont--24%          New Englan--11%
--------------------  -----------------------  ----------------------  ----------------------
6 Ecoregion Strata    Long Island  New Jersey  Glaciated  Unglaciated  Glaciated  Unglaciated
Percent of SU            23.4%       41.6%       12.5%       11.4%       6.8%        4.4%
Square Miles            1,412       2,507         751         685        409         267
In contrast, the Coastal Plain is underlain by a thick wedge of unconsolidated sediments that form permeable units of sand and gravel interbedded with poorly permeable units of silt and clay. These sediments differ in areal extent and thickness, but generally dip and thicken southeastward to about 6,500 feet thick at the southern tip of NJ. The Kirkwood-Cohansey aquifer system and the outcrop of the Potomac-Raritan-Magothy aquifer system are the principal surficial aquifers in the NJ Coastal Plain. Groundwater pumpage from confined systems exceeds pumpage from surficial systems by 3 to 1, but since NJ water supply permits for pumpage from confined systems are fully allocated, most of the future population growth in the Coastal Plain will depend directly on surficial sources for supply. Glacial deposits of sand and gravel overlie most of LI and form the surficial aquifer. To large extent these systems are underlain and hydraulically connected to the deeper Magothy aquifer, the principal source of water for LI.

Average annual precipitation ranges from 42 to 52 inches south-to-north, and annual snowfall ranges from 13 in the south to more than 50 inches in the north. Precipitation is evenly distributed throughout the year. Average annual temperature ranges from 56 to 50 oF south to north. Average annual runoff is 21-23 inches in NJ and on LI, but is significantly lower (from <3 to 10 inches) for many LI streams due to the heavy groundwater pumpage on the western part of LI. Annual groundwater recharge varies from 20 to 22 inches for the more permeable aquifers, but is estimated to be less than half that for the bedrock systems of the study area.

The principal river systems within the study unit are the Hackensack (202 mi2), Passaic (950 mi2), Raritan (1,105 mi2), Toms (192 mi2), Mullica (569 mi2), and Great Egg Harbor (347 mi2) Rivers in NJ. Many other smaller rivers and streams drain the Coastal Plain, including the Peconic River (75 mi2) on LI. Middle and downstream reaches of the Hackensack, Passaic, and Raritan Rivers receive urban runoff and treated effluent from point sources. Upstream reaches of these and most other rivers in the study are mixed agricultural, forested, and/or urban land use.

LI and the Coastal Plain of NJ have relatively flat slopes of sandy soils that allow rapid infiltration of rainfall. In fact, 75 to 90 percent of streamflow is derived from groundwater discharge over much of the Coastal Plain (Kirkwood-Cohansey aquifer system). The New England and Piedmont provinces have steeper slopes of thin, clayey soils, which produce runoff more rapidly than Coastal Plain soils. Much of western LI, northeastern NJ, and the corridor between New York City and Philadelphia consists of heavily urbanized areas that yield runoff more rapidly. Groundwater pumpage considerably reduces baseflow in streams on the western portion of LI.

Streams in northern New Jersey generally have upland and lowland portions. The upland portions exhibit steeper gradients, tend to be swift-flowing at higher discharge rates, and have very heterogeneous substrates ranging from bedrock, boulders, and cobbles in riffles to finer particles in depositional areas. Lowland or downstream valley portions have lower gradients, tend to be slower-flowing, and also have very heterogenous substrates perhaps with a tendency towards finer materials and more depositional areas than upland reaches. In the Coastal Plain, streams generally have low gradients, tend to be slow-flowing, and have more homogeneous substrates with bottom materials ranging from sand and gravel to silt and muck.

These habitat variations result in benthic invertebrate communities that exhibit distinct differences in species composition between the northern New Jersey upland/lowland and Coastal Plain systems (NJDEP, 1994). The greatest diversity of pollution-intolerant species has been found in streams of the New England province and areas of the outer Coastal Plain. This is due in part to the varied substrate composition, presence of forest cover, and in part to the generally better surface-water quality conditions in the New England and outer Coastal Plain than in the Piedmont and inner Coastal Plain. The Piedmont and inner Coastal Plain are subject to greater urban, industrial, and agricultural influence, which are generally associated with poorer water and habitat quality and lower invertebrate population density or species diversity. The natural water quality (low pH, alkalinity, and nutrient levels) and habitat (finer grained and unstable bed materials) of the Coastal Plain, in general, results in more depauparate communities and, thereby, reflects lower richness and diversity than other provinces.

Drainage patterns of the study area streams are largely dendritic. Natural lakes are virtually nonexistent in the Coastal Plain, although small man-made impoundments, formed by small earthen and/or rock dams, are common in both New Jersey and on Long Island. Literally hundreds of small impoundments and run-of-the-river dams exist in northern New Jersey. Many of these smaller dams throughout the study area are remnent from their use in providing sources of water power for a multitude of reasons in earlier times. The study area contains 13 major water-supply reservoirs, most north of the Fall Line, and receives about 100 Mgal/d of flow diverted from the Delaware River to the Raritan River basin for water supply. In fact, water-supply facilities in most river systems are highly connected and transfer of water is common. Major water uses in the study unit include domestic, commercial, industrial, mining, power production, and crop irrigation.

Physiography                                            Coastal Plain     Piedmont  New England

Location                                                LI         NJ      NE-NJ      NE-NJ
Annual precipitation at selected NWS stations           45         45        48         48
[climate division average used in model]               [46]       [44]      [53]       [53]
(1961-90), in inches

Annual runoff for period of record at selected       *3 to 21      21        23         23
stream gages, in inches (*affected by GW pumpage)

Annual runoff from 1961-90 water-balance-model          20         17        25         25
estimates using climate division data, in inches

Estimated annual groundwater recharge, in inches       22         20        8.6(unglac)  ?(bedrock)
(from reports), in inches (by aquifer type)                            ?(glaciat) 22(glaciat)
----------------------------------------------------------------------------------------------------                                                             -Cohansey
Total freshwater withdrawals for the LINJ is 1,617 Mgal/d, serving over 10 million people and related infrastructure. Surface-water withdrawals account for 37% (613 Mgal/d), most of which is in the northern NJ portion. These figures do not include the New York City surface water imports from outside sources to western LI (Queens and Kings Counties). Groundwater withdrawals account for 63% (1,004 Mgal/d) of the LINJ water use; 44% of which is on LI, 37% in southern NJ, and 19% in northern NJ. Only 20 to 40% of the total water use is groundwater from confined aquifers, indicating that much of the used resources in the LINJ are either SW or surficial GW and are, therefore, highly vulnerable to contamination.

         WATER USE IN THE STUDY AREA-- Total freshwater withdrawals for the LINJ is 1,617 Mgal/d.
SU Strata           LI Coastal Plain 1990  |    NJ Coastal Plain 1991-92      |  Piedmont/New England 1991-92
                                           |           Kirkwood-              |
GW Source          Magothy  Glacial  Lloyd | Confined  Cohansey  Unclassified | Bedrock  Glacial  Unclassified
GW Mgal/d             330      92      15  |    221       74         82       |   74       67        49
% of total            20%      6%      1%  |    14%       5%         5%       |   5%       4%        3%

SW Source           LI Coastal Plain 1990  |    NJ Coastal Plain 1991-92      |  Piedmont/New England 1991-92
SW Mgal/d                   ? NYC imports  |                 70               |                543
% of total                     --          |                 4%               |                33%

Information related to NAWQA can be obtained from:

NAWQA Project Chief, USGS
810 Bear Tavern Road, Suite 206
West Trenton, New Jersey 08628
Phone 609-771-3943

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