U.S. Department of the Interior

U.S. Geological Survey

Scientific Investigations Report 2009–5127

Prepared in cooperation with the

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

Rhode Island Water Resources Board

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
Cover. Photograph shows Wood River at Hope Valley, Rhode Island. (Photograph by Peter Flinker, Dodson Associates, Ltd.)
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

By Gardner C. Bent, Phillip J. Zarriello, Gregory E. Granato, John P. Masterson, 

Donald A. Walter, Andrew M. Waite, and Peter E. Church

Part 1. Water Resources in the Pawcatuck River Basin

By Gardner C. Bent, Andrew M. Waite, and Peter E. Church

Part 2. Simulation of Water-Use and Land-Use Changes on 

Streamflow with a Precipitation-Runoff Model (HSPF)

By Phillip J. Zarriello

Part 3. Simulated Effects of Withdrawals on Groundwater Flow 

(MODFLOW Models)

By John P. Masterson

Part 4. Conjunctive-Management Models as Tools for 

Water-Resources Planning

By Gregory E. Granato and Donald A. Walter

Part 5. HSPF and MODFLOW—Capabilities, Limitations, and 

Integration

By Phillip J. Zarriello

Prepared in cooperation with the

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

the Rhode Island Water Resources Board

Scientific Investigations Report 2009–5127

U.S. Department of the Interior

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

KEN SALAZAR, Secretary

U.S. Geological Survey

Marcia K. McNutt, Director

U.S. Geological Survey, Reston, Virginia: 2011

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reproduce any copyrighted materials contained within this report.

Suggested citation:

Bent, G.C., Zarriello, P.J., Granato, G.E., Masterson, J.P., Walter, D.A., Waite, A.M., and Church, P.E., 2011, 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, 254 p., at http://pubs.usgs.gov/sir/2009/5127.
iii

Contents

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

Part 1. Water Resources in the Pawcatuck River Basin........................................................................1

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a PrecipitationRunoff Model (HSPF) .......................................................................................................................2

Part 3. Simulated Effects of Withdrawals on Groundwater Flow (MODFLOW Models)...................2

Part 4. Conjunctive-Management Models as Tools for Water-Resources Planning.........................2

Introduction.....................................................................................................................................................3

Purpose and Scope ..............................................................................................................................5

Description of the Study Area ............................................................................................................6

Previous Investigations........................................................................................................................6

Part 1. Water Resources in the Pawcatuck River Basin......................................................................11

Climate..................................................................................................................................................11

Geologic Setting..................................................................................................................................13

Groundwater........................................................................................................................................15

Recharge.....................................................................................................................................15

Water Levels...............................................................................................................................15

Surface Water.....................................................................................................................................19

Streamflow..................................................................................................................................20

Continuous Stations .........................................................................................................20

Partial-Record Stations ...................................................................................................30

Baseflow......................................................................................................................................30

Ponds and Wetlands .................................................................................................................31

Water Withdrawals ............................................................................................................................31

Municipal Withdrawals ............................................................................................................31

Nonmunicipal Withdrawals .....................................................................................................31

Agricultural Withdrawals .........................................................................................................37

Golf-Course Withdrawals.........................................................................................................37

Predicting Turf-Farm and Golf-Course Irrigation..................................................................41

Wastewater Discharge and Return Flow........................................................................................43

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a PrecipitationRunoff Model (HSPF) .....................................................................................................................45

Effects of Withdrawals on Streamflow ...........................................................................................46

Usquepaug-Queen and Beaver Rivers Region .....................................................................48

Eastern Pawcatuck River Region............................................................................................51

Lower Wood River Region........................................................................................................54

Magnitude of Flow Alteration Relative to Streamflow ........................................................57

Effects of Potential Future Land Use and Water Use on Streamflow........................................58

Method for Estimating Land-Use Change..............................................................................58

Method for Estimating Future Water Use..............................................................................59

Effects on Streamflow...............................................................................................................63

Part 3. Simulated Effects of Withdrawals on Groundwater Flow (MODFLOW Models).................65

Effects of Pumping under Constant and Varying Recharge Conditions ....................................65

Effects of Varying Pumping-Well Distance with Constant Pumping Rates...............................72
iv

Effects of Varying Pumping-Well Distance with Varying Pumping Rates .................................73

Part 4. Conjunctive-Management Models as Tools for Water-Resources Planning.......................85

Streamflow-Response Coefficients.................................................................................................85

Potential Allowable Streamflow-Depletion Criteria......................................................................95

Well-Site Selection for Groundwater Withdrawals ......................................................................98

Use of Community Wells for Irrigation ..........................................................................................100

Post-Optimization Analysis .............................................................................................................103

Part 5. HSPF and MODFLOW—Capabilities, Limitations, and Integration......................................107

Hydrologic Models—HSPF and MODFLOW ................................................................................107

Functional Differences between HSPF and MODFLOW ............................................................107

Comparison of Three Example HSPF and MODFLOW Results..................................................108

Example 1. Effects of a Pumped Well on Streamflow in Meadow Brook......................108

Example 2. Effects of Withdrawals near Diamond Bog....................................................111

Example 3. Effects of Converting from Surface-Water to Groundwater 

Withdrawals................................................................................................................112

Integrating HSPF and MODFLOW Models....................................................................................116

Testing of HSPF and MODFLOW Integration in the Usquepaug-Queen River...............116 

Summary and Conclusions.......................................................................................................................117

Part 1. Water Resources in the Pawcatuck River Basin...........................................................117

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a 

Precipitation-Runoff Model (HSPF)..................................................................................118

Part 3. Simulated Effects of Withdrawals on Groundwater Flow (MODFLOW Models)......119

Part 4. Conjunctive-Management Models as Tools for Water-Resources Planning............120

Part 5. HSPF and MODFLOW—Capabilities, Limitations, and Integration.............................120

Example 1. Effects of a Pumped Well on Streamflow in Meadow Brook......................120

Example 2. Effects of Withdrawals near Diamond Bog....................................................120

Example 3. Effects of Converting from Surface-Water to Groundwater 

Withdrawals................................................................................................................121

Acknowledgments.....................................................................................................................................121

References Cited........................................................................................................................................122

Introduction........................................................................................................................................122

Part 1. Water Resources in the Pawcatuck River Basin...........................................................125

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a 

Precipitation-Runoff Model (HSPF)..................................................................................127

Part 3. Simulated Effects of Withdrawals on Groundwater Flow (MODFLOW Models)......127

Part 4. Conjunctive-Management Models as Tools for Water-Resources Planning............128

Part 5. HSPF and MODFLOW—Capabilities, Limitations, and Integration.............................129

Appendix Part 1. Classification Tables for Logistic Regression Equations for Irrigation..............131

Appendix Part 2. Precipitation-Runoff Model Development and Calibration .................................139

Precipitation-Runoff Model.............................................................................................................143

Functional Description of Hydrologic Simulation Program-FORTRAN (HSPF).......................143

Database ............................................................................................................................................145

Representation of the Basin ...........................................................................................................145

Development of Hydrologic Response Units (HRUs) ..................................................................145

Impervious Areas (IMPLNDs).........................................................................................................145

Pervious Areas (PERLNDs) .............................................................................................................147
v

Stream Reaches (RCHRES) .............................................................................................................151

Hydraulic Characteristics (FTABLES)............................................................................................155

Model Calibration..............................................................................................................................155

Automated Parameter Estimation (PEST).....................................................................................155

Model Fit.............................................................................................................................................159

Tributary Streams..............................................................................................................................179

Groundwater Underflow..................................................................................................................182

Sensitivity Analysis...........................................................................................................................182

Simulated Hydrologic Budgets and Flow Components ..............................................................186

Model Uncertainty and Limitations................................................................................................190

References Cited...............................................................................................................................191

Appendix Part 3. Development of Groundwater Flow Models..........................................................193

Development of Groundwater-Flow Models ................................................................................195

Model Discretization and Boundaries...........................................................................................195

Spatial Discretization .......................................................................................................................195

Hydrologic Boundaries ....................................................................................................................199

Temporal Discretization and Initial Conditions ............................................................................200

Hydrologic Stresses .........................................................................................................................200

Recharge............................................................................................................................................200

Pumping..............................................................................................................................................201

Hydraulic Properties.........................................................................................................................201

Model Calibration and Limitations .................................................................................................202

References Cited...............................................................................................................................220

Appendix Part 4. Conjunctive-Management Models for the Eastern Pawcatuck and 

Lower Wood River Model Areas................................................................................................221

Introduction........................................................................................................................................224

Formulation of the Conjunctive-Management Model.................................................................224

Management-Model Objective Function......................................................................................224

Streamflow-Depletion Criteria........................................................................................................228

Water-Withdrawal Criteria..............................................................................................................231

Seasonal Water-Demand Criteria..................................................................................................239

Response-Matrix Technique for Solution of the Conjunctive-Management Model..............242

References Cited...............................................................................................................................254
vi

Figures

Introduction

I–1. Map showing location of the Pawcatuck River Basin study area and groundwater 

model extents, southwestern Rhode Island and southeastern Connecticut......................4

I–2. Map showing location of surficial geology in the Pawcatuck River Basin, 

southwestern Rhode Island and southeastern Connecticut.................................................7

I–3. Map showing generalized land use (1995) in the Pawcatuck River Basin, 

southwestern Rhode Island and southeastern Connecticut.................................................8

Part 1. Water Resources in the Pawcatuck River Basin

1–1. Map showing location of climatological stations in and near the Pawcatuck River 

Basin, southwestern Rhode Island and southeastern Connecticut...................................12

1–2. Graphs showing monthly (A) precipitation and (B) mean temperature at the National 

Oceanic and Atmospheric Administration National Weather Service (NOAA-NWS) 

University of Rhode Island (URI) climate station in the Pawcatuck River Basin, 

southwestern Rhode Island and southeastern Connecticut, 2000–04...............................14

1–3. Map showing location of U.S. Geological Survey continuous streamflow-gaging 

stations and partial-record stations in the Pawcatuck River Basin, southwestern 

Rhode Island and southeastern Connecticut.........................................................................16

1–4. Map showing location of U.S. Geological Survey groundwater observation wells 

in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut..................................................................................................................................18

1–5. Graph showing groundwater levels in selected U.S. Geological Survey observation 

wells in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................19

1–6. Graphs showing mean monthly streamflows for selected long-term U.S. Geological 

Survey streamflow-gaging stations in the Pawcatuck River Basin, southwestern 

Rhode Island and southeastern Connecticut.........................................................................26

1–7. Map showing location of U.S. Geological Survey pond-level stations in the Pawcatuck 

River Basin, southwestern Rhode Island and southeastern Connecticut ........................33

1–8. Map showing location of major water-supply wells and wastewater treatment 

facilities in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut..................................................................................................................................34

1–9. Graphs showing monthly water withdrawal patterns for major suppliers in the 

Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut, 

2000–04 .........................................................................................................................................36

1–10. Graph showing average 24-hour irrigation-withdrawal rates for metered turf farms 

in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................39

1–11. Graph showing average 24-hour irrigation-withdrawal rates for metered golf courses 

in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................40
vii

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a 

Precipitation-Runoff Model (HSPF)

2–1. Map showing focus reaches where the effects of water-withdrawal and land-use 

changes were examined with the Hydrologic Simulation Program-FORTRAN (HSPF) 

model of the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut..................................................................................................................................47

2–2. Graphs showing flow-duration curves of simulated daily mean streamflow (1960–2004) 

under no withdrawals (LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), 

current withdrawals with selected irrigation withdrawals converted from surfacewater to groundwater sources (LT–CDSWR), and current withdrawals with potential 

new withdrawals (LT–CDWRB) at (A) Queen River (QUEN4, RCHRES 9); (B) Usquepaug 

River (QUEN7, RCHRES 20); (C) Beaver River (BEAV3, RCHRES 43); and (D) Taney Brook 

(TANE1, RCHRES 45), Pawcatuck River Basin, southwestern Rhode Island....................49

2–3. Graphs showing simulated hourly streamflow in August 2002 under no withdrawals 

(LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), current withdrawals with 

selected irrigation withdrawals converted from surface-water to groundwater sources 

(LT–CDSWR), and current withdrawals with potential new withdrawals (LT–CDWRB) at 

(A) Queen River (QUEN4, RCHRES 9); (B) Usquepaug River (QUEN7, RCHRES 20); 

(C) Beaver River (BEAV3, RCHRES 43); and (D) Taney Brook (TANE1, RCHRES 45), 

Pawcatuck River Basin, southwestern Rhode Island ..........................................................50

2–4. Graphs showing flow-duration curves of simulated daily mean streamflow (1960–2004) 

under no withdrawals (LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), current withdrawals with selected irrigation withdrawals converted from surface-water 

to groundwater sources (LT–CDSWR), and current withdrawals with potential new 

withdrawals (LT–CDWRB) at (A) Chipuxet River (CHIP2, RCHRES 32); (B) Chipuxet River 

(CHIP3, RCHRES 33); (C) Pawcatuck River (PAWC1, RCHRES 34); and (D) Chickasheen 

Brook (CHIC2, RCHRES 36), Pawcatuck River Basin, southwestern Rhode Island.........52

2–5. Graphs showing August 2002 simulated hourly streamflow under no withdrawals 

(LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), current withdrawals with 

selected irrigation withdrawals converted from surface-water to groundwater sources 

(LT–CDSWR), and current withdrawals with potential new withdrawals (LT–CDWRB) at 

(A) Chipuxet River (CHIP2, RCHRES 32); (B) Chipuxet River (CHIP3, RCHRES 33); 

(C) Pawcatuck River (PAWC1, RCHRES 34); and (D) Chickasheen Brook (CHIC2, 

RCHRES 36), Pawcatuck River Basin, southwestern Rhode Island...................................53

2–6. Graphs showing flow-duration curves of simulated daily mean streamflow (1960–2004) 

under no withdrawals (LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), current withdrawals with selected irrigation withdrawals converted from surface-water 

to groundwater sources (LT–CDSWR), and current withdrawals with potential new 

withdrawals (LT–CDWRB) at (A) Meadow Brook (MEAD2, RCHRES 48); (B) Pawcatuck 

River (PAWC4, RCHRES 50); (C) Wood River (WOOD5, RCHRES 63); and (D) Wood River 

(WOOD6, RCHRES 65), Pawcatuck River Basin, southwestern Rhode Island..................55

2–7. Graphs showing August 2002 simulated hourly streamflow under no withdrawals 

(LT–NoDmd), current (2000–04) withdrawals (LT–CDmd), current withdrawals with 

selected irrigation withdrawals converted from surface-water to groundwater sources 

(LT–CDSWR), and current withdrawals with potential new withdrawals (LT–CDWRB) 

at selected model reaches at (A) Meadow Brook (MEAD2, RCHRES 48); (B) Pawcatuck 

River (PAWC4, RCHRES 50); (C) Wood River (WOOD5, RCHRES 63); and (D) Wood River 

(WOOD6, RCHRES 65), Pawcatuck River Basin, southwestern Rhode Island..................56

2–8. Graph showing percentage of time the ratio of average summer withdrawals (2002–04) 

to simulated mean daily streamflow without withdrawals (1960–2004) is equaled or 

exceeded at selected reaches in the Pawcatuck River Basin, southwestern 

Rhode Island................................................................................................................................57
viii

2–9. Map showing representation of 1995 land use simulated in the Hydrologic Simulation 

Program-FORTRAN (HSPF) of the Pawcatuck River Basin, southwestern Rhode Island 

and southeastern Connecticut.................................................................................................60

2–10. Map showing representation of buildout land use simulated in the Hydrologic 

Simulation Program-FORTRAN (HSPF) of the Pawcatuck River Basin, southwestern 

Rhode Island and southeastern Connecticut.........................................................................61

2–11. Graphs showing flow-duration curves of simulated daily mean streamflow (1960–2004) 

under no withdrawals (LT–NoDmd), current withdrawals (LT–CDmd), and potential 

buildout conditions representing effects of change in land-use only (LT–BldCD), 

change in water-use only (LT–95LFD), and the combined effects of land-use and 

water-use change (LT–BldFD) at (A) Chipuxet River (CHIP1, RCHRES 31); (B) Beaver 

River (BEAV3, RCHRES 43); (C) Wood River (WOOD6, RCHRES 65); and (D) Pawcatuck 

River (PAWC8, RCHRES 80), Pawcatuck River Basin, southwestern Rhode Island and 

southeastern Connecticut.........................................................................................................64

Part 3. Simulated Effects of Withdrawals on Groundwater Flow (MODFLOW 

Models)

3–1. Map showing geographic extent, surficial geology, observation wells, proposed 

withdrawal sites, simulated model boundary conditions, and outflow points from HSPF 

subbasins for the lower Wood River model in the Pawcatuck River Basin, southwestern Rhode Island.........................................................................................................................66

3–2. Graph showing effects of simulated pumping at well RIW–481A on baseflow in 

Meadow Brook in the lower Wood River model area (MEAD2, RCHRES 48) in the 

Pawcatuck River Basin, southwestern Rhode Island ..........................................................67

3–3. Schematic showing groundwater discharge from a hypothetical aquifer to a stream 

with (A) no pumping; (B) pumping at a such a rate (Q1) that the well captures some 

water that would otherwise discharge to the surface-water body; and (C) pumping at 

a higher rate (Q2) that results in the reversal of groundwater flow direction and in the 

flow of water out of the surface-water body into the aquifer (induced infiltration)........68

3–4. Graph showing change in baseflow in the Meadow Brook at HSPF subbasin MEAD2 

outlet (RCHRES 48) in response to simulated pumping at well RIW–481A in the lower 

Wood River model area in the Pawcatuck River Basin, southwestern Rhode Island ....69

3–5. Graph showing comparison of the changes in water levels at observation wells MW–9 

and Chariho in response to simulated pumping at well RIW–481A in the lower Wood 

River model area in the Pawcatuck River Basin, southwestern Rhode Island................69

3–6. Graph showing effects of simulated pumping at well RIW–550 on baseflow in the 

Wood River at HSPF subbasin WOOD5 outlet (RCHRES 63) in the lower Wood River 

model area in the Pawcatuck River Basin, southwestern Rhode Island..........................70

3–7. Graph showing change in baseflow in the Wood River at HSPF subbasin WOOD5 outlet 

(RCHRES 63) in response to simulated pumping at well RIW–550 in the lower Wood 

River model area in the Pawcatuck River Basin, southwestern Rhode Island................71

3–8. Graph showing comparison of the changes in baseflows in Diamond Brook and the 

Wood River at HSPF subbasin WOOD5 outlet (RCHRES 63) in response to simulated 

pumping at well RIW–550 in the lower Wood River model area in the Pawcatuck River 

Basin, southwestern Rhode Island..........................................................................................72

3–9. Graph showing change in water levels at Diamond Bog in response to simulated 

pumping at well RIW–550 in the lower Wood River model area in the Pawcatuck River 

Basin, southwestern Rhode Island..........................................................................................73

3–10. Maps showing changes in water levels at Diamond Bog in (A) March 2000 and 

(B) March 2002 in response to simulated pumping at well RIW–550 in the lower Wood 

River model area in the Pawcatuck River Basin, southwestern Rhode Island................74
ix

3–11. Graph showing effects of simulated pumping at different well locations RIW–458, 

RIW–458A, and RIW–458B on baseflow in the Wood River at HSPF subbasin WOOD5 

outlet (RCHRES 63) and the Meadow Brook at HSPF subbasin MEAD2 outlet 

(RCHRES 48) in the lower Wood River model area in the Pawcatuck River Basin, 

southwestern Rhode Island ......................................................................................................75

3–12. Map showing model extent and boundary conditions used in the eastern Pawcatuck 

River model area in the Pawcatuck River Basin, southwestern Rhode Island................77

3–13. Maps showing locations of potential groundwater irrigation wells between the Beaver 

and Usquepaug Rivers in the eastern Pawcatuck River model area, HSPF subbasin 

outlets BEAV3 (RCHRES 43) and QUEN7 (RCHRES 20), in the Pawcatuck River Basin, 

southwestern Rhode Island for (A) six irrigation wells; (B) two irrigation wells; and 

(C) one irrigation well.................................................................................................................78

3–14A–C.Graphs showing model-calculated baseflow (A), changes in model-calculated baseflow (B), and percent change in model-calculated baseflow (C), in three proposed 

groundwater irrigation withdrawal scenarios on baseflow in the Beaver River at HSPF 

subbasin BEAV3 outlet (RCHRES 43) in the eastern Pawcatuck River model area in the 

Pawcatuck River Basin, southwestern Rhode Island ..........................................................79

3–15A–C.Graphs showing model-calculated baseflow (A), changes in model-calculated baseflow (B), and percent change in model-calculated baseflow in three proposed groundwater irrigation withdrawal scenarios on baseflow (C), in the Beaver River at HSPF 

subbasin QUEN7 outlet (RCHRES 20) in the eastern Pawcatuck River model area in the 

Pawcatuck River Basin, southwestern Rhode Island ..........................................................82

Part 4. Conjunctive-Management Models as Tools for Water-Resources 

Planning

4–1. Map showing the eastern Pawcatuck River conjunctive-management model 

(EPRCMM) area with three streamflow-constraint sites (defined in table 4–2) and 20 

existing or potential water-withdrawal sites (defined in table 4–1) in the Pawcatuck 

River Basin, southwestern Rhode Island................................................................................87

4–2. Map showing the lower Wood River conjunctive-management model (LWRCMM) area 

with four streamflow-constraint sites (defined in table 4–2) and 12 existing or potential 

water-withdrawal sites (defined in table 4–1) in the Pawcatuck River Basin, southwestern Rhode Island ................................................................................................................88

4–3A. Graphs showing selected examples of simulated response coefficients for streamflowconstraint sites on the Beaver (at BEAVM), Usquepaug-Queen (at QUEENM), and 

Pawcatuck (at PAWCD) Rivers, in the eastern Pawcatuck River conjunctive-management model (EPRCMM) area in the Pawcatuck River Basin, southwestern Rhode 

Island, for three hypothetical wells at different distances between the rivers ...............91

4–3B. Graphs showing selected examples of simulated response coefficients for streamflowconstraint sites on the Wood River (at WOOD5 and WOOD6), Meadow Brook (at 

MEAD2), and Pawcatuck (at PAWC4) Rivers, in the lower Wood River conjunctivemanagement model (LWRCMM) area in the Pawcatuck River Basin, southwestern 

Rhode Island, for three hypothetical wells at different distances between the rivers...92

4–4. Graphs showing the annual pattern in streamflow depletion caused by withdrawals 

from potential water-withdrawal sites at hypothetical well (A) RIW–458, (B) RIW–458A, 

and (C) RIW–458B indicating in the Wood River (WOOD6, RCHRES 65) in the lower 

Wood River conjunctive-management model (LWRCMM) area in the Pawcatuck River 

Basin, southwestern Rhode Island..........................................................................................94
x

4–5. Graphs showing monthly streamflow-duration curves showing the percentage of oneday-minimum September streamflows that would equal or exceed a selected streamflow value at selected sites in the (A) eastern Pawcatuck River conjunctive-management model (EPRCMM) area and the (B) lower Wood River conjunctive-management 

model (LWRCMM) area in the Pawcatuck River Basin, southwestern Rhode Island ....96

4–6. Graph showing conjunctive-management-model yield relations between potential 

allowable streamflow depletion criteria in the Wood River (WOOD6, RCHRES 65) and 

total annual groundwater withdrawals at the specified Rhode Island withdrawal rates 

from hypothetical wells RIW–458, RIW–458A, and RIW–458B in the lower Wood River 

conjunctive-management model (LWRCMM) area in the Pawcatuck River Basin, 

southwestern Rhode Island ......................................................................................................97

4–7. Graph showing conjunctive-management-model yield relations between potential 

allowable streamflow depletion criteria in the Wood River (WOOD6, RCHRES 65) and 

total annual groundwater withdrawals from hypothetical agricultural locations that 

follow irrigation-withdrawal patterns and groundwater withdrawals at the specified 

Rhode Island withdrawal rates from hypothetical wells RIW–458, RIW–458A, or RIW–

458B in the lower Wood River conjunctive-management model (LWRCMM) area in the 

Pawcatuck River Basin, southwestern Rhode Island ..........................................................99

4–8. Graph showing conjunctive-management-model yield relations between potential 

allowable streamflow depletion criteria in the Usquepaug-Queen River (QUEENM) and 

total annual groundwater withdrawals from hypothetical agricultural locations that 

follow irrigation-withdrawal patterns in the eastern Pawcatuck River conjunctivemanagement model (EPRCMM) area in the Pawcatuck River Basin, southwestern 

Rhode Island ..............................................................................................................................102

4–9. Graph showing daily-mean flow-duration curves showing the percentage of time 

estimated streamflow was equaled or exceeded in the Usquepaug-Queen River in the 

eastern Pawcatuck River conjunctive-management model (EPRCMM) area in the 

Pawcatuck River Basin, southwestern Rhode Island at QUEENM, the streamflow 

constraint site for the period 1960–2004 ...............................................................................104

4–10. Graphs showing estimated streamflow in the Usquepaug-Queen River at streamflow 

constraint site QUEENM in the eastern Pawcatuck River conjunctive-management 

model (EPRCMM) area in the Pawcatuck River Basin, southwestern Rhode Island for 

the period 1960–2003 ................................................................................................................105

Part 5. HSPF and MODFLOW—Capabilities, Limitations, and Integration

5–1. Map showing Hydrologic Simulation Program-FORTRAN (HSPF) and the modular 

groundwater-flow model (MODFLOW) representation of Meadow Brook and lower 

Wood River area, Pawcatuck River Basin, southwestern Rhode Island ........................109

5–2. Graph showing streamflow from January 1, 2000, through September 30, 2004, under 

2000–04 (current) conditions and under current conditions with a well pumped at 

constant rate of 1 million gallons per day (pumped) simulated by the precipitationrunoff model Hydrologic Simulation Program-FORTRAN (HSPF) and the modular 

groundwater-flow model (MODFLOW) in lower Meadow Brook (MEAD2, RCHRES 48), 

Pawcatuck River Basin, southwestern Rhode Island ........................................................110

5–3. Map showing Hydrologic Simulation Program-FORTRAN (HSPF) and modular groundwater-flow model (MODFLOW) representation of the lower Beaver River area, 

Pawcatuck River Basin, southwestern Rhode Island ........................................................113
xi

Tables

Introduction

I–1. Overview of characteristics and scenarios used in the HSPF, MODFLOW, and conjunctive-management models for the Pawcatuck River Basin, southwestern Rhode Island 

and southeastern Connecticut, that are described in Parts 2, 3, and 4 of this report.......5

Part 1. Water Resources in the Pawcatuck River Basin

1–1. Types of climatological data collected at U.S. Geological Survey stations and 

compiled from National Oceanic and Atmospheric Administration National Weather 

Service (NOAA-NWS) stations in and near the Pawcatuck River Basin, southwestern 

Rhode Island and southeastern Connecticut, 2000–04 ........................................................11

1–2. U.S. Geological Survey observation wells in which groundwater levels were 

measured in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................17

1–3. U.S. Geological Survey continuous streamflow-gaging stations operated in the 

Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut, 

2000–04 .........................................................................................................................................21

1–4. U.S. Geological Survey partial-record stations measured in the Pawcatuck River 

Basin, southwestern Rhode Island and southeastern Connecticut, 2000–04 ..................22

1–5. Streamflow and estimated baseflow for selected U.S. Geological Survey streamflowgaging stations in the Pawcatuck River Basin, southwestern Rhode Island and 

southeastern Connecticut, 2000–04 and 1942–2004..............................................................25

1–6. Relation of U.S. Geological short-term streamflow-gaging stations and partial-record 

stations to nearby long-term index streamflow-gaging stations used to estimate 

streamflow records in the Pawcatuck River Basin, southwestern Rhode Island and 

southeastern Connecticut, 2000–04.........................................................................................27

1–7. U.S. Geological Survey pond-level stations in the Pawcatuck River Basin, 

southwestern Rhode Island and southeastern Connecticut, 2000–04...............................32

1–8. Water withdrawals for major water suppliers in the Pawcatuck River Basin, 

southwestern Rhode Island and southeastern Connecticut, 2000–04...............................35

1–9. Summary of irrigation withdrawals for metered turf farms and golf courses in 

the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................38

1–10. Annual groundwater withdrawals at golf course GP2A partially located in the 

Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut, 

1994–2004 .....................................................................................................................................40

5–4. Graphs showing simulated streamflow from (A) May through September 2002 and (B)

January 1, 2000, through September 30, 2004, under current conditions with selected 

irrigation withdrawals converted from surface-water to groundwater sources with the 

precipitation-runoff model Hydrologic Simulation Program-FORTRAN (HSPF) and the 

modular groundwater-flow model (MODFLOW) in lower Beaver River (BEAV3, RCHRES 

43, 01117471), Pawcatuck River Basin, southwestern Rhode Island...............................114

5–5. Graph showing effects of time-step averaging of estimated irrigation withdrawals, 

May through September 2002, in the lower Beaver River (BEAV3, RCHRES 43, 

01117471), Pawcatuck River Basin, southwestern Rhode Island.....................................115
xii

1–11. Summary statistics for logistic-regression analyses of the equations for estimating 

the probability of irrigation on a specific day at a (A) turf farm, (B) golf course with 

surface-water withdrawals, and (C) golf course with groundwater withdrawals in 

the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut, 2000–04 .................................................................................................................42

Part 2. Simulation of Water-Use and Land-Use Changes on Streamflow with a 

Precipitation-Runoff Model (HSPF)

2–1. Summary of model simulations and target data-set numbers for Hydrologic Simulation 

Program-FORTRAN (HSPF) of the Pawcatuck River Basin, southwestern Rhode Island 

and southeastern Connecticut.................................................................................................46

2–2. Area of Hydrologic Response Units (HRUs) represented for 1995 land use and potential 

buildout land use in the Hydrologic Simulation Program-FORTRAN of the Pawcatuck 

River Basin, southwestern Rhode Island and southeastern Connecticut ........................59

2–3. Domestic water-use rates for residential land-use categories used to estimate potential water use under buildout conditions in the Pawcatuck River Basin, southwestern 

Rhode Island and southeastern Connecticut.........................................................................62

Part 4. Conjunctive-Management Models as Tools for Water-Resources 

Planning

4–1. Characteristics of existing and potential water-withdrawal sites in the eastern 

Pawcatuck and lower Wood River conjunctive-management model areas, Pawcatuck 

River Basin, southwestern Rhode Island................................................................................89

4–2. Characteristics of selected streamflow constraint sites in the eastern Pawcatuck and 

lower Wood River conjunctive-management model areas, Pawcatuck River Basin, 

southwestern Rhode Island ......................................................................................................90

4–3. Irrigation management-model scenarios for existing and potential water-withdrawal 

sites in the eastern Pawcatuck River conjunctive-management model (EPRCMM) 

area, Pawcatuck River Basin, southwestern Rhode Island..............................................101
xiii

Conversion Factors, Datum, and Abbreviations

Inch/Pound to SI

Multiply By To obtain

Length

inch (in.) 25.4 millimeter (mm)

foot (ft) 0.3048 meter (m)

mile (mi) 1.609 kilometer (km)

Area

acre 4,047 square meter (m2

)

square mile (mi2) 2.590 square kilometer (km2)

Volume

million gallons (Mgal) 3,785 cubic meter (m3

)

cubic foot (ft3) 0.02832 cubic meter (m3)

Flow rate

miles per hour (mi/hr) 1,609 meter per hour (m/hr)

cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s)

cubic foot per second per square mile 

[(ft3/s)/mi2]

0.01093 cubic meter per second per square 

kilometer [(m3/s)/km2]

gallon per year (gal/yr) 0.003785 cubic meter per year (m3

/yr)

gallons per year per yard cubic meter per year per meter

gallons per year per acre cubic meter per year per hectare

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

/s)

million gallons per day per acre 

[(Mgal/d)/ac]

cubic meter per day per hectare 

[(m3/d)/hectare]

inch per acre (in/ac) millimeter per hectare

inch per year (in/yr) 25.4 millimeter per year (mm/yr)

Hydraulic conductivity

foot per day (ft/d) 0.3048 meter per day (m/d)

Transmissivity*

foot squared per day (ft2/d) 0.09290 meter squared per day (m2/d)

Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows:

 °C=(°F–32)/1.8

Vertical coordinate information is referenced to the National Geodetic Vertical Datum of 1929 

(NGVD 29) or to the North American Vertical Datum of 1988 (NAVD 88), as specified.

Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83).

Altitude, as used in this report, refers to distance above the vertical datum.

Transmissivity: The standard unit for transmissivity is cubic foot per day per square foot times 

foot of aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot 

squared per day (ft2/d), is used for convenience.
xiv

ACRONYMS AND ABBREVIATIONS

ABF Aquatic Baseflow

AIC Akaike Information Criterion

ANNIE Interactive hydrologic analyses and data management software program

CGAP Channel Geometry Analysis software program

DSN Data Set Number associated with the Watershed Data Management database

EPRCMM Eastern Pawcatuck River conjunctive-management model

ET Evapotranspiration

FBWR Fisherville Brook Wildlife Refuge

FTABLE Function table that defines the relation between depth, storage, and 

 discharge of water in a reach

GENFTBL GENerate FTaBLe software program

GENSCN GENerate SCeNarios software program

GIS Geographic information system

HAP Hunt-Annaquatucket-Pettaquamscutt

HRU Hydrologic response unit

HSPEXP Expert system for the HSPF model

HSPF Hydrologic Simulation Program–FORTRAN

IDCONS Constituent identification attribute associated with the Watershed Data 

 Management database

IDLOCN Stream reach identification attribute associated with the Watershed Data 

 Management database (for example, BEAV3 identifies the lower Beaver River)

IDSCEN Scenario identification attribute associated with the Watershed Data 

 Management database

IHM Integrated Hydrologic Model

IMPLND HSPF impervious-area land element

LID Low-impact development

LULC Land Use Land Cover

LWCMM Lower Wood conjunctive-management model

MAGIC University of Connecticut–Map and Geographic Information Center

METCMP METerologic CoMPutation software

MFE Model-fit efficiency

MODFLOW Modular groundwater-flow model

MULT Multiplier field in uci file of HSPF model

NIC Narragansett Improvement Company

NOAA National Oceanic and Atmospheric Administration
xv

NPDES National Pollutant Discharge Elimination System

NRCS Natural Resources Conservation Service

NWIS National Water Information System

NWS National Weather Service

PERLND HSPF pervious-area land element

PET Potential evapotranspiration

PEST Parameter estimation program

PROVID Providence–T.F. Green Airport, Warwick, Rhode Island

RCHRES HSPF river or reservoir reach; the accompanying number identifies the reach 

 in the model input file.

RIDEM Rhode Island Department of Environmental Management

RIGIS Rhode Island Geographic Information Systems

RIWRB Rhode Island Water Resources Board

SA Special action in the HSPF program

SSURGO Soil Survey Geographic Database produced by the NRCS

STR Stream-routing package in MODFLOW

STRMDEPL Analytical program to compute streamflow depletion from a pumped well

SWSTAT Surface-water statistics program

uci HSPF user control input file

URI University of Rhode Island

USGS U.S. Geological Survey

WDM Watershed Data Management database

WUSG Pawcatuck Watershed Water Use Stakeholders Group
Abstract

The Pawcatuck River Basin, in southwestern Rhode 

Island and southeastern Connecticut, is an important highquality water resource that provides water for domestic and 

public supplies, irrigation, recreation, and a rich aquatic ecosystem. Streamflow records for several rivers in the basin indicate that during the summer, withdrawals could be affecting 

aquatic habitat and diversity, water quality, and the value of 

the rivers as scenic and recreational resources. Concerns over 

the effects of water withdrawals on streamflow, pond levels, 

groundwater levels, and aquatic habitat in the basin prompted 

the development of surface-water, groundwater, and conjunctive-management models. Separate models were developed 

because linking surface-water and groundwater models was 

not feasible in this geologic setting. Each individual model 

provided an accurate representation of the part of the hydrologic system under consideration. A precipitation-runoff 

model was developed for the entire basin on the basis of the 

Hydrologic Simulation Program-FORTRAN (HSPF) model. 

Groundwater-flow models were developed for the lower Wood 

River and the eastern Pawcatuck River areas in the basin on 

the basis of groundwater-flow models (MODFLOW). In addition, conjunctive-management models were developed for 

subareas of the two groundwater model areas. These models 

were used to evaluate current conditions, long-term conditions, water-management alternatives, and land-use changes 

in the basin. Additionally, the results from MODFLOW were 

compared to the results of a streamflow-depletion algorithm in 

the HSPF model.

Part 1. Water Resources in the Pawcatuck 

River Basin

Climate, streamflow, groundwater-level, pond-level, and 

water-use data were collected throughout the 303-squaremile Pawcatuck River Basin during 2000–04 to support 

development of the models. Additionally, hydrogeologic 

data were compiled for the modeling efforts from previous 

studies throughout the basin. Climate data were collected at 

two sites in the basin and compiled for four National Weather 

Service sites. Streamflow data were collected at 18 continuous 

streamflow-gaging stations for at least 2 years of the study 

period. Monthly streamflow measurements were collected 

at 36 partial-record stations for at least 1.5 years. Daily 

streamflows for these partial-record stations were calculated 

by using the mathematical procedure Maintenance of Variance 

Extension (MOVE.1). Groundwater-level data were collected 

monthly or more frequently at 11 wells and continuously at 

8 wells for a least part of the study period in the basin. Pondlevel data were collected at 23 ponds for about 1.5 years 

during the study period. Water-withdrawal data were compiled 

from 5 large municipal suppliers for 16 wells in the basin. 

Data on withdrawals for irrigation were collected for 11 turffarm sites and 3 golf courses. These data were used to develop 

logistic-regression equations to estimate the probability of 

irrigation on a specific day during the irrigation season for 

unmetered turf farms, surface-water withdrawal golf courses, 

and groundwater withdrawal golf courses using climatic data 

on total precipitation and potential evapotranspiration during 

the preceding days. Average hourly withdrawal rates were also 

estimated by using data collected on hourly irrigation patterns 

at the 11 turf-farm sites and 3 golf courses. Using the logistic 

regression equations predicted days of irrigation during 

the study period and the average hourly irrigation patterns; 

the irrigation rates for unmetered turf farms, surface-water 

withdrawal golf courses, and groundwater withdrawal golf 

courses could be estimated.

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

By Gardner C. Bent, Phillip J. Zarriello, Gregory E. Granato, John P. Masterson, Donald A. Walter, 

Andrew M. Waite, and Peter E. Church
2 Effects of Water Withdrawals and Land-Use Changes on Streamflows and Groundwater Levels in Pawcatuck River Basin

Part 2. Simulation of Water-Use and Land-Use 

Changes on Streamflow with a PrecipitationRunoff Model (HSPF)

The precipitation-runoff model HSPF was developed 

and calibrated for the Pawcatuck River Basin to evaluate the 

effect of withdrawals and land-use change on streamflow. The 

model was calibrated to the period of January 1, 2000, to 

September 30, 2004, with measured and estimated flows at 

17 continuous-record streamflow-gaging stations and 34 

partial-record stations. Graphical comparison and statistical 

analysis with observed flows indicate that the model is 

generally well calibrated. 

Simulated streamflows for the 1960–2004 period were 

used to evaluate the effects of (1) no withdrawals, (2) current 

(2000–04) withdrawal, (3) conversion of selected surfacewater-irrigation withdrawals to groundwater withdrawals, 

(4) future water-supply demands, and (5) land-use change. 

In general, the largest differences between simulations of 

current water demands and no demands were calculated 

for the eastern Pawcatuck River subbasins–Chipuxet River 

(two locations), Chickasheen Brook, and the headwaters of 

the Pawcatuck River. The effects of switching from direct 

surface-water withdrawals to groundwater withdrawals at 

selected sites were most pronounced in the daily mean flowduration curves for the Beaver and Chipuxet Rivers, which 

drain subbasins where irrigation withdrawals can affect a 

large percentage of low flows. Hourly flow fluctuations in the 

August 2002 hydrograph caused by irrigation withdrawals 

from surface water were greatly reduced or eliminated entirely 

by switching to groundwater withdrawals in subbasins where 

irrigation demands are prevalent. Potential new withdrawals 

in the eastern Pawcatuck River subbasins resulted in zero flow 

in the lower Chipuxet River and decreased the lowest flows 

under current withdrawals by as much as 90 percent compared 

to simulations with no withdrawals.

Simulations of land-use change evaluated the effects of 

(1) land-use change only, (2) change in water demands only, 

and (3) combined effects of land-use change and change in 

water demands. Overall, about 10 percent of the basin was 

classified as developed in 1995, but about 50 percent of the 

basin could be developed within the constraints used in the 

analysis. Future water-use demands in the basin were estimated to be about 4 times greater for domestic use and about 

6 times greater for commercial and industrial use at buildout 

compared to current (1995–99) use. In general, simulations 

under buildout conditions indicated that high flows increase 

slightly and low flows decrease slightly as a result of land-use 

change relative simulations under current (1995) conditions, 

but changes in flows generally were not noteworthy. The 

extent to which streamflow changes in response to development depends on how the land is developed; the pattern and 

extent of development can differ widely and produce effects 

different from those simulated, particularly in localized areas.

Part 3. Simulated Effects of Withdrawals on 

Groundwater Flow (MODFLOW Models)

Groundwater-flow models (MODFLOW) were developed 

for the lower Wood River and eastern Pawcatuck River areas 

in the Pawcatuck River Basin for the purposes of assessing 

the potential effects of groundwater pumping on streamflows 

and water levels at proposed irrigation and water-supply sites 

in the study area. The results of the MODFLOW models and 

a streamflow-depletion algorithm in the HSPF model were 

compared, and alternatives were evaluated for the conjunctive 

management of the ground- and surface-water resources of 

the basin. 

The model simulations included analyses of the effects 

of constant and varying pumping and constant and varying 

recharge rates, the effects of constant pumping and varying 

recharge rates, and the effects of different well distances from 

streams under constant and varying pumping rates. Simulations were made to compare and contrast the effects of these 

simulations on rivers with both low and high streamflows to 

determine if the responses of these rivers and the surrounding 

aquifer to the changes in simulated stresses differed with river 

size (large versus small). 

Simulation results indicate that streamflow depletion is 

similar between large and small rivers for constant pumping and recharge scenarios as well as during periods when 

simulated streamflow was at or above average. In both cases, 

streamflow-depletion rates were about the same as the simulated pumping rates in nearby wells. During dry periods, such 

as summer (June through August) and early fall (September 

and October), when simulated streamflows in small rivers is at 

or near zero, the small rivers are no longer a source of water 

to pumped wells. In this case, aquifer storage becomes the 

primary source of water to the pumped wells; this withdrawal 

from storage results in much greater drawdowns in the nearby 

aquifer than would have occurred near large rivers or small 

rivers with moderate streamflow.

Analysis done to determine the effects of relocating 

irrigation-withdrawal wells away from a river shows that the 

effects of seasonally variable pumping on streamflow, such 

as for turf-farm and golf course irrigation, can be reduced 

by increasing the distance from the wells to the river. This is 

due to the lag time in the response of the rivers to the pumping stress. As a result, summer irrigation pumping from wells 

located further away from a river did not affect streamflow 

until later in the fall (October and November) when streamflows are typically higher than in the summer because of the 

lower pumping and higher recharge in the fall. 

Part 4. Conjunctive-Management Models as 

Tools for Water-Resources Planning

Results from conjunctive-management-model simulations 

may be used to balance groundwater and surface-water 

withdrawals needed for water supply and aquatic-habitat 
Introduction 3

protection. Conjunctive-management models were developed 

for two selected areas in the Pawcatuck River Basin to 

evaluate the potential for improvements in water-withdrawal 

strategies in the basin. Two conjunctive-management models, 

described herein as the eastern Pawcatuck River conjunctivemanagement model (EPRCMM) and the lower Wood River 

conjunctive-management model (LWRCMM) were developed. 

A total of 250 applications of the models were developed 

and tested for the eastern Pawcatuck River (105 applications) 

and lower Wood (145 applications) areas. The conjunctivemanagement model combines results of statistical analysis 

of water-use data, simulations by the transient numerical 

groundwater models developed for two selected areas in the 

basin, and results of streamflow simulations by the basinwide 

Hydrologic Simulation Program-FORTRAN model. This 

information is used to formulate linear optimization models 

for water-resource management. These management models 

were developed and tested to illustrate the potential effects of 

the conversion of surface-water withdrawals to groundwater 

withdrawals, withdrawal-well network design, withdrawal 

capacity, and streamflow-depletion criteria on the maximum 

obtainable water yield in each of the two model areas. In 

both areas, conjunctive-management models using maximum 

withdrawal capacities of 1.0, 1.4, and 2.0 million gallons per 

day (Mgal/d) were tested to illustrate the dynamic relations 

among depletion criteria, network design (the number, type, 

and location of withdrawal sites), and the production capacity 

of the water-withdrawal network. The results indicate that 

the conversion of surface-water withdrawals to groundwater 

withdrawals for irrigation has the potential benefit of increases 

in total water yields for a given level of depletion. The 

simulated addition of potential future production wells to these 

scenarios indicates that groundwater withdrawals are preferred 

in management models designed to maximize withdrawals 

for a fixed set of depletion criteria because these wells would 

withdraw water throughout the year instead of only during 

the low-flow irrigation season (summer and early fall). In the 

EPRCMM area, total annual withdrawals range from about 

400 million gallons per year (Mgal/yr) at allowable depletions 

that are 25 percent of the minimum monthly one-day 

streamflow to 1,200 to 2,400 Mgal/yr depending on the 

number of active withdrawal sites, maximum sustainable 

withdrawal capacities, and allowable streamflow depletions. 

Similarly, in the LWRCMM area, total annual withdrawals 

range from about 500 Mgal/yr at allowable depletions that 

are 25 percent of the minimum monthly one-day streamflow 

to 1,200 to 3,500 Mgal/yr depending on the number of active 

withdrawal sites, maximum sustainable withdrawal capacities, 

and allowable streamflow depletions.

Water-resource managers rely on tools such as HSPF and 

MODFLOW to address water-resources issues by simulating 

alternative management strategies. The choice of model, or 

even the need for a model, however, largely depends on the 

questions posed. Each model has strengths and weaknesses 

related to the differing hydrologic processes the models are 

intended to simulate and the spatial and temporal scales of the 

models. Comparison of selected results simulated by these 

two models demonstrates these limitations and the judgment 

required to determine the suitability of a particular model for 

making management decisions.

Introduction

The 303-mi2 Pawcatuck River Basin is located in southwestern Rhode Island and southeastern Connecticut (fig. I–1). 

The high-quality water in the basin is important for domestic 

and public supplies, irrigation, recreation, and the aquatic 

ecosystem. The U.S. Environmental Protection Agency (2005) 

reports that this area of Rhode Island has a high biodiversity, 

with 85 percent of the State’s globally rare species and 

65 percent of the State’s rare and unique natural communities. 

The basin has a large area of irrigated agricultural land 

(4.82 mi2) (primarily turf farms) and 11 golf courses 

(0.76 mi2) that typically need irrigation during the dry periods 

of the summer when streams and groundwater levels are typically at their lowest levels (Natural Resources Conservation 

Service, 2003). The U.S. Environmental Protection Agency 

(2005) reports that the Pawcatuck River Basin has the highest 

concentration of turf farms in the Nation. Water withdrawals in 

the basin may be affecting aquatic habitat and diversity, water 

quality, and the value of the rivers as a scenic and recreational 

resource. Additionally, there are concerns over the effects of 

water withdrawals on ponds, groundwater levels, and aquatic 

habitat. The basin was designated as a sole-source aquifer 

by the U.S. Environmental Protection Agency, 1988, 2005. 

Thus, management of water resources in the basin to ensure 

sustainable supplies and adequate water for aquatic habitat is 

of concern to governmental agencies, environmental organizations, and private citizens. These concerns are intensified by 

rapid development and population growth in the region and 

the likelihood of greater demands for clean water in the future.

The U.S. Department of Agriculture, Natural Resources 

Conservation Service (NRCS) is a Federal agency that works 

with communities to improve and protect their soil, water, and 

other natural resources. The NRCS in Rhode Island works 

closely with the agricultural community to meet water needs 

and use water effectively for the production of agricultural 

products while maintaining the aquatic habitat, water quality, and water used for recreation. The Rhode Island Water 

Resources Board (RIWRB) is the principal State agency 

concerned with sustainable water supplies. The RIWRB works 

closely with the Rhode Island Department of Administration’s 

Statewide Planning Program to develop and refine policies 

affecting water supply, including emergency planning (Rhode 

Island Water Resources Board, 2002). In 1999, the Rhode 

Island General Assembly designated the RIWRB as the sole 

authority to devise fair and equitable allocation of state water 

resources and to ensure that long-term considerations of water 

supply prevail over short-term considerations.
4 Effects of Water Withdrawals and Land-Use Changes on Streamflows and Groundwater Levels in Pawcatuck River Basin

C

Windham Co.

New London Co.

Greenwich Co.

Washington Co.

71°50' 71°40' 71°30'

41°40'

41°30'

41°20' B L O C K I S L A N D

S O U N D

L O N G I S L A N D S O U N D

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

Hopkinton

Voluntown

Sterling

Coventry

West Greenwich East Greenwich

Richmond

South

Kingstown

North

Kingstown

Charlestown

Westerly

Stonington

North Stonington

Exeter

Beaver River

River

River

Wood

River

Chickasheen Brook

Pawcatuck

Pawcatuck

Tomaquag Brook

Queen River

Wood River

Ashaway

River

ShunockRiver

Meadow Brook

Usquepaug River

Chipuxet River

Watchaug

Pond Chapman

Pond

Worden

Pond

Breakheart

Pond

Tucker

Pasquiset Pond

 Pond Cedar

 Swamp

Brook

RHODE ISLAND

CONNECTICUT CONNECTICUT

RHODE ISLAND

0 2.5 5 MILES

0 2.5 5 KILOMETERS

Pawcatuck Basin

RHODE 

ISLAND

71°45' 71°30' 71°15'

42°

41°40'

41°20'

Base from U.S. Geological Survey digital data,

North American Datum of 1983,

Rhode Island State Plane projection, 1:24,000

EXPLANATION

State boundary

County boundary

Town boundary

Basin boundary

River or stream

Model boundary

Lower Wood River

Model Area

Eastern Pawcatuck River

Model Area

Figure I–1. Location of the Pawcatuck River Basin study area and groundwater model extents, southwestern Rhode Island 

and southeastern Connecticut.
Introduction 5

The NRCS and RIWRB began a cooperative study with 

the U.S. Geological Survey (USGS) in 2002 to develop a 

physically based precipitation-runoff model, groundwater 

models, and conjunctive-management models for selected 

areas of the Pawcatuck River Basin. The results of these 

models will assist the NRCS, RIWRB, State, and local 

communities in understanding how streamflow, groundwater 

levels, and pond levels in the basin may be affected by human 

activities such as withdrawals for water supply and irrigation. 

The models also will allow simulation of possible future 

water-management alternatives to evaluate their effects on 

streamflows, groundwater levels, and pond levels. In addition, 

data collected during this study will provide information 

necessary for stream-habitat assessments and for use in watermanagement decisions at all levels. 

Purpose and Scope

This report describes the development and application of 

a precipitation-runoff model based on the Hydrologic Simulation Program-FORTRAN (HSPF) (Bicknell and others, 

2000), groundwater models based on MODFLOW (Harbaugh 

and others, 2000), and conjunctive-management models for 

the Pawcatuck River Basin. It also presents climatological, 

hydrological, and water-use data collected between 2000 and 

2004 to support development and calibration of the models. 

Information on differences related to streamflow depletion 

between results obtained from HSPF and MODFLOW are 

also discussed in the report. The report also includes information about the study area, climate, streamflow, hydrogeology, 

groundwater and pond levels, water use, methods used to 

obtain the data, and logistic-regression equations developed to 

predict the likelihood of turf-farm and golf-course irrigation.

The report is organized as follows: Part 1—Water 

resources of the basin; Part 2—HSPF modeling results; 

Part 3—MODFLOW modeling results; Part 4—Conjunctivemanagement modeling results; and Part 5—Comparison of 

results from HSPF and MODFLOW modeling. Appendixes at 

the back of the report provide supporting information concerning data used in the models, calibration of the models, 

modeling runs, and other technical aspects of the study. The 

characteristics and scenarios run for the HSPF, MODFLOW, 

and conjunctive-management models (Parts 2, 3 and 4 of the 

report, respectively) are summarized in table I–1. 

Table I–1. Overview of characteristics and scenarios used in the HSPF, MODFLOW, and conjunctive-management models for the 

Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut, that are described in Parts 2, 3, and 4 of this report.

Part 2: HSPF model Part 3: MODFLOW models Part 4: Conjunctive-management models

Characteristics

Spatial domain Entire basin 1. Lower Wood River area.

2. Eastern Pawcatuck area.

1. Lower Wood River area.

2. Lower Usquepaug-Queen River and 

 Beaver River subbasins (part of eastern 

 Pawcatuck area).

Calibration period 2000–04 2000–04 Not applicable.

Run period 1960–2004 2000–04 1960–2004.

Time step Hourly Monthly and weekly Daily and monthly.

Constraints Not applicable Not applicable 1. Maximum rates of streamflow depletion 

 at selected sites.

2. Minimum and maximum withdrawal

 rates at selected sites.

3. Seasonal withdrawal patterns.

Scenarios run

No water withdrawals Yes No Not applicable.

Current water withdrawals Yes Yes Not applicable.

Conversion of surface-water irrigation 

withdrawals to ground-water 

withdrawals

Yes Yes, for selected locations Yes, for selected locations.

Proposed future water-supply withdrawals Yes Yes, for selected locations Yes, for selected locations.

Buildout: (1) land-use changes only, 

(2) water-demand changes only, and 

(3) combined effects of both land-use 

water-demand changes

Yes No No.
6 Effects of Water Withdrawals and Land-Use Changes on Streamflows and Groundwater Levels in Pawcatuck River Basin

Description of the Study Area

The Pawcatuck River Basin is in southwestern Rhode 

Island in Washington and Kent Counties and in southeastern 

Connecticut in New London and Windham Counties 

(fig. I–1). Land area in the basin totals 303 mi2, of which 

246 mi2 is in Rhode Island and 57 mi2 is in Connecticut. Ten 

towns in Rhode Island and four towns in Connecticut are 

partially or wholly within the basin. In 1990, the basin population was approximately 61,500, and the estimated population during the late 1990s was approximately 67,000 (Wild 

and Nimiroski, 2004). The Pawcatuck River Basin is part of 

the Seaboard Lowland section of the New England physiographic province (Denny, 1982). The topography north of the 

Pawcatuck River is characterized by gently rolling hills with 

northeast-southwest trending valleys in the eastern part of the 

basin and northwest-southeast trending valleys in the western 

part of the basin. South of the Pawcatuck River, the topography is mainly flat. Altitudes are as high as 629 ft on Bald 

Hill in West Greenwich, R.I., in the northern part of the basin. 

The Pawcatuck River generally flows from east to southwest 

before discharging into the Atlantic Ocean (fig. I–1). Climate 

in the basin is classified as moist continental. Mean annual 

precipitation is about 51.8 inches per year (in/yr), and the 

mean annual temperature is about 50°F in the basin (National 

Oceanic and Atmospheric Administration, 2002). The Pawcatuck River’s major tributaries, from east to west, are the 

Chipuxet, Usquepaug-Queen, Beaver, Wood, Ashaway, and 

Shunock Rivers. Surficial geology in the basin is mainly glacial stratified deposits along the major river valleys and glacial 

till or exposed bedrock in the upland area (fig. I–2). Along 

the southern border of the basin is the Charlestown glacial 

moraine, which acts as a physical barrier to surface-water flow 

and directs the Pawcatuck River to its discharge point in the 

southwestern part of the basin. 

Land use in the basin is about 61 percent forested, 

14.8 percent wetlands (2.3 percent nonforested wetlands 

and 12.5 percent forested wetlands), 10 percent developed 

(residential, commercial, industrial, and transportation), 

9.6 percent open space in undeveloped areas, 2.7 percent 

water bodies (lakes and ponds), and 1.9 percent irrigated land 

(golf courses and agriculture). The irrigated agricultural lands, 

primarily turf farms, are mainly in the eastern part of the 

basin. The developed area is mainly the southwest part of the 

basin, including the towns of Westerly, R.I., and Stonington, 

Conn. (fig. I–3). 

Previous Investigations

Many studies done by the USGS have investigated the 

groundwater and surface-water resources and the water quality 

of the Pawcatuck River Basin and its subbasins. Groundwater 

resources in the basin were investigated from the late 1940s 

to the mid-1990s by Allen and Jeffords (1948), Allen and 

others (1966), Gonthier and others (1974), Dickerman (1984), 

Dickerman and Ozbilgin (1985), Johnston and Dickerman 

(1985), Dickerman and others (1990), Dickerman and Bell 

(1993), and Dickerman and others (1997). These studies 

compiled and collected information on the hydrogeology of 

the basin, particularly aquifer properties that were then used 

to develop groundwater-flow models. The groundwaterflow models were used to evaluate the effects of pumping 

alternatives on water levels, baseflow, and wetlands in the 

sand and gravel valley-fill deposits. The hydrogeologic, 

streamflow, and water-quality data collected in these studies 

were presented in data reports by Allen and others (1963), 

Dickerman (1976), Dickerman and Johnston (1977), 

Dickerman and Silva (1980), Dickerman and others (1989), 

and Kliever (1995). The hydrogeology and recharge for the 

contributing area to a water-supply well in the southwestern 

and central part of the basin were recently described by Friesz 

(2004) and Friesz and Stone (2007), respectively. 

The Pawcatuck River Basin encompasses all or 

parts of 12 USGS quadrangles: the Ashaway, Carolina, 

Coventry Center, Hope Valley, Kingston, Oneco, Old 

Mystic, Quonochontaug, Slocum, Voluntown, Watch Hill, 

and Wickford USGS quadrangles. The USGS has published 

geologic maps describing the surficial and bedrock geology 

of these quadrangles (Power, 1957, 1959; Moore, 1958, 

1959, 1964, 1967; Kaye, 1961; Schafer, 1961, 1965, 1968; 

Feininger, 1962, 1965a,b,c; Harwood and Goldsmith, 1971a,b; 

Goldsmith, 1985). The USGS has also published groundwater 

maps describing the bedrock contours, water-table altitudes, 

well locations, and till and stratified sand and gravel deposits 

of these quadrangles (Bierschenk, 1956; Bierschenk and 

Hahn, 1959; Hahn, 1959; Johnson and Marks, 1959; Mason 

and Hahn, 1959, 1960; Johnson and others, 1960; LaSala and 

Hahn, 1960; LaSala and Johnson, 1960; Mason and others, 

1960; Randall and others, 1960; Johnson, 1961a,b). 

Recently, studies related to streamflow and aquatic 

habitat in the Pawcatuck River Basin have focused on the 

Usquepaug-Queen River subbasin. Armstrong and Parker 

(2003) characterized the aquatic habitat, stream temperature, 

and fish communities in the subbasin. In that study, minimum 

streamflow requirements for fish habitat were identified by 

standard flow-setting techniques for selected riffle sites. 

Zarriello and Bent (2004) developed a precipitation-runoff 

model based on HSPF to evaluate the effects of water 

withdrawals and land-use changes on streamflows in the 

Usquepaug-Queen River subbasin. The study by Zarriello 

and Bent (2004) was the pilot study for the present study of 

the Pawcatuck River Basin. In the early 1990s, a regionalized 

regression equation for southern Rhode Island streams was 

developed by Cervione and others (1993) for estimating the 

7-day low flow that is expected to occur once every 10 years 

(commonly referred to as the 7Q10). Additionally, they also 

provided estimates of low-flow durations (for the 80th, 90th, 

95th, 98th, and 99th percentiles) and the 7Q10 for 22 partialrecord stations in the Pawcatuck River Basin. All 22 partialrecord stations were also monitored for streamflow during the 

present study. 
Introduction 7

C

71°50' 71°40' 71°30'

41°40'

41°30'

41°20' B L O C K I S L A N D

S O U N D

L O N G I S L A N D S O U N D

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

Hopkinton

Voluntown

Plainfield Sterling

Coventry

West Greenwich

East Greenwich

Richmond

South

Kingstown

North

Kingstown

Charlestown

Westerly

Stonington

North Stonington

Exeter

Griswold

Preston

Beaver River

Wood

River

River

Chickasheen Brook

Pawcatuck

Queen River

Wood River

Tomaquag Brook

Ashaway River

Shunock

River

Meadow Brook

Usquepaug River

Chipuxet River

Watchaug Pond Chapman Pond

Worden

Pond

Breakheart Pond

Tucker

Pond Pasquiset

 Pond

RHODE ISLAND

CONNECTICUT

0 2.5 5 MILES

0 2.5 5 KILOMETERS

EXPLANATION

Glacial stratified deposits

Till and bedrock outcrops

Charlestown Moraine

River

Pawcatuck

Base from U.S. Geological Survey digital data, 

North American Datum of 1983,

Rhode Island stateplane projection, 1:24,000,

Surficial geology from Rhode Island Geographic Information System (RGIS), 1995

Surficial geologic deposits

Political boundaries

State

Basin

Town

Hydrologic boundary

Cedar

 Swamp

Brook

GREENWICH CO.

WASHINGTON CO.

Figure I–2. Location of surficial geology in the Pawcatuck River Basin, southwestern Rhode Island and southeastern 

Connecticut.
8 Effects of Water Withdrawals and Land-Use Changes on Streamflows and Groundwater Levels in Pawcatuck River Basin

Exeter North

Kingstown

South

Kingstown

Voluntown

North

Stonington

Stonington

Coventry

Sterling

West Greenwich

Richmond

Charlestown

Westerly

Hopkinton

East

Greenwich

Plainfield

Griswold

71o37' 30" 71o 71 30' o 71 45' o

52' 30"

42o

37'30"

41o

22'30"

41o

30'30"

0 1 2 3 4 5 MILES

0 1 2 3 4 5 KILOMETERS 6 7 8

Base from U.S. Geological Survey digital data,

North American Datum of 1983

Rhode Island stateplane projection, 1:24,000

Land-use data from Rhode Island Geographic Information System (RIGIS), 1995 RHODE ISLAND CONNECTICUT

EXPLANATION

Land use—Land cover

Industrial, commercial,

 and transportation

High-to-moderate 

 density residential

Moderate-to-low 

 density residential

Open space

Forest

Nonforested wetland

Forested wetland

Golf course

Turf farm

Other irrigated agriculture

Water

State

Town

Basin

Boundaries

Figure I–3. Generalized land use (1995) in the Pawcatuck River Basin, southwestern Rhode Island and southeastern Connecticut.
Introduction 9

Water-use information was compiled for the 5-year 

period 1995–99 by Wild and Nimiroski (2004) for the 

Pawcatuck River Basin. This compilation includes domestic, 

public, commercial, and agricultural uses. Data from that 

study were used to supplement the water-use information 

collected during the present study.

Numerous other water-resource-related studies for the 

Pawcatuck River Basin have been published by other Federal, 

State, and local government agencies, as well as universities, 

watershed organizations, and consulting firms. For example, 

Desbonnet (1999) provided a general overview of ground- and 

surface-water resources, water uses, and management issues 

in the Pawcatuck River Basin. One of the management issues 

discussed is the need to develop quantitative models for evaluating the effects of withdrawals on water resources.

Several statewide water-resources studies include 

information on the Pawcatuck River Basin. Information on 

groundwater-resources was provided for the basin by Allen 

(1953), Lang and others (1960), Lang (1961), Johnston 

(1988), and Trench (1991, 1995). Guthrie and Stolgitis (2000) 

provided information on the areal extent and bathymetry of 

lakes and ponds. DeSimone and Ostiguy (1999) provided 

hydrogeologic, water-quality, land-use, and other spatial data 

to identify factors that contribute to the relative vulnerability 

of groundwater in the basin to contamination. Information has 

been collected and compiled for the water use in the basin in 

previous studies by Horn and Craft (1991), Craft and others 

(1995), Korzendorfer and Horn (1995), Medalie (1996), and 

Horn (2000). 

Hydrogeologic studies of adjacent river basins that 

included small areas of the Pawcatuck River Basin are 

those by Barlow and Dickerman (2001a,b) in the HuntAnnaquatucket-Pettaquamscutt (HAP) Basin to the northeast 

and Masterson and others (2007) in the South Coastal Basin 

to the south. Dickerman and others (1997) and Barlow and 

Dickerman (2001a) determined that groundwater discharges 

to the HAP Basin in the upper part of the Queens Fort Brook, 

which is a tributary subbasin of the Usquepaug-Queen River 

subbasin, and in the upper part of the Chipuxet River Basin 

(northeastern part of Pawcatuck River Basin). Masterson and 

others (2007) provided detailed hydrogeologic information 

and developed a groundwater-flow model for the southern 

border of the basin in the salt-pond region of Rhode Island. 

The model area includes parts of the Pawcatuck River Basin—

the eastern part of the Chipuxet River subbasin and area south 

of the Pawcatuck River, with the Chipuxet River and the 

Pawcatuck River as the northern model boundary. Masterson 

and others (2007) identified many small areas along the 

southern border of the Pawcatuck River Basin that contribute 

groundwater flow to the salt-pond region of Rhode Island. 

Hydrogeologic studies for adjacent river basins include those 

by Craft (2001), Granato and others (2003), and Granato and 

Barlow (2005) in the Big River Basin to the north. 
THIS PAGE INTENTIONALLY LEFT BLANK
Prepared by the Pembroke and Reston Publishing 

Service Centers.

For more information concerning this report, contact:

Office of the Deputy Director

U.S. Geological Survey

Rhode Island Water Science Center

42 Albion Road, Suite 107

Lincoln, RI 02865

or visit our Web site at:

http://ri.water.usgs.gov
Bent and others—Simulated Effects of Water Withdrawals and Land-Use Changes on Groundwater Levels in the Pawcatuck—Scientific Investigations Report 2009–5127