U.S. Department of the Interior

U.S. Geological Survey

Circular 1340

Prepared in cooperation with the 

U.S. Department of Agriculture Natural Resources Conservation Service and the

Rhode Island Water Resources Board 

Effects of Water-Management Strategies on

Water Resources in the Pawcatuck River Basin, 

Southwestern Rhode Island and

Southeastern Connecticut
Front cover: Wood River at Hope Valley, Rhode Island. Photo by Peter Flinker, Dodson Associates, Ltd.
Wyoming Pond on the Wood River at Wyoming.

Effects of Water-Management Strategies on 

Water Resources in the Pawcatuck River Basin, 

Southwestern Rhode Island and 

Southeastern Connecticut

By Robert F. Breault, Phillip J. Zarriello, Gardner C. Bent, John P. Masterson, 

Gregory E. Granato, J. Eric Scherer, and Kathleen M. Crawley

Prepared in cooperation with the 

U.S. Department of Agriculture Natural Resources Conservation Service and the 

Rhode Island Water Resources Board 

Circular 1340

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

KEN SALAZAR, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2009

For more information on the USGS—the Federal source for science about the Earth, 

its natural and living resources, natural hazards, and the environment:

World Wide Web: http://www.usgs.gov

Telephone: 1-888-ASK-USGS

Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the 

U.S. Government.

Although this report is in the public domain, permission must be secured from the individual copyright owners to 

reproduce any copyrighted materials contained within this report.

Suggested citation:

Breault, R.F., Zarriello, P.J., Bent, G.C., Masterson, J.P., Granato, G.E., Scherer, J. E., Crawley, K. M., 2009, Effects 

of water-management strategies on water resources in the Pawcatuck River Basin, southwestern Rhode Island and 

southeastern Connecticut: U.S. Geological Survey Circular 1340, 16 p.; available online at 

http://pubs.usgs.gov/circ/circ1340.

Library of Congress Cataloging-in-Publication Data

Information from the Library of Congress is pending.
Figures

1. Map showing Pawcatuck River Basin, southwestern Rhode Island and 

southeastern Connecticut...........................................................................................................3

2. Graphs showing monthly precipitation measured at the University of Rhode Island 

and daily mean streamflow measured at the Pawcatuck River at Westerly (USGS 

station 01118500) during 2000–04 ...............................................................................................4

3. Graphs showing flow paths of precipitation to a stream under (A) natural conditions,

(B) intercepted groundwater by a pumped well, and (C) induced infiltration by a 

pumped well ..................................................................................................................................5

4. Graphs showing average monthly water use in the Pawcatuck River Basin during 

2000–04 for (A) public supply and (B) irrigation.......................................................................6

5. Graphs showing hourly streamflow simulated in August 2002 for the (A) upper 

Pawcatuck River, (B) lower Chipuxet River, (C) Usquepaug River, and (D) lower 

Beaver River under no withdrawals, current (2000–04) withdrawals, and current 

withdrawals with selected instream irrigation withdrawals replaced by 

groundwater withdrawals...........................................................................................................8

6. Schematic diagram of groundwater withdrawals from different well locations

between the relatively large Wood River and the smaller Meadow Brook........................9

7. Graph showing simulated effects of irrigation withdrawals on streamflow as the well 

distance from a stream increases; the effects on streamflow are damped and spread 

out over time as the distance of the well from the stream increases ...............................10

8. Map showing simulated water-management strategy that replaces six instream 

irrigation withdrawals with groundwater withdrawals between the lower Beaver and 

Usquepaug Rivers.......................................................................................................................11

9. Graph showing simulated streamflow changes that result from replacing six instream 

irrigation withdrawals in the lower Beaver and Usquepaug Rivers with groundwater 

withdrawals between the rivers ..............................................................................................12

10. Map showing groundwater-model simulated changes in water levels in the Diamond 

Bog area in the Wood River subbasin for March 2000 and March 2002...........................13

11. Maps showing representation of the simplified land use in the Pawcatuck River 

Basin simulated by the Hydrologic Simulation Program–FORTRAN model under 1995 

conditions and projected buildout conditions .......................................................................15

Contents

Abstract...........................................................................................................................................................1

Introduction.....................................................................................................................................................2

Water Resources ..................................................................................................................................4

Water Use .............................................................................................................................................6

Assessment of Water-Management Strategies.......................................................................................6

Effects of Current Water Use on Streamflow...................................................................................6

Effects on Streamflow of Replacing Surface-Water Withdrawals with Groundwater 

Withdrawals.............................................................................................................................9

Effects of Groundwater Pumping on the Water Table..................................................................13

Effects of Potential Changes in Land Use and Water Use...........................................................14

Summary........................................................................................................................................................16

References Cited..........................................................................................................................................16

iii
iv

Multiply By To obtain

Length

inch (in.) 2.54 centimeter (cm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

square mile (mi2

) 2.590 square kilometer (km2) 

Flow rate

cubic foot per second (ft3

/s) 0.02832 cubic meter per second (m3/s)

million gallons per day (Mgal/d) 0.04381 cubic meter per second (m3

/s)

Flow rate in Mgal/d or ft3

/s can be converted by: Mgal/d*1.547 = ft3/s or ft3/s*0.6463 = Mgal/d.

Conversion Factors and Datums
Effects of Water-Management Strategies on 

Water Resources in the Pawcatuck River Basin, 

Southwestern Rhode Island and 

Southeastern Connecticut

By Robert F. Breault, Phillip J. Zarriello, Gardner C. Bent, John P. Masterson, 

Gregory E. Granato, J. Eric Scherer, and Kathleen M. Crawley

Abstract

The Pawcatuck River Basin in southwestern Rhode Island and southeastern Connecticut 

is an important high-quality water resource for domestic and public supplies, irrigation, 

recreation, and the aquatic ecosystem. Concerns about the effects of water withdrawals 

on aquatic habitat in the basin have prompted local, State, and Federal agencies to explore 

water-management strategies that minimize the effects of withdrawals on the aquatic 

habitat. As part of this process, the U.S. Geological Survey in cooperation with the U.S. 

Department of Agriculture Natural Resources Conservation Service and the Rhode Island 

Water Resources Board completed a study to assess the effects of current (2000–04) and 

potential water withdrawals on streamflows and groundwater levels using hydrologic 

simulation models developed for the basin. The major findings of the model simulations are:

•	 Moving highly variable seasonal irrigation withdrawals from streams to groundwater 

wells away from streams reduces short-term fluctuations in streamflow and increases 

streamflow in the summer when flows are lowest. This occurs because of the 

inherent time lag between when water is withdrawn from the aquifer and when it 

affects streamflow.

•	 A pumped well in the vicinity of small streams indicates that if withdrawals exceed 

available streamflow, groundwater levels drop substantially as a consequence of 

water lost from aquifer storage, which may reduce the time wetlands and vernal pools 

are saturated, affecting the animal and plant life that depend on these habitats. 

•	 The effects of pumping on water resources such as ponds, streams, and wetlands can 

be minimized by relocating pumping wells, implementing seasonal pumping schemes 

that utilize different wells and pumping rates, or both.

•	 The effects of projected land-use change, mostly from forest to low- and mediumdensity housing, indicate only minor changes in streamflow at the subbasin scale 

examined; however, at a local scale, high flows could increase, and low flows could 

decrease as a result of increased impervious area. In some instances, low flows could 

increase slightly as a result of decreased evapotranspiration from the loss of deeprooted vegetation (forest) associated with development.

•	 In some subbasins where large areas of agricultural lands were converted to low- and 

medium-density housing, low flows increase because the consumptive domestic 

water use was projected to be less than consumptive agricultural water use. All 

agricultural water use was for irrigation purposes and was assumed to be lost from 

the basin through evapotranspiration.

Wood River at Hope Valley. Photo by the State of Rhode Island Department of Environmental Management
Lateral-move irrigation system used on turf farms. 

Canoeing on Barber Pond near West Kingston. 

The basin has 11 golf courses that use water for irrigation.

2 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Introduction

The Pawcatuck River Basin in southwestern 

Rhode Island and southeastern Connecticut 

is known for its biologically diverse aquatic 

habitat and its yield of high-quality water that 

is used for a variety of purposes (fig. 1). Nearly 

two-thirds of the State’s rare and unique natural 

communities can be found within this basin. 

Water resources are also important for irrigation, 

domestic and public water supply, recreation, and 

the scenic beauty of the basin. The primary water 

use is for municipal supply, with withdrawals 

mainly in the eastern and southwestern parts of 

the basin, but seasonal irrigation is also a major 

water use in parts of the basin.

In 2005, the U.S. Environmental Protection 

Agency reported that the Pawcatuck River Basin 

had the highest concentration of turf farms in 

the Nation. These farms are irrigated mostly in 

the summer when streamflows and groundwater 

levels are typically at their lowest. Streamflow 

data indicate that irrigation withdrawals from 

streams appreciably decrease summer low flows. 

Future groundwater withdrawals, mainly by 

municipal suppliers, are also of concern because 

of their potential effects on streamflows and 

groundwater levels.

In response to these concerns, the U.S. 

Department of Agriculture Natural Resources 

Conservation Service (NRCS) and the Rhode 

Island Water Resources Board (RIWRB) began 

a cooperative study with the U.S. Geological 

Survey (USGS) in 2002 to evaluate the water 

resources of the basin, the hydrologic effects of 

water use, water-management alternatives, and 

potential hydrologic changes that might result 

from future land-use and water-use changes. The 

results of this investigation will assist the NRCS, 

the RIWRB and other State agencies, and local 

communities in understanding how streamflows 

and water levels are affected by current wateruse practices, and how these practices may be 

modified to meet water-supply needs while also 

meeting recreation and aquatic-life needs. 

This report describes the major findings of 

that study, in particular, the potential effects of 

water-management strategies on streamflows 

and water levels in the Pawcatuck River Basin. 

Additional information about the study and its 

findings can be found in the U.S. Geological 

Survey Scientific Investigations Report 2010–

5127 (Bent and others, in press).
Glacial stratified deposits

Till and bedrock outcrops

Charlestown moraine

Water

River

Basin boundary

Public-supply well

USGS streamgage

 and identifier

University of

 Rhode Island

 climatological

 station

Surficial geologic deposits

Hydrology

EXPLANATION

01118500

Base from U.S. Geological Survey digital data, 1:24,000,

Rhode Island state plane projection. 1983 North American datum CONNECTICUT RHODE ISLAND

Hopkinton

Voluntown

Sterling

Plainfield

Coventry

West Greenwich East Greenwich

Richmond

South

Kingstown

North

Kingstown

Charlestown

Westerly

Stonington

North Stonington

Exeter

Watchaug Pond Chapman Pond

Worden

Pond

Pasquiset

 Pond

Cedar

Swamp

Brook

A T L A N T I C O C E A N

Beaver River

River

River

Wood

River

Chickasheen Brook

Pawcatuck

Pawcatuck

Tomaquag Brook

Queen River

Wood River

Ashaway River

Shunock

River

Meadow

Brook

Usquepaug River

Chipuxet River

71°50' 71°40' 71°30'

41°40'

41°30'

41°20'

71°45' 71°15'

42°

41°20' 0 4

0 5 10 KILOMETERS

10 MILES

Pawcatuck River

Basin

RHODE 

ISLAND

0 5 MILES

0 5 KILOMETERS

01118500

Introduction 3

Figure 1. Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut.
4 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Water Resources

The Pawcatuck River Basin (fig. 1) covers 

an area of about 303 mi2

 that includes the Wood 

River (89.2 mi2

), Usquepaug-Queen River 

(36.6 mi2

), Ashaway River (28.2 mi2), Chipuxet 

River (17.3 mi2

), Shunock River (16.3 mi2), 

Beaver River (12.5 mi2

), Meadow Brook 

(7.21 mi2

), and Chickasheen Brook (6.55 mi2). 

The surficial geology of the basin is mainly 

glacial stratified deposits of sand, gravel, silt, and 

clay along the major river valleys and glacial till 

or exposed bedrock in the upland areas, with the 

Charlestown moraine, a mostly sand and gravel 

glacial deposit, forming the southern border of 

the basin (fig. 1). Postglacial deposits consisting 

of flood-plain alluvium along rivers and streams, 

organic peat, and muck (swamp deposits) are 

present in some areas. Thick (100 to 200 ft) 

deposits of valley-fill sand and gravel compose 

the major aquifers in the basin and are the 

primary source of public water supply. The basin 

is designated as a sole source aquifer by the 

U.S. Environmental Protection Agency (Federal 

Register, 1988).

All water for public supply, irrigation, 

and streamflow in the basin originates from 

precipitation. Annual precipitation is, on 

average, about 52 in/yr (or, on average, about 

4.3 in/month) at the University of Rhode 

Island climatological station (fig. 1 and 2). If 

all precipitation left the basin as streamflow 

this would equal about 1,160 ft3

/s; however, 

mean daily flow at the USGS streamgage 

near the mouth of the Pawcatuck River at 

Westerly, RI (01118500; fig. 1) is about 580 ft3

/s 

(fig. 2), or about 50 percent of the average 

annual precipitation in the basin. The remaining 

50 percent of the precipitation leaves the basin by 

a combination of evaporation, plant transpiration, 

and withdrawals that are transferred out of 

the basin.

The precipitation that eventually 

discharges to streams follows complex flow 

paths across and through the landscape. These 

flow paths are categorized simply as surface 

runoff; shallow subsurface flow referred to 

as interflow; and deeper subsurface flow that 

provides recharge to the aquifer and eventually 

discharges to streams as baseflow (fig. 3A). 

Mean daily flow = 580 ft3/s

Mean monthly precipitation = 4.3 in/month

1,600

1,400

1,200

1,000

800

600

400

200

0

2000 2001 2002 2003 2004

2000 2001 2002 2003 2004

MONTHLY MEAN STREAMFLOW, 

IN CUBIC FEET PER SECOND

0

2

4

6

14

12

8

10

MONTHLY TOTAL 

PRECIPITATION, IN INCHES

The Usquepaug River and Glen Rock Reservoir at Usquepaug.

Figure 2. Monthly precipitation measured at the University of Rhode Island 

and monthly mean streamflow measured at the Pawcatuck River at Westerly 

(USGS station 01118500; location shown in fig. 1) during 2000–04.
Introduction 5

C Induced Infiltration by a Pumped Well

Pumped

well

If the groundwater table drops below the 

stream level, the pumped well induces 

infiltration from the stream, typically under 

dry (low recharge) conditions. 

Losing 

stream

B Intercepted Baseflow by a Pumped Well

Pumped

well

Pumped well intercepts 

groundwater that otherwise 

would discharge to a stream,

pond, or wetland.

Stream

Evapotranspiration

Recharge Evaporation

Water table

Surface runoff

Shallow subsurface runoff

Groundwater flow

A Natural Conditions

Groundwater 

discharge to streams

Stream

Figure 3. Flow paths of precipitation to a stream under (A) natural conditions, 

(B) intercepted groundwater by a pumped well, and (C) induced infiltration by 

a pumped well. A pumped well captures groundwater that would otherwise 

discharge to a stream, induces infiltration from the stream, or both; if the rate 

of withdrawal exceeds the rate of streamflow, induced infiltration can cause 

the stream to stop flowing.

The amount of water that moves along each 

of these flow paths is governed by soils, 

surficial geology, imperviousness, slope, and 

other factors that influence the hydrologic 

response to precipitation. During low-flow 

periods, baseflow is often the only component 

of streamflow.

Groundwater withdrawals can affect 

streamflow in several ways. A pumped well 

that captures groundwater that would otherwise 

discharge to streams (fig. 3B) ultimately 

decreases streamflow in proportion to the 

withdrawal. If groundwater withdrawals are 

large enough that the water level in the stream 

is greater than the water level in the underlying 

aquifer, water seeps from the stream into the 

aquifer (induced infiltration) and could become 

a direct source of water to the pumped well 

(fig. 3C). If the pumping rate exceeds the rate 

of streamflow or the rate of induced infiltration, 

the difference between the two comes from 

water stored in the aquifer. As more water 

is removed from aquifer storage, drawdown 

increases as does the area of influence of the 

pumped well; these conditions are important 

in assessing the effects of pumping on nearby 

surface-water features, such as ponds, wetlands, 

and vernal pools.

Regardless of whether groundwater 

pumping results in captured baseflow or induced 

infiltration from the stream, the streamflow is 

reduced in direct proportion to the pumping 

rate when the pumping rate is constant and 

water is not removed from aquifer storage. If 

the pumping rate varies, however, as is typical 

of irrigation withdrawals, there is a time lag 

between the change in the withdrawal rate 

and the rate of streamflow depletion that is 

largely controlled by the aquifer properties 

and the distance of the pumped well from the 

stream. Managing the effects of groundwater 

withdrawals on streamflow and other hydrologic 

features requires a quantitative understanding 

of this lag effect, which can be represented in 

simulation models to determine optimal well 

locations and pumping rates to minimize the 

effects of pumping on streamflows during 

critical low-flow periods.
6 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Water Use 

The primary uses of water in the basin are public 

supply and irrigation. Public supply is exclusively derived 

from groundwater, whereas water for irrigation, at present, 

is primarily withdrawn from surface-water sources. Water 

withdrawals from the five major municipal suppliers averaged 

about 7 Mgal/d for the 2000–04 period, with a maximum 

average monthly pumping rate of 10 Mgal/d in July (fig. 4A). 

Although these withdrawals vary over the year, the publicsupply withdrawals are more evenly distributed than irrigation 

withdrawals, which typically begin in May, peak in July, and 

end in October (fig. 4B), but are are still highly variable during 

this time depending on weather conditions. Measured and 

estimated irrigation withdrawals during 2000–04 over this 

six-month period averaged about 4 Mgal/d, with a maximum 

monthly rate of about 8 Mgal/d in July. Irrigation withdrawals 

are primarily for turf farms and golf courses. Additional 

information about water use in the basin can be found in Bent 

and others (in press) and Wild and Nimiroski (2004).

Assessment of Water-Management 

Strategies

Simulation models (see sidebar to the right) were 

developed to assess basinwide and local-scale watermanagement strategies, including evaluation of the effects on 

streamflow under:

• current (2000–04) water withdrawals,

• replacing irrigation surface-water withdrawals with 

groundwater withdrawals, and

• potential changes in land use and water use. 

Effects of Current Water Use on Streamflow

The precipitation-runoff model HSPF (Hydrologic 

Simulation Program–FORTRAN by Bicknell and others, 2000) 

was developed for the entire basin to evaluate the effects of 

average 2000–04 water withdrawals on streamflows over longterm climatic conditions (1960–04). The model simulations 

focused on river reaches in 12 subbasins that were of greatest 

interest to the project Technical Advisory Committee (TAC) 

because of withdrawals and ecological importance. Simulation 

of flow alteration by current withdrawals (2000–04) and 

alternative withdrawals were compared to simulations of flows 

with no withdrawals in each of the focus subbasins. The results 

indicate that streamflow in the upper Pawcatuck River above the 

confluence with the Usquepaug River and in the lower Chipuxet 

River, followed by the Usquepaug River and lower Beaver 

Figure 4. Average monthly water use in the Pawcatuck 

River Basin during 2000–04 for (A) public supply and (B)

irrigation. Water use varies over the year, but the public-supply 

withdrawals are more evenly distributed than the irrigation 

withdrawals, which occur mostly during the summer.

0

4

8

12

16

20

WATER WITHDRAWALS,

IN MILLION GALLONS PER DAY

Public supply

Turf farms

Golf courses

J F M A M J

MONTHS

J A S O N D

0

4

8

12

16

20

AVERAGE IRRIGATION,

IN MILLION GALLONS PER DAY

B
Assessment of Water-Management Strategies 7

Eastern Pawcatuck River 

model area

Lower Wood River 

model area

PRECIPITATIONRUNOFF MODEL

GROUNDWATER MODELS

The precipitation-runoff model HSPF 

(Hydrologic Simulation Program–

FORTRAN by Bicknell and others, 2000), 

was developed for the entire basin for 

evaluating current and alternative watermanagement strategies and the effects of 

potential land-use and water-use change 

on streamflow. The simulation results 

focused on 12 subbasins highlighted.

The USGS groundwater flow model (MODFLOW, 

Harbaugh and others, 2000) was developed for two 

subregions—the lower Wood River and the 

eastern Pawcatuck River—to further evaluate 

current and alternative water-management 

strategies on streamflow and groundwater levels. 

Subbasin boundary

Basin boundary

Water

Wood River

Lower Wood River

Pawcatuck River

Meadow Brook

Taney Brook

Lower Beaver River

Usquepaug River

Chickasheen Brook

Chipuxet River

Lower Chipuxet River

Upper Pawcatuck

Queen River

Subbasins

The models developed can simulate a wide range of conditions, but modifications to the model 

structure may be required to represent other potential conditions. As for all models, consideration of inherent limitations and uncertainties of the models should be given to the interpretation of the simulation results. 

0 5 MILES

0 5 KILOMETERS

0 5 MILES

0 5 KILOMETERS
8 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Figure 5. Hourly streamflow simulated in August 2002 for the (A) upper Pawcatuck River, (B) lower Chipuxet River, (C)

Usquepaug River, and (D) lower Beaver River under no withdrawals (black line), current (2000–04) withdrawals (red line), 

and current withdrawals with selected instream irrigation withdrawals replaced by groundwater withdrawals (green line). 

Subbasins are shown on the precipitation-runoff model sidebar.

0

2

4

6

8

D Lower Beaver River

C Usquepaug River

0

4

8

12

16

20

AUGUST 2002

0

2

4

6

8

10

12

14 B Lower Chipuxet River

0

2

4

6

8

10

12

14

16

18

20

A Upper Pawcatuck River

STREAMFLOW, IN CUBIC FEET PER SECOND

No withdrawals

Current withdrawals

Instream withdrawals replaced by groundwater withdrawals

2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
Assessment of Water-Management Strategies 9

River, are most affected by withdrawals compared to the other reaches. 

During August 2002, the driest month during the 2000–04 data-collection 

period, withdrawals decreased streamflow in the upper Pawcatuck and 

lower Chipuxet Rivers by about 70 percent (fig. 5A and B, respectively), by 

about 19 percent in the Usquepaug River (fig. 5C), and by about 34 percent 

in the lower Beaver River (fig. 5D). Streamflows in the upper Pawcatuck 

River were affected mainly by municipal water-supply withdrawals, the 

lower Chipuxet River was affected by both irrigation and municipal-supply 

withdrawals, and the Usquepaug River and lower Beaver River were 

affected by irrigation withdrawals. All water for municipal and irrigation 

withdrawals was assumed lost from the basin through out-of-basin transfers 

and evapotranspiration, respectively. HSPF simulations also indicate 

that moving irrigation withdrawals out of rivers to groundwater sources 

appreciably damped intradaily flow fluctuations (fig. 5B, C, and D). 

Effects on Streamflow of Replacing Surface-Water 

Withdrawals with Groundwater Withdrawals

The groundwater-flow model MODFLOW (Harbaugh and others, 

2000) was developed for the lower Wood and the eastern Pawcatuck 

River model areas (sidebar) to further analyze the interaction between 

groundwater and surface water in the basin. The lower Wood River model 

was used to simulate several hypothetical well locations between the Wood 

River and Meadow Brook to illustrate the effects of pumping on large and 

small rivers; the model was also used to evaluate groundwater level changes 

by a hypothetical well in Diamond Bog area. The eastern Pawcatuck 

River model focused on changes in baseflow caused by replacing instream 

withdrawals with groundwater wells away from streams.

The streamflow response to pumping from a nearby well depends 

on the distance of the well from the stream and the flow in the stream—

pumping a well close to the Wood River (well A; fig. 6) decreases 

streamflow in the Wood River more than pumping a well farther from the 

river (well B); but conversely, pumping well B decreases flow in Meadow 

Brook more than pumping well A. The steady-state simulation of well A, 

A

B

NOT TO SCALE

Wood River Meadow

Brook

Figure 6. Schematic diagram of groundwater withdrawals from different well locations between the relatively large Wood 

River and the smaller Meadow Brook. If well A is pumped, about 90 percent of the water comes from baseflow to or induced 

infiltration from the Wood River with the remaining 10 percent coming from baseflow to or induced infiltration from Meadow 

Brook; if well B is pumped, about 67 percent of the water comes from baseflow to or induced infiltration from the Wood River 

with the remaining 33 percent from baseflow to or induced infiltration from Meadow Brook.

The Pawcatuck River Basin provides an ecologically 

rich aquatic habitat.
Meadow Brook near Wood River Junction.

10 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

about 20 percent of the distance from the Wood River to Meadow Brook, 

indicates that most of the pumped water (about 90 percent) comes from 

baseflow to or induced infiltration from the Wood River, and the remaining 

10 percent comes from baseflow to or induced infiltration from Meadow 

Brook. The steady-state simulation of well B, about equally far from the 

Wood River and Meadow Brook, indicates that about 67 percent of the 

water pumped comes from baseflow to or induced infiltration from the 

Wood River and the remaining 33 percent comes from baseflow to or 

induced infiltration from Meadow Brook.

This example shows how moving the location of a pumped well 

changes the flow in Wood River and Meadow Brook, but another important consideration is the relation between the rate of pumping and the rate 

of streamflow. Streamflow near the hypothetical wells during 2000–04 

averaged about 180 ft3/s in the Wood River and about 10 ft3/s in Meadow 

Brook. As a result, if well A were pumped at 1.0 Mgal/d (about 1.6 ft3/s), 

the mean daily flow in the Wood River would decrease by less than one 

percent; however, if well B were pumped at the same rate, the mean daily 

flow in Meadow Brook would decrease by about 5 percent. During lowflow periods, the same pumping rate would have a much greater effect on 

streamflow because the ratio of withdrawals to streamflow would be much 

larger. For example, during August 2002, streamflow near the hypothetical wells averaged about 16 ft3

/s in the Wood River and about 0.2 ft3/s in 

Meadow Brook. Thus, if well A is pumped at 1.0 Mgal/d, streamflow in the 

Wood River would decrease by about 9 percent; however, if well B were 

pumped at the same rate, Meadow Brook would stop flowing.

The previous example focused on the effects of pumping continuously at a constant rate, which would more likely be used for public-supply 

withdrawals than for irrigation withdrawals, which are highly dependent 

on weather conditions. During the 2000–04 period, most of the irrigation 

water used in the basin was obtained directly from streams and, as is true of 

most irrigation withdrawals, demand was high when streamflows were low. 

To reduce the effects of pumping water directly from streams, the NRCS 

sought information on the effects of replacing instream withdrawals with 

groundwater withdrawals from wells moved away from streams.

Figure 7. Simulated effects of irrigation withdrawals on streamflow as the well distance from a stream increases; the 

effects on streamflow are damped and spread out over time as the distance of the well from the stream increases. Daily 

mean withdrawal data from figure 27, Zarriello and Bent, 2004.

0

0.2

0.4

0.6

0.8

RATE, IN CUBIC FEET PER SECOND

JUNE JULY AUGUST SEPTEMBER OCTOBER NOVEMBER

50 feet

2,500 feet

1,500 feet

1,000 feet

Streamflow-depletion rate for pumped 

wells offset from the river by

500 feet

Daily mean withdrawal rate 

observed in the Usquepaug-Queen 

subbasin in 2000
Low flows in some parts of the basin can be very low; flow 

at the time this photo was taken was 0.004 ft3/s, but the 

estimated average flow in this reach is about 2.7 ft3/s.

Assessment of Water-Management Strategies 11

Figure 8. Simulated water-management strategy that replaces six instream irrigation withdrawals (orange 

hexagons) with groundwater withdrawals (yellow dots) between the lower Beaver and Usquepaug Rivers.

Simulations indicate that replacing instream irrigation withdrawals 

with groundwater withdrawals from wells moved away from the streams 

alters the timing and magnitude of the pumping effects on streamflow. 

Instream withdrawals have an instantaneous effect on streamflow equal to 

the pumping rate. On the other hand, the response of streamflow to groundwater withdrawals is damped as the well is moved farther from the stream 

(fig. 7). It should be noted that, although the effects of withdrawals on 

streamflow are damped, streamflow is still reduced by the amount of water 

pumped; however, for highly variable irrigation withdrawals, the damped 

streamflow response typically mitigates the instantaneous effects of direct 

surface-water withdrawals (fig. 7).

The relocation of instream pumps to groundwater wells could appreciably improve low flows in the lower Beaver and Usquepaug Rivers 

because irrigation withdrawals in this area are large relative to typical 

summer streamflows. Six instream withdrawals, five from the Beaver River 

and one from the Usquepaug River, were replaced by six hypothetical 

well withdrawals placed between these rivers (fig. 8). Groundwater-model 

simulations indicate that baseflow increased by about 1.3 ft3

/s during July 

to September of 2002 in both the lower Beaver and Usquepaug Rivers 

and decreased during the fall months relative to direct surface-water 41° 27' 0" 

Pawcatuck Rive

B

r

eaver

Usquepaug River

Beaver Riv

er

0 0.2 0.4 0.6 0.8 1.0 MILES

0 0.2 0.4 0.6 0.8 1.0 KILOMETERS

EXPLANATION

Instream withdrawal

Hypothetical groundwater 

 withdrawal

Streamgage

Base from Rhode Island Geographic Information System (RIGIS) 

orthophotographic data, 1:12,000, 2004

Rhode Island stateplane coordinate system.

1983 North American datum
12 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

0

10

20

30

40

50

60

JAN. FEB. MAR. APR. MAY JUNE JULY AUG. SEPT. OCT. NOV. DEC.

 BASEFLOW, IN CUBIC FEET PER SECOND

Increase in baseflow

Decrease in baseflow

EXPLANATION

Beaver River

Usquepaug River

Groundwater 

withdrawals

Instream

withdrawals

Groundwater 

withdrawals

Instream

withdrawals

Figure 9. Simulated streamflow changes that result from replacing six instream irrigation withdrawals in the lower Beaver and 

Usquepaug Rivers with groundwater withdrawals between the rivers (locations shown on fig. 8). Groundwater withdrawals increased 

summer low flows compared with instream irrigation withdrawals because of the delayed effect of pumping on streamflow. During 

August 2002, streamflows increased by about 43 and 9 percent in the Beaver and Usquepaug Rivers, respectively.

Direct withdrawals from the Pawcatuck River near Wood River Junction. Watchaug Pond, a major surface-water body in the basin. 
Assessment of Water-Management Strategies 13

withdrawals (fig. 9). Although the increase 

in summer baseflow was similar, the percent 

change in flow was determined by the amount of 

baseflow simulated in the rivers, which during 

August 2002 averaged about 3.0 and 14 ft3/s in 

the Beaver and Usquepaug Rivers, respectively. 

Thus, a 1.3 ft3/s increase in flow during this 

period is equivalent to a 43- and a 9-percent 

increase in flow in the Beaver and Usquepaug 

Rivers, respectively. The benefit of shifting 

withdrawals to groundwater is that, by the fall, 

streamflows are typically increasing and the 

effects of pumping represent a smaller fraction 

of the total streamflow in the fall compared to 

the summer.

Effects of Groundwater Pumping on 

the Water Table

Relocating instream withdrawals to 

groundwater withdrawals typically increase 

summer low flows as shown; however, pumping 

from groundwater also lowers the water table, 

which can adversely affect nearby surface waters 

such as ponds and wetlands. For this reason 

groundwater-model simulations were also used to 

evaluate the effects of withdrawals on the water 

table in the Diamond Bog area, one of the most 

ecologically sensitive habitats in Rhode Island 

(Colin Apse, The Nature Conservancy, written 

commun., 2005). Simulations indicate that during 

a normal spring (March 2000) a hypothetical 

well pumped at 1 Mgal/d lowered the water table 

by less than 0.5 ft, but during the relatively dry 

spring of March 2002, the same well pumped 

at the same rate extended the 0.5-ft drawdown 

contour beyond the Diamond Bog area (fig. 10). 

The reason for this difference is attributed to the 

flow in Diamond Brook; when flowing, the brook 

is a source of water to the well through induced 

infiltration. When the brook is dry, the water that 

flows to the well is from groundwater storage and 

the water table is lowered. This example shows 

that under certain conditions the hydroperiod, the 

length of time that wetlands and vernal pools are 

wet, can be reduced, and thus can affect aquatic 

communities that depend on these resources.

Figure 10. Groundwater-model simulated changes in water levels in 

the Diamond Bog area in the Wood River subbasin for March 2000 and 

March 2002. Changes in water levels under normal and dry conditions are 

indicated by the change in the 0.5-ft drawdown contour. During normal 

spring conditions (March 2000), the effects of pumping were limited primarily 

to changes in streamflow in Diamond Brook. During unseasonably dry 

conditions (March 2002), pumping caused flow in the brook to stop. As a 

result the 0.5-ft drawdown contour extended into the Diamond Bog area.

Well

EXPLANATION

0.5-foot drawdown contour during

 a normal spring (March 2000)

0.5-foot drawdown contour during 

a dry spring (March 2002)

Wood River

Diamond Brook

Diamond Bog

area

Base from Rhode Island Geographic Information System (RIGIS) 

orthophotographic data, 1:12,000, 2004

Rhode Island stateplane coordinate system.

1983 North American datum
Traveling-gun irrigation system used on turf farms.

Water provides irrigation for crops.

Wetlands are an extensive and ecologically important feature of the basin.

14 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Effects of Potential Changes in Land Use and 

Water Use

Changes in streamflow that could result from land-use 

change and associated water-use change under potential 

buildout conditions were evaluated by HSPF simulations 

of the effects of (1) land-use change only, (2) water-use 

change only, and (3) the combined effects of land- and 

water-use change. Land-use change was determined mostly 

on the basis of a statewide map of potential buildout that 

was compiled under the provisions outlined in the Rhode 

Island Comprehensive Planning and Regulation Act of 

1988. In 1995, about 10 percent of the basin was classified 

as developed, but the potential buildout indicates that as 

much as 50 percent of the basin could be developed in the 

future (fig. 11). This buildout analysis assumed that lands 

not already developed nor protected from development, 

including irrigated lands with the exception of golf courses, 

were developable. Simulated buildout changes include the 

following: 

• The largest land-use change was from forest to lowto-medium-density residential development;

• Total public and self-supplied water use in the basin 

at buildout was estimated at 22 Mgal/d, or about 

four times the water use reported for 1995–99 (Wild 

and Nimiroski, 2004), but 80 percent of this new 

demand was assumed to be returned to the basin 

through on-site septic disposal; and

• Total commercial and industrial water use in the 

basin at buildout was estimated at about 7.5 Mgal/d, 

or six times the reported 1995–99 commercial and 

industrial water use (Wild and Nimiroski, 2004), but 

most (80 percent) was also returned through on-site 

septic disposal.

In general, simulations indicate that high flows would 

increase slightly because of increased impervious area 

under buildout conditions compared to 1995 land-use 

conditions; as impervious area increases, more precipitation 

flows to streams as surface runoff that flows at a faster rate 

to streams than subsurface-flow components. For the same 

reasons, the simulations indicate that low flows decrease 

slightly because less rainfall infiltrates into the soil; as a 

result, recharge to the aquifer and the baseflow contribution 

to streams decrease. In some streams, low flows may 

increase slightly because the net domestic consumptive 

use at buildout is less than current consumptive irrigation 

water use, or because the decreased infiltration due to 

increased impervious area at buildout is more than offset 

by decreased evapotranspiration losses resulting from the 

removal of trees associated with development, or both.
Assessment of Water-Management Strategies 15

Land Use—Land Cover

Industrial, commercial, transportation

Medium- to high-density residential

Low- to moderate-density residential

Open space

Forest

Nonforested wetlands

Forested wetlands

Golf course

Turf farm

Other irrigated agriculture

Rivers/streams

Ponds

71°52' 30" 71°30'

42°37'30"

41°22'30"

EXPLANATION

1995

Exeter

North

Kingstown

South

Kingstown

Voluntown

North

Stonington

Stonington

Coventry Sterling

West Greenwich

Richmond

Charlestown

Westerly

Hopkinton

East

Greenwich

CONNECTICUT

RHODE ISLAND

0 1 2 3 4 5 MILES

0 2 4 6 8 KILOMETERS

Buildout 71°52' 30" 71°30'

42°37' 30"

41°22' 30"

North

Stonington

Richmond

Westerly

Hopkinton

Exeter

North

Kingstown

South

Kingstown

Voluntown

North

Stonington

Stonington

Coventry Sterling

West Greenwich

Richmond

Charlestown

Westerly

Hopkinton

East

Greenwich

CONNECTICUT

RHODE ISLAND

0 1 2 3 4 5 MILES

0 2 4 6 8 KILOMETERS

Base from Rhode Island Geographic Information System (RIGIS) 

orthophotographic data, 1:12,000, 2004

Rhode Island stateplane coordinate system.

1983 North American datum

Figure 11. Representation of the simplified 

land use in the Pawcatuck River Basin 

simulated by the Hydrologic Simulation 

Program–FORTRAN model under 1995 

conditions and projected buildout conditions.
Meadow Brook near Carolina.

16 Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Rhode Island and Connecticut

Summary

The Pawcatuck River Basin in southwestern Rhode Island and southeastern Connecticut is 

known for its high-quality water resources and its biologically diverse aquatic ecosystems. Water 

from the basin is used primarily for public supply and irrigation. Concerns about the effects of water 

withdrawals prompted a cooperative investigation in 2002 by the U.S. Geological Survey, the Natural 

Resources Conservation Service, and the Rhode Island Water Resources Board, to improve the 

understanding of water resources of the Pawcatuck River Basin and to assess the hydrologic effects 

of potential water-management strategies. As part of this study, a precipitation-runoff model (HSPF) 

was developed for the entire basin, and two groundwater models (MODFLOW) were developed 

for subareas of the basin. The results of the model simulations quantified the effects on streamflow 

of existing water withdrawals, which can be large in some parts of the basin, but also showed that 

alternative water-management strategies, such as replacing instream irrigation withdrawals with 

groundwater withdrawals away from streams, may reduce the effect of withdrawals on low flows. The 

benefits are shown to be site specific, but the modeling tools developed to simulate the hydrology of 

the Pawcatuck River Basin can be used to analyze other possible site-specific management practices. 

For example, if a new commercial, industrial, agricultural, or municipal water supply is needed, the 

tools developed here could be used to identify optimal groundwater-well locations, assess the effects 

of withdrawals on streamflows and groundwater levels, and determine the best pumping schemes to 

minimize effects of withdrawals. 

References Cited

Bent, G.C., Zarriello, P.J., Granato, G.E., Masterson, J.P., Walter, D.A., Waite, A.M., and Church, 

P.E., in press, Simulated effects of water withdrawals and land-use changes on streamflows and 

groundwater levels in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut: U.S. Geological Survey, Scientific Investigations Report 2009–5127. 

Bicknell, B.R., Imhoff, J.C., Kittle, J.L., Jr., Jobes, T.H., and Donigian, A.S. Jr., 2000, Hydrological 

Simulation Program–FORTRAN User’s manual for release 12: Mountain View, Calif., AQUA 

TERRA Consultants, variously paged.

Federal Register, 1988, Sole source stratified-drift area designation for the Pawcatuck Basin stratifieddrift area system, Rhode Island and Connecticut: Federal Register, v. 53, no. 93, May 13, 1988.

Harbaugh, A.W., Banta, E.R., Hill, M.C., and Anderman, E.R., 2000, MODFLOW-2000, The U.S. 

Geological Survey modular groundwater model—User guide to modularization concepts and the 

groundwater flow process: U.S. Geological Survey Open-File Report 00–92, 121 p. 

Wild, E.C., and Nimiroski, M.T., 2004, Estimated water use and availability in the Pawcatuck Basin, 

southern Rhode Island and southeastern Connecticut, 1995–99: U.S. Geological Survey Scientific 

Investigations Report 2004–5020, 72 p.

U.S. Environmental Protection Agency, 2005, South County, RI, watersheds: Fact Sheet/Spring 2005, 

EPA 901–F–05–012, 2 p., accessed March 3, 2007, at http://www.epa.gov/Region1/eco/specialp/

southcounty06.pdf.

Zarriello, P.J., and Bent, G.C., 2004, A precipitation-runoff model for the analysis of the effects of 

water withdrawals and land-use change on streamflow in the Usquepaug-Queen River Basin, Rhode 

Island: U.S. Geological Survey Scientific Investigations Report 2004–5139, 75 p.
Prepared by the Pembroke Publishing Service Center.

For more information concerning the research in this report, contact:

Deputy Director 

USGS Massachusetts-Rhode Island

Water Science Center, Rhode Island Office

42 Albion Road, Suite 107

Lincoln, RI 02865

or visit our Web site at:

http://ri.water.usgs.gov/
Breault and others—Effects of Water-Management Strategies on Water Resources in the Pawcatuck River Basin, Southwestern Rhode Island and Southeastern Connecticut—Circular 1340

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