Analog-Model Analysis of Regional 

Three-Dimensional Flow in the 

Ground-Water Reservoir of 

Long Island, New York

GEOLOGICAL SURVEY PROFESSIONAL PAPER 982

Prepared in cooperation with

the Nassau County Department of Public Works,

the Suffolk County Department of Environmental Control,

the Suffolk County Water Authority, and

the New York State Department of Environmental Conservation

Analog-Model Analysis of Regional 

Three-Dimensional Flow in the 

Ground-Water Reservoir of 

Long Island, New York

By RUFUS T. GETZEN

GEOLOGICAL SURVEY PROFESSIONAL PAPER 982

Prepared in cooperation with

the Nassau County Department of Public Works,

the Suffolk County Department of Environmental Control,

the Suffolk County Water Authority, and

the New York State Department of Environmental Conservation

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1977
UNITED STATES DEPARTMENT OF THE INTERIOR 

THOMAS S. KLEPPE, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Getzen, Rufus T.

Analog-model analysis of regional three-dimensional flow in the ground-water reservoir of Long Island, New York

(Geological Survey Professional Paper 982)

Bibliography: p. 47-49.

Supt.ofDocs.no.: I 19.16:982

1. Groundwater flow-New York (State)-Long Island-Electromechanical analogies. 2. Groundwater flow-New York (State)-

Long Island-Data processing. 3. Water, Underground-New YOrk (State)-Long Island-Electromechanical analogies. 4.

Water, Underground-New York (State)-Long Island-Data processing. I. Nassau Co., N. Y. Dept. of Public Works. II. Title:

Analog-model analysis of regional three-dimensional flow in the groundwater reservoir of Long Island. . . II. Series: United

States Geological Survey Professional Paper 982. 

TC176.G48 551.4'9'0974721 76-608323

For sale by the Superintendent of Documents, U.S. Government Printing Office

Washington, D.C. 20402

Stock Number 024-001-02936-7
CONTENTS

Page 

_ 1 

_ 1 

_ 1 

1

Abstract- _ _ ____________

Introduction ___________________________________

Background _________________________________

Purpose and scope ___________________________________

Previous work __________________________________ 2

Location and general physiography of study area__ _ ______ 3

Acknowledgments ______________________________ 3

Units of measure ______________________________________ 4

Hydrogeology of Long Island ______________________________ 4

Prominent physiographic features and their role in the hydrology of Long Island _____________________________ 6

Geologic features _________________________________ 6

Distribution of hydraulic conductivity and storage coefficient 8 

Surface water ________________________________________ 11

Lakes __________________________________ 11

Streams ____________________________________________ 12

Page

Hydrogeology of Long Island Continued

Boundaries between saltwater and fresh ground water ____ 13 

Water table _____________________________ 18

Model design _____________________________________________ 19

Basic analog concepts and similarity coefficients __________ 19

Model matrix ______________________________________ 22

Boundary conditions ____________________________________ 27

Summary of design criteria ______________________ 31

Model-prototype comparisons ______________________________ 31

Performance criteria ___________________________ 31

Steady-state evaluation ________________________________ 32

Unsteady-state evaluation _______________________ 37

Summary and conclusions _________________________________ 45

References cited _______________________________________ 47

FIGURE

ILLUSTRATIONS

Page

1. Index map of Long Island, N.Y., showing area of investigation _________________________ ________________ 3

2. Cross-sectional diagram showing major components of the hydrologic cycle on Long Island ______ __ ___ __ 4

3. Map showing physiographic features that influence Long Island hydrology _____________ ____ ____________ 7

4. Hydrogeologic sections through the Long Island ground-water reservoir and map locating sections _______-__---__ 8

5-12. Map showing:

5. Saturated thickness of the upper glacial aquifer on Long Island _____________________ _____ ______ 12

6. Thickness of the Jameco aquifer _____________________________________________________ ______ 13

7. Saturated thickness of the Magothy aquifer_____________________________________________________ __ 14

8. Confining bed overlying the Magothy aquifer ________________________________________________________ 14

9. Estimated hydraulic conductivity of the upper glacial aquifer __________________------_ ____________ 15

10. Estimated hydraulic conductivity of the Magothy aquifer ____________________________ __________ 15

11. Estimated hydraulic conductivity of the Jameco aquifer _________________________ ________ __ 16

12. Values of specific yield estimated for the water table ______________________--------- ________________ 17

13. Diagram of section across a stream valley ____________________________________ __--------_------- ---------- 17

14. Map showing major Long Island streams ________________________________________-__ _____ _____ 18

15. Schematic hydrologic section of seaward boundary of fresh ground water_____________________ ____ ____ 18

16. Diagram showing finite-difference representation and notation of hydrologic section through the Long Island

ground-water reservoir ___________________________________________________--------_- -___ _____ 21

17. Map view of finite-difference grid _________________-____________-___---------_-_-------- ________________ 23

18-22. Map showing distribution of transmissivity about each node in:

18. Level 1 of the model _____ _ ________ _ ______________________________________ 24

19. Level 2 of the model ____ _ _________________ _ ________ _ _ ______ _ ________ - _ 25

20. Level 3 of the model __________________________________________________- 26

21. Level 4 of the model ______________________________________ _ _ _ ____ _ _____ 26

22. Level 5 of the model ___________________________________________________- 27

23. Map showing distribution of estimated values of (Az7KB ) between nodes in levels 1 and 2 of the model __________ 27

24. Map showing distribution of estimated values of (Az'/KB ) between nodes in levels 2 and 3 of the model ______ 28

25. Map showing distribution of estimated values of (Az'/Kn) between nodes in levels 3 and 4 and 4 and 5 of the model -___ 28

26. Schematic representation of method for producing transient analog stresses ___________________________--------- 30

27. Circuit diagram of model stream (A) and prototype stream channel (B) ______________________________________ 31

28. Map showing distribution of prototype mean annual precipitation, 1951-65, and of steady-state recharge to the

model _______________________________________________________________ 32

29. Profiles showing simulated, steady-state, water table on western Long Island compared with 1903 prototype watertable profiles and map locating profiles _________________________________________________________ 33

ill
IV CONTENTS

FIGURE 30. Map showing comparison of steady-state model water table with 1903 water table in central Long Island ________ 34

31. Map showing comparison of steady-state model water table with 1970 water table in eastern Long Island ________ 34

32. Map showing comparison of steady-state model head with 1971 prototype head at base of Magothy aquifer in eastern

Long Island __________________________________________________________ 35

33. Distribution of head and bed-parallel components of ground-water flow along two hydrologic sections through the

model Long Island ground-water reservoir _________________________________________ 36

34. Graph of changes in annual recharge used to simulate the 1962-66 drought on Long Island.--__ ____________ 37

35. Map showing distribution of the decline in net recharge used to simulate the 1962-66 drought on Long Island _ 38

36. Map showing comparison of observed and simulated water-table declines as a result of the 1962-66 drought _ 38

37. Graph of estimated islandwide changes in pumping, manmade recharge, and net stress between 1903 and 1963 __ 44

38. Map showing comparison of simulated decline in water table between 1903 and 1961 on western Long Island with

observed decline ______________________________________________________________ 45

39. Map showing simulated decline in water table due to pumping on western Long Island between 1903 and 1942 -_ 46

40. Map showing locations of wells used for water level changes in table 4 __________________________________ 47

TABLES

TABLE

h

I

K

Kx

K

K

Page

Hydrogeologic units of Long Island __________________________________________________________ 11

Streamflow comparisons __________________________________________________________________ 37

Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses 

between 1903 and 1963______________________________________________________ 39

Comparison of model and prototype water-level changes for selected wells between 1951 and 1963 ____________ 47

SYMBOLS AND ABBREVIATIONS

[Basic physical dimensions given in parentheses]

similarity coefficients for relating hydrologic quantities to their electronic counterparts

amperes

capacitance (coulombs/volt)

centimetres (length)

reciprocal centimetres (1/length)

centimetres per second Darcy velocity (length/time)

centimetres per day (length/time)

coulombs

electromotive potential (volts)

feet (length)

feet per day (length/time)

cubic feet per second (Iength3/time)

gallons per day per square foot ( = 1 Meinzer Unit; unit 

gradient and prevailing ground-water temperature 

presumed)

head, ground-water potential (length)

electric current (coulombs/time)

hydraulic conductivity (length/time)

hydraulic conductivity in x, y, z directions, respectively; gradient and discharge are assumed to be 

measured in same direction (length/time)

hydraulic conductivity in various directions; first 

subscript denotes direction of discharge, second 

subscript direction of gradient. K is a symmetric 

tensor, so no change in quantity results from reversing subscript (length/time)

maximum principal hydraulic conductivity (length/ 

time)

KB

m 

m3/s

mA

Mgal/d

(Mgal/d)/mi2

pf

Q

Q

minimum principal hydraulic conductivity (length/

time)

metres (length) 

cubic metres per second volumetric discharge

(Iength3/time)

milliamperes (lO^x coulombs/sec) 

million gallons per day (Iength3/time) 

million gallons per day per square mile volumetric

recharge rate (length/time) 

picofarads (10"12 xcoulombs/volt) 

volumetric discharge rate (Iength3/time) 

electric charge (coulombs)

components of Darcy velocity (length/time)

resistance (ohms)

specific storage; storage per unit volume (I/length)

specific yield (dimensionless)

second (time)

transmissivity (Iength2/time)

time

model time (as opposed to real time)

volume (length3 )

dimensions in arbitrary directions (length)

dimensions corresponding to principal conductivities 

finite-difference operator, A.t=.r 1 -jc0
CONTENTS

CONVERSION TABLE

[The following conversions are given to four significant digits. Equivalent metric and English units in the text, however, have the same relative accuracy]

Metric

centimetres (cm)

centimetres (cm)

centimetres per second

(cm/s)

centimetres per second

(cm/s)

centimetres per year

(cm/yr)

Multiply by

3.937 xlO-1

3.281 xlO-2

2.835xl03

2.223 xlO4

1.868 xlO'2

English

inches (in.)

feet (ft)

feet per day (ft/d)

gallons per day per square

feet [(gal/d)/ft2]

million gallons per day

per square mile

[(Mgal/d)/mi2]

Metric

cubic metres per second

(m3/s)

cubic metres per second

(m3/s)

kilometres (km)

metres (m)

square kilometres (km2 )

square metres (m2 )

metres per kilometre

(m/km)

Multiply by

3.531x10

2.282x10

6.214X10'1

3.281

3.861 xlO-1

1.076x10

5.280

English

cubic feet per second

(ft3/s)

million gallons per day

(Mgal/d)

miles (mi)

feet (ft)

square miles (mi2)

square feet (ft2 )

feet per mile (ft/mi)

ANALOG-MODEL ANALYSIS OF REGIONAL

THREE-DIMENSIONAL FLOW IN THE 

GROUND-WATER RESERVOIR OF LONG ISLAND, NEW YORK

By RUFUS T. GETZEN

ABSTRACT

A three-dimensional analog model of the ground-water system beneath Long Island, N.Y., provides a practical means for studying 

anisotropic flow on a regional scale. Constructional and operational 

techniques influence the simulation almost as much as model design 

does. Usefulness and accuracy of the model depend on (1) inherent 

and practical limitations of the finite-difference method, (2) accuracy 

and completeness of the data base, and (3) accuracy of the assumptions and approximations that were made in applying the simulation 

technique to this particular ground-water reservoir.

Reliable data used in design of the model are (1) horizontal hydraulic conductivity and thickness of three major aquifers, (2) extent 

of confining beds, (3) specific yield, and (4) locations of streams. Estimates of vertical hydraulic conductivity and specific storage were 

applied to the model. Most spatially fixed model boundaries are good 

representations of prototype (real-world) boundaries. Most dynamic 

boundaries are only approximately represented, and some dynamic 

boundaries require application of unproved assumptions. The simulated ground-water reservoir generally agrees with prototype hydrology, and the model is being used for predictive studies.

INTRODUCTION

BACKGROUND

More than one-third of the 7.3 million people on 

Long Island are wholly dependent on ground water as 

a source of water, and the remaining two-thirds use 

some ground water. More significantly, Nassau and 

Suffolk Counties, which together constitute more than 

85 percent of the land area of Long Island, depend entirely upon ground water for all their water needs. The 

populations of Nassau and Suffolk Counties are growing rapidly, and the governing bodies of these counties 

are already planning for a time in the foreseeable future when the consumptive-use rate will reach the rate 

of total recharge to the ground-water reservoir.

Use of ground-water resources presents several problems that differ from those encountered in use of 

surface-water supplies. Most of these problems arise 

from or can be reduced to three basic conditions: (1) 

The properties of ground-water reservoirs, or aquifers, 

are fundamentally geologic and their investigation 

proceeds with great expense, great difficulty, and much 

guesswork; (2) ground-water reservoirs are interconnected over large areas, and seemingly isolated human

activities and natural events can influence water 

quantity and quality over wide areas; (3) ground water 

moves at such slow rates that movement from the 

point of recharge to the point where the water is ultimately discharged typically requires decades or centuries, and direct observation of this movement is usually impossible.

One of the most powerful tools available to the 

ground-water hydrologist for predicting the behavior 

of large, complex aquifer systems such as the one on 

Long Island is a model a mathematical or physicalmathematical technique for simulating the physics of 

ground-water flow. Such models require much simplification of the geometry and properties of the aquifers. 

The most frequent simplification is that the aquifer 

material is isotropic; that is, its hydraulic conductivity 

is the same in all directions at any given point. This 

simplification is seldom even approximately correct 

(Hubbert, 1940, p. 826), but because of flow geometry, 

it is commonly assumed to have little adverse effect on 

the accuracy of flow predictions.

The present study, investigating ground-water flow 

on Long Island, indicates that the anisotropy of the 

aquifers is a major factor controlling the effects of 

ground-water development and that these effects must 

be considered in managing Long Island's water resources. One of the principal goals of this report is to 

provide a physically sound practical basis for analyzing anisotropic flow on a regional scale.

PURPOSE AND SCOPE

This report discusses design, construction, and operation of a three-dimensional electrical analog model of 

the ground-water system beneath Long Island, N.Y. 

Because the streams of Long Island are important as 

boundaries within the aquifer system, some aspects of 

stream hydrology are also represented by this model, 

but the design of the model limits its major uses to 

predicting regional or general changes in groundwater head or flow. This report describes sources and 

types of data used in designing the model, some of the
ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

basic concepts and assumptions that underlie its operation, calibration of the model in terms of historical 

hydrologic data, probable sources of inaccuracy in its 

results, and certain conclusions on the behavior of 

anisotropic aquifers.

A prime use of the model will be to anticipate the 

response of the flow system to various expected and 

proposed stresses. These stresses can take the form of 

pumping or recharge through wells, streams, or basins. 

A model of this type cannot be used for water-quality 

predictions, although crude estimates and general 

trends in water quality can be derived from hydrologic 

information gained from the model. Several of the 

proposed water-management schemes have been modeled; results of some of this modeling are the subject of 

additional reports in this series of publications.

PREVIOUS WORK

Previous research, on which this study is dependent, 

is of two types: (a) Development of theory and 

techniques for analysis of ground-water flow; and (b) 

studies of Long Island's water resources, which have 

provided (1) information on the geologic background, 

(2) hydrologic data, and (3) general understanding of 

the hydrologic situation on Long Island.

The geology of Long Island has been studied extensively since the mid-nineteenth century, and a massive 

literature has accumulated. Some of the more important early papers are those by Mather (1843), Upham 

(1879), Dana (1890), Hollick (1893, 1894), Woodworth 

(1901), and Salisbury (1902). DeVarona (1896) and 

Freeman (1900) studied the water resources of the 

western part of Long Island. The report by Veatch, 

Slichter, Bowman, Crosby, and Horton (1906) is a comprehensive study of the geology and the water resources of the entire island but does not include quantitative data on the hydrologic properties of the 

ground-water reservoir.

Few quantitative data on aquifer properties were 

available before 1950, but some controlled pumping 

tests were made by C. E. Jacob, J. G. Ferris, W. V. 

Swarzenski, M. A. Warren, and N. J. Lusczynski at 

various times between 1935 and 1950 (Jacob, 1939, 

1941, 1945; McClymonds and Franke, 1972) and 

yielded data of varying quality and quantity. 

McClymonds and Franke (1972), working with lithologic logs and acceptance tests from about 1,300 wells, 

compiled estimates of the transmissivity and the bedparallel hydraulic conductivity for the major aquifers 

of Long Island. These estimates have been used in the 

current study.

Geologic and hydrogeologic features of Long Island 

have been described in comprehensive reports by other

authors since the 1906 report by Veatch, Slichter, 

Bowman, Crosby, and Horton (Fuller, 1914; Suter and 

others, 1949). Detailed geology of smaller areas is described in reports by Isbister (1966), Lubke (1964), 

Perlmutter and Geraghty (1963), Pluhowski and Kantrowitz (1964), Swarzenski (1963), Soren (1971), and 

Jensen and Soren (1974).

The present investigation is not the first U.S. 

Geological Survey study of Long Island's water resources to use analog modeling techniques, but with 

some exceptions, the previous studies were not published, largely because of inadequacies or inaccuracies 

in the models. In October 1964, plans were begun for 

constructing an analog model of Long Island's aquifers. 

These plans resulted in the construction of a two-layer 

regional flow model of the western half of Long Island. 

Attempts to verify this model against historical and 

synthetic data produced inconsistent results. Experimentation over a period of 2 years with this model 

failed to bring it into tolerable agreement with all 

known aspects of Long Island's hydrology. This model 

indicated that a two-layered concept was inadequate 

for describing the ground-water flow system beneath 

Long Island. Part of the difficulty in obtaining an 

adequate representation of the hydrologic system was 

insufficient data on the confining beds that overlie 

parts of the Magothy aquifer.

In 1966, a steady-state axisymmetric analog of flow 

to a single well was used in the interpretation of pumping tests at Bay Park, Long Island. Experimentation 

with cross-sectional models of the aquifer system was 

begun in 1968. Results from a model of this type were 

used by Franke and Cohen (1972) to compute regional 

rates of ground-water movement. Additional crosssectional modeling'was done by Franke and Getzen 

(1975). A series of modeling experiments, in which the 

vertical and the horizontal conductivities of aquifers 

and confining beds, rates of recharge, and other hydrologic parameters were varied systematically, demonstrated the importance of anisotropy in controlling regional ground-water flow on Long Island. Some of the 

results of this series of experiments serve as basic 

starting points for the design of the three-dimensional 

model discussed in this report.

In 1971, work was begun on the model that is the 

subject of the present report. Construction of the model 

was completed in less than 4 months, but testing and 

modification of the model were not completed until 

early 1974. This analog model represents threedimensional regional flow in the ground-water reservior on Long Island. The digital modeling techniques 

that were available at the time this model was begun 

could not supply the needed accuracy and resolution 

when used on computers of the size commonly avail-
INTRODUCTION

able. Existing analog techniques could be easily 

adapted to simulate three-dimensional, anisotropic 

flow; because development of an adequate digital 

model would require much experimentation, the author chose the analog approach.

Two Long Island modeling studies that were not 

done by the Geological Survey were (a) a crosssectional Hele-Shaw model (Wilson, 1970) and (b) a 

single-aquifer digital model of the southeastern part of 

Long Island (Fetter, 1971). The Hele-Shaw model is 

sophisticated in concept and design and uses composite 

anisotropic permeabilities (Collins and others, 1972; 

Collins and Gelhar, 1970).

LOCATION AND GENERAL 

PHYSIOGRAPHY OF STUDY AREA

Long Island is bounded on the north by Long Island 

Sound, on the east and south by the Atlantic Ocean, 

and on the west by New York Bay and the East River 

(fig. 1). The island parallels the New York and Connecticut coasts for about 190 kilometres (120 miles) and 

has an area of about 3,600 square kilometres (1,400 

square miles), including several smaller islands that 

are within the same political boundaries. The eastern 

end of Long Island is divided into two narrow forks by 

the Peconic Bay, and the southern edge of the island is 

fringed with an almost continuous line of barrier 

beaches. The forks and barrier beaches are not included in the primary study area shown in figure 1.

Data from the barrier beaches were used in designing 

and testing the model, but no predictive capability was 

developed for these areas. The area of the two forks 

(east of Shinnecock Canal and Mattituck Creek) was 

not used.

The island is divided into four counties, two of which 

(Kings and Queens Counties) are within the political 

boundaries of New York City. Kings, Queens, Nassau, 

and Suffolk Counties have areas of 202, 298, 754, and 

2,390 square kilometres (78, 115, 291, and 923 square 

miles), respectively.

ACKNOWLEDGMENTS

Parts of this report were included in the author's 

Ph.D dissertation, Department of Geology, University 

of Illinois. Publication rights have been given to the 

Geological Survey.

Prof. O. L. Franke of City College, New York City 

University, assisted the author in gathering the data 

for this report. Prof. Franke also examined the report 

for technical accuracy.

Mr. D. E. Vaupel provided unpublished stream data. 

He and several of his assistants provided qualitative 

and quantitative information about Long Island 

streams, both orally and written, on several occasions 

during 1971-73.

Laboratory assistants B. H. Cohen, M. E. Eskenazi, 

Daniel Gillen, Natale Guadagnino, and R. F. Lingner 

built the model; they and A. W. Harbaugh and Donald

74

41 

HINNECOCK CANAL

EXPLANATION

Project area

Base from U.S. Geological Survey, 1:250,000 series: 

Scranton, Hartford, 1962; New York, 1957; 

Newark, Providence, 1947

FIGURE 1. Long Island, N.Y., showing area of investigation.
ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Hockheiser assisted in testing and modifying the 

model.

UNITS OF MEASURE

Metric units were used in this study, but not for field 

data and not until after most of the model design and 

construction were completed. Metric units have been 

given preference in the text, but some illustrations, 

adapted from other sources, could not be easily modified and are reproduced here in their original units. 

Where these illustrations are referred to in the text, 

the original units in the illustrations are mentioned 

first. This inconsistency seems unavoidable.

HYDROGEOLOGY OF LONG ISLAND

The hydrologic cycle on Long Island, as in most 

places, tends towards a state of dynamic equilibrium. 

That is, the naturally occurring outputs of water tend 

to balance the inputs, and the pattern of flow remains 

fairly constant over long periods of time. The sun provides the energy to maintain the hydrologic cycle by 

evaporating water at low altitudes and releasing it at 

higher altitudes in the form of precipitation. Precipitation is indicated by (A) in figure 2, which outlines the 

major components of the hydrologic cycle; evaporation 

is shown by (B). Rates of evaporation are greatest 

where bodies of surface water are directly exposed to 

sun and wind, but some evaporation occurs across the 

entire surface of the island.

Some of the precipitation occurs over bodies of surface water or within such a short distance from them 

that the water reaches these surface-water bodies 

without infiltrating the soil. Such direct runoff accounts for a small percentage of the total precipitation 

on Long Island, and, except in areas with storm sewers, 

is an infrequent event.

Water is also transpired to the atmosphere by plants 

(C). On Long Island, the sum of the quantities of transpiration and evaporation is almost always less than 

precipitation. Net natural recharge to the groundNOT TO SCALE

FIGURE 2. Major components of the hydrologic cycle on Long Island: (A) precipitation, (B) evaporation, (C) transpiration, (D) unsaturated ground-water flow, (E) surface seepage, (F) salty water, (G) saturated ground-water flow, (H) glacial aquifer, (I) Magothy 

aquifer, (J) Lloyd aquifer, (K) dispersion into salty ground water, (L) deep pumpage returned to surface, and (M) deep pumpage 

returned to salty water. Arrows show inferred direction of water movement.
HYDROGEOLOGY OF LONG ISLAND

water reservoir is the difference between precipitation 

and the sum of evaporation and direct runoff. The 

ground-water reservoir is that part of Long Island's 

rocks and sediments that is saturated with freshwater 

(G), but recharge does not usually enter this saturated 

zone without first passing through an unsaturated 

zone (D) in which the interstices (openings between 

sedimentary particles) are only partly filled with liquid 

water. Part of the interstitial volume is occupied by 

water vapor and other gases. The ground-water reservoir is separated from the unsaturated zone by the 

water table a surface along which the interstitial 

pressure is equal to atmospheric pressure. The top part 

of the reservoir (H), the glacial aquifer, is a water-table 

aquifer; its upper surface is the water table. Some of 

the water in the water-table aquifer is discharged directly to the surface as springs and as seepage to 

streams, lakes, and marshes. Collectively, these discharge points (E) are known as seeps. The remainder of 

the water in the water-table aquifer flows into other 

hydrogeologic units (I and J). The Magothy aquifer (I) 

and the Lloyd aquifer (J) are distinguished from the 

glacial aquifer (H) by differences in lithology and 

geologic origins, by differences in physical properties, 

or by the fact that water flows within each aquifer 

more readily than from one aquifer to another.

Water from all three aquifers (H, I, and J) is eventually discharged to salty surface water, either directly 

or through intervening sediments containing mixed 

freshwater and salty water (K). This discharge and 

most other components of the hydrologic cycle are 

inputs and outputs in relation to the ground-water reservoir. These inputs and outputs form the natural 

stresses and boundary conditions to the reservoir.

Flow within the ground-water reservoir is controlled 

by three factors driving forces, resistive forces, and 

changes in storage. A flow system in dynamic equilibrium maintains a constant flow rate and a flow pattern 

that does not change with time; hence, there are no 

changes in storage. Although the Long Island flow system tends towards dynamic equilibrium, such equilibrium is not perfectly achieved. There are small, local 

changes in flow patterns (and in storage) resulting 

from waves and tides and daily fluctuations in precipitation. There are larger changes in flow resulting from 

climatic changes and human activities; these are discussed later in this section. Driving forces within the 

reservoir result from differences in the potential 

energy at different points within the reservoir. Two 

sources of potential energy are pressure and direct action of gravity. The sum of the gravitational potential 

and pressure potential at any point is the groundwater head at that point, and the driving force equals 

the gradient of head. Both the direction and the magnitude of the driving force differ from point to point 

within the reservoir. On a macroscopic scale (a scale 

that includes a statistically significant number of interstices), the spatial variation in head can be described by piecewise continuous functions.

Resistive forces result from friction between the 

moving fluid and the surfaces of the sedimentary particles. The forces are described by the term hydraulic 

conductivity, which includes such factors as density 

and viscosity of the water and microscopic geometry of 

the sedimentary fabric. Not only does the geometry of 

the sedimentary fabric differ from point to point in the 

reservoir, but the fabric usually has a directional aspect, so that the hydraulic conductivity perpendicular 

to bedding at any point is less than the conductivity 

parallel to bedding. The first characteristic is described 

as nonhomogeneity, the second as anisotropy; both 

characteristics are true of the sediments that compose 

the Long Island ground-water reservoir.

The glacial aquifer (H in fig. 2) shows the least 

nonhomogeneity and the least anisotropy of any Long 

Island aquifer. At the other extreme, the hydraulic 

conductivity in the direction of bedding in the Magothy 

aquifer ranges through an order of magnitude or more 

along any bedding plane and through several orders of 

magnitude from top to bottom. The conductivity of the 

latter aquifer is also significantly lower perpendicular 

to bedding than it is along the bedding. Very little is 

known about the hydraulic conductivity of the Lloyd 

aquifer (J), but very little water flows through this 

aquifer (Franke and Getzen, 1975).

Properties of the water throughout a reservoir are 

usually assumed to be constant, and differences in hydraulic conductivity are assumed to be the result of 

differences in the medium (the sediments); but these 

assumptions cannot always be made. Salty water has a 

density different from that of freshwater; hot water is 

less dense and less viscous than cool water, and water 

flowing through sanitary landfills may have a viscosity 

and density quite different from those of the native 

ground water.

Flux (flow per unit area) through any part of the 

reservoir is equal to the product of the hydraulic gradient and the hydraulic conductivity. For isotropic 

aquifers, direction of flow is directly downgradient; but 

for anisotropic aquifers, such as those that constitute 

the Long Island ground-water reservoir, direction of 

flow may diverge from the direction of the gradient.

More than half the natural discharge from the reservoir is through seepage to streams and marshes. The 

remainder of the natural discharge is to salty surface 

water, either directly or through mixing with the salty 

ground water that surrounds Long Island. The 

mechanism through which this mixing occurs is poorly
ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

understood; theoretical models, such as Cooper (1959) 

and the Gheyben-Herzberg theory (Glover, 1959), do 

not seem to fit the Long Island situation (Upson, 1966). 

Beneath the barrier islands along Long Island's south 

shore, fresh ground water is found at depths where it 

should be salty according to both equilibrium models. 

Two explanations for this have been proposed (1) that 

the salty ground water is not in equilibrium with 

present-day heads along Long Island's south shore and 

that the fresh ground water there is a relic of the island's last glaciation; or (2) that the salty water is in 

equilibrium with the heads but that the conditions for 

equilibrium are modified by the osmotic effects of clay 

within the lower part of the reservoir. Neither of these 

explanations can be wholly proved or disproved. Other 

possible explanations are that presently observed 

heads reflect human influences or that Long Island's 

climate is significantly drier than it was a few centuries ago. However, observed heads in the water-table 

aquifer indicate little or no change during the past 70 

years throughout most of the eastern half of Long Island, and there is very little evidence to support the 

hypothesis of much greater precipitation at any time 

since the last major glaciation.

Human influences on the hydrologic cycle are of 

three types: (1) Reduction of recharge through paving 

and storm sewers, (2) removal of water from deeper 

aquifers through wells and recharge to the water-table 

aquifer through cesspools and basins, and (3) removal 

of ground water through wells and discharge to the 

ocean through sewers. These last two are shown as new 

components to the hydrologic cycle (L and M, fig. 2). All 

three human influences result in immediate changes 

in the amount of ground water in storage, followed by 

spreading changes in head and flow patterns as the 

system seeks a new equilibrium. All three human influences were active in Kings and western Queens 

Counties from the mid-nineteenth century until the 

early 1940's. The flow system responded to this stress 

by (1) reduced heads, (2) reduced streamflow, and (3) 

intrusion of salty water into the more highly conductive parts of the reservoir. Human influences of all 

three types have been active in Queens and Nassau 

Counties since the 1940's, and the system has responded by (1) reduced heads and (2) reduced streamflow. Seepage to the bottoms of the surrounding saltwater bodies has been reduced somewhat, but to date 

(1975) little saltwater intrusion has been observed. 

Human influences in Suffolk County have generally 

been limited to removal of water from deep aquifers 

and recharge to the water-table aquifer. The only observed response has been a decline of head at depth in 

the western one-third of Suffolk County.

Human activities have also affected quality of 

ground water on Long Island. Cesspool effluent, industrial wastes, road salt, contaminated runoff from 

highways and parking lots, decomposing wastes in 

sanitary landfills, chemical fertilizers and pesticides, 

animal feces, and leaking sewer mains have all degraded the quality of recharge water. Large parts of 

the ground-water reservoir now contain water of less 

than desirable quality. The glacial aquifer is affected 

over most of the western half of the island and the 

Magothy aquifer in the west-central part of the island 

where the movement of ground water is predominantly 

in a downward or down-and-lateral direction. Pumping 

from the lower part of the Magothy aquifer is accelerating the downward movement of the contaminated recharge water. This study, although it analyzes 

movement of ground water, does not attempt to explain 

or predict changes in water chemistry.

PROMINENT PHYSIOGRAPHIC FEATURES

AND THEIR ROLE IN THE 

HYDROLOGY OF LONG ISLAND

The physiographic features of Long Island are a result of its geologic history; there is a conspicuous geographic relationship between many of these features 

and the hydrologic features of Long Island, not only 

because of their role in determining the gross geometry 

of the flow system but also because of the close connection between the topographic features and the underlying geology. The most prominent physiographic features are related to Pleistocene glaciation. These are 

(1) the east-west trending hills in the northern and 

central parts of the island and their eastward extensions, which form the north and south forks, (2) the 

gently sloping plain that extends southward from the 

hills, and (3) the deeply eroded headlands along the 

north shore. Other important features are the barrier 

beaches along the south shore, the shoreline, and the 

major streams.

The Harbor Hill Moraine, which forms the northern 

line of east-west trending hills, extends from Kings 

County to Orient Point on the north fork (fig. 3). The 

southern line of hills, which make up the Ronkonkoma 

Moraine, extends from northwestern Nassau County 

eastward to Montauk Point. These moraines were deposited near the southern terminus of glacial ice sheets 

and have an altitude ranging from 70 to 90 m (210 to 

270 ft) in most places.

GEOLOGIC FEATURES

The consolidated bedrock that underlies Long Island 

in overlain by a wedge-shaped body of unconsolidated 

sediments (fig. 4). The bedrock is at or near land sur-
HYDROGEOLOGY OF LONG ISLAND

41 

Base from U.S. Geological Survey, 1:250,000 series: 

Scranton, Hartford, 1962; New York, 1957; 

Newark, Providence, 1947

FIGURE 3. Physiographic features that influence Long Island hydrology.

face in the northwestern part of Long Island and has a 

regional southeastward slope of about 0.7 degrees 

(about 12 m/km or 63 ft/mi). The bedrock has an extremely low hydraulic conductivity (not measured); the 

contact between it and the Cretaceous sediments can 

be considered to be the lower boundary of the groundwater flow system. The Cretaceous sediments and 

overlying deposits that are saturated with fresh, moving ground water constitute the ground-water reservoir.

Pertinent information on the reservoir rocks is summarized in table 1. Figures 4-8 show what was known 

of the gross geometry of the reservoir rocks at the time 

the three-dimensional model was constructed (1971). 

These illustrations are regional, hydrogeological interpretations used in the current study. Additional 

geologic data were acquired after the study began; improper model performance suggested some discrepancies in the geologic data before the new data were acquired. Other recently acquired geologic data are insignificant to the regional hydrology but would have to 

be considered in hydrologic analyses of small areas.

The lowermost aquifer, the Lloyd, directly overlies 

the bedrock. The Lloyd consists mainly of gravelly 

sand with lenses of silty sand and clay. Seepage into 

the Lloyd aquifer is limited by the overlying Raritan 

clay, which has a fairly uniform thickness of 60-90 m 

(200-300 ft) and probably has a very low hydraulic 

conductivity (Franke and Getzen, 1975). The Raritan

clay, even though silty and sandy in places, appears 

dense and well-compacted almost everywhere it has 

been seen, but it has been seen at only a few widely 

scattered localities. The Raritan is penetrated by only 

a few wells and is exposed in only a few places on the 

north shore of western Long Island. The clay is missing 

from the sequence in small areas of northwestern Long 

Island.

The Magothy aquifer, which probably includes parts 

of several poorly defined Cretaceous formations 

(Perlmutter and Todd, 1965), consists of a series of beds 

of fine to medium sand interbedded with clay and 

sandy or silty clay. Several of these beds seem to be 

fairly extensive, but none, apparently, can be traced 

for more than a few kilometres. The degree of consolidation of the sand beds varies from loose to moderately 

indurated, and their texture varies from silty to 

gravelly. Only rarely does the thickness of a single 

sand bed exceed 15 m (47 ft), but the thickness of some 

sandy zones that have only a few thin clay beds scattered through them are 50 m (160 ft) or more. Thickness of the clay beds range from a few millimetres to 20 

m (66 ft); in many places, the beds are thicker in the 

upper part of the sequence than in the lower part.

The Magothy aquifer is overlain by several Cretaceous and post-Cretaceous units of low to very low hydraulic conductivity. Among these units are silty, 

sandy clay beds of the Monmouth Group along the 

south shore of Long Island. The beds thicken seaWard.
ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Clays of the Monmouth Group are not found on western Long Island. There, the Magothy aquifer is overlain by the Jameco Gravel, evidently a fluvio-glacial 

deposit on an erosional surface in the Magothy. A 

fringe of Pleistocene clay that surrounds the island extends a few kilometres inland along much of the south 

shore and in several places on the north shore. This 

fringing clay is almost always referred to as the Gardiners Clay but may include material of diverse 

geologic origins (Upson, 1970). Material identified in 

well logs as Gardiners Clay generally ranges in thickness from 2 to 120 m (6 to 400 ft). The areas of the 

thickest parts of the clay are very small. The clay in 

the subsurface near the south shore seems to thicken 

slightly in a seaward direction, but its seaward extent 

is largely unknown.

The upper glacial aquifer consists primarily of sand 

and gravel, which is glaciofluvial and glaciodeltaic in 

origin. Even the end-morainal features on much of 

Long Island seem to be associated with deformed deposits of stratified drift rather than till (Mills and 

Wells, 1974). Several tills within and above the 

stratified drift have been identified in the northern 

part of the island, and several extensive clays, evidently glaciolacustrine in origin, are found within the 

stratified drift.

DISTRIBUTION OF HYDRAULIC 

CONDUCTIVITY AND STORAGE COEFFICIENT

Regional trends in the hydraulic conductivity of the 

upper glacial and Magothy aquifers on Long Island 

have been mapped by McClymonds and Franke (1972). 

These trends, shown in figures 9 and 10, are sufficiently accurate for a regional ground-water model, although the ground-water reservoir is not completely 

defined by them. The Jameco aquifer, which is highly 

conductive, is important in western Long Island. Figure 11 shows the areal extent and estimated hydraulic 

conductivity of the Jameco aquifer. Although the 

Jameco aquifer is a distinct geologic unit (Soren, 1971), 

it is continuous with the Magothy aquifer over much of 

its area and has been considered in this study as a 

high-permeability zone at the top of the Magothy 

aquifer. Several additional but minor hydrogeologic 

units are also part of the Long Island ground-water 

reservoir and are lumped here with major units.

Estimates of hydraulic conductivity mapped in 

figures 9-11 are for flow parallel to bedding (bed parallel) (McClymonds and Franke, 1972, p. Ell). Similar 

estimates for flow perpendicular to bedding (bed normal) within each aquifer have not been published. 

Franke and Getzen (1975), in working with steadystate, cross-sectional models, conclude that an

41" -

0 5 10 15 20 25 MILES

i i i i i

Base from U.S. Geological Survey, 1:250,000 series: 

Scranton, Hartford, 1962; New York, 1957; 

Newark, Providence, 1947

FIGURE 4. Locations of and typical sections through the Long Island ground-water reservoir showing major hydrogeologic units.

(Geology after Swarzenski, 1963; Isbister, 1966; Jensen and Soren, 1974.)
HYDROGEOLOGY OF LONG ISLAND

A' B

800

Magothy aquife^rj_^-v>^\. :\^_-^^^.

,. METRES 

r-100

- 50

-100

-150

- 200

- 250

SEA 

LEVEL

200 -

400 -

600 -

800

XvX Upper XvXvX-Xv glacial X;vXvXvXv aquifer-X-XvX-XvX

 \::t]:::.\:^\:::;-.\ff:f::^::f^

:r^:- Magothy aquifer '^' ' '^^ '''^\'.'^^'§^ 

'^^\ ' ::}J.; ;'. '. .-. '.-' ^: -^^'- ^ ' S^^^^^^ 

l^^^'^^^-'^'^

XSmithtown

p^^SxvX P.^H'^rxWvxJ^^^'

ii^.'^^X-X-XOX-X^-X^XvX-X/fe'.^r^^T . - -^ ' .l^-- : i??sxvXvAvXvX'"-Xv;ix' -^ : / '^<^'- \ \ .

 .-^*A- . . V.V.V.VAVlJ.V.V.TX. ' . Dai-I+on ^lov/ 

i^\\' ' ' ' ' ^ ' ' K-'-Vvi^l^X ' ' . 4i§I? Cl3^

' ' ' ^'^r^-'^'l- sXs\v;> '.:: '. " ""

 '.' . . /.' '.~^--- ' '. . 

 .' Magothy aquifer

 =_ METRES 

r 100

- 50

SEA

LEVEL

- 50

- 100

- 150

- 200

- 250

GardlnersvXvXvXv/Upperx'v- glacial ; ; ; aquifer 

'' vX; glacial .; ;.;.; aquifer;.;.;.;

'

 ^?Monmouth undifferentiated'- ' '.'' ^ ^

800

0 5 10 15 20 KILOMETRES 

VERTICAL SCALE GREATLY EXAGGERATED

FIGURE 4. Continued.
10 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

TABLE 1. Hydrogeologic units of Long Island

[From McClymonds and Franks, 1972, p. E5-E6]

System

Quaternary

Series

Holocene

Plesitocene

Geologic unit1

Recent deposits: Artificial fill,

salt marsh deposits, stream

alluvium, and shoreline deposits.

Upper Pleistocene deposits

 Unconformity? 

Gardiners Clay

 Unconformity? 

Jameco Gravel

 Unconformitv 

Hydrogeologic

unit

Recent

deposits

Upper

glacial 

aquifer

Gardiners

Clay

Jameco

aquifer

Approximate

maximum

thickness

(metres)

15

180

90

90

Depth

from land

surface

to top

(metres)

0

0-15

15-120

15-170

Character of deposits

Sand, gravel, clay, silt, organic mud,

peat, loam, and shells. Colors are

gray, brown, green, black, and yellow. Recent artificial-fill deposits of

gravel, sand, clay, and rubbish.

Till (mostly along north shore and in

moraines) composed of clay, sand,

gravel, and boulders forms Harbor

Hill and Ronkonkoma terminal

moraines. Outwash deposits (mostly

between and south of terminal

moraines, but also interlayered with

till ) consist of quartzose sand, fine to 

very coarse, and gravel, pebble to

boulder sized. Glaciolacustrine deposits (mostly in central and eastern

Long Island) and marine clay (locally 

along south shore ) consist of silt, clay,

and some sand and gravel layers; includes the "20-foot clay" in southern

Nassau and Queens Counties. Colors

are mainly gray, brown, and yellow;

silt and clay locally are grayish

green. Contains shells and plant remains, generally in finer grained

beds; also contains Foraminifera.

Contains chlorite, biotite, muscovite,

hornblende, olivine, and feldspar as

accessory minerals; "20-foot clay"

commonly contains glauconite.

Clay, silt, and few layers of sand and

gravel. Colors are grayish green and

brown. Contains marine shells,

Foraminifera, and lignite; also locally contains glauconite. Altitude of

top generally is 50-80 feet below

mean sea level. Occurs in Kings,

Queens, and southern Nassau and

Suffolk Counties; similar clay occurs

in buried valleys near north shore.

Sand, fine to very coarse, and gravel to

large-pebble size; few layers of clay

and silt. Gravel is composed of crystalline and sedimentary rocks. Color

is mostly dark brown. Contains chlorite, biotite, muscovite, hornblende,

and feldspar as accessory minerals.

Occurs in Kings, Queens, and southern Nassau Counties; similar deposits occur in. buried valleys near

north shore.

Water-bearing properties

Permeable sandy beds beneath barrier

beaches yield fresh water at shallow

depths, brackish to salty water at

greater depth. Clay and silt beneath

bays retard saltwater encroachment

and confine underlying aquifers.

Stream floodplain and marsh deposits

may yield small quantities of water

but are generally clayey or silty and

much less permeable than the underlying upper glacial aquifer.

Till is poorly permeable; commonly

causes perched-water bodies and impedes downward percolation of water

to underlyingbeds. Outwash deposits

are moderately to highly permeable;

specific capacities of wells tapping

them range from about 10 to more

than 200 gal/min per ft (gallons per 

minute per foot I of drawdown. Good to

excellent infiltration characteristics.

Glaciolacustrine and marine clay deposits are mostly poorly permeable 

but locally have thin, moderately

permeable layers of sand and gravel; 

generally retard downward percolation of ground water. Contains freshwater except near the shore lines. Till

and marine deposits locally retard

saltwater encroachment.

Poorly permeable; constitutes confining

layer for underlying Jameco aquifer.

Locally, sand layers yield small

quantities of water.

Moderately to highly permeable; contains mostly freshwater, but brackish

water and water with high iron content occurs locally in southeastern

Nassau and southern Queens Counties. Specific capacities of wells in the

Jameco range from about 20 to 150

gal/min per ft of drawdown.

adequate representation of aquifer properties near the 

center of Long Island must include a substantial degree of anisotropy; bed-normal conductivities onetenth to one-twenty-fourth of bed-parallel conductivity 

are suggested for the upper glacial aquifer, and bednormal conductivities one-thirtieth to one-sixtieth of 

bed-parallel conductivity are suggested for the 

Magothy aquifer. These ranges of anisotropy are supported by four recent aquifer tests. One test in the 

Magothy aquifer indicated an anisotropy of 1:30; three 

in the upper glacial aquifer indicated anisotropy ranging from 1:1.8 to 1:2.8. These tests, however, are inconclusive and may not be representative of the aquifers. 

Reliable data for the conductivity of the confining 

beds (Gardiners Clay and other clays in the deposits of

Cretaceous-Quaternary age that overlie the Magothy 

aquifer) are not available. A vertical conductivity of 

2.5 xlO"5 cm/s (0.07 ft/d), characteristic of similar clay 

beds in Connecticut and Maryland, is reasonable for 

these units. Subsequent sensitivity tests conducted on 

the cross-sectional models of Long Island (Franke and 

Getzen, 1975) indicate that this estimate may be about 

one order of magnitude too high but that relative to the 

other parameters tested regional flow is insensitive to 

the conductivity of these beds. On a regional scale, 

horizontal flow in the confining beds is probably negligible.

Field data for storage coefficients of Long Island 

aquifers are meagre. The few data that are available 

indicate that the specific yield of the unconfined
HYDROGEOLOGY OF LONG ISLAND 

TABLE 1. Hydrogeologic units of Long Island Continued

11

System

Tertiary (?i

Cretaceous

Precambrian

Series

Pliocene!?)

Upper 

Cretaceous

Geologic unit 1

Mannetto Gravel

 Unconformity 

Magothy (?) 

Formation2

Raritan 

Formation

 Unconiwiiiiii,^ 

Clay Member

Lloyd Sand 

Member

Bedrock

Hydrogeologic

unit

(Commonly 

included

with upper

glacial

aquifer, i

Magothy 

aquifer

Raritan Clay

Lloyd 

aquifer

Bedrock

Approximate

maximum

thickness

(metres)

90

340

90

150

Depth

from land

surface

to top

(metres)

0-35

0-180

20-460

60-550

0-820

Character of deposits

Gravel, fine to coarse, and lenses of 

sand; scattered clay lenses. Colors are

white, yellow, and brown. Occurs

only near Nassau-Suffolk County

border near center of island.

Sand, fine to medium, clayey in part;

interbedded with lenses and layers of

coarse sand and sandy and solid clay.

Gravel is common in basal 50-200

feet. Sand and gravel are quartzose.

Lignite, pyrite, and iron oxide concretions are common; contains muscovi te, magnetite, rutile, and garnet as

accessory minerals. Colors are gray, 

white, red, brown, and yellow.

Clay, solid and silty; few lenses and 

layers of sand; little gravel. Lignite 

and pyrite are common. Colors are

gray, red, and white, commonly variegated.

Sand, fine to coarse, and gravel, commonly with clayey matrix; some

lenses and layers of solid and silty 

clay; locally contains thin lignite

layers and iron concretions. Locally

has gradational contact with overlying Raritan clay. Sand and most of 

gravel are quartzose. Colors are yellow, gray, and white; clay is red locally.

Crystalline metamorphic and igneous

rocks; muscovite-biotite schist,

gneiss, and granite. A soft, clayey

zone of weathered bedrock locally is

more than 100 feet thick.

Water-bearing properties

Highly permeable, but occurs mostly 

above water table. Excellent infiltration characteristics.

Most layers are poorly to moderately

permeable; some are highly permeable locally. Specific capacities of

wells in the Magothy generally range

from 1 to about 30 gal/min per ft of

drawdown, rarely are as much as 80

gal/min per ft of drawdown. Water is

unconfined in uppermost parts;

elsewhere is confined. Water is generally of excellent quality but has 

high iron content locally along north

and south shores. Constitutes principal aquifer for public-supply wells in

western Long Island except Kings

County, where it is mostly absent.

Has been invaded by salty ground

water locally in southwestern Nassau

and southern Queens Counties and in

small areas along north shore.

Poorly to very poorly permeable; constitutes confining layer for underlying 

Lloyd aquifer. Very few wells produce

appreciable water from these deposits.

Poorly to moderately permeable.

Specific capacities of wells in the

Lloyd generally range from 1 to about 

25 gal/min per ft of drawdown, rarely

are as much as 50 gal/min per ft of

drawdown. Water is confined under 

artesian pressure by overlying Raritan clay; generally of excellent quality but locally has high iron content.

Has been invaded by salty ground

water locally in necks near north

shore, where aquifer is mostly shallow and overlying clay is discontinuous. Called "deep confined aquifer" in

some earlier reports.

Poorly permeable to virtually impermeable; constitutes virtually the

lower boundary of ground-water reservoir. Some hard, freshwater is contained in joints and fractures but is

impractical to develop at most places;

however, a few wells near the western

edges of Queens and Kings Counties

obtain water from the bedrock.

"Names are those used in reports by the Geological Survey.

2The use of the term "Magothy(?i Formation" has been abandoned. The post-Raritan.Cretaceous deposits are divided into the Magothy Formation and Matawan Group undifferentiated and the Monmouth Group undifterentiated.

aquifer north of the Harbor Hill terminal moraine is 

generally less than it is in the outwash plain south of 

the moraine (unpublished data in Geological Survey 

files). A specific yield (water-table storage coefficient) 

of 0.10 was estimated for the area north of the line 

shown in figure 12 and a coefficient of 0.18, south of 

this line. Water-table storage coefficients were assumed for the upper glacial aquifer throughout most of 

Long Island. In two small areas in the north-central 

part of the island, the top of the saturated zone is below 

the glacial deposits and the top of the Magothy aquifer 

is unconfined with a storage coefficient of 0.10. These 

specific yields are minimal for sediments with a porosity of 25-30 percent. A minimal value of 2xlO" 8 cm~ 1

(6xlO" 7 ft l) for compressive storage was also assumed. 

These estimates were based on a general appraisal of 

the lithology; subsequent aquifer tests tend to corroborate these values.

SURFACE WATER

LAKES

As described by Veatch, Slichter, Bowman, Crosby, 

anjd Horton (1906), lakes and ponds on Long Island 

ocfcur in three different hydrologic environments. Lake 

Success is an example of a perched lake. This type of 

lake is separated from the main water table by nearly 

impervious strata and is common on the groundmorainal deposits that form the more elevated parts of
12 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

EXPLANATION

Line of equal thickness of saturated material, October 1965 

Intervals, 30 and 60 metres (100 and 200 feet)

10 15 20 25 MILES

I I I

i i i i i Unsaturated area

0 5 10 15 20 25 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 5. Saturated thickness of the upper glacial aquifer on Long Island. (After McClymonds and Franke, 1972, pi. 1.)

the island. These lakes do not influence, nor, for the 

most part, are they influenced by the main water table.

A second type of lake, one that is dependent on the 

regional water table, is much more abundant on eastern Long Island. Lake Ronkonkoma is the largest lake 

of this type, but Artist Lake, Long Pond, Deer Pond, 

Swan Pond, Great Pond, Big Fresh Pond, and Poxabogue Pond are other examples (Veatch and others, 

1906, p. 63). Water is exchanged more or less freely 

between this type of lake and the ground-water reservoir, and when water is pumped from a lake of this 

type or evaporates from its surface, the lake becomes a 

ground-water sink; it is a large "natural well." Both 

types of lakes are unimportant to the regional 

ground-water system.

Dammed streams constitute a third class of lakes 

(fig. 13). Depending on whether the water level in such 

lakes is maintained above or below the surrounding 

ground-water table, such lakes can function as either 

ground-water sources or sinks of a local nature. Figure 

13 shows that dammed streams retard the seepage of 

ground water into the streams along the lakeshore. 

The basic effect of these lakes on the ground-water 

reservoir is to modify the regional gradients in their 

vicinities decreasing the shorewards gradients in the 

areas above the dams and increasing gradients below 

the dams. Such a lake causes a reversal in the water 

table slope adjacent to the stream, which prevents 

ground-water seepage into the stream, but the effect on 

both streamflow and the water table is small a short

distance upstream or downstream of the lake. In the 

regional analysis, each lake of this type is treated as a 

stream reach with little or no ground-water seepage.

STREAMS

The Nissequogue River, which has the highest average flow of any Long Island stream, had an average 

discharge of 1.18 m3/s (40.3 ft3/s) between 1943 and 

1970 (U.S. Geological Survey, 1972, p. 37). There are 

four other major streams with discharges greater than 

0.5 m3/s (17 ft3/s) Peconic, Carmans, Connetquot, and 

Carlls Rivers. Most of the larger streams and all those 

with an average discharge greater than 0.3 m3/s 

(10 ft3/s), except the Nissequogue and Peconic Rivers, 

discharge along the south shore. Except for a few in the 

western part of the island, the streams of Long Island 

receive most of their flow from ground-water seepage 

(Cohen and others, 1968, p. 62). Seventy-five of these 

streams (fig. 14) are large enough so that each affects 

the water table and patterns of flow within the 

ground-water reservoir over an area greater than 

2 km2 ; all together, these streams drain more than 

13.4 m3/s (300 Mgal/d) from the ground-water reservoir.

The streams are of interest because of the way in 

which they are affected by changing ground-water 

levels and because of their changing rates of seepage 

from the ground-water reservoir. Even small fluctuations in water-table elevation can cause pronounced 

changes in stream discharge. Changes in stream dis-
41 'OQ'

HYDROGEOLOGY OF LONG ISLAND

45'

13

45'

40 30'

EXPLANATION

: 

ISLAND 'X-:- ;:;:-: ;: 

^s- ^

SOUND

Line of equal thickness 

Intervals, 15 and 30 metres (50 and 100 feet)

Approximate limit of Jameco aquifer

Base from U.S. Geological Survey, 1:250,000 series 

New York, 1957; Newark, 1947

FIGURE 6. Thickness of the Jameco aquifer. (After McClymonds and Franke, 1972, fig. 13).

charge are of interest because of (a) recreational uses of 

freshwater lakes, (b) the influence of stream discharge 

on the salinity of the brackish-water bodies surrounding Long Island and the resulting effects on shell fishing and general marsh ecology, and (c) the large 

amounts of ground water that are diverted from

streams to wells where pumping of the wells causes a 

slight lowering of the regional water table.

BOUNDARIES BETWEEN SALTWATER 

AND FRESH GROUND WATER

Fresh ground water comes into contact with both
14 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

EXPLANATION

210

Line of equal thickness of saturated

material, October 1965 

Interval, 30 metres (100 feet)

I I I I 

10 15 20 25 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 7. Saturated thickness of the Magothy aquifer. (After McClymonds and Franke, 1972, pi. 2.)

10

I

15

I

20

I

25 MILES 

I

I 

10

1 I I

15 20 25 KILOMETRES

Contact, dashed where approximately located

Confining beds

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 8. Extent of Gardiners Clay and other Cretaceous-Pleistocene deposits that constitute a composite confining bed overlying 

the Magothy aquifer. (Geology after Perlmutter and Geraghty, 1963 and N. E. McClymonds, written commun., 1970.)

salty surface water and salty ground water. The salty 

surface water surrounding Long Island is a significant 

boundary to the ground-water reservoir. Any fluctuations in head along the bottoms of the surface-water 

bodies are independent of head within the groundwater reservoir; the bottom is said to be a specifiedpotential boundary. Waves and tides fluctuate so 

rapidly that the fluctuations are usually ignored, and 

the boundary is treated as one along which the head is 

constant, or invariant with time and horizontal direc-
HYDROGEOLOGY OF LONG ISLAND 15

^ «a°3o<

,,-,-.-, ,,-^11 

'ATLANTIC

Ore/it South Bay: Iti

EXPLANATION

-f

OCEAN -1500-

-f

10

I

15

I

20

I_

I I T I I I 

0 5 10 15 20 25 KILOMETRES

25 MILES

_|

Line of equal hydraulic conductivity

Interval, 500 gallons per day per square

foot (20 metres per day)

Unsaturated area

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 9. Estimated hydraulic conductivity of the upper glacial aquifer. (After McClymonds and Franke, 1972, pi. 1.)

I 

10

10

I

I 

15

15

I

20

I

25 MILES

I

20 25 KILOMETRES

Line of equal hydraulic conductivity

Interval, 100 gallons per day per square

foot (4 metres per day)

5&S5555555555& 

Approximate limit of Magothy aquifer

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 10. Estimated hydraulic conductivity of the Magothy aquifer. (After McClymonds and Franke, 1972, pi. 2.)

tion. Because salty water is more dense than freshwater, the head along the boundary is a function of 

saltwater depth. At the bottoms of bays and oceans, 

freshwater heads at the sediment-water interface must 

balance the head resulting from the density 

difference about 2.5 percent of the surface-water

depth if the body is seawater, proportionately less if 

the surface water is less dense than seawater. The 

head condition just described must always be met 

along the boundary between fresh ground water and 

salty surface water, regardless of whether the system 

is in equilibrium. The same head condition must be
16 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

41"00' 74 00'

45' 73 30'

45'

40° 30'

EXPLANATION

7500

Line of equal hydraulic conductivity

Interval, 500 gallorts per day per square

foot (20 metres per day)

Approximate limit of Jameco aquifer

5 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

New York, 1957; Newark, 1947

FIGURE 11. Estimated average hydraulic conductivity of the Jameco aquifer. (After McClymonds and Franke, 1972, fig. 14.)

met for the boundary between fresh ground water and 

salty ground water if dynamic equilibrium is to be 

maintained, if the salty ground water is assumed to be 

static, and if the only net forces acting on the ground 

water are head gradients arising from gravitational 

forces (Hubbert, 1940, p. 868-870, 924-926).

Figure 15 is a diagram of the seaward boundary of 

fresh ground-water flow on Long Island showing (A) 

the surface along which freshwater head must balance 

the head caused by density differences between freshwater and saltwater and (B) the surface along which 

freshwater head seems to balance saltwater heads and
HYDROGEOLOGY OF LONG ISLAND 17

\ I I I 

10 15 20 25 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 12. Values of specific yield estimated for the water table.

FIGURE 13. Section across a stream valley showing water table before (A-B) and after (A-B') pond is created by damming a stream. 

The pond causes a reversal in the water-table slope which prevents 

ground-water seepage into the stream. (After Veatch and others, 

1906.)

meets conditions for a classical equilibrium interface 

as described by Hubbert (1940, p. 868-870); (C) indicates that surface along which freshwater head seems 

not to balance saltwater head and along which conditions for a classical equilibrium interface are not met. 

An earlier discussion (p. 6) indicated that failure of 

heads along surfaces marked (C) to meet the conditions 

for a classical equilibrium interface could result from 

either (1) nonequilibrium conditions or (2) modification 

of the conditions for equilibrium by osmotic effects of 

the clays at and below the top of the Magothy aquifer. 

The difference in density between fresh and salty 

water tends to keep the two separated with the fresh 

ground water on top; under steady-state conditions, the

interface is represented by limiting flowlines of the 

fresh and salty water flow systems. A limiting flowline 

is mathematically equivalent to a no-flow or impermeable boundary, although there is no physical impermeable boundary. Fresh or salty ground water can move 

across the interface through two processes (a) bulk 

displacement of one type of fluid by the other or (b) 

dispersion or mixing of the two fluids. Under 

nonsteady flow conditions, either process can cause 

movement of the interface, but the interface would 

move at velocities several orders of magnitude less 

than the velocity at which potential transients are 

transmitted through the confined parts of the 

ground-water reservoir. Transient changes in head are 

transmitted across the interface as though the interface were nonexistent, but because the interface is 

generally some distance offshore in the confined aquifers of Long Island, head changes at the interface resulting from human activities on the island will generally be small. Movement of the interface resulting from 

onshore pumping would accordingly be slow. Cooper 

(1959) provides a useful discussion of the physics of 

saltwater intrusion, and Lusczynski and Swarzenski 

(1966) describe the occurrence of intrusion on Long 

Island.

Although the preceding conclusion is true for the 

interface in the confined aquifer along most of the 

south shore of Long Island, it is not true everywhere. 

In parts of Kings, Queens, and Nassau Counties, the 

interface is landward of the shoreline and adjacent to
18 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Note: See table 2 for explanation of lettering on streams. Some of the 

streams (mostly in Queens County) 

have been replaced by sewers and are 

25 KILOMETRES not listed in the table

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 14. Locations and letter designations used for major Long Island streams.

SOUTH NORTH 

Water tabli

NOT TO SCALE

major pumping centers, the aquifers are thinner and 

more highly permeable than average for Long Island, 

and the confining unit is discontinuous; consequently, 

the interface can move rapidly (locally in excess of 

10 m/yr or 33 ft/yr) in response to onshore pumping.

WATER TABLE

The water table, or free surface, is a boundary to the 

ground-water reservoir that can move in time. In recharge areas on Long Island, the flux (rate of flow per 

area) to the water table generally occurs as unsaturated flow and, therefore, is not affected by heads 

within the reservoir. In discharge areas, the rate at 

which water leaves the reservoir at the water table is 

related to heads within the reservoir but is ultimately 

controlled by evapotranspiration rates. One way of 

treating the water table is to ignore the how and the 

why of changes in flux across it and to treat it as a 

surface across which the flux is entirely controlled by 

events external to the aquifer except at points where

FIGURE 15. Schematic hydrologic section of seaward boundary of 

fresh ground-water flow on the south shore of Long Island showing 

(A) the surface along which freshwater head must balance the 

head caused by the density difference between freshwater and 

salty surface water, (B) the surface along which freshwater head 

seems to balance saltwater head in the aquifer, and (C) the surface 

along which freshwater head seems not to balance static saltwater 

head.
MODEL DESIGN 19

the water table intersects seeps (streams and springs). 

At those seeps, flow out of the upper surface of the 

aquifer is a linear function of the gradient towards the 

seep; the seep is maintained at a potential denned by 

its altitude.

MODEL DESIGN

BASIC ANALOG CONCEPTS AND SIMILARITY COEFFICIENTS

The sediments of the Long Island aquifer system are 

clearly anisotropic in their hydraulic conductivity, 

which is maximum parallel to the bedding and 

minimum at right angles to it. They are likewise 

heterogeneous, with extreme variations in hydraulic 

conductivity from place to place. The flow of ground 

water of uniform density and viscosity through a 

medium of this sort can be described in terms of two 

equations, as follows:

K> 

K,

Kxz

Kyz

KZ2

dh/dx 

dh/dy 

dh/dz

and

dx

+ . + 

dy dz

Ss dh 

dt

(1)

(2)

where K^, Kxy, . . ., are the components of the hydraulic 

conductivity tensor; h represents hydraulic head; qx ,qy , 

and qz are the components of the Darcy velocity, or flow 

per unit area; t is time; and Ss is the specific storage. In 

this formulation, both the hydraulic conductivity tensor and the specific storage are considered functions of 

position that is, the medium is considered 

heterogeneous as well as anisotropic. The coordinate 

directions, x, y, and z, are chosen arbitrarily. (See, for 

example, Collins, 1961, p. 63 and 72.)

Direct electrical simulation of equations 1 and 2 

could be accomplished by using complex circuitry; for 

example, by using certain negative resistance elements. But this would be a difficult and costly procedure. A considerable simplification is possible if the 

medium can be considered orthotropic that is, having 

three perpendicular principal axes of conductivity 

along at least one of which the conductivity attains its 

maximum value and along at least one of which the 

conductivity has its minimum value and if the coordinate axes can be taken along these principal axes of 

conductivity. In the Long Island system, two of the 

principal axes can be taken parallel to the bedding. In 

these directions, designated x' and y', the hydraulic 

conductivity has its maximum value, KA . The third 

principal axis, designated 2', can be taken at right angles to the bedding. In this direction, the conductivity

has its minimum value, KB . If the coordinate axes are 

taken along x', y', and z', equations 1 and 2 can be 

reduced to:

d ~dx /KA dh\ + _d_(KA dh\ 

'\ dx'/ dy'\ dy')

_d_/KB dh\ = S8 dh 

dz'\ dz') ~ dt'

(3)

Equation 3, which is easily simulated electrically, 

accounts for the heterogeneity of the system that is, 

variation of KA , KB , and Ss with position but assumes 

that the directions of maximum and minimum conductivity remain the same throughout the system. This is 

not strictly true in the Long Island aquifers because 

the dip of the sediments varies slightly with map location and with depth. The electrical simulation used in 

this analysis approximates equation 3 at each individual point in the aquifer but also partly accounts for 

variation in direction of the principal axes. In this 

sense, the simulation represents the ground-water system more accurately than does equation 3. In the process, however, additional errors are introduced. The errors are described later in this section.

Electrical simulation is accomplished by dividing 

the aquifer into blocks as shown in figure 16. Figure 

16A represents a typical hydrologic section through 

the island; figure 16B illustrates the division of the 

aquifer into blocks along this section. The two uppermost layers of blocks represent the upper glacial 

aquifer, and the three lower layers represent the 

Magothy aquifer. The layers are aligned along the 

high-conductivity axes; that is, they are parallel to the 

bedding at all points. Because of the exaggeration of 

the vertical scale, both the dip of the various layers and 

the differences in dip between the layers seem to be 

much greater in figure 16 than they are. All dips are on 

the order of 1 degree.

Figure 16C shows one of the blocks of figure 16B and 

an array of seven nodal points in the neighborhood of 

this block. The head at each nodal point is indicated by 

the subscript notation shown in the figure. The central 

node lies at the centroid of the block shown in the 

figure, and the surrounding nodes are assumed to lie at 

the centroids of the six surrounding blocks. In terms of 

finite differences in head, the equation for approximate 

inflow along the x' axis is

(4)
20 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

where the subscript 1 indicates that the various terms 

are taken between node 1 and node 0. The hydraulic 

conductivity, KA ^, is an average value for this interval, 

as is the flow area (Ay'Az'V The symbol (hx'\ is simply the distance between node 1 and node 0. Equation 4 

can be obtained by applying Darcy's law to flow 

through the right face of the block, expressing the de-

/ J/i rivative by a Taylor series expansion, and neglectox 

ing terms of higher order than the first in the resulting

series. 

The equation for approximate outflow along the x'

axis is

Kt

(Ax')2

(5)

where subscript 2 indicates values for the interval between node 0 and node 2. Therefore, inflow minus outflow in the x' direction is approximately

(Ax') 2

(h0 -h2 )

(6)

Similar expressions, using parallel subscript notation, 

can be developed for inflow minus outflow in the y' and 

z' directions. When this is done, the total inflow minus 

outflow may be equated approximately to the rate of

r)h accumulation of fluid in storage in the block, SS (AF) 

C/t

where AV represents the volume of the block. 

This leads to the equation

(Ax')! (A*')2

(h Q -h2)

gB6(Ax'A;y')6

(h 5 -h0) -

(Az')f

(h0 -h

:'\ + (Ax')2 ^ (A/)3 + (4y')4

at (7)

Equation 1 is simplified considerably by making 

Ax'=Ay' for all blocks. In this case,

KAl (Az'), (hj-h0) - KA2 (Az')2 (h Q -h2) 

KA3 (Az')3 (h3 -h0 ) - KA4 (Az')4 (h0 -h4)

KB5

(Az')t

Ax'A/

(h5 -hQ ) -

KB (Ax'A/)

(Az') B +(Az') 6

dt (8)

Equation 8 may be regarded as a finite-difference (in 

space) approximation to equation 3, using the block 

configuration shown in figures 16 and 17 and keeping 

Ax'=Ay throughout. As suggested previously, however, equation 8 simulates conditions in the aquifer 

(equations 1 and 2) more closely than it simulates 

equation 3. Equation 3 requires that the principal conductivity axes remain fixed throughout the system, 

whereas in reality they do not. A simulation of field 

conditions that is superior in certain ways to one that 

would be given by a direct, finite-difference approximation of equation 3 can be obtained by changing the 

orientation of the blocks to follow approximately the 

changing directions of maximum and minimum conductivity.

Errors associated with a finite-difference approximation using a uniform rectangular mesh have received 

extensive attention in the literature; for example, 

Karplus, (1958, p. 103-108). If, as in this example, the 

mesh is not perfectly rectangular, additional errors are 

introduced. The increase in Az' in the downdip direction implies that the downdip flow through a block 

must diverge, rather than remain entirely parallel to 

x'; thus, it cannot be completely accounted for by a

r\ -i

term approximating only-r-^.In addition, the upper or

lower surface of a block may not be perfectly perpendicular to a line between the centroid of the block and 

that of the overlying or underlying block. In this case, 

flow across the surface cannot be exactly described in 

terms of a head difference between the centroids. Magnitude of the errors generated by these causes is difficult to estimate and would vary from place to place 

in the system. However, because the dip is very low 

and the changes in dip are both small and very 

gradual, errors of this sort would probably be negligible throughout the system.

A direct electrical analog of equation 8 is easily constructed. Karplus and Soroka (1959), Skibitzke (1961), 

Bermes (1960), and Walton and Prickett (1963) discuss 

both the theoretical basis and the technique of such 

electrical simulation. Figure 16D shows an electrical 

configuration in which six resistors are used to connect 

a central node, or junction, with six surrounding nodes.
MODEL DESIGN 

A

21

-SEA LEVEL

- - 300

- 400

0 5 MILES

I I I I i i

I I I I I I

0 5 KILOMETRES

FIGURE 16. Finite-difference representation and notation of hydrologic section through the Long Island 

ground-water reservoir (thickness greatly exaggerated): A, A typical hydrologic section. B, This section 

divided into blocks, or finite-differences. C, Expansion of one block from this section showing the principal conductivity axes, x', y', andz'; also head at the centroid of this block, h0 , and at the centroids of six 

surrounding nodes, hlt h2 , . . . he .D, An electrical analogy for flow in this block with voltages E0 . . . E6 

analogous to heads ho . . . h6 , resistances Rl .. .Re , and capacitance C0 .
22 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

A capacitor connected to the central node provides 

electrical storage at this point. Voltage at the central 

node is designated EO . and voltages at the surrounding 

nodes are designated Ei,. . . E6 , respectively, which 

parallels the notation used for heads in equations 4 

through 8. The current (Ji) toward the central node 

through resistor R i is given by Ohm's law as

(9)

where Ri is the resistance between the central node 

and node 1. The current (72 ) from the central node to 

node 2 is similarly given by

/,= (E0 -E2 ). (10)

Expressions similar to equations 9 and 10 can be 

obtained for the currents toward and away from the 

central node in the other directions. The algebraic sum 

of these currents must equal the rate of accumulation 

of charge on the capacitor at the central node, which is

C dE given by - ''where C represents the capacitance. 

at

This leads to the equation

R

dE

fl (ID

Equation 11 is of the same form as 8, where voltage is

analogous to head, the terms I

Ri '"R* are analogous

to the terms KAl(kz')i . KA4 (^z'\,the terms R 5 and

p , . ffB5 (Ax'A/) , /ffi6 (Ax'Ay') , R6 are analogous to ^ and - ,and

(Az')5

Co is analogous to

Thus, if a three-dimensional network of resistors and 

capacitors is constructed and subjected to electrical 

stresses that are proportional to hydraulic stresses in 

the ground-water system, the voltage of each node of 

the network should vary in proportion to the head in 

the corresponding block of figure 16B. Equation 11 

provides a means by which head changes in response to 

proposed or assumed stresses can be predicted without 

resort to extended field experiment.

For the uppermost layer of a three-dimensional 

analog network, the termKBs of equation 8 is zero; the

term - of equation 11 is similarly taken as zero. For

the lowermost layer, the terms KB and -= are zero. If

6 #6

the uppermost layer corresponds to a water-table zone, 

the capacitance C at each node in this layer is taken to 

represent the term Sy Ax: 'Ay', where Sy represents 

specific yield, rather than the specific storage term of 

equation 8; in an interval that includes the water table, virtually all withdrawal from storage is sustained 

by dewatering rather than by release from compressive 

storage.

The electrical analogy may be summarized in terms 

of four similarity coefficients, any three of which may 

be considered independent. These are as follows:

V = 

h =

Q =

t

A2 E

A3 I

A4 t',

where the quantities left of the equal sign are prototype1 (real world) quantities and those on the right 

are model quantities. V is volume of water, q is electrical charge, h is head, E is electrical potential, Q is rate 

of discharge of water, / is electrical current, t is prototype time compared with model time t'; and the coefficients A !~A 4 have the dimensions necessary for the 

appropriate conversions. The model study is described 

in terms of the following units:

V (cubic metres) = 2.484 x!013 (m3/coul)x<7

(coulombs)

h (metres) = 2.0(m/volt) xE(volts) 

Q (cubic metres/day = 4.967 xl07 (m3/d/amp)x/

(amperes) 

t (days) = 5xW5 (d/s)xt' (seconds).

MODEL MATRIX

This model was designed around the similarity coefficients (Aj-A4 ) and the data presented earlier in this 

report. The aquifers were split into several zones. The 

five levels of the model correspond to five zones of the 

prototype. None of these zones or levels corresponds to 

a distinct sand unit within an aquifer. In order to comply with the restrictions discussed in the section on 

basic analog concepts, the zones are approximately 

parallel to bedding within each aquifer, and, therefore, 

they vary in thickness and altitude from point to point. 

The bed-normal spacing, Az', between finite-difference 

nodes ranges from zero (where an aquifer pinches out)

'The term "prototype" is used to designate the real-world hydrologic system as opposed to 

the model hydrologic system.
MODEL DESIGN

up to about 120 m (400 ft). The bed-parallel node spacings, Ax', and Ay', are both 6,000 ft (1,829 m) for all the 

zones. The finite-difference grid in figures 165 and 17 

shows the even-numbered rows and columns that are 

spaced at 6,000-ft (1,829-m) intervals. The nodes are 

"volume centered"; that is, they are at the centroids of 

the volumes they represent.

On the basis of the values of hydraulic conductivity 

in figures 9-11 and of aquifer thicknesses in figures 

5-7, the model area for each of the five levels was subdivided into areas in which the bed-parallel hydraulic 

conductivity and thickness could be assumed to be reasonably uniform. Figures 18 and 19 show the distribution of transmissivity (product of thickness and bedparallel hydraulic conductivity) about each node in 

levels 1 and 2 of the model, which represent the upper 

glacial aquifer. Specified-potential boundaries are 

shown by the symbol "*", and impermeable or no-flow 

boundaries by "<£"on these maps. Figure 20 shows the 

transmissivity assigned to level 3; this level includes 

the Jameco aquifer and the upper third of the Magothy 

aquifer. Distribution of transmissivity in levels 4 and 

5, representing the middle third and lower third of the 

Magothy aquifer, are mapped in figures 21 and 22.

All vertical resistances were computed on a nodeby-node basis because of the complex variations in 

thickness, aquifer conductivities, and confining beds 

that they represent. In computing vertical resistances, 

an anisotropy of 1:10 was assumed for the upper glacial 

and Jameco aquifers and 1:40 for the Magothy aquifer. 

Thickness of the confining beds overlying the Magothy 

aquifer is divided between levels 2 and 3. Figures 

23-25 show the distribution of estimated values of 

(&z'/KB ). Because Rz ' is directly proportional to

23

x-^-and Ax'Ay is constant throughout the 

Kr>

model, Rz ~ can be computed directly from the values 

mapped in figures 23-25. The distribution of estimated 

values of(Az'/KB ) between levels 4 and 5 is the same as 

that given in figure 25 for levels 3 and 4, except that 

the lower level is not quite as extensive.

The Lloyd aquifer (table 1; fig. 4) was not included in 

this model. The aquifer is well isolated from the remainder of the ground-water reservoir by the Raritan 

clay (Franke and Getzen, 1975), and its hydrologic 

properties are poorly known (McClymonds and 

Franke, 1972; Jensen and Soren, 1974). The Lloyd 

aquifer is used as a source of water in only a few places 

on Long Island. Thus, its inclusion is not necessary 

either for utilization or for correct operation of the 

model. The top of the Raritan clay was treated as an 

impermeable bottom for the flow system.

Lack of detailed information on specific storage of 

the aquifers required a somewhat more general assignment of capacitance. Two different values of 

capacitors, corresponding to the two areas shown in 

figure 12, were used in level 1. In a few places where 

the upper glacial aquifer is not saturated ( figs. 4, 5), 

capacitors appropriate to water-table storage coefficients were used for the corresponding nodes in level 3 

(fig. 16). Level 2 was assigned a compressive storage 

coefficient where it represents saturated material. Because level 2 is closely connected, both electronically 

and hydrologically, to level 1, it exhibits all the characteristics of a water-table aquifer except when subjected 

to very fast transient stresses.

Figure 8 and the geologic cross sections in figure 4

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 17. Finite-difference grid used for constructing the three-dimensional model of Long Island, and location of section A-A'.
24 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

FIGURE 18. Distribution of transmissivity (product of thickness and bed-parallel hydraulic conductivity) about each node in level 1

(uppermost level) of the model.

show that there are no continuous island-wide confining beds stratigraphically above the Raritan clay. 

Upper Cretaceous sandy clays (correlated with the 

Monmouth Group by Jensen and Soren, 1972), the 

Gardiners Clay, and the Pleistocene Smithtown and 

"20-ft" clays together comprise an aggregate confining 

unit that is stratigraphically above the Magothy 

aquifer around the fringes of Long Island. The 

Magothy aquifer and deeper parts of the glacial aquifer 

exhibit confined hydrologic behavior.

Compressive storage controls short-term response of 

confined aquifers such as the Magothy aquifer and 

deeper parts of the glacial aquifer on Long Island; 

water-table, or gravity, storage controls long-term response. Compressive storage contributes to the total 

storage in all aquifers but is usually of negligible importance in unconfined aquifers. None of the Long Island aquifer tests before construction of the model provide data that are adequate for separating the two 

types of storage. An average specific storage of 

2xlO-8 enr1 (6.IxlCTft'1 ) was assumed. This value, 

multiplied times an average thickness of 200 m (650 ft) 

yields the storage coefficient of 4xlO~4 , which was distributed uniformly to all nodes except where watertable storage was assigned. Rigorously, the amount of 

storage assigned each node should be proportional to 

the volume represented by the node. This was not done

because of the lack of data to support the storage coefficient that was assumed. The author considered that 

the assigned storage would have to be modified during 

model testing, so one value of capacitor was used 

throughout. During testing, this assignment of storage 

seemed adequate.

Four aquifer tests after the construction of the model 

indicate a specific storage for these semiconfined aquifers ranging from 10 '7 to 10'6 cm4 (3 x 10~6 to 3 x 10'5 ft A ) 

(Getzen, 1974, p. 53), at least one order of magnitude 

greater than the values used in the model design. Even 

with the larger values, the effects of elastic storage on 

long-term response are insignificant when compared 

with water-table storage for most of the Long Island 

reservoir. Around the fringes of the island, where the 

confining unit is thickest and more nearly continuous 

and where the overlying units are saturated with seawater, model accuracy is more sensitive to the accuracy of the assumed value for specific storage. This 

sensitivity is one reason to question the model's predictive capability in the offshore area.

The large size of the model caused some concern 

about the effects of stray capacitance on performance of 

the model. The mechanics of construction require large 

amounts of wire connecting nodes on each level to the 

corresponding nodes on the levels above and below, 

and much of this wire (more than 70,000 ft or 21,000
MODEL DESIGN 25

EXPLANATION

Model node

Specified-potential boundary 

Impermeable boundary (no transmissivity) 

Transmissivity=93 square metres per day 

Transmissivity=160 square metres per day 

Transmissivity=220 square metres per day 

Transmissivity=2 80 square metres'per day 

Transmissivity=330 square metres per day 

Transmissivity=550 square metres per day 

Transmissivity=760 square metres per day 

Transmissivity=9SO square metres per day

FIGURE 18. Continued.

EXPLANATION

Model node t Transmissivity=l

Specified-potential boundary r Transmissivity=l

Impermeable boundary (no transmissivity) « Transmissivity=l

Transmissivity=370 square metres per day M Transmissivity=3

Transmissivity=500 square metres per day Transmissivity=3

Transmissivity=930 square metres per day i Transmissivity=5

Transmissivity=990 square metres per day K Transmissivity =5

,200 square metres per day 

,500 square metres per day 

,700 square metres per day 

,000 square metres per day 

,700 square metres per day 

,300 square metres per day 

,900 square metres per day

FIGURE 19.-Distribution of transmissivity (product of thickness and bed-parallel hydraulic conductivity) about each node in level 2

of the model.
26 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

EXPLANATION

Model node r Transmissivity:

Impermeable boundary « Transmissivity=

Transmissivity^ 120 square metres per day H Transmissivity:

Transmissivity=310 square metres per day ' Transmissivity:

Transmissivity=620 square metres per day J Transmissivity1

Transmissivity=990 square metres per day « Transmissivity:

Transmissivity=1,5SO square metres per day <- Transmissivity1

: 1,740 square metres per day 

:2,200 square metres per day 

:3,600 square metres per day 

: S,SOO square metres per day 

=6,300 square metres per day 

=9,100 square metres per day 

=15,000 square metres per day

FIGURE 20. Distribution of transmissivity (product of thickness and bed-parallel hydraulic conductivity) about each node in level 3

of the model.

EXPLANATION

+ Model node c Transmissivity=620 square metres per day 

 Impermeable boundary (no transmissivity) » Transmissivity=990 square metres per day 

» Transmissivity^ 120 square metres per day E Transmissivity= 1,600 square metres per day 

B Transmissivity=310 square metres per day « Transmissivity= 1,700 square metres per day

FIGURE 21. Distribution of transmissivity (product of thickness and bed-parallel hydraulic conductivity) about each node in level 4

of the model.

m) must be bundled into tight cables. Preconstruction 

estimates of the capacitance between adjacent nodes 

were on the order of 3-10 pf (picofarads). Postconstruction measurements have indicated that stray capacitance may be as high as 15 pf between some nodes.

Although some nodes near boundaries show a total 

capacitance to ground of 45 pf, most of the nodes in the 

interior part of the model have a total capacitance of 

26-31 pf with respect to ground. Therefore, some variation in aquifer storage is not accounted for in design
MODEL DESIGN 27

EXPLANATION

* Model node < Transmissivity=620 square metres per day

 Impermeable boundary (no transmissivity) D Transmissivity=990 square metres per day 

« Transmissivity=120 square metres per day E Transmissivity= 1,500 square metres per day 

a Transmissivity=310 square metres per day r Transmissivity=l,700 square metres per day

FIGURE 22. Distribution of transmissivity (product of thickness and bed-parallel hydraulic conductivity) about each node in level 5

of the model.

EXPLANATION

Bed-normal thickness/bed-normal hydraulic conductivity 

» 5.6 days E 22 days > 57 days « 130 days 

B 6.8 days < 26 days « 68 days ' 170 days 

c 10 days « 39 days L 81 days « 220 days 

0 15 days » 48 days " 99 days s 290 days

FIGURE 23. Distribution of estimated values of(bz'/Kg) between nodes in levels 1 and 2 of the model, where (bz'/Kg) is thickness

divided by bed-normal hydraulic conductivity.

criteria, but the discrepancy seems negligible when 

compared with the design capacitance of 27 pf per 

node.

BOUNDARY CONDITIONS

Five types of boundary conditions are incorporated 

into model design: (1) Boundaries across which no flow 

occurs; (2) boundaries along which the potential is denned by potential sources external to the model; (3) 

boundaries across which the flow is defined by external 

sources; (4) internal stresses whose magnitude and location are defined by external sources; and (5) stream 

boundaries across which the flow is controlled by both 

internal and external events. (As used here, the only

differences between a boundary of type 3 and one of 

type 4 are size and position. In other authors' terminology, all specified-flux boundaries are referred to as 

"stresses.")

1. No-flow boundaries The top of the Raritan clay is 

assumed to be an impermeable or no-flow boundary as 

is the interface between freshwater and salty water in 

the Magothy aquifer. Unfortunately, the interface is 

not a fixed boundary for steady-state flow and is no 

boundary at all for unsteady flow. Even if it were a 

boundary, the position of the interface in the Magothy 

aquifer is virtually unknown. The assumption is that 

somewhere offshore is a point beyond which freshwater
28 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

EXPLANATION

Bed-normal thickness/ bed-normal hydraulic conductivity

o 120 days 

c 130 days 

r 180 days 

< 220 days 

' 500 days 

K 640 days 

L 750 days 

» 950 days

1,200 days 

1,300 days 

1,600 days 

1,900 days 

2,300 days 

2,900 days 

3,200 days

3,500 days 

3,900 days 

15,000 days 

26,000 days 

150,000 days 

480,000 dats 

1,000,000 days

FIGURE 24. Distribution of estimated values of (&z'/KB ) between nodes in levels 2 and 3 of the model, where (te'/KB ) is thickness

divided by bed-normal hydraulic conductivity.

EXPLANATION

Bed-normal thickness/bed-normal hydraulic conductivity

220 days 

230 days 

290 days 

350 days 

430 days 

900 days 

1,100 days

1,500 days 

1,900 days 

2,600 days 

3,200 days 

3,900 days 

4,800 days 

5,700 days

6,200 days 

6,800 days 

7,400 days 

9,000 days 

9,900 days 

12,000 days 

13,000 days

FIGURE 25. Distribution of values of (&z'/KB ) between nodes in levels 3 and 4 and between nodes in levels 4 and 5 of the model, where

(kz'/KB ) is thickness divided by bed-normal hydraulic conductivity.

flow and the effect of head changes on the island are 

negligible. The Magothy aquifer was simply terminated several miles offshore during construction of the 

model. Location of this termination was then adjusted
MODEL DESIGN 29

during calibration and verification procedures until 

the steady-state heads and vertical gradients resembled the prototype heads and gradients beneath the 

barrier beaches as far seaward as prototype data 

permit.

2. Known-potential boundaries The shoreline 

around the island is a specified-potential boundary for 

the upper glacial aquifer. This potential is determined 

by external voltage sources and serves as a reference 

altitude for most model measurements. The upper surface of the Gardiners Clay offshore is maintained at 

the same potential as the shoreline. This is equivalent 

to assuming that (a) the density of seawater is not significantly different from that of freshwater and (b) that 

head losses in the sea-bottom sediments above the clay 

are negligible. These assumptions are acceptable because the depths of salty water above the clay are 

small and because the quantity of freshwater leaking 

through the offshore part of the Gardiners Clay is 

small.

3. Specified-flux boundaries Recharge to the upper 

surface of the model can be either steady-state or 

steady-state with superposed transients. In each of 

these recharge modes, this surface is a specified-flux 

boundary. The flux into each node is equal to the longterm average recharge for the area in the first mode, 

but in the second the flux varies with time as well as 

space. Flux across the water table is controlled by external current sources and resistor networks that divide the current into the proper proportions for each 

water-table node. Steady-state rates of recharge are 

controlled by current-regulated power supplies; recharge rates that vary with time are achieved by 

superposing a transient current on the steady-state 

current. In the latter case, op amps (operational 

amplifiers) with diode-protected low-impedence output 

and resistance networks are used to isolate the transient electronic sources from the steady-state source.

Most models are designed to analyze response to 

transient stresses without reference to steady-state recharge. The way in which the streams are simulated in 

the experiments described herein rendered such operation undesirable, as explained in (5).

4. Internal stresses Sources and sinks at nodes that 

are not on a bounding surface of the model are referred 

to as internal stresses. Stresses of this type include 

pumping from the aquifer system and (or) injection 

through wells and basins. These stresses are supplied 

by pulse generators and function generators, whose 

output is buffered by op amps. The op amps isolate the 

outputs of the pulse generators from each other so that 

it is possible to produce "step" and "ramp" approximations for stresses that vary with time. "Step" and 

"ramp" approximations, in which stresses change

either in discrete steps or as a linear function of time, 

can be good approximations for many stresses. Although "ramp" and "step" functions may be gross representations of historical prototype stresses that vary 

irregularly in time and space, the model reservoir, as 

the prototype, tends to smooth out the response to 

rapidly changing stresses. The results are usually acceptable. The electrical stress is provided by currents 

(equivalent to rates of recharge and discharge) that 

vary with time. The low output impedence of the op 

amps makes this possible. Figure 26 shows the system 

for producing transient stresses.

The slow-rate generator shown in figure 26 provides 

a common reference time for measuring instruments 

as well as the signal generating equipment. Delay 

units start different pulse generators at various times 

after this reference time.

5. Stream boundaries Streams are nonlinear boundaries on the system; their effect varies as a function of 

head within the model. Streams in the model have 

been represented by several different types of electrical 

circuits, all of which have been developed empirically 

without any attempt to represent the equations for 

open-channel flow. For the steady-state calibration 

studies, the streams were modeled by simple resistor 

networks as is shown in figure 27.

In order for these steady-state streams to represent 

the prototype streams, two conditions must be met at 

each stream node: (1) Flow out of the model network 

through each node must represent seepage into the 

stream reach represented by the node, and (2) head at 

the node must represent an "average" elevation of the 

water table in the area represented by the node. (This 

average elevation is assumed to be equal to the elevation of the stream surface). In the model (fig. 27A), a 

string of resistors was connected in parallel with the 

stream nodes. Thus, the voltage drop across each resistor in the string equalled the voltage drop between 

successive stream nodes of the model. The current flowing into each junction along the string of resistors (that 

is, leaving each stream junction of the model network) 

represents the ground-water seepage into the stream 

reach. Current (IR in fig. 27A) carried by any resistor in 

the string represents the sum of all the seepage currents upstream from that point. In Long Island, where 

streams derive almost all their flow from ground-water 

seepage, this current must increase downstream in a 

normal, steady-state configuration.

Each resistor was chosen so that when the voltage 

drop across the resistor (Ej-E^) was proportional to the 

head drop (h^-h^) between successive node points in 

the steady-state prototype system (fig. 275), the current IR1 through the resistor was proportional to the 

cumulative discharge QRl in the stream reach. This
30 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Waveformdelay 

generator

Variablepulse

generator

r~

Variablepulse

generator

Variablepulse 

generator

Variablepulse

Pulse 

amplifier

Pulse 

amplifier

Pulse 

amplifier

1

Variablepulse 

generator

VariablePulse 

generator

Pulse 

amplifier

Pulse 

amplifier

Pulse 

amplifier

Pulse Pulse Pulse Pulse Pulse Pulse

DISTRIBUTION 

NETWORKS

TO DISCHARGING NODES ON MODEL- TO RECHARGING NODES

) shown in circles

TRIGGER FOR MEASURING INSTRUMENTS

FIGURE 26. Method for producing transient analog stresses. The distribution networks allow superposition of waveforms so that complex patterns of pumping and recharge can be approximated.

insured that, at every junction, the seepage currents Is 

would be proportional to the ground-water seepage Qs 

into the stream in the block represented by the junction. The configuration in figure 27A assures that, 

when the steady-state voltages,^,!^ -En , correctly 

represent steady-state heads, hlt h2 , . . . hn , along the 

channel, the current out of each stream node will be 

proportional to the seepage into the stream in that reach.

The type of circuit in figure 27'A can only represent 

ground-water seepage to a stream in the steady-state 

configuration for which the circuit was specifically designed, not in a transient situation in which heads beneath the stream may change with time. In the prototype system, seepage to streams rapidly decreases to 

zero as heads decline; when heads fall below stream 

level, the direction of seepage is reversed. If the flow in 

the affected stream reach is sustained by inflow to the 

stream in upstream areas, this seepage into the aquifer 

may continue; however, if the head in all upstream 

areas has similarly dropped below stream level, the 

stream will simply dry up everywhere above the first 

point at which ground-water head exceeds stream 

level. In the dried-up part of the stream, there will be

no seepage in either direction between the stream and 

the ground-water system. Behavior of this type was 

observed in nearly all streams on Long Island during 

the drought of the 1960's.

To simulate the type of stream-aquifer condition observed during the drought, the circuit in figure 27 was 

modified by replacing each stream resistor with a resistor and diode in series. The diodes and resistors were 

chosen so that with potentials^, E2 , . . . En representing the prototype steady-state heads hlt h2 , . . . hn , the 

forward resistance of each diode-resistor combination 

would be the same as the resistance of the resistor 

alone in figure 27A. If downstream gradients (that is, 

the voltage drop between successive nodes) were to decrease as a result of transient stresses, the diode resistance would increase and would effectively stop 

streamflow in the affected reach. If, for example, EI 

were to decline while E2 remained constant, when 

Ei-E2 dropped below the junction threshold voltage for 

the diode between nodes 1 and 2, the current IR1 would 

drop to zero. Reduction of IRI would result in a reduction in IR2 and in the current carried by each subsequent reach of the simulated stream. As heads 

throughout the model aquifer continued to decline in
MODEL-PROTOTYPE COMPARISONS 31

Streem network' 

I

R3

-r I R4

R5

Aquifer network'

FIGURE 27. Circuit diagram of a model stream (A) showing voltages 

E1 ,E2 , . . . En and currents IR1 ,IR2 , . . . IRn along the stream and 

currents 7^, IS2 , . . . ISii into the stream. A prototype stream 

channel (B) indicates the values of head (hlt h2 , . . . h,, ), represented by the voltages, and discharges QR and Qs represented by 

the currents in the model. Each junction in the model network 

represents one of the aquifer blocks in the prototype.

response to a simulated drought, E2 would eventually 

decline until E2-E3 was less than the threshold voltage 

for that diode and IR2 would decrease to zero. The 

stream would be shortened at its head.

Although model operation with the two stream circuits, as well as model operation without streams, 

proved useful for the model-performance analyses described in the section "Model-Prototype Comparisons," 

they were not adequate for some predictive studies. A 

third circuit, different in concept and more difficult in 

execution, has been used for predictive studies. Because the third circuit was not used in any of the 

analyses described in this report, a description of that 

circuit will be deferred to a later report (A. W. Harbaugh and R. T. Getzen, written commun., 1975).

SUMMARY OF DESIGN CRITERIA

Conditions of the ground-water reservoir that must

be correctly represented by the model are as follows:

(1) Geometry and distribution of hydraulic conductivity in the reservoir rocks. For Long Island, distribution of conductivity is three dimensional, and magnitude of conductivity is direction dependent. The 

finite-difference network must be alined with the directions of the principal conductivities.

(2) Average magnitude of the specific storage of the 

reservoir rocks and spatial distribution of storage.

(3) Location of boundaries of the hydrologic system 

and nature of the boundaries. Where this is not completely possible, the boundaries were designed to have 

minimal effect on the internal parts of the model. The 

lower boundary of the Magothy aquifer and the 

saltwater-freshwater interface are not exactly represented by the model. The model attempts to minimize 

the effects of these boundaries.

(4) Historical data on internal stresses to the reservoir and electronic-exciting circuitry capable of representing these stresses.

(5) Ground-water discharge to surface-water bodies. 

Where this seepage is to streams and its magnitude is 

likely to change drastically as a function of small head 

changes within the ground-water reservoir, the model 

must be capable of correctly representing the change in 

seepage.

If the model can reproduce observed and calculated 

distributions of head in response to observed (historical) stresses and synthetic stresses, all the preceding 

conditions are assumed to have been met. The model is 

then said to be "calibrated" or "verified." Such a verification procedure does not prove that the model 

ground-water reservoir will respond correctly to all 

stresses; it only shows that the representation of responses to a certain range of stress situations seems to 

correlate with observed prototype response.

MODEL-PROTOTYPE COMPARISONS

PERFORMANCE CRITERIA

Model performance is generally evaluated in terms 

of the preceding design criteria. Most of these criteria 

cannot be adequately defined by prototype data. The 

best known of these criteria on Long Island is the general configuration of the water table. Historical data 

describing the water table are shown from Burr, Herring, and Freeman (1904); Veatch, Slichter, Bowman, 

Crosby, and Horton (1906); Jacob (1945); Isbister 

(1959); and Kimmel (1971). In a thin, isotropic aquifer, 

the configuration of the water table would be adequate 

for defining correct steady-state operation of the model. 

The same cannot be said for regional flow systems in 

thick, anisotropic sedimentary sequences (Freeze and 

Witherspoon, 1967, p. 632-633). Sufficient data to
32 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

permit description of the head distribution at other 

depths have been acquired only recently (Kimmel, 

1971; Jensen and Soren, 1974). Because measurements 

are almost never made before ground-water development begins, data that reflect human as well as 

climatological influences on the ground-water system 

must be used to estimate and extrapolate the distribution of steady-state head.

Model performance is measured by two types of 

tests steady-state tests, which measure the model's 

ability to represent average or predevelopment hydrologic conditions, and unsteady-state tests, which compare the model's response to transient stresses with 

prototype response to historical stresses.

Evaluation of unsteady (transient) model performance requires two types of data quantitative measurements of the stress (pumping, recharge, fluctuating 

lake levels, and other boundary conditions) and historical responses (changes in head and discharge over 

long periods of time) of the system to those stresses. 

Two types of unsteady stresses were considered in 

evaluating model performances: (1) Changes in net recharge that resulted from the severe drought of the 

early 1960's and (2) historical pumping records from 

major wells or well fields in western Long Island. Data 

for magnitude of the type 1 stresses are from Cohen, 

Franke, and Foxworthy (1968), and for type 2 from 

records compiled by New York State Water Power and

Control Commission and by county agencies. Simulated response to the climatological stress was compared with the observations by Cohen, Franke, and 

McClymonds (1969). Response and recovery of the 

simulated water table to pumping stresses was compared with water-table data compiled by Lusczynski 

(1952) and from other sources cited in the preceding 

paragraph. Data from several of these sources are reproduced in subsequent illustrations for comparison 

with model response.

In addition to stress and head data, records of stream 

discharge are compared with simulated stream discharge. Streams on Long Island are seldom gaged at 

more than one point along their length; except for a 

few seepage runs and qualitative information about 

tidal fluctuations and location of the heads of streams 

in varying hydrological circumstances, there is only 

one point on each stream at which the model can be 

compared with prototype data.

STEADY-STATE EVALUATION

The average annual ground-water recharge has been 

estimated to be 58 cm (23 in.) for a water-budget area 

that excludes the highly urbanized areas and low-lying 

coastal areas of Long Island (Cohen and others 1968, p. 

44-45). This value was used as a starting point for 

steady-state calibration of the model but yielded unsatisfactory results. The estimate of Cohen, Franke,

15 MILES

Base from 

Hartford,

U.S. 

1962

Geological Survey, 1:250,000 series:

; New York, 1957; Newark, 1947 EXPLANATION

Recharge, in centimetres per year

-722-

43-46 46-49 49-52 52-55

Line of equal annual average precipitation

Interval, 5 centimetres per year

(2 inches per year)

FIGURE 28. Distribution of prototype mean annual precipitation, 1951-65, and of steady-state recharge to the model. (Mean annual

precipitation modified from Miller and Frederick, 1969.)
MODEL-PROTOTYPE COMPARISONS 33

AK 

AM 

AO 

AQ 

AS 

AU 

AW 

AV 

BA

10 15 MILES

0 5 10 15 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 29. Simulated, steady-state, water-table profiles and locations on western Long Island compared with 1903 prototype watertable profiles. Major production wells near profiles in 1903 are also shown. Prototype data from Burr, Hering, and Freeman (1904).

and Foxworthy (1968) seems to be too high if applied to 

the entire island. Several factors influence the rates of 

recharge; the most important seem to be (a) rate and 

duration of precipitation, (b) infiltration characteristics of the surficial sediments, (c) thickness of the unsaturated zone, and (d) local relief. Precipitation is not 

uniformly distributed over Long Island (fig. 28) but is 

noticeably greater near the center of the island than 

elsewhere. The soils of the morainal parts of Long Island tend to be less permeable than the soils of the 

outwash areas. Thus, there is a tendency for a greater 

proportion of the precipitation to run off near the north 

shore. Steep slopes, like those on the north shore, tend 

to cause precipitation to run off faster than it does on 

gentle slopes. Much more of the water that infiltrates 

the soil is lost to plant roots and to evaporation where 

the water table is close to the surface; a smaller proportion of rainfall becomes part of the ground-water reservoir in low-lying, swarnpy areas than in areas of 

greater altitude. The combination of all these factors 

does not reduce to an equation from which the steadystate recharge values shown in figure 28 could be 

calculated. These known factors make the recharge 

distribution in figure 28 seem reasonable, but other 

factors, unknown or misunderstood, could influence recharge rates in entirely different ways. The distribution of model recharge shown in figure 28 was obtained through a "tuning" process. The gross estimate 

by Cohen, Franke, and Foxworthy (1968) was assumed 

to be acceptable; distribution of this recharge was modified by trial and error until a reasonable water table 

was obtained. 

With the recharge distribution shown in figure 28,

SOUTH

A

Pumping centers, 

Model steady-statex

NORTH

A' 

-i 150

-I 150

- 100 z

10 MILES

iIII \ 

5 10 KILOMETRES

FIGURE 29. Continued.
34 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Line of equal prototype head

Line of equal simulated head

Intervals, 5 and 10 metres (16.4 and

32.8 feet) I I I I

10 15 20 25 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 19S7; Newark, 1947

FIGURE 30. Comparison of steady-state model water table with 1903 water table in central Long Island. (Prototype data from Veatch

and others, 1906.)

LONG ^JtjMM)

iipi Mo;

QUEENS 

KINGS ~ l COUNTY 

COUNTY

*

OC£4Af

EXPLANATION

I 

10

10

I

15

I

20

I

25 MILES

_J

15 20 25 KILOMETRES

Line of equal prototype head

Line of equal simulated head 

Intervals, 5 metres (16.4 feet)

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 31. Comparison of steady-state model water-table with 1970 water table in eastern Long Island. (Prototype data from

Kimmel, 1972.)

the model produced the steady-state, water-table configuration that is compared with observed prototype 

water-table data in figures 29-31. Figure 29B shows 

water-table profiles along three lines of section in 

western Long Island; locations of these lines of section 

are shown in figure 29. Pumpage and other manmade

hydrologic disturbances began in western Long Island 

and gradually spread eastward. The 1903 water levels 

for the westernmost part of the island reflect these 

manmade disturbances. The steady-state model 

analysis did not simulate these manmade effects, and, 

therefore, agreement between the model results and
MODEL-PROTOTYPE COMPARISONS 35

Line of equal prototype head

Line of equal model head 

Interval, 5 metres (16,4 feet)

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 32. Comparison of steady-state simulated head near the base of the Magothy aquifer with 1971 prototype head. (Prototype

data from Jensen and Soren, 1974.)

the 1903 water levels is poor for the westernmost line 

of section A-A' in figure 29. The agreement improves 

progressively to the east as the manmade effects diminish. The poor agreement along line A-A' may also 

reflect that the model design is based on saturated 

thickness of the glacial aquifer in 1970; the saturated 

thickness in 1903 was considerably greater than it was 

in 1970 for part of Kings County. Model performance 

in the westernmost part of Long Island could not be 

justified by the preceding comparison but was justified 

by unsteady-state performance (next section).

For the eastern two-thirds of the modeled area, 

agreement between the prototype water table and 

model results was good, as shown by the maps of 

figures 30 and 31. Figure 30 shows a comparison of 

steady-state model results with a water-table map by 

Veatch, Slichter, Bowman, Crosby, and Horton (1906) 

covering eastern Nassau and western Suffolk Counties. Effects of pumpage were negligible in these areas 

at that time. Because the map by Veatch, Slichter, 

Bowman, Crosby, and Horton (1906) does not include 

the easternmost one-third of the modeled area, figure 

31 shows a comparison of model results with 1970 

water-table contours by Kimmel (1972) for Suffolk 

County. Again, the effects of pumpage on water levels 

in Suffolk County were small in 1970.

Comparison of heads near the base of the Magothy 

aquifer in 1971 with simulated steady-state head in 

model level 5 is shown in figure 32. Data for only the 

eastern half of the island are shown; heads in the lower 

part of the Magothy aquifer have been noticeably affected by pumping in the western half of the island.

Extent of agreement between prototype and model 

heads is not perfect but is within a few metres for most 

of the reservoir for which reliable data are available on 

undisturbed natural (predevelopment) potential. Some 

of the disagreement is probably due to differences in 

data interpretation; for example, other water-table 

maps such as that by Cohen, Franke, and Foxworthy 

(1968, plate 2E), do not show the same pronounced 

high in southeastern Suffolk County as that indicated 

by the 15-m (49-ft) closed contour in this area in 

figure 31.

Distribution of normal, steady-state head along two 

typical model hydrologic sections is shown in figure 33. 

Although there are no satisfactory prototype data for 

comparison, model head and flow data given in the 

hydrologic sections are useful for understanding the 

flow system.

Table 2 compares long-term average stream discharge with values of steady-state stream discharge 

from the model. Where a range of discharge is given for 

the simulated stream discharge, the prototype gage is 

near the division between two stream reaches on the 

model. Most pairs of model and prototype stream discharges agree within ±5 percent, and all pairs except 

for about ten streams agree within ± 10 percent. Only 

short streams and streams that have extremely high or 

extremely low gradients have model discharges that 

differ significantly from prototype discharges. The difference between total stream discharge as modeled and 

the long-term average for all prototype streams com-
36 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

LEVEL

1200

1400-

1600

L- 500

EXPLANATION

Head, in metres

Bed-parallel flow components in cubic 

metres per day per kilometre of width 

(bed-normal components not shown)

METRES 

r SEA LEVEL

2000 4000 6000 8000 10,000 FEET

1400 -

1600

-400

L-500

1000 2000 3000 METRES

FIGURE 33. Distribution of head and bed-parallel components of ground-water flow along two hydrologic sections through the 

model Long Island ground-water reservoir. Rates of flow are for a 1-kilometre-wide strip. Locations of sections are shown 

in figure 4.
MODEL-PROTOTYPE COMPARISONS 37

TABLE 2. Stream/low comparisons

Code shown for 

streams in 

figure 141 Stream name

Average

discharge

(cubic metres

per second)

Model

discharge

(cubic metres

per second)

B Valley Stream _______________ 0.165 0.186

C Pines Brook ________________ .141 .150

D South Pond __-____--_-__________--_ .083 .094

E Parsonage Creek. _ _ __ _ .117 .100

F Milburn Creek__________.___________ .242 .271

G East Meadow Brook __ _ ___ .473 .575

H Cedar Swamp Creek ____--_-__-_____ .239 .265

I Newbridge Creek -_-________-- .066 2 .048 to .070

J Bellmore Creek __________ __ .310 .435

L Seamans Creek __________ .054 .050 to .058

M Seaford Creek ________________ .054 .064 to .084

N Massapequa Creek________________ .339 .304 to .438

O Carman Creek ___________ _ .120 .136 to .154

P Amityville Creek ___________ .110 .059 to .102

Q Great Neck Creek ___________ .071 .075 to .142

R Strongs Creek ______________ .054 .052 to .082

S Neguntatogue Creek _____ __ _ .108 .066

T Santapogue Creek ___________ .126 .165

U Carlls River ________________________ .772 1.01

	.967 1.05

V Sampawams Creek____________ .342 .397

W Shookwams Creek ________________ .031 .034 to .055

X Willets Creek __ .071 .074 to .100

Y Trues Creek ________________________ .051 .058

Z Cascade Creek__________________ .071 .048 to .080

AA Penataquit Creek ____________ .175 .185 to .212

AB Awixa Creek ____ _________ .054 .063

AC Orowoc Creek ._ __ _ _______ .074 .080

AD Pardees Pond _______ _______ .174 .066 to .107

AE Champlin Creek ________ _ .207 .247 to .343

AF West Brook ________________________ .120 .096

AG Rattlesnake Brook ________________ .262 .248 to .277

AH Connetquot River ___ ________ 1.10 1.02

AI Green Creek_________________ .128 .131

AJ Brown Creek (west) ___________ .231 .245

AK Brown Creek (east) __ ______ .231 .245

AL Tut Hills Creek ___________ _____ .174 .116 to .171

AM Patchogue Creek ________________ .595 .528 to .653

AN Swan River _______________ .365 .354

AO Mud Creek ___ _____ _ _ ______ .153 .145 to .154

AP Motts Brook._______________ .051 .013 to .070

AQ Beaverdam Creek _______________ .046 .039

AR Carmans River _ __________ .048 .055

	.678 .518

AS Forge River _____________ _ .274 .298

AT Terrel River ___________________ .071 .069

AU Little Seatuck __________________ .128 .135

AV Seatuck Creek _________________ .162 .205

AW East River____________________ .071 .082

AX Beaverdam Creek ___________ .068 .055 to .057

- AY Aspatuck Creek _____________ .063 .070

AZ Quantuck Creek ________ ____ .060 .069

BA Whitney Lake _______ _ ___ .071 .061

BB Roslyn Brook ____________________ .051 .066

BC Glen Cove Creek____________ .202 .206

BD Island Swamp Brook __________ .026 .031

BE Mill Neck Creek _______________ ____ .268 .121

BF Cold Spring Brook ___ _ _ ____ .126 .130

BG Mill Creek ____________ _ ___ .085 .047

BH Stony Hollow Run _____ ____ .034 .046

BJ NE Nissequogue _____________ .051 .086

	.111 .114 

	1.18 1.28 

BK Wading River _________ ___ .028 .026

BL Saw Mill Creek _____________ .077 .042

BM Peconic River _ _ .986 1.00

BN Little River ______ ___ .125 .137 to .168

BO White Brook______________________ .077 .086

'Codes for only 64 of 75 streams plotted in figure 14 are listed. Eleven of the 75 streams, 

most of them in Queens County, have been replaced by sewers.

2A range of discharge indicates that prototype gage falls at or near division between two 

reaches on model.

bined is less than 5 percent. The ability of the simulated streams to represent prototype discharge correctly at one or two points (the gages) on each stream 

does not mean that the overall representation is correct. There are no prototype data relating changes in 

seepage along the entire length of each stream to 

changes in the water table, but the general agreement 

of the model response with the available historical 

data strongly suggest that the response of the prototype system is closely simulated by the model.

-Long-term average recharge

o

liJ 5

tr

LU

u 10

15

20

25

35 H 

Z

LIJ 

O 

DC 40

LU

: : : : : : : : : : : : : : : : : : : : : : : : : : : : 1964

1962

1963

1965 1966

FIGURE 34. Changes in annual recharge used to simulate the 

1962-66 drought on Long Island.

UNSTEADY-STATE EVALUATION

Two historical stresses were used for unsteady-state 

evaluation. The first of these, the drought of 1962-66, 

was simulated by using estimates of the reduction in 

recharge during the drought (Cohen and others, 1968, 

plate 4E). Yearly deviation from the long-term, average annual recharge, derived from the estimates, is 

shown in figure 34. This stress has two causes: (1) Reduced precipitation and (2) sporadically occurring precipitation. During the drought, intense storms were 

the source of much of the precipitation. Although most 

precipitation on Long Island is rapidly absorbed by the 

soil, intense storms contribute large amounts of runoff 

to streams and fill surface ponds that evaporate. Very 

little of the storm precipitation becomes ground-water 

recharge.

The intensity of the drought stress, as given by 

Cohen, Franke, and Foxworthy (1968) and in figure 34, 

is a net or total stress. Just as was the case with average recharge distribution (fig. 28), the areal distribution of drought shown by the map in figure 35 was 

derived by a trial-and-error procedure aimed at reproducing the prototype response. Distribution of stress, 

mapped in figure 35 in terms of deviation from the 

islandwide areal average stress, was assumed to be 

constant from year to year during the drought. The 

trial-and-error method involved trying three different 

stress distributions: (1) Drought stress was uniformly 

distributed over the entire island; (2) stress in the lowlying parts of the island was five times greater than 

that in the higher, central part of the island; and (3) 

stress in the low-lying parts of the island was twice as 

great as that in the center of the island as depicted in 

figure 35. In each of these three stress distributions,
38 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947 EXPLANATION

25 percent greater than 

average stress

10 percent greater than 

average stress

Average stress

x xX/x

10 percent less than 

average stress

25 percent less than 

average stress

FIGURE 35. Distribution of the decline in net recharge used to simulate the 1962-66 drought on Long Island. The distribution is 

given in terms of deviation from the islandwide areal average of the stress.

LONG ,,^&mi>. ,

»., ,:^ip|P|l^lP;5;;gife:A.:,,..,- *?< m^.-^.^^mm:^T^^K»mm^mmmm:m»

-f

0CE/UV

10

i

15

I

20

I

I I I I I I 

0 5 10 15 20 25 KILOMETRES

25 MILES 

_J

EXPLANATION

Line of equal prototype 

head decline, 1962-66

Line of equal simulated head decline, 1962-66 

Intervals, 1 and 0.5 metres (3.3 and 1.6 feet)

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

FIGURE 36. Comparison of observed and simulated water-table declines as a result of the 1962-66 drought. (Prototype water-table

decline from Cohen and others, 1969.)

the total stress during each time period was equal to 

the quantity indicated in figure 34.

Simulated response to the assumed stress situation 

is compared with the net-change map (fig. 36) presented by Cohen, Franke, and McClymonds (1969, fig.

10), who mapped the change in the water table between 1961 and 1966. Their map does not show net 

changes in New York City and western Nassau County 

because changes in water levels there are the result of 

other influences. Changes in recharge caused by pav-
MODEL-PROTOTYPE COMPARISONS 39

TABLE 3. Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses in western 

Long Island during the periods 1903-33, 1934-42, 1943-50, and 1951-63. Unstressed nodes are not listed

[Accuracy of these measurements is about ±2 percent or ±40 cubic metres per day, whichever is greater]

LEVEL 1 LEVEL 2 LEVEL 3

YEARS-. 1903-33 1934-42 19*3-50 1951-63

MODEL

NODE CUBIC METRES PER DAY

1903-33 1934-43 19*3-50 1951-63 

CUBIC METRES PEA DAY

1903-33 1934-43 19*3-50 1951-63 

CUBIC METRES PER DAY

10 BK

12 B6

1* BC

1* RE

1* B6

1* BI

16 BC

16 BE

16 B6

16 BI

16 BK

16 BN

17 BA

18 BB

18 BC

18 BE

18 B6

18 BI

19 AZ

19 B6

20 AW

20 AY

20 BA

20 BC

20 BG

20 BI

22 *U

22 AW

22 AY

22 BA

22 B6

2* AU

2* BA

2* BG

26 BA

?6 BC

26 B6

26 BI

28 BC

28 BE

28 BG

28 BI

30 BC

30 BE

30 B6

30 BI

31 BI

32 BC

32 B6

32 BI

32 BO

3* AY

3* BE

3* BI

36 AY

-12920.

-99*0.

-88*0.

-22160.

-7*50.

-500.

-20670.

-7950.

-5*60.

0.

-5020.

-6*60.

-12820.

-10180.

0.

0.

0.

-29810.

-92*0.

-*9?0.

-3*30.

-3530.

-9090.

-8350.

0.

0.

-3230.

-89*0.

-3*80.

-3*80.

-990.

-3680.

-3130.

0.

-16*0.

-3130.

-6360.

0.

-18*0.

-2*8*0.

-5070.

-8*50.

-21360.

-7950.

-*970.

0.

-1*90.

0.

0.

0.

0.

-3970.

-11920.

-1990.

0.

-99*0.

-8690.

-7750.

-18980.

-7950.

-6950.

-17730.

-6950.

-99*0.

0.

-*520.

0.

-10980.

-8890.

0.

0.

0.

-13910.

-8050.

-**20.

-19*0.

-20*0.

-7950.

-7300.

0.

0.

-18*0.

-**70.

-1990.

-1990.

0.

-2090.

0.

0.

0.

0.

-9090.

0.

0.

-*970.

-7300.

0.

-1990.

-11920.

-7950.

0.

0.

0.

0.

0.

0.

-*970.

-7950.

-500.

0.

-5960.

-*970.

-**20.

-10680.

-6950.

-5960.

-9980.

-3970.

-7950.

0.

-3530.

0.

-6160.

-5070.

0.

0.

0.

-10930.

-*620.

-3*30.

-1790.

-18*0.

-*520.

-*170.

0.

0.

-1690.

-**70.

-18*0.

-18*0.

0.

-19*0.

0.

0.

0.

0.

-12120.

0.

0.

-13*10.

-97*0.

0.

-990.

-12*20.

-89*0.

0.

0.

0.

0.

0.

0.

0.

-89*0.

-500.

0.

-2980.

-20*0.

-1790.

-*970.

-1*90.

0.

-*620.

-16*0.

-990.

0.

-500.

0.

-28BO.

-2090.

0.

0.

0.

-1990.

-1B90.

-500.

-19*0.

-20*0.

-18*0.

-1690.

0.

0.

-18*0.

-**70.

-1990.

-1990.

0.

-2090.

0.

0.

0.

0.

-11570.

0.

0.

-13910.

-9290.

0.

0.

-16390.

-11920.

0.

0.

0.

0.

0.

0.

0.

-99*0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-990.

0.

0.

0.

0.

0.

0.

-1990.

0.

0.

0.

0.

0.

0.

0.

-3970.

-5120.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-*820.

0.

0.

0.

0.

0.

-550.

0.

0.

0.

-7950.

0.

0.

0.

0.

-8*50.

-*50.

-12920.

0.

0.

0.

0.

0.

0.

0.

-20860.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-5*60.

0.

0.

0.

-3*80.

0.

0.

0.

0.

-10930.

-**70.

-3970.

0.

0.

0.

0.

0.

0.

0.

-99*0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-1790.

0.

0.

0.

-200.

0.

0.

0.

0.

-11920.

-1*90.

-500.

0.

0.

0.

0.

0.

0.

0.

-990.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

, o.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-99*0.

0.

0.

-3870.

-3870.

0.

-600.

0.

0.

0.

0.

0.

-6060.

0.

-600.

-1990.

-15900.

-3970.

0.

0.

-8*50.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-600.

0.

0.

-19*0.

-19*0.

0.

-8*0.

0.

0.

0.

0.

0.

-300.

0.

-8*0.

-990.

-5960.

-5560.

0.

0.

-*070.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-300.

0.

0.

0.

0.

0.

-10*0.

0.

0.

0.

0.

0.

-300.

0.

-10*0.

-1290,

-3780.

-**70.

0.

0.

-1190.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-2090.

0.

0.

0.

0.

0.

0.

0.

-2090.

-2380.

-990.

-5560.

0.

0.

0.

0.

ing and building, ground-water withdrawals through 

pumping wells, and sewering have strongly affected 

the water table in the western part of Long Island. 

Considering the assumptions that underlie the recharge estimates (Cohen and others, 1968, p. 44), the 

extent of agreement between simulated and observed 

changes in the water table is quite satisfactory. 

Although direct measurements of net recharge are

not available only gross estimates based on other 

components of the hydrologic cycle, some of which can 

only be approximated the decline in recharge during 

a drought would probably be distributed unequally. 

The assumed distribution of stress (fig. 35) is not unrealistic because the erratic frequency and intensity of 

precipitation during the drought (Cohen and others, 

1969, p. F8) resulted in much greater runoff than nor-
40 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

TABLE 3. Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses in western 

Long Island during the periods 1903-33, 1934^42, 1943-50, and 1951-63. Unstressed nodes are not listed Continued

LEVEL 1 LEVEL 2 LEVEL 3

YEARS 1903*33 1934-42 1943-50 1951-63 1903-33 1934-42 1943-50 1951-63 1903-33 1934-4? 1943-50 1951-63

MODEL 

NODE CUBIC METRES PEA DAY CUBIC METRES PER DAY CUBIC METRES PER DAY

36 BC -350. -4330. -5120. -6950. 0.

36 BE -5960. -5960. -6950. -7950. 0.

36 BG -350. -4220. -5020. -6810. 0.

36 BI 0. 0. 0. 0. 0.

36 BK -1490. -500. -500. 0. 0.

36 BP 0. 0. -1290. -2140. 0.

38 BC 0. 0. 0. 0. 0.

38 BE -350. -4370. -5170. -7050. 0.

38 8G 0. 0. 0. 0. 0.

38 BI 200. 990. 1090. 600. 0.

38 BK -14900. -4970. -7450. 840. 0.

38 BM -9940. 4620. 4970. 4620. 0.

40 AS 0. 0. 0. 0. 0.

40 AW 0. 0. -1690. -2830. 0.

40 BA -3680. 0. 0. 0. 0.

40 BG 450. 2190. 2980. 100. 0.

40 BI 250. 1140. 1690. -300. 0.

40 BK 3380. 20*0. 2930. 2780. 0.

40 BM -14900. -5960. -3970. -5960. 0.

40 BO 2680. 400. 450. 890. 0.

42 AM 0. 0. 400. 2880. 0.

42 AY 0. 0. 400. 2580. 0.

42 8A 0. 550. 1840. 2140. 0.

42 8C 500. 2240. 2830. 0. 0.

42 BE 500. 2240. 2880. 0. 0.

42 BG 0. 0. 0. 1790. 0.

42 BI 450. 2190. 2930. 0. 0.

42 BK -24RO. 0. 0. 0. 0.

42 BM 3330. 400. 0. 1640. 0.

44 AO 0. 350. 350. 550. 0.

44 AQ 0. -990. -1490. -2480. 0.

44 AM 0. 450. 1640. 1740. 0.

44 BA 350. 1490. 1940. 0. 0.

44 BE 0. 400. 200. 650. 0.

44 BI 50. 1540. 2190. 1590. 0.

44 BK 0. -1440. 0. 0. 0.

44 BM 0. 1640. 1040. -500. 0.

44 BO 0. 0. 0. 0. 0.

45 BB 0. 450. 1590. 1690. 0.

46 AS 500. 0. 0. 0. 0.

46 AU 0. 0. 600. 2630. 0.

46 AV 0. 0. 0. 0. 0.

46 AM 0. 0. 0. 0. 0.

46 AX 0. 550. 2730. 4470. 0.

46 AY 0. 0. 0. 0. 0.

46 BA 0. 0. 0. 0. 0.

46 8C 0. 0. 0. 0. 0.

46 BD 100. 1090. 150. 250. 0.

46 BE 0. 0. 0. 0. 0.

46 BI 50. 1590. 2830. 1940. 0.

46 BK 0. -1540. 0. 0. 0.

46 BM -2480. -500. -1990. -2480. 0.

47 AZ 0. 1640. 3280. 2480. 0.

47 BB 0. 790. 1040. 1890. 0.

47 BO -990. 0. 0. 0. 0.

mal. Most of the increased runoff was near the coast

because the water table there is near land surface and

closely spaced streams give good surface drainage.

Also, storm-sewer systems near the coast route storm

runoff directly to the surrounding bays. Inland, where

streams are fewer and where there is a thick unsaturated zone, runoff and natural evapotranspiration are

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -790. -2980. -3830. -8350.

0. 0. 0. 0. -2980. -4170. -8450.

0. 0. 0. -700. -2980. -500. 100.

0. 0. 0. -700. -3970. -4970. -500.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. -990. -990. -990.

0. 0. 0. -790. -2980. -3830. -8350.

0. 0. 0. -700. -2530. -3280. -7200.

0. 0. 0. -790. -2980. -3970. -5960.

0. 0. 0. -1990. -2780. -3080. -5560.

0. 0. 0. -500. -3480. -4720. -10930.

0. 0. 0. -200. -500. -500. -600.

0. 0. 0. -1990. -4970. -4970. -5960.

0. 0. 0. -9940. -9940. -7950. -4971.

0. 0. 0. -1490. -4970. -5960. -6950.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -250. -1590. -1390. -5120.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. -450. -2730.

0. 0. 0. 0. 0. -350. -2240.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -600. -2290. -2680. -3480.

0. 0. 0. 0. 0. 0. -2190.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -600. -2330. -2780. -3580.

0. 0. 0. -250. -1640. -1440. -5170.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. -450. -1690.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -500. -1590. -1590. -2480.

0. 0. 0. 0. -600. -600. -1190.

0. 0. 0. -250. -1540. -1340. -4970.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -700. -3830. -3*30. -4970.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. -550. -1890.

0. 0. 0. 0. 0. -250. -990.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. -350. -1290.

0. 0. 0. -400. -1790. -2980. -3580.

0. 0. 0. -400. -1490. -30*0. -7950.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -100. -1290. -1690. -3480.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -790. -4520. -4570. -5960.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

minor. In the central part of the island, even storm

water quickly infiltrates beyond the reach of plant

roots and solar heat, and runoff from buildings and

paved areas is disposed of through dry wells and recharge basins; consequently, the irregular frequency of

precipitation does not result in increased runoff. Thus,

on the basis of observations, the assumed distribution
MODEL-PROTOTYPE COMPARISONS 41

TABLE 3. Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses in western 

Long Island during the periods 1903-33, 1934-42, 1943-50, and 1951-63. Unstressed nodes are not listed Continued

YEARSMODEL 

NODE

48 AM

*8 AN

48 AY

48 BC

48 BE

48 B6

48 8K

48 BM

48 BO

49 AY

49 BE

49 B6

49 BM

50 AS

50 AU

50 AW

50 AY

50 BC

50 BE

50 BK

50 BM

51 AM

51 BC

52 AO

52 AO

52 AU

52 AY

52 BC

52 BI

52 BK

52 BM

53 BH

53 BJ

54 AM

54 AU

54 AM

54 AY

54 BA

54 BC

54 BI

54 BM

54 BO

55 AT

55 BB

55 BF

55 BH

56 AL

56 AM

56 AQ

56 AT

56 AZ

56 BA

56 BB

56 BC

56 BE

LEVEL 1 LEVEL 2

1903-33 1934-43 1943-50 1951-63 1903-33 1934-43 1943-50 1951-63 

CUBIC METRES PEH DAY CUBIC METRES PER DAY

0.

100.

0.

350.

150.

0.

50.

100.

0.

100.

0.

1440.

0.

-500.

0.

0.

0.

0.

0.

100.

0.

300.

0.

0.

0.

0.

-300.

550.

0.

0.

-5960.

-300.

0.

100.

0.

100.

0.

0.

0.

0.

0.

-15900.

-250.

550.

-250.

0.

100.

100.

0.

-300.

0.

0.

0.

0.

0.

0.

700.

0.

3430.

1090.

0.

1640.

1740.

0.

500.

1140.

8150.

1640.

-2980.

0.

0.

250.

0.

0.

1740.

0.

1140.

0.

0.

0.

0.

-2730.

1140.

0.

890.

-3970.

-2480.

0.

400.

0.

400.

550.

0.

0.

0.

0.

-11920.

-1990.

1140.

-2330.

0.

400.

400.

0.

-2480.

750.

0.

0.

0.

0.

0.

940.

0.

1690.

200.

0.

2290.

2380.

0.

500.

1740.

11280.

1090.

-2480.

-500.

0.

350.

0.

0.

2330.

0.

1990.

-50.

0.

0.

-550.

-300.

1690.

0.

1490.

-3970.

-300.

0.

4470.

-450.

300.

700.

0.

0.

0.

0.

-12420.

-250.

1640.

-250.

0.

3730.

4520.

0.

-300.

840.

0.

-150.

0.

0.

0.

0.

0.

3280.

100.

0.

1490.

1690.

0.

0.

2330.

11230.

400.

-29AO.

-500.

0.

0.

0.

0.

1440.

0.

0.

1640.

0.

0.

-1590.

-300.

5370.

3580.

5960.

-3970.

-300.

1490.

1040.

-1390.

1440.

0.

0.

0.

0.

0.

-2980.

-250.

3870.

-250.

7450.

990.

1040.

0.

-300.

30AO.

0.

4770.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

LEVEL 3

1903-33 1934-42 1943-50 

CUBIC METRES PER OAY

0.

-200.

-200.

-400.

-150.

-1790.

-250.

-500.

-6950.

0.

0.

0.

0.

-5960.

0.

-450.

0.

0.

-150.

-250.

-500.

0.

0.

-600.

-600.

-150.

0.

-750.

0.

0.

-500.

0.

0.

0.

-150.

-150.

0.

-400.

-400.

0.

-1140.

-5020.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-300.

0.

0.

0.

0.

-600.

-600.

-2480.

-1290.

-8940.

-1590.

-3480.

-3970.

0.

0.

0.

0.

-2580.

0.

-990.

-400.

0.

-1390.

-1640.

-2730.

0.

0.

-890.

-890.

-550.

0.

-1490.

0.

0.

-2730.

0.

0.

0.

-400.

-500.

-450.

-650.

-550.

0.

-450.

-2040.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-500.

0.

0.

0.

0.

-840.

-750.

-3380.

-1690.

-12420.

-1390.

-5220.

-4970.

0.

0.

0.

0.

-1990.

0.

-1390.

-400.

0.

-1840.

-1440.

-3230.

0.

0.

-1190.

-1090.

-550.

0.

-2190.

0.

0.

-3230.

0.

0.

0.

-400.

-500.

-790.

-890.

-790.

0.

-1040.

-4720.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-500.

0.

-250.

0.

1951-63

-2580.

-2290.

-2190.

-5960.

-3480.

-14900.

-5070.

-11920.

-6950.

0.

0.

0.

0.

-2580.

0.

-3480.

-600.

0.

-3730.

-5170.

-3970.

0.

0.

-1640.

-1540.

-1640.

0.

-4870.

-4870.

-4870.

-3970.

0.

0.

0.

-1190.

-1490.

-1290.

-2330.

-2140.

-7450.

-200.

-890.

0.

0.

0.

0.

0.

0.

-400.

0.

0.

-2980.

0.

-4920.

-1990.

(fig. 35) is defensible, and the simulated response 

shown in figure 36 provides a better comparison with 

prototype head decline than the other two cases that 

were tried. However, figure 36 indicates that a better 

match to observed water-table decline could have been 

obtained with a stress distribution intermediate between the one shown in figure 35 and a perfectly

uniform distribution.

The second historical stress was obtained from 

pumping records that show a large increase in 

ground-water withdrawals in Kings County between 

1899 and 1919. A similar increase occurred in Queens 

County during the mid 1930's and in Nassau County 

during World War II and the Korean War. Because of
42 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

TABLE 3. Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses in western 

Long Island during the periods 1903-33, 1934^2, 1943-50, and 1951-63. Unstressed nodes are not listed Continued

LEVEL 1 LEVEL 2 LEVEL 3

YEARS 1903-33 1934-42 1943-50 1951-63 1903-33 1934-42 1943-50 1951-63 1903-33 1934-42 1943-50 1951-63

TRJBeT 

NODE CUBIC METRES PER DAY CUBIC METRES PER DAY CUBIC METRES PER DAY

56 86 0. 0. 400. 3970.

56 BI 0. 0. 0. 990.

56 BO -9390. -13060. -6260. -1540.

57 BE 0. 0. 250. 1640.

58 AR 100. 400. 400. 1690.

58 AY 100. 400. 350. 1290.

58 BA 0. 0. 0. 0.

58 BE 0. 0. 350. 5510.

58 B6 0. 0. -990. 1390.

58 BI 0. 0. 0. 0.

58 BK 0. 0. 0. 0.

58 BM 0. 0. -100. 9490.

58 BO -8490. -11770. -5660. -1440.

59 BI 0. 0. 300. 2480.

60 AQ 250. -990. -990. -1490.

60 AY 100. 400. 350. 1340.

60 BA 0. 0. 400. 7310.

60 BI 0. 0. 0. 550.

60 BK -300. -2430. -300. -300.

 0 BM -11920. -11920. -8450. -990.

60 BM 0. 0. 0. 0.

61 BN -109AO. -11970. -8490. -2480.

62 BA 0. 0. 0. 1640.

62 BC 0. 0. 0. 3630.

62 BI 0. 0. 0. 0.

62 BJ 0. 0. 0. 1040.

62 BK 0. 0. 0. 0.

62 BL -250. -2330. -250. -250.

62 BM 0. 0. 0. 0.

62 BO 0. 0. 0. 0.

62 BM 0. 0. 0. 0.

63 BF 0. 0. 350. 0.

63 BL 0. 0. 0. 2430.

63 BN -10880. -11870. -8400. -2480.

64 AQ 0. 0. 0. 0.

64 AM 100. 400. 400. 1490.

64 AY 0. 0. 0. 0.

64 BA 0. 0. 0. 1740.

64 BC 0. 0. 0. 0.

64 BE 0. 0. 0. 0.

64 B6 0. 450. 790. 750.

64 BH 0. 0. 500. 1340.

64 BI 0. 0. 0. 0.

64 BK 0. 0. 0. 0.

64 BM 0. 0. 0. 2730.

64 80 -11920. -13910. -8940. -990.

64 BP 0. 890. 1490. 1140.

64 BM 0. 0. 0. 0.

65 BO 0. -2480. -2480. 1440.

66 AS 0. 0. 0. 0.

66 AT 0. 0. 0. 2830.

66 AV 0. 0. 0. 0.

66 AM 0. 0. 0. 1090.

66 AY 100. 400. 450. 1540.

66 BE 0. 0. 0. 0.

deteriorating water quality, many wells in

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

Kings

County were abandoned during the periods 1932-36

and 1940-42. For simulation, changes in pumping

were assumed to occur instantaneously at 1903, 1934,

1943, and 1951. The complexity of this model

(228 pumping areas in model levels 2 and 3

changing discharge rates at four different times

stress

, each

, table

0. 0. 0. 0. 0. -350. -3380.

0. 0. 0. 0. 0. 0. -650.

0. 0. 0. -600. -600. -2780. -1990.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -150. -500. -500. -1490.

0. 0. 0. 0. 0. 0. -1990.

0. 0. 0. 0. 0. -250. -5020.

0. 0. 0. 0. 0. -350. -3530.

0. 0. 0. 0. 0. -400. -3970.

0. 0. 0. 0. 0. 0. -9940.

0. 0. 0. 0. 0. 0. -5370.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. -100. -400. -400. -1090.

0. 0. 0. 0. 0. 0. -4970.

0. 0. 0. 0. 0. -500. -447 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -2190.

0. 0. 0. -200. -890. -600. -1040.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -1540.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -400.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -350.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -1190.

0. 0. 0. -200. -200. -400. -200.

0. 0. 0. -200. -840. -600. -940.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -650.

0. 0. 0. -200. -600. -600. -1840.

0. 0. 0. -200. -600. -600. -1790.

0. 0. 0. 0. 0. 0. -790.

0. 0. 0. 0. 0. 0. -550.

0. 0. 0. 0. 0. 0. -990.

0. 0. 0. 0. -450. -790. -1290.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. -200. -990.

0. 0. 0. 0. 0. 0. -940.

0. 0. 0. 0. 0. 0. -3630.

0. 0. 0. 0. 0. 0. -4720.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -100.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -1590.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -1390.

0. 0. 0. 0. 0. 0. -1340.

0. 0. 0. 0. 0. 0. 0.

0. 0. 0. 0. 0. 0. -990.

3) cannot be adequately represented on a map.

Nevertheless, the complexity of the prototype stress is

considerably greater than the model stress.

After being used for cooling, water from many wells

was returned to the ground through basins or shallow

wells. Before 1961, most sewage in Nassau County was

disposed of through cesspools and septic tanks. Water
MODEL-PROTOTYPE COMPARISONS 43

TABLE 3. Net recharge (positive) and withdrawal (negative) at each model node used to simulate manmade historical stresses in western 

Long Island during the periods 1903-33, 1934-42, 1943-50, and 1951-63. Unstressed nodes are not listed Continued

LEVEL 1I LEVEL 2 LEVEL 3

YEARS 1903-33 1*34-42 1943-50 1*51-63 1903-33 1934-42 1943-50 1951-63 1903-33 1934-42 1943-50 1951-63 

UMCL 

NODE CUBIC METRES PER DAY CUBIC METRES PER DAY CUBIC METRES PER DAY

66 B6

66 BK

6« AU

70 AY

70 BA

70 86

70 BK

70 BN

71 AY

72 AM

72 AY

72 BM

73 BL

75 AR

76 AS

76 BK

7« AS

7« BE

7« BK

 0 AM

80 BK

80 BM

 1 BL

 2 AS

82 BC

 2 BO

82 81

83 BA

84 BL

 4 BM

 4 BY

86 AT

86 AU

 8 BI

BB BY

90 BY

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

100.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-ISO.

1190.

2*30.

0.

1190.

so.

250.

100.

940.

11*0.

5170.

0.

700.

3330.

0.

1340.

150.

1290.

100.

300.

0.

350.

150.

650.

0.

250.

0.

150.

150.

0.

0.

700.

0.

150.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

0.

-650.

0.

-940.

-940.

0.

0.

0.

0.

-1090.

-4970.

-600.

0.

0.

-3280.

-940.

-100.

-1190.

-100.

-350.

-100.

-700.

0.

-650.

-350.

0.

-100.

0.

0.

-150.

-150.

0.

-650.

-150.

-150.

-150.

was returned to the ground in the model through 112 

recharge areas, whose rates of recharge changed 

simultaneously with changes in pumping rate. Estimates of recharge are much less precise than estimates 

of pumping. On the basis of available information, the 

following assumptions were made: (a) Recharge from 

cooling water equals 90 percent of water pumped for 

this purpose; (b) recharge from domestic and commercial water equals 20 percent of water pumped for these 

purposes in sewered areas; (c) recharge from domestic 

and commerical water equals 75 percent of water 

pumped for these purposes in unsewered areas; (d) the 

remaining water is lost to evaporation or discharged to 

tidewater and does not return to the ground-water reservoir; and (e) all recharge water goes to the shallow 

aquifer. Changes in islandwide recharge, pumping, 

and net stress are given for the period 1903-63 in 

figure 37. 

Pumping and recharge were simulated without

streams. On western Long Island, where most of the 

pumping was done, the streams were mostly small; 

many of them had already disappeared by the time a 

regular stream-gaging program was begun. Thus, the 

contribution to ground water from diverted streamflow 

is largely unknown but is probably small. Inclusion of 

streams in this simulation was considered unnecessary, but ommission of streams adversely affected 

model accuracy in some areas.

Response to historical pumping and recharge is 

mapped in figures 38 and 39. Figure 38 and table 4 

compare observed head changes with those measured 

on the model. Figure 38 shows good general agreement 

between model and prototype head changes, but many 

details are lost because of the coarse grid of the model. 

Local defects in simulation also result from the large 

time steps between changes in pumping rates. The difference between prototype and model drawdown in 

northwest Queens County (fig. 38) indicates some type
44 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

JCUU

100

0

0 +

0

0

X -

>-

^

0 100

oc

111

Q.

uj 200

OC

H

tu

5 _ 

0 30°

m

o

z 400

w

m

E 500

H

600 

-inn

i i I i

Recharge^ ( 

-

.

-

p^

I I |

Net stress.

i i i

-

-

_

-

-

-

-

_

-

Withdrawal^

i i 

40

20

+

0 - <

Q

__ EC

20 uj

Q.

(/)

40 §

_J

60 5

.

~^

80 r

_i

100 5

Z

120 $

uj

OC

140 w

160 

180

1900 1910 1920 1930 1940 

YEAR

1950 1960 1970

FIGURE 37. Estimated islandwide changes in pumping, manmade 

recharge, and net stress between 1903 and 1963. These estimates 

were used in unsteady-state calibration of the model. They do not 

include water returned to the same node from which it is pumped.

of model or data deficiency. Comparison of figures 38 

and 39 suggests that this deficiency is due to inadequate pumping data. Prototype data for 1961 

(fig. 38) shows localized drawdown of 8 m (26 ft) and 

more in northwest Queens County. This drawdown is 

not seen in the model data for 1961 but is seen in the 

model data for 1942 (fig. 39). Apparently, pumping 

data for 1942-61 are incomplete, probably because 

drainage pumped from railroad tunnels was not included in pumping data. Model and prototype drawdowns for 1942 cannot be compared because of insufficient prototype data for that year. The author did not 

attempt to modify the stress to obtain a better comparison between model and prototype drawdowns. 

Near the north shore (northeastern Queens County, for 

example) are many localized faults in the simulation, 

which can be seen in most model tests. These faults 

result from inability of the coarse model grid to match 

the fine-scale variations in boundaries. However, icemargin deformation of the sediments along the north 

shore creates local barriers to ground-water flow that 

were not modeled.

The general trend of model drawdown in Kings and 

Queens Counties, where most of the pumping on Long 

Island was done, matches the overall pattern in prototype drawdown quite well, not only in 1961 (fig. 38) 

but also at several other times as well. If the differences between the 1903 prototype water table and the 

steady-state model results in these counties (fig. 29) 

had been the result of poor model design, one would 

expect the unsteady-state model response to differ from 

prototype response by 50-100 percent, as was seen in 

the steady-state comparison. Averaging prototype 

drawdowns over areas of several square miles results 

in better agreement between prototype and model 

drawdowns than is shown in figure 38. Good comparison of unsteady-state model and prototype response is 

evidence that the discrepancy in the comparison of 

steady-state model and prototype response is chiefly 

the result of pre-1903 pumping, which the steady-state 

model did not simulate.

In the preceding test, the model was operating in the 

unsteady-state mode without natural recharge. Model 

streams were not flowing. The simulation is noticeably 

inaccurate where it does not account for diverted 

streamflow. In prototype situations, where wells were 

close to streams, they received part of their discharge 

from diverted streamflow. Wells 36, 37, 45, and 47 

(table 4; fig. 40) are examples of this type of inaccuracy.

SUMMARY AND CONCLUSIONS

Problems in water resources evaluation that cannot 

be analyzed directly can be analyzed through model 

simulation. The Long Island ground-water reservoir 

was simulated by a three-dimensional analog model. 

Experience has shown that ground-water flow in thick, 

anisotropic aquifer systems such as the system on Long 

Island cannot be adequately described by twodimensional methods but can be satisfactorily described by a three-dimensional model.

Boundaries of the Long Island ground-water reservoir are three dimensional, and the resulting natural 

patterns of ground-water flow are three dimensional. 

When wells and other human influences affect only the 

upper surface of the ground-water reservoir, some of 

the three-dimensional aspects of the natural flow system can be ignored; but the present state of groundwater development on Long Island, which superposes a 

new three-dimensional flow pattern on the preexisting, 

three-dimensional, natural flow system, requires 

three-dimensional analysis. Three-dimensional 

analysis is not only more difficult than twodimensional analysis; it is less certain because data on 

hydraulic conductivity normal to the strata are much 

less abundant than data on hydraulic conductivity 

parallel to the strata and because compensating errors 

make evaluation of three-dimensional simulation 

more uncertain than evaluation of two-dimensional
4-TQG' 7 4" 00'

SUMMARY AND CONCLUSIONS

45'

45

73 30'

45'

40 30'

EXPLANATION

6

Line of equal prototype water-table decline,

1903-61 

Interval, 2 metres (6.56 feet)

Line of equal simulated water-table decline,

1903-61 

Interval, 2 metres (6.56 feet)

5 KILOMETRES

Base from U.S. Geological Survey, 1:250,000 series: 

New York, 19 57; Newark, 1947

FIGURE 38. Comparison of simulated decline in water table between 1903 and 1961 on western Long Island with observed decline.

(Prototype data modified from Perlmutter and Soren, 1962.)

simulations.

Model-prototype comparisons indicate that this 

model simulates the Long Island ground-water reservoir adequately, but that care is required in modeling 

some types of stresses. Good results cannot be obtained

when stresses cause significant changes in saturated 

thickness of the ground-water reservoir. Any change in 

saturated thickness causes a change in an aquifer's 

transmissivity that this modeling technique cannot 

simulate; when the change exceeds 10-15 percent of
46 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

41 00'

45'

40 30'

74° 00'

EXPLANATION

Line of equal head decline, 1903-42 

Intervals, 1 and 2 metres (3.3 and 6.6 feet)

45' 73 30'

Base from U.S. Geological Survey, 1:250,000 series: 

New York, 1957; Newark, 1947

FIGURE 39. Simulated decline in water table due to pumping on western Long Island between 1903 and 1942.

the total saturated thickness (about 15 m or 50 ft of 

drawdown for most of Long Island), the error resulting 

from the divergence of prototype and simulated 

transmissivity becomes significant. Offshore head 

measurements in the model are not reliable; boundary 

conditions there are not well understood. Several different circuits were used to simulate stream-aquifer 

relationships, but because these circuits were developed empirically, not on the basis of open-channel 

flow equations, the usefulness of each type of stream 

circuit is limited to a few stress situations. Extremely 

localized stresses near the mouths of streams can give
REFERENCES CITED 47

Base from U.S. Geological Survey, 1:250,000 series: 

Hartford, 1962; New York, 1957; Newark, 1947

OCFA1\

EXPLANATION

.10 

Location of well 10

FIGURE 40. Locations of wells used (or water-level changes in table 4.

TABLE 4. Comparison of model and prototype water-level changes for 

selected wells between 1951 and 1963

Well1

l

2_

3_

4_

5,

6_

9_

H

12

14

15

16- _

18

20_

22_

23_-

24_

25_

Prototype 

change 

(m)

. _ 20.20

_ - 1.5

. _ .50

. _ 5.1

. _ 1.0

. _ 3.0

. _ 2.0

_ _ 1.2

. _ -.20

_ _ -.40

-.50

_ _ -3.0

_ _ -4.0

- _ -.70

. _ -2.0

_ .- -1.0

_ _ -1.0

_ _ -2.0

_ .- -1.5

_ _ -.20

_ _ -2.5

_ _ -.20

-.30

-1.2

Model change

(m)

1.7

4.4

0 to 3 1.0

4.0

2.0 to 3.0

4.8 to 5.8

1.2 to 2.0

.80 to 1.0

.10 to -.60

0 to - .60

-.60 to -.80

-1.8 to -3.0

-1.4 to -2.4

-1.4 to -1.6

-.24

0 to -.24

0 to -.18

-1.0

-2.4 to -2.6

-2.6

-1.2

-2.0

-1.4 to -2.0

Well

28_

29_

30_

33_

34_

35_

38_

39_

42_

43 _

44_

46_

49

Prototype 

change

(ml

-2.0

-.10

.0

-.20

-1.0

_ -1.0

_ _ -.30

-.60

.03

.30

.40

.30

.0

.30

.40

.30

.0

-.03

.03

Model change 

(m)

.10 to -.40

0 to .80

-1.2

-.60

-1.8

-.50 to .60

0 to -.40

0 to -.20

1.0 to 1.8

.80

.40 to .50

.20 to .40

.20

.20 to .30

.20 to .30

.20

0 to .02

.22 to .26

.14 to .16

.04

'Well locations shown in figure 40.

"Positive changes indicate increasing water levels between 1951 and 1963; negative 

changes indicate decreasing water levels.

3Range of values indicates that prototype well lies between two model nodes having 

different changes in water level.

a distorted picture of stream discharge with almost any 

stream circuit.

The apparent inability of the steady-state model to 

match the 1903 water table in western Queens County 

is shown (by good unsteady performance in that area) 

to result from pumping interference in 1903, not from 

incorrect conductivities or boundaries in the model. 

This model, however, cannot simulate the fine structure of the hydrologic features in the north shore area; 

predictive results near the north shore may not be 

satisfactory.

The desired end product of model design, construction, and calibration is predictive capability. The ultimate purpose of the model is to predict response of the 

ground-water flow system to future stresses. Three 

types of stresses are considered: (a) Natural stresses, 

such as prolonged drought; (b) stresses caused by 

human activity, which are unforeseen or unplanned, 

including changes in recharge rate that result from 

paving and other construction activities such as dams, 

quarries, landfills, and recharge basins; and (c) 

planned water-management schemes. Examples of 

water-management alternatives are discussed briefly 

by Cohen, Franke, and Foxworthy (1968, p. 94-105); 

two plans are discussed exhaustively in Greeley and 

Hansen (1971) and Holzmacher, McLendon, and Murrell (1968). Several examples of each type of stress 

have been modeled. Results of these model tests and a 

description of the hydrologic and electrical assumptions underlying the tests are contained in other reports.

REFERENCES CITED

Bermes, B. J., 1960, An electric analog model for use in quantitative 

hydrologic studies: U.S. Geol. Survey open-file rept.

Burr, W. H., Hering, Rudolph, and Freeman, J. R., 1904, Report of 

the Commission on additional water supply for the city of New 

York: New York, Martin B. Brown Co., 980 p.

Cohen, Philip, Franke, O. L., and Foxworthy, B. L., 1968, An atlas of 

Long Island's water resources: New York Water Resources 

Comm. Bull. 62, 117 p.

Cohen, Philip, Franke, O.L., and McClymonds, N. E., 1969, Hydrologic effects of the 1962-66 drought on Long Island, New York: 

U.S. Geol. Survey Water-Supply Paper 1879-F, 18 p.

Collins, M. A., and Gelhar, L. W., 1970, Ground water hydrology of 

the Long Island aquifer system: Dept. Civil Eng., Massachusetts 

Inst. Technology, Hydrodynamics Lab. Rept. No. 122, 185 p.

Collins, M. A., Gelhar, L. W., and Wilson, J. L., Ill, 1972, Hele-Shaw
48 ANALOG-MODEL ANALYSIS OF REGIONAL THREE-DIMENSIONAL FLOW, LONG ISLAND, NEW YORK

model of Long Island aquifer system: Am. Soc. Civil Engineers 

Proc., Jour. Hydraulics Div., v. 98, no. HY6, p. 1701-1714.

Collins, R. E., 1961, Flow of fluids through porous materials: New 

York, Reinhold Publishing Co., 270 p.

Cooper H. H., Jr., 1959, A hypothesis concerning the dynamic balance of fresh water and salt water in a coastal aquifer: Jour. 

Geophys. Research, v. 64, no.4, p. 461-467.

Dana, J. D., 1890, Long Island Sound in the Quaternary age, with 

observations on the submarine Hudson River channel: Am. 

Jour. Sci., 3d ser., v. 40, p. 425-437.

De Varona, I. M., 1896, History and description of the water supply 

of the city of Brooklyn: Brooklyn Commissioner of Public Works, 

306 p.

Fetter, D. W., Jr., 1971, The hydrogeology of the south fork of Long 

Island, New York: Indiana University, unpub. Ph. D. thesis, 

236 p.

Franke, O. L., and Cohen, Philip, 1972, Regional rates of groundwater movement on Long Island, New York: U.S. Geol. Survey 

Prof. Paper 800-C, p. C271-C277.

Franke, O. L., and Getzen, R. T., 1975, Evaluation of hydrologic 

properties of the Long Island ground-water reservoir using 

cross-sectional electric-analog models: U.S. Geol. Survey openfile report 75-679, 80 p.

Freeman, J. R., 1900, Report upon New York's (city) water supply: 

New York, Martin B. Brown Co., 587 p.

Freeze, R. A., and Witherspoon, P. A., 1967, Theoretical analysis of 

regional groundwater flow, II: Effect of water table configuration 

and subsurface permeability variations: Water Resources Research, v. 3, no. 2, p. 623-634.

Fuller, M. L., 1914, Geology of Long Island, New York: U.S. Geol. 

Survey Prof. Paper 82, 231 p.

Getzen, R. T., 1974, The Long Island ground-water reservoir; a case 

study in anisotropic flow: Urbana-Champaign, 111., University of 

Illinois, unpub. Ph. D. thesis, 130 p.

Glover, R. E., 1959, The pattern of fresh-water flow in coastal aquifers: Jour. Geophys. Research, v. 64, no. 4, p. 457-459.

Greeley and Hansen, 1971, Report on comprehensive public water 

supply study, county of Nassau, New York: Contract CPWS-60 

by Greeley and Hansen, Engineers, for country of Nassau and 

New York State Department of Health, 243 p.

Hollick, Arthur, 1893, Preliminary contributions to our knowledge 

of the Cretaceous formation of Long Island and eastward: New 

York Acad. Sci. Trans., v. 12, p. 222-237.

 1894, Some further notes on the geology of the north shore of 

Long Island: New York Acad. Sci. Trans., v. 13, p. 122-130.

Holzmacher, R. G., McLendon, S. C., and Murrell, N. E., 1968, Report 

on comprehensive public water supply study, Suffolk County, 

New York: Contract CPWS-24 by Holzmacher, McLendon, and 

Murrell, Consulting Engineers, for county of Suffolk and New 

York State Department of Health, 224 p.

Hubbert, M. K., 1940, The theory of ground-water motion: Jour. 

Geology, v. 48, no. 8, p. 785-944.

Isbister, John, 1959, Ground-water levels and related hydrologic 

data from selected observation wells in Nassau County, Long 

Island, New York: New York State Water Power and Control 

Comm. Bull. GW-41, 42 p.

 1966, Geology and hydrology of northeastern Nassau County, 

Long Island, New York: U.S. Geol. Survey Water-Supply Paper 

1825, 89 p.

Jacob, C. E., 1939, Fluctuations in artesian pressure produced by 

passing railroad trains as shown in a well on Long Island, New 

York: Am. Geophys. Union Trans., v. 20, pt. 4, p. 666-674.

 1941, Notes on the elasticity of the Lloyd sand on Long Island, 

New York: Am. Geophys. Union Trans., v. 22, pt. 3, p. 783-787.

 1945, Correlation of ground-water levels and precipitation on

Long Island, New York: New York State Water Power and Control Comm. Bull. GW-14, 20 p.

Jensen, H. M., and Soren, Julian, 1972, Hydrogeologic data from 

selected wells and test holes in Suffolk County, Long Island, 

New York: Long Island Water Resources Bull. 3, 35 p. 

-1974, Hydrogeology of Suffolk County, Long Island, New

York: U.S. Geol. Survey Atlas HA-501, 2 sheets. 

Karplus, W. J., 1958, Analog simulation: New York, McGraw-Hill

Book Co., 434 p. 

Karplus, W. J., and Soroka, W. W., 1959, Analog methods [ 2d ed. ]:

New York, McGraw-Hill Book Co., 483 p. 

Kimmel, G. E., 1971, Water-level surfaces in the aquifers of western

Long Island, New York, in 1959 and 1970: U.S. Geol. Survey

Prof. Paper 750-B, p. B224-B228. 

-1972, The water table on Long Island, New York, in March

1970: Long Island Water Resources Bull. 2, 8 p.

Lubke, E. R., 1964, Hydrogeology of the Huntington-Smithtown 

area, Suffolk County, New York: U.S. Geol. Survey WaterSupply Paper 1669-D, 68 p.

Lusczynski, N. J., 1952, The recovery of ground-water levels in 

Brooklyn, New York, from 1947 to 1950: U.S. Geol. Survey Circ. 

167, 29 p.

Lusczynski, N. J., and Swarzenski, W. V., 1966, Saltwater encroachment in southern Nassau and southeastern Queens Counties, Long Island, New York: U.S. Geol. Survey Water-Supply 

Paper 1613-F, 76 p.

McClymonds, N. E., and Franke, O. L., 1972, Water-transmitting 

properties of aquifers on Long Island, New York: U.S. Geol. 

Survey Prof. Paper 627-E, 24 p.

Mather, W. W., 1843, Geology of the first geological district, in Geology of New York, pt. 1. Nat. History of New York, pt. IV, New 

York State Mus. Nat. History: Albany, N.Y., Carroll and Cook, 

653 p.

Mills, H. D., and Wells, P.O., 1974, Ice-shove deformation and glacial stratigraphy of Port Washington, Long Island, New York: 

Geol. Soc. America Bull., v. 85, p. 357-364.

Miller, J. F., and Frederick, R. H., 1969, The precipitation regime of 

Long Island, New York: U.S. Geol. Survey Prof. Paper 627-A, 

21 p.

Perlmutter, N. M., and Geraghty, J. J., 1963, Geology and groundwater conditions in southern Nassau and southeastern Queens 

Counties, Long Island, New York: U.S. Geol. Survey WaterSupply Paper 1613-A, 205. p.

Perlmutter, N. M., and Soren, J., 1962, Effects of major water-table 

changes in Kings and Queens Counties, New York City: U.S. 

Geol. Survey Prof. Paper 450-E, p. E136-E139.

Perlmutter, N. M., and Todd, Ruth, 1965, Correlation and 

Foraminifera of the Monmouth Group (Upper Cretaceous), Long 

Island, New York: U.S. Geol. Survey Prof. Paper 483-1, 24 p.

Pluhowski, E. J., and Kantrowitz, I. H., 1964, Hydrology of the 

Babylon-Islip area, Suffolk County, Long Island, New York: 

U.S. Geol. Survey Water-Supply Paper 1768, 119 p.

Salisbury, R. D., 1902, Description of New York City: U.S. Geol. 

Survey, Geol. Atlas, Folio 83.

Skibitzke, H. E., 1961, Electronic computers as an aid to the analysis 

of hydrologic problems: Internat. Assoc. Sci. Hydrology, Pub. 52, 

p. 706-742.

Soren, Julian, 1971, Ground-water and geohydrologic conditions in 

Queens County, Long Island, New York: U.S. Geol. Survey 

Water-Supply Paper 2001-A, 39 p.

Suter, Russell, de Laguna, Wallace, and Perlmutter, N. M., 1949, 

Mapping of geologic formations and aquifers of Long Island, 

New York: New York State Water Power and Control Comm. 

Bull., GW-18, 212 p.

Swarzenski, W. V., 1963, Hydrogeology of northwestern Nassau and
REFERENCES CITED 49

northeastern Queens Counties, Long Island, New York: U.S.

Geol. Survey Water-Supply Paper 1657, 90 p. 

Upham, Warren, 1879, Terminal moraines of the North Atlantic ice

sheet: Am. Jour. Sci., 3d ser., v. 18, p. 81-92, 197-209. 

Upson, J. E., 1966, Relationships of fresh and salty ground water in

the northern Atlantic Coastal Plain of the United States: U.S.

Geol. Survey Prof. Paper 550-C, p. C235-C243. 

 1970, The Gardiners Clay of eastern Long Island, New

York a reexamination: U.S. Geol. Survey Prof. Paper 700-B,

p. B157-B160. 

U.S. Geological Survey, 1972, Water resources data for New York,

Part 1, Surface water records, 1971: U.S. Geol. Survey open-file

rept., 302 p.

Veatch, A. C., Slichter, C. S., Bowman, Isaiah, Crosby, W. O., and 

Horton, R. W., 1906, Underground water resources of Long Island, New York: U.S. Geol. Survey Prof. Paper 44, 394 p.

Walton, W. C., and Prickett, T. A., 1963, Hydrogeologic electric 

analog computers: Am. Soc. Civil Engineers Proc., Jour. Hydraulics Div., v. 89, no. HY6, p. 67-91.

Wilson, J. W., Ill, 1970, A Hele-Shaw model for the study of the Long 

Island ground water system: Cambridge, Mass., Massachusetts 

Inst. Technology, unpub. M.S. thesis, 89 p.

Woodworth, J. B., 1901, Pleistocene geology of portions of Nassau 

County and Borough of Queens: New York State Mus. Bull., no. 

48, p. 618-679.

r>U.S. GOVERNMENT PRINTING OFFICE: 1976 - 789-025/26