Preliminary Results of 

Hydrologic Studies at 

Two Recharge Basins on 

Long Island, New York

By G. E. SEABURN

HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON 

LONG ISLAND, NEW YORK

GEOLOGICAL SURVEY PROFESSIONAL PAPER 627-C

Prepared in cooperation with the New York 

State Department of Conservation, Division 

of Water Resources; the Nassau County 

Department of Public Works; the Suffolk 

County Board of Supervisors; and the 

Suffolk County Water Authority

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1970
UNITED STATES DEPARTMENT OF THE INTERIOR 

WALTER J. HICKEL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

Washington, D.C. 20402 - Price 35 cents (paper cover)
CONTENTS

Glossary of symbols and terms.______________________

Abstract_ _-------_--_--_______-_-__-_____________

Introduction. ______________________________________

Purpose and scope of the water-budget study______-

Purpose and scope of this report._________________

Previous studies._______________________________

Acknowledgments__ _ __________________________

Use and general description of recharge basins on Long 

Island ___________________________________________

Location and description of test basins ________________

Instrumentation of test basins_____-_____-_______-____

Description of apparatus______________________

Page

IV

Cl

1

1

2

2

2

3

4

7

7

Pag-? 

Instrumentation of test basins Continued

Measurement of basin storage.___________________ C?

Results of the study.______--_____-__---_---_-----_- 8

Time response of the system________-_-_-___-___- 8

Rainfall-runoff relations _________________________ 10

Infiltration rates at the Westbury basin.__________ 12

Ground-water recharge-_________-__---___--____- 12

Summary and conclusions ________________________ 13

References cited---__-_-------_-----------_--------- 14

Appendix. _________________-________--_----_-__--__ 14

Procedures used to calibrate the weirs at the Westbury and Syosset recharge basins __-_-_---____ 14

ILLUSTRATIONS

Page 

FIGURE 1. Map showing location and general geographic features of Long Island____-_____--_-__--_ Cl

2. Photograph of typical recharge basin in Nassau County.-....------------------------- 3

3. Map showing location of Westbury and Syosset recharge basins and selected rain gages in

Nassau County.________-___-_-__________-___________-_---_--------_--_------- 4

4. Aerial photograph of the Westbury recharge basin and its drainage area_________________ 5

5. Aerial photograph of the Syosset recharge basin and its drainage area_______-_--_--__--_ 6

6. Diagrammatic section showing the drainage system and location of measuring instruments

at the Westbury recharge basin______.__________________-__--_--_-_-_-_------- 7

7. Sketch of inflow-measuring apparatus located in manhole nearest each recharge basin _____ 8 

8-13. Graphs showing:

8. Relations between water depth, water-surface area, and volume of storage for the

Westbury recharge basin_______-______________________-_--_-____-_------- 8

9. Rainfall, inflow, basin storage, and water-table elevation for a storm on October 18,

1967, at the Westbury recharge basin_______-_____--__--------_--_------- 9

10. Relation between rainfall and inflow to the Westbury recharge basin, 1966-67____ 10

11. Relation between rainfall and inflow to the Syosset recharge basin, 1966-67. ________ 11

12. Average infiltration rates calculated for 5-minute intervals at the Westbury recharge

basin for the storm on October 18, 1967 ___-_______-_--__-----___-_--------- 12

13. Relation between depth of water and average infiltration rate calculated for 5-minute

intervals in the Westbury recharge basin, during the storm of October 18, 1967 __ _ _ 13

14. Rating curve for V-notch weir at the Westbury recharge basin_ ___________________----_- 15

15. Rating curve for V-notch weir at the Syosset recharge basin. ____________________________ 16

TABLES

Page

TABLE 1. Summary of data on the drainage areas of the Westbury and Syosset recharge basins. _____ C4

2. Summary of data on the Westbury and Syosset recharge basins_______----__------_----- 4

3. Selected values of rainfall and inflow for Westbury and Syosset recharge basins derived from

trend lines in figures 10 and ll_____________________-__-__---------__------------ 12

4. Rainfall, inflow, and average infiltration rates for selected storms in 1967 at the Westbury

recharge basin__________________________________________-___--_---_----_------- 13

in
GLOSSARY OF SYMBOLS AND TERMS

A Cross-sectional area of flow, in square feet.

D Hydraulic depth in feet; D=A/T. Also used as pipe diameter, in feet.

d Depth of water, in feet.

E Specific energy, in feet; the energy per pound of water 

at any section of a channel measured with respect to 

the channel bottom; E=d-\-V2 .

20

F Froude number; a dimensionless ratio of inertia forces 

to gravity forces; F=V/ t/gD.

9 Acceleration of gravity, in feet per second per second.

Invert The lowest point on the internal cross section of a 

conduit.

n Coefficient of channel roughness; Manning's "n", in ft1 /6 

Q Discharge, in cubic feet per second.

R Hydraulic radius, in feet; the cross-sectional area divided by the length of the part of the stream in contact 

with its containing conduit (wetted perimeter).

Reach A segment of stream length parallel to flow.

S Slope of water surface, channel bottom, and (or) energy 

line, in feet per foot.

T Channel width, in feet.

V Velocity, in feet per second.

A Net incremental change.

IV
C2 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YOBK

and Suffolk Counties (the other two counties on the 

island) are about 290 and 920 square miles, respectively; 

these counties had a combined population of about 2.5 

million people in 1965.

Although the New York City part of Long Island 

derives most of its water supply from surface-water 

sources in the Delaware and Hudson River basins 

(mainly in upstate New York), both Nassau and Suffolk 

Counties derive their entire water supply from wells 

tapping an extensive underlying ground-water reservoir. Because of present large demands on the groundwater system, particularly in Nassau and Suffolk Counties, and because of the prospect of increased demands 

as Long Island continues to develop rapidly, knowledge 

about the hydrologic system with special emphasis on 

water conservation and management is a matter of 

vital concern to the present population and to the millions of people who will depend on ground-water 

reserves in the future.

Considerable information is available about the water 

resources of Long Island as a result of more than 30 

years of study by the U.S. Geological Survey in cooperation with New York State and county agencies. 

Although those studies meet many of the needs for data 

on specific water problems, better quantitative information about the islandwide hydrologic system and the 

relations and interactions among the various components of the system is needed for water management. To 

provide that water information, a comprehensive waterbudget study presently is being made by the Geological 

Survey in cooperation with the New York State Department of Conservation, Division of Water Resources; 

Nassau County Department of Public Works; Suffolk 

County Board of Supervisors; and Suffolk County 

Water Authority.

The major objectives of the water-budget study are:

(1) to summarize and interpret pertinent existing information about the hydrologic system of Long Island and

(2) to fill several gaps in the knowledge of the hydrologic system. The results of these studies are being 

published in a series of coordinated reports. In some 

of the reports, information is developed for all of Long 

Island; in others, the primary area of concern is limited 

to Nassau and Suffolk Counties.

PURPOSE AND SCOPE OP THIS REPORT

Direct runoff on Long Island has increased as a result 

of urban development specifically, as a result of the 

construction of impervious surfaces, such as streets, 

parking lots, and buildings. The increased runoff and 

the method of disposing of the runoff has had a significant impact on the hydrologic system of the island.

Two major methods of storm-water disposal are 

presently used in Nassau and Suffolk Counties: (1) 

discharge through storm drains directly into streams 

which convey storm flow rapidly into tl 3 adjacent bays 

and the ocean and (2) discharge through storm drains 

into nearby open pits (called recharge basins or sumps). 

Direct runoff to recharge basins, the subject of this 

report, is pertinent to any comprehensive analysis of 

the Long Island hydrologic system because the bulk of 

this runoff recharges the ground-wate*- reservoir. Direct runoff to streams is the subject of another study 

in this report series (Seaburn, 1969).

The study described in this report war concerned with 

two recharge basins in Nassau Courty. The major 

objective of the study was to define the rainfall-inflow 

relations for each of the two basins, including the time 

of travel of runoff to the basins. Other items studied 

were: (a) the rate of infiltration of the inflow through 

the bottom and sides of one of the bas: ns and (b) the 

rate of movement of water from one of the basins to 

the water table.

PREVIOUS STUDIES

Artificial ground-water recharge on Long Island has 

been described by several authors, including Leggette 

and Brashears (1938); Brashears (1941, 1953); Johnson (1948, 1955); Parker, Cohen, and Foxworthy 

(1967); and Cohen, Franke, and Foxworthy (1968). 

Most of these authors have been concerned with the role 

of recharge wells on Long Island or have presented a 

broad overview of the subject of artificial recharge on 

Long Island. Several other authors have discussed recharge basins in moderate detail and have estimated 

recharge rates for several basins (Brashears, 1946; 

Welsch, 1949; Parker and others, 1967). The most pertinent quantitative study of recharge basins on Long 

Island to date (1968) was made by Brice, Whitaker, 

and Sawyer (1956).

ACKNOWLEDGMENTS

The author is grateful to numerous personnel of the 

Nassau County Department of Public Works, especially 

to Mr. Emmett Bowker, for helping to chose appropriate basins for the study, and to Mr. Charles Kirstner, 

who supervised the drilling of the water-table observation well. Lockwood, Kessler and Bar+lett, consulting 

engineers, supplied the aerial photogrpphs.

The report was prepared under the immediate supervision of Bruce L. Foxworthy, former hydrologist in 

charge, Mineola subdistrict, and his successor, Philip 

Cohen, and under the general direction of Garald G. 

Parker, District chief, New York District.
HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YORK

PRELIMINARY RESULTS OF HYDROLOGIG STUDIES AT TWO RECHARGE BASINS

ON LONG ISLAND, NEW YORK

By G. E. SEABTTRNABSTRACT

More than 2,000 recharge basins on Long Island are used to 

dispose of storm runoff from residential and industrial areas 

and highways. Two of these basins have been instrumented to 

measure the response time of runoff generated from a rainfall 

event and to study inflow patterns and the infiltration rates of 

the selected basins.

The time lag recorded at the Westbury test basin from the 

start of rainfall to the start of inflow ranged from 5 to 20 

minutes. The time lag from the beginning of inflow to the initial 

response of the basin-stage recorder located about 120 feet from 

the discharging culvert ranged from 10 to 20 minutes. The time 

lag from the start of rainfall to the initial rise in the water table 

was between 2 and 8 hours.

The ratio of storm-water inflow to rainfall at the Westbury 

basin ranged from 0.08 to about 0.20, and the average ratio for 

more than 1 year of record was about 0.14. The ratio of stormwater inflow to rainfall at the Syosset basin ranged from 0.02 

to 0.15, and the average ratio for more than 1 year of record 

was about 0.10. The average ratio of storm-water inflow to 

rainfall closely approximates the ratio of paved street area to 

total drainage area of both basins.

The estimated average annual volume of ground-water recharge resulting from inflow to the basins and subsequent percolation to the underlying water table in 1967 was 7.5 acre-feet 

for the Westbury recharge basin and 10 acre-feet for the Syosset 

recharge basin.

The average infiltration rate at the Westbury recharge baslr 

for 12 storms during the summer and fall of 1967 was 211 gallon? 

per day per square foot.

INTRODUCTION

PURPOSE AND SCOPE OF THE WATER-BUDGET 

STUDY

Long Island, which extends from the southeasterr 

part of the mainland of New York State east-northeastward about 120 miles into the Atlantic Ocean, har 

a total area of about 1,400 square miles (fig. 1). Two 

boroughs of New York City (Kings and Queens Counties) occupy slightly less than 200 square miles of the 

western part of the island, and have a combined population of about 4.5 million people. The areas of Nassau

FIGURE 1. Location and general geographic features of Long Island.

 1
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS

USE AND GENERAL DESCRIPTION OF RECHARGE 

BASINS ON LONG ISLAND

In 1935, as a result of a long-range drainage plan 

developed by Welsch (1935), the Nassau County Sanitation Commission decided to develop a system of short 

storm-sewer lines terminating in open basins or pits 

(commonly referred to as recharge basins) to dispose 

of most of the storm runoff in the county instead of 

discharging the runoff directly into streams or into the 

tidewaters of the Atlantic Ocean and Long Island 

Sound. This decision was made partly on the assumption that in much of Long Island this system would be 

more economical than the alternative of building long 

trunk sewers that discharged into streams or tidewater.

Recharge basins on Long Island are unlined pits (fig. 

2) of various shapes and sizes which are excavated below 

land surface, mostly in moderately to highly permeable 

sand and gravel deposits of glacial outwash. The basins 

range in area from about 0.1 to 30 acres and average 

about 2 acres. Their average depth is about 10 feet, but 

some are about 25 feet deep. Generally, recharge basins 

are used only where the water table is sufficiently deep

to remain below the floor of the basin all, or at least 

most of the time. Therefore, only a few recharge basins 

are located in nearshore areas, where the water table is 

within a few feet of the land surface.

About 500 basins are maintained in Nassau County 

mainly by the Nassau County Department of Public 

Works. A few are also maintained by the towns and 

some by private owners. Suffolk County has about 1,400 

basins, most of which are maintained by the towns. In 

addition, about 135 basins (50 in Nassau County and 

about 85 in Suffolk County) are maintained by the New 

York State Department of Highways.

The basins can be grouped into two general types 

those with, and those without, overflow structures. However, most of the basins are equipped with some type of 

overflow structure that is, when the capacity of the 

basin is exceeded, overflow water is carried by pipes, 

flumes, or gutters to another recharge basin or to a nearby stream.

Design criteria for recharge basins on Long Island 

have evolved for the most part on a trial-and-error basis 

during the last 30 years. At present, the criteria used

FIGURE 2. Typical recharge basin in Nassau County.
C4 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YORK

to design the size of a recharge basin in Nassau County 

are those that have been established by the Department 

of Public Works. Two major criteria are used in Nassau 

County to design a basin that has an overflow structure 

(or structures). First, the required size (volume) of the 

basin below the overflow elevation is estimated by multiplying (a) the volume of water equivalent to 5-inches 

of rainfall on the total drainage area of the basin by 

(b) a factor ranging from 40 to 90 percent. The factor 

selected is based on conditions in the drainage area, 

such as land slope and percentage of area occupied by 

streets and parking lots. A runoff factor of 40 percent 

is used in most residential areas, and the factor used in 

industrial areas is as much as 90 percent to allow for the 

usually higher proportion of impervious surfaces in 

these areas. Second, the elevation of the overflow structure must not be more than 10 feet above the floor of the 

basin. Infiltration into the floor and sides of the basin 

is neglected in the design, and this provision results in 

an additional factor of safety.

Only a few basins are built without overflow structures; these are termed "dead-end" basins. Because the 

operation of these basins varies widely, depending upon 

local conditions, firm regulations regarding their size 

have not been established.

All recharge basins in Nassau County have two or 

more levels. The lower level (the floor of the basin) is at 

the elevation of the invert of the inflow pipes, and this 

level acts as a settling pool to collect inflowing sediment 

and trash. The higher level, commonly about 2 feet 

above the floor, serves as a platform for maintenance 

work when the lower level is flooded The higher level 

also facilitates infiltration of water into the ground inasmuch as it remains comparatively free of sediment.

The design criteria used to construct recharge basins 

in Suffolk County are similar to those used in Nassau 

County. In Suffolk County, however, the construction 

of recharge basins is regulated mostly by the towns 

rather than by the county.

LOCATION AND DESCRIPTION OF TEST BASINS

The two recharge basins that were studied during the 

investigation described in this report are in residential 

areas that are typical of much of surburban Nassau 

County. One basin is in the village of Westbury; the 

other is about 7 miles northeast in the village of Syosset 

(fig. 3). The drainage area of the Westbury recharge 

basin is about 15.0 acres; the basin is rectangular in 

shape (fig. 4), and the average land-surface gradient is 

about 13 feet per mile to the south. The drainage area of 

the Syosset recharge basin is about 28.8 acres; this basin 

also is rectangular in shape (fig. 5), and the land-surface gradient is about 20 feet per mile to the south. 

Pertinent information regarding the drainage areas of

Basin

Area Depth 

(acres) (feet)

0.5

1.0

12 

14

Volume i Diameter of 

(million inflow pipe 

gallons) (inches)

0. 71 

2.09

24 

30

the Westbury and Syosset recharge basins is summarized in table 1. Additional information about the Westbury and Syosset recharge basins is given in table 2.

TABLE 1. Summary of data on the drainage areas of the 

Westbury and Syosset recharge basins

Area of Ratio of Total im- Ratio of

Drainage Number streets street pervious total imBasin area of houses in drain- area to area in pervious

(acres) in drain- age area drainage drainage area to

age area (acres) area area drainage

(acres) area

Westbury.___ 15.0 52 1.7 0.11 4.8 0.32 

Syosset__ ______ 28.8 90 3.9 .13 10.2 .35

1 Total impervious area includes streets, driveways, sidewalks, and roofs. 

TABLE 2. Summary of data on the Westbury and Syosset recharge

1 Below the overflow elevation.

TLANTIC OCEAN

234 MILES 

i I I

FIGUBE 3. Location of Westbury and Syosset artificial recharge 

basins and rain gages in Nassau County.
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS C5

FIGURE 4. Aerial photograph of the Westbury recharge basin ana its drainage area. Photograph by

Lockwood, Kessler, and Bartlett.

361-168 O 69 2
C6 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YORK

FIGUBE 5. Aerial photograph of the Syosset recharge basin and its drainage area. Photograph by

Lockwood, Kessler, and Bartlett.
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS C7

The major reasons that these two basins were chosen 

for study were that each basin was characterized by (1) 

a clearly defined drainage area and a relatively simple 

drainage system, (2) a single inflow pipe, and (3) structures in which instruments could be adequately protected from vandalism. The two basins are very similar in most pertinent characteristics; therefore, subsequent comments about one basin apply equally to the 

other, unless noted otherwise.

In both drainage areas, runoff collects in street gutters and flows by gravity into street inlets that are interconnected by storm sewers which carry the runoff 

to the recharge basin. The bottoms of the street inlets 

are unlined (fig. 6); therefore, some runoff percolates 

through the bottoms of these inlets into the underlying 

zone of aeration. Manholes, used for inspection and 

maintenance, provide access to the storm sewers at all 

breaks in line and grade.

INSTRUMENTATION OP TEST BASINS

Both the Westbury and Syosset recharge basins were 

instrumented to measure and record inflow to the basins 

and precipitation near the drainage areas of the basins. 

In addition, the Westbury basin was instrumented to

measure the depth of water in the basin and fluctuations 

of the water table beneath the basin. A diagrammatic 

section of the drainage system and the location of the 

measuring instruments at the Westbury recharge basin 

are shown in figure 6. The inflow structures and the arrangement, of the inflow-measuring instruments ar^ 

similar at the Syosset recharge basin.

DESCBIPTION OF APPARATUS

The apparatus for measuring and recording inflow 

to each recharge basin includes a compound V-notcl 

weir in the mouth of the inflow pipe entering the manhole nearest to each basin, a stilling well connected to 

the smooth concrete inflow pipe behind the weir, and 

a digital recorder to monitor water-level fluctuations in 

the stilling well (fig. 7). The selected locations of the 

weirs prevented backwater interference, and the manholes provided safe locations for the instruments.

The angle between the sides of the small V-notch is 

30°, and the angle of the broader part is 120°. The 

design is a compromise between optimum hydraulic 

control and minimum channel constriction. The height 

of the small notch is equal to one-fourth the diameter 

of the inflow pipe, and the larger part of the weir exRecharge basin

Water-table 

observation well 

and recorder

Street inlet

chamber (open bottomed)

Basin-stage 

recorder

Shed

-/

±100'

.Gravel

'.±35

.; Water table

FIGUBE 6. Diagrammatic section showing the drainage system and location of measuring instruments at the

Westbury recharge basin (not to scale).
C8 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YOFTC

Digital

(Punched-tape) 

recorder

Counter 

weight

Piezometer tube

connected to stilling

well

Cleanout hole

FIGURE 7. Sketch of inflow-measuring apparatus located in 

manhole nearest each recharge basin.

tends to a height equal to about one-half the diameter. 

The weir was cut from %-inch stainless-steel plate, and 

the edges of the weir were beveled to a sharp edge.

The piezometric head on the weir is measured 

through a vertical tube, three-fourths of an inch in 

diameter, inserted flush with the inside surface of the 

pipe 3 inches upstream from the weir (fig. 6). The tube 

transmits the head on the weir to a nearby stilling well 

which is equipped with a water-level recorder. The 

recorder was set to record (punch) every 5 minutes.

Weighing-bucket recording rain gages were installed 

as close to the recharge basins as practical. The Westbury gage is about 300 yards southeast of the basin, 

and the Syosset rain gage is about 2,300 yards north of 

the basin (fig. 3). Small plastic rain gages were also installed in each basin.

The water-table observation well at the Westbury 

basin is 4 inches in diameter and is equipped with a 

stainless-steel screen that is set in coarse sand and gravel 

about 50 feet below the floor of the basin. The depth to 

the water table was about 35 feet in 1967.

The characteristics of the inflow structures at the 

basins and the somewhat unusual design of the weirs 

resulted in the need to use detailed and moderately 

complex procedures to calibrate the weirs. These procedures are described in the appendix to this report (p. 

CM).

MEASUREMENT OF BASIN STORAGE

A detailed topographic survey of tH Westbury recharge basin was made to define the relations between 

depth of water in the basin, as measured by the basinstage recorder, and water-surface arer- and volume of 

storage in the basin. These relations arc shown in figure 

8. The small increase in the water-surface area between 

the values of water depth of 1.0-2.0 feet is the result 

of the two levels of the Westbury recharge basin.

RESULTS OF THE STUDY

Precipitation data for more than 75 rainfall events 

(ranging from about 0.10 to 5 inches) and concurrent 

inflow to the Westbury and Syosset recharge basins 

were obtained from midsummer 1966 to January 1968. 

Data on basin stage and fluctuations of the water table 

were obtained at the Westbury recharge basins for 

about 20 rainfall events from June T.967 to January 

1968.

TIME RESPONSE OF THE ST'STEM

In general, the time lag from the beginning of rainfall to the beginning of inflow to the basin (measured 

at the weir) ranged from 5 to 20 minutes. This time lag 

was caused mainly by filling of depressions in the 

gutters, inlets, and pipes upstream from the weir. The 

time lag between measurable inflow at the weir in the 

Westbury basin and the initial resporse of the basinstage recorder ranged from 10 to 20 minutes. This lag 

reflected the time required for the water to flow from 

the weir to the basin-stage recorder, which is at the 

lowest elevation on the basin floor about 120 feet from

^-Approximate extent 

of lower part of basin

1000 2000 3000 4000 5000 6000

WATER-SURFACE AREA, IN SQUARE FEET,

AND VOLUME OF STORAGE, IN CUBIC FEET

7000 8000

FIGURE 8. Relations between water depth, water-surface area, 

and volume of storage for the Westbury recharge basin.
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS C3

the weir. The time lag between the start of rainfall and 

the initial rise of the water table ranged from 2 to 8 

hours.

Many factors were responsible for the time lags described in the preceding paragraph; however, the most 

significant probably were the intensity and magnitude 

of the rainfall and antecedent soil-moisture conditions.

An example of the relations between rainfall, inflow,

basin storage, and fluctuations of the water table at tl ^ 

Westbury recharge basin is shown in figure 9. Total 

rainfall during the storm, which lasted for about 3 

hours, was about 1.45 inches. During the first 20 minufe-s, 

the intensity of the storm was more than 1 inch per hour. 

Inflow to the basin was first measured at the weir 5 

minutes after rainfall began. Total inflow was equivalent to 0.35 inch in the entire drainage area, or about

0.5

12 24 36 48 60 72 84 96 108

r>O 

u u

4

U- LLJ

Z m 2

_ LL- * 

0

4000

3000

12 24 36 48 60 72 84 96 108

O

Ou

£5 2000

r> 

z u

< ^

1000

62.9

62.5 -

"- 62.0 - 

61.9 4 12 24 36 48 

TIME SINCE RAINFALL BEGAN, IN HOURS

60 72 84 96

108

108

FIGURE 9. Rainfall, inflow, basin storage, and water-table elevation for a storm on October 18, 1967, at the Westfoury

recharge basin.
CIO HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YORK

24 percent of the total rainfall. Standing water was 

measured at the basin-stage recorder about 15 minutes 

after the beginning of rainfall and .about 10 minutes 

after the inflow was first noted at the weir. The water 

table began to rise about 4 hours after rainfall began.

RAINFALL-INFLOW RELATIONS

The relations between rainfall and inflow (expressed 

in inches of rainfall on each drainage area) for the 

Westbury and Syosset recharge basins are shown in 

figures 10 and 11, respectively. The points in both figures 

are widely scattered because, in addition to the total

amount of rainfall, inflow also is related to the duration, 

intensity, time distribution, and direction of movement 

of a storm, antecedent soil-moisture conditions, and several other factors. The scatter of points for the Syosset 

basin (fig. 11) is larger than that for the Westbury data, 

especially for the smaller storms. This greater scatter 

may partly be a result of the fact that the Syosset drainage area has a drainage-collection network that includes 

nine open-bottom street inlets as compared to only one 

open-bottom inlet in the Westbury drainage area. Each 

of these street inlets acts as a small recharge basin, 

thereby disposing of some runoff before it reaches -the

0.1

z

u

z

o

0.01

0.001

0.01 0.1 1 10

RAINFALL, IN INCHES 

FIGURE 10. Relation between rainfall and inflow to the Westbury recharge basin, 1966-67.
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS Cll

main recharge basin. This factor probably is responsible 

for some of the scatter of all the data obtained at the 

Syosset recharge basin, but it likely had a greater effect 

during the smaller storms.

Table 3 gives some representative values and selected 

ratios of inflow to rainfall calculated from the trend 

lines in figures 10 and 11. These data show that both 

inflow and the ratio of inflow to rainfall increase as total 

rainfall increases. Also, the ratio of inflow to rainfall is 

larger at the Westbury recharge basin than at the Syosset basin. The difference between the ratios of inflow to 

rainfall for Westbury and Syosset (table 3), which is

about 5-8 percent, probably is largely a measure of tl 3 

effect of the previously mentioned street inlets in tl Q> 

Syosset drainage area on reducing inflow to the Syosset 

basin.

The average measured ratio of inflow to rainfall in 

1967 was 0.14 at the Westbury basin and 0.10 at the Syosset basin. This closely approximates the ratio of street 

area to the total drainage area that is, 0.11 for the 

Westbury drainage area and 0.13 for the Syosset drainage area (table 1). This close approximation suggests 

that in small suburban drainage areas with similar infiltration characteristics, the volume of runoff is related

0.1

u

z

o

0.01

0.001

0.01 0.1 1 10

RAINFALL, IN INCHES 

FIGURE 11. Relation between rainfall and inflow to the Syosset recharge basin. 1966-67.
C12 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YOF.K

to the proportion of street area in the drainage area. Of 

course, for storms with large magnitudes or high intensities, additional areas, such as driveways, sidewalks, 

and lawns, also contribute runoff by overflowing onto 

the streets.

TABLE 3. Selected values of rainfall and inflow for Westbury and 

Syosseet recharge basins derived from the trend lines in figures 10 

and 11

Westbury recharge basin

Rainfall 

(inches)

0.1. __.__.__-._

. 5 __ _________

1.0_____-.._-._

2. 0___ _ ______

3. 0________--._

4. 0____________

Inflow 

(inches)

0. 008

. 076

. 18

.39

. 60

.81

Ratio of 

inflow to 

rainfall

0 08 

15 

18 

19 

20 

20

Syosset recharge basin

Inflow 

(inches)

0. 0025 

. 036 

.095 

.25 

. 40 

. 59

Ratio of 

inflow to 

rainfall

0 02 

07 

10 

12 

13 

15

INFILTRATION BATES AT THE WESTBURY BASIN

Rates of infiltration through the bottom of the Westbury recharge basin were calculated from the inflow and 

basin-storage data using the continuity equation,

Infiltration=Inflow ± A Storage, (1)

where the symbol, A, indicates the net incremental 

change in storage. Evapotranspiration losses are believed to have been negligible and, therefore, these losses 

were neglected. A graph of the computed rate of infiltration at the Westbury basin for a storm on October 

18,1967, is shown in figure 12. The infiltration rate during this storm ranged from 10 to 510 gpd per sq ft (gallons per day per square foot) and averaged 277 gpd 

per sq ft.

The relation between depth of water and the infiltration rate at the Westbury recharge basin is shown in 

figure 13. The sequentially plotted points are average 

infiltration rates for 5-minute intervals. It is apparent 

that the depth of water in the basin and the infiltration 

rate are not closely nor directly related. Other factors 

that probably influence infiltration rates significantly, 

include antecedent soil-moisture conditions, water temperature, barometric pressure, and differences in permeability of the soil materials in different parts of the 

basin.

In a previous study, Brice, Whitaker, and Sawyer 

(1956) related infiltration rates to the depth of water 

in a recharge basin on Long Island. They also concluded 

that many factors affect infiltration rates, and that there 

was no simple relation between depth of water and infiltration rates.

Infiltration rates and other pertinent data for several 

storms in 1967 are given in table 4. The average infiltration rate during these storms in the summer and fall of

1967 was 211 gpd per sq ft. The depth of water in the 

lowest part of the basin never exceeded 2 feet and rarely 

exceeded 1.5 feet.

Estimates of rates of infiltration by others have 

ranged widely. Brice, Whitaker, and Sawyer (1956) 

reported infiltration rates ranging from 20 to 400 gpd 

per sq ft when the depth of water in the basin that they 

studied was artifically maintained at 1 foot. Welsch 

(1949) determined an average infiltration rate of 23 gpd 

per sq ft for 14 recharge basins rangir. % in size from 2 

to 9 acres. The depth of water in thepe basins ranged 

from 0.5 to 9 feet.

GROUND-WATER RECHAPOE

Virtually all the water that enters tl Q, Westbury and 

Syosset recharge basins infiltrates into the ground within a few hours and almost always within a day after 

water first flows into the basin. Accordingly, the amount 

of inflow consumed by evapotranspiration is negligible; 

so for practical purposes it can be assumed that all, 

or almost all, the inflow to these two basins ultimately 

recharges the ground-water reservoir. On the basis of 

this assumption and using the approximate relations 

between inflow to the basins and precipitation described

500 -

400 -

300

Z 200 -

100 -

Average infiltration rate 

277 gpd per sq ft

1 2 3

TIME, IN HOURS, SINCE RAINFALL BEGAN

FIGURE 12. Average infiltration rates calculated for 5-niinute 

intervals at the Westbury recharge basin for the storm on 

October 18, 1967.
PRELIMINARY RESULTS OP HYDROLOGIC STUDIES AT TWO RECHARGE BASINS C13

0 100 200 300 400 500 

INFILTRATION RATE, IN GALLONS PER DAY PER SQUARE FOOT

FIGURE 13. Relation between depth of water and average infiltration rate calculated for 5-rnmute intervals in the Westbury recharge basin, during the storm of October 18, 1967.

ill the previous paragraphs, the estimated ground-water 

recharge in 1967 resulting from inflow to the Westbury 

and Syosset basins was 7.5 and 10 acre-feet, 

respectively.

Average precipitation in the area of these recharge 

basins is about 44 inches (Cohen and others, 1968, p. 31). 

Because 1967 was a year of near-average precipitation 

(about 42 in.), runoff for these developed drainage areas 

probably also was near average during that year. Therefore, the estimates of ground-water recharge are assumed to be roughly equal to the average annual groundwater recharge resulting from inflow to the two basins.

SUMMARY AND CONCLUSIONS

More than 2,000 recharge basins on Long Island are 

used to dispose of storm runoff from residential and 

industrial areas and highways. Two of these basins have 

been instrumented to collect data on inflow and time of 

response from a rainfall event. Inflow to both basins 

was determined by recording the flow over a compound 

V-notch weir placed in the mouth of the inflow pipe to

the manhole nearest each recharge basin. At one basin 

the depth of water in the basin was recorded simultaneously with inflow to measure the change in basin 

storage and water-surface area. Average rates of infiltration were calculated from this data. An observation 

well was installed to monitor the fluctuations of tH 

water table resulting from the influx of the recharge 

water.

The time lag recorded 'at the Westbury test basin, 

from the start of rainfall to the start of inflow, ranged 

from 5 to 20 minutes. The time lag from the beginning 

of inflow to the initial response of the basin-stage recorder ranged from 10 to 20 minutes. The time lag from 

the start of rainfall to the initial rise in the water table 

was between 2 and 8 hours.

The ratio of inflow to rainfall at the Westbury basin 

ranged from 0.08 to about 0.20 and averaged about 0.14. 

The ratio of inflow to rainfall at the Syosset basin 

ranged from 0.02 to 0.15 and averaged about 0.10. Inflow 

to the Syosset basin was affected by numerous openbottomed street inlets which act as small recharge 

basins, thus reducing the total amount of inflow thr.t 

reaches the basin.

The average ratio of inflow to rainfall closely approximates the ratio of street ar^a to total area, which 

suggests that rainfall directly on the streets provides a 

large proportion of the direct runoff.

The average infiltration rate at the Westbury basin 

determined from storms during the summer and fall cf 

1967 and 211 gpd per sq ft. The Westbury recharge 

basin seems to be typical of most well-operating basirs 

on Long Island. Accordingly, as a first approximation, 

this average rate of infiltration probably is a reasonable 

order of magnitude for other similar basins in the area.

TABLE 4. Rainfall, inflow, and average infiltration rates for 

selected storms in 1967 at the Westbury recharge basin

Date'

Rainfall 

(inches)

Inflow 

(inches)

Average infiltration rate 

(gallons pe~

day per 

square foot)

1867

July 23 A.__ ____ ._.

23 B_---___--_,__.__

25___---__-----_--__

Aug. 9____-_______-___ _

10 _- -_ ___ _ _.

25 A__--__-_-___-.__

25C_________-._____

26__. _______________

27_-______.___-____-

Sept.16---- -_

Oct. 18------------------

25_. _________-._.._.

0. 13

. 18

.42

.42

. 15

1.77

. 71

.37

. 33

. 55

1.45

.60

0. 016 

.029 

. 049 

.058 

. 042 

.283 

. 118 

.063 

.074 

.067 

.385 

.063

209 

285 

145 

180 

173 

270 

186 

137 

242 

2(H 

277 

157

_._ 211

' Capital letters represent the chronological order of two or more distinct stems 

occurring on the same day.
C14 HYDROLOGY AND SOME EFFECTS OF URBANIZATION ON LONG ISLAND, NEW YOPK

The estimated ground-water recharge in 1967 was 

roughly 7.5 acre-feet for the Westbury basin and 10 

acre-feet for the Syosset basin. This estimate probably 

is representative of the average annual recharge for 

these two recharge basins, inasmuch as 1967 was a year 

of near-average precipitation on Long Island, which, in 

turn, resulted in near-average runoff.

REFERENCES CITED

Brashears, M. L., Jr., 1941, Ground-water temperature on Long 

Island, New York, as affected by recharge of warm water: 

Econ. Geology, v. 36, no. 8, p. 811-828.

 1946, Artificial recharge of ground water on Long Island, 

N.Y.: Econ. Geology, v. 41, no. 5, p. 503-516.

 - 1953, Recharging ground-water reservoirs with wells and

basins: Mining Eng., v. 5, p. 1029-1932.

Brice, H. D., Whitaker, C. L., and Sawyer, R. M., 1956, A progress 

report on the disposal of storm water at an experimental 

seepage basin near Mineola, N.Y.: U.S. Geol. Survey openfile report, 34 p., 22 figs., 2 pis.

Chow, V. T., 1959, Open-channel hydraulics: New York, McGrawmil Book Co., 680 p.

Cohen, Philip, Franke, O. L., and Foxworthy, B. L., 1968, An 

atlas of Long Island's water resources: New York State 

Water Resources Comm. Bull. 62, p. 30.

Johnson, A. H., 1948, Ground-water recharge on Long Island: 

Am. Water Works Assoc. Jour., v. 40, no. 11, p. 1159-1166.

 1955, Conservation of ground-water on Long Island: Am. 

Water Works Assoc. Jour., v. 47, no. 4, p. 348-354.

Leggette, R. M., and Brashears, M. L., Jr., 1938, Ground water 

for air conditioning on Long Island, N.Y.: Am. Geophys. 

Union Trans., v. 19, pt. 1, p. 412-418.

Parker, G. G., Cohen, Philip, and Foxworthy, B. L., 1967, Artificial recharge and its role in scientific water management 

with emphasis on Long Island, N.Y.: Am. Water Resources 

Assoc., National Symposium on ground-water hydrology, San 

Francisco, Calif., Proc. p. 193-213.

Seaburn, G. E., 1969, Effects of urban development on direct 

runoff to East Meadow Brook, Nassau County, N.Y.: U.S. 

Geol. Survey Prof. Paper 627-B (in press).

Welsch, W. F., 1935, Comprehensive drainage plan for Nassau 

County, New York summary report: Nassau County Sanitation Comm., 23 p.

 1949, Conservation of ground-water resources, Nassau 

County, N.Y.: Water Works Eng., v. 102, no. 8, p. 708-710, 

741-746.

APPENDIX

PROCEDURES USED TO CALIBRATE THE WEIRS AT 

THE WESTBURY AND SYOSSET RECHARGE BASINS

To calibrate the weirs at the Westbury and Syosset 

recharge basins, flow from nearby fire hydrants was 

measured volumetrically by two methods before and 

after the water passed the weir. The first method involved determining the time required to fill two 55-gallon drums. The second method involved the construction 

of a temporary brick dam on the apron of the outlet 

structure in the recharge basin. This dam allowed 

nearly 1,000 gallons of water to be collected behind the 

dam in the outlet pipe and the bottom of the manhole.

Discharge was measured by determining the time required to fill this volume with water flowing over the 

weir under steady-flow conditions. The maximum flow 

that could safely be obtained from the f re hydrants was 

about 600 gpm (1.34 cfs). The two different volumetric 

methods provided an adequate check on the discharge 

determinations. In all cases the difference between discharge measurements by the two methods was less than 

1 percent.

During each of the calibration tests, the head on the 

weir was watched closely to insure that steady flow was 

established and maintained throughout each run, and a 

record of the water-stage fluctuations was obtained by a 

continuous recorder.

The rating curves for the Westbury and Syosset weirs 

are shown in figures 14 and 15. The measured discharges 

are shown as dots; the solid line is an average curve 

defining the discharges in the range of the field measurements. The broken lines represent computed extensions of the rating curve; the computational procedures 

are discussed in the following paragraphs.

Because in certain large storms tl;e instantaneous 

peak discharges were greater than the maximum measured discharges, the rating curves were extended upward to estimate these maximum discharges. The rating 

curves were extrapolated by the combination of two 

theories critical flow and uniform flow.

Critical flow is defined as the condition for which the 

Froude number (F) is equal to unity or, more commonly, at which the specific energy (E) is a minimum 

for a given discharge (Chow, 1959, p. 42). Critical 

depth is the depth of a given flow v^hen the specific 

energy is a minimum.

Critical flow occurs above the crest of the weir in the 

control section, which is defined as the section where the 

flow changes from subcritical to supercritical and where 

the specific energy of the flow is a minimum. As a close 

approximation, the water depth at the measuring point 

3 inches upstream from the weir is assumed to be critical 

depth. The following relation, developed from the 

Froude number, describes the flow through the control 

section:

(2)

where Q is discharge, in cubic feet jnr second, A and 

T are the area of flow, in square feet, and water-surface 

width, in feet, respectively, at the control section, and 

g is the acceleration due to gravity, in feet per second 

per second. Since A and T describe the configuration 

of the cross section as a function of the depth of flow, 

equation 2 can be solved for the discharge, Q, at various 

depths of flow to develop a stage-discharge relationship.
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EXPLANATION

Field-rated Hows

Curve based on 

critical-flow analysis

Curve based on 

normal-flow analysis

1

^

0.1 1 10

-il.O 

-0.9 

-0.8

-°-7 d 

-0.6 0

-0.5

oI «

OS

§ 

§

f

1

DISCHARGE, IN CUBIC FEET PER SECOND

FIGURE 15. Bating curve for V-notch weir at the Syosset recharge basin.
PRELIMINARY RESULTS OF HYDROLOGIC STUDIES AT TWO RECHARGE BASINS C17

For discharges where the depth of flow is small (d/D 

less than, or about equal to, 0.5) the streamlines above 

the measuring point are virtually parallel to the channel 

bottom, and the hydrostatic law of pressure distribution 

is applicable that is, the pressure distribution over the 

cross section is hydrostatic and is proportional to the 

depth below the free surface. As the depth of flow increases, the effects of drawdown over the weir extend 

farther upstream and begin to affect the pressure distribution in the vertical plane above the measuring 

point. A slight error in the critical-flow relation (eq 

2) is introduced when the resulting curvilinear streamlines cause a deviation from the hydrostatic pressure 

distribution over the measuring point. This error increases with increasing depth. Therefore, for large 

depths of flow, equation 2 does not accurately describe 

the flow through the control section at the measuring 

point.

An additional error is introduced at large flow depths. 

The water-surface width, T7 , decreases as the depth of 

flow increases in a circular pipe. As a consequence the 

calculated values of flow using equation 2 become increasingly large, which is contrary to the characteristics 

of open-channel flow in a circular pipe (Chow, 1959, 

p. 134-136).

At larger depths of flow, therefore, the flow was 

estimated by using uniform-flow theory. This theory 

is based on energy losses due to friction throughout 

the flow reach. Uniform flow has the characteristics that 

(1) the depth, water area, velocity, and discharge are 

constant at every section in the channel and (2) the 

energy line, water surface, and channel bottom are all 

parallel (Chow, 1959, p. 89). The depth of flow at uniform flow is called normal depth. The discharge in

the smooth concrete inflow pipe was assumed to be uniform and to be described by Manning's equation,

(3)

n

where n is Manning's coefficient of roughness, R is the 

hydraulic radius, in feet, and S is the slope of the energy 

line, water surface, and channel bottom, in feet per foot. 

Q and A were defined previously.

The discharge was actually calculated by using a 

modified form of equation 3 that employs a ratio of 

conveyance (Aft2/a ), because the roughness and slope 

of the channel do not change. That is,

(4)

Subscript 1 refers to the hydraulic conditions at the 

highest measured discharge on the field-rated curve, 

and subscript 2 refers to the hydraulic conditions at any 

other discharge. In figures 14 and 15, the theoretical 

curve based on the critical-flow method merges smoothly 

with the curve of the rated points, and the two theoretical curves merge with each other very smoothly below 

about d/D = 0.75, where d is the depth of flow above 

the crest of the weir, in feet, and D is the diameter of 

the pipe, in feet.

At large depths of flow the rating defined by criticaldepth analysis is an upper limit to the actual rating 

curve, and the rating defined by uniform-flow analysis 

is probably a lower limit. Therefore, the actual rating 

curve above d/D=0.76 is yet undefined but probably 

lies between these two limiting curves. In this study, 

however, only those discharges corresponding to flow 

depths less than d/D=0.75 were used.

US. GOVERNMENT PRINTING OFFICE: 1868 O-361-168