ABSTRACT

The Pawcatuck River Basin, in southwestern Rhode Island and southeastern Connecticut, is an important high-quality 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.

Contents

Abstract

Introduction

 

Part 1. Water Resources in the Pawcatuck River Basin

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

Climate

Geologic Setting

Groundwater

Surface Water

Water Withdrawals

Wastewater Discharge and Return Flow

 

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

By Phillip J. Zarriello

Effects of Withdrawals on Streamflow

Effects of Potential Future Land Use and Water Use on Streamflow

 

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

By John P. Masterson

Effects of Pumping under Constant and Varying Recharge Conditions

Effects of Varying Pumping-Well Distance with Constant Pumping Rates

Effects of Varying Pumping-Well Distance with Varying Pumping Rates

 

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

By Gregory E. Granato and Donald A. Walter

Streamflow-Response Coefficients

Potential Allowable Streamflow-Depletion Criteria

Well-Site Selection for Groundwater Withdrawals

Use of Community Wells for Irrigation

Post-Optimization Analysis

 

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

By Phillip J. Zarriello

Hydrologic Models—HSPF and MODFLOW

Functional Differences between HSPF and MODFLOW

Comparison of Three Example HSPF and MODFLOW Results

Integrating HSPF and MODFLOW Models

 

Summary and Conclusions

Acknowledgments

References Cited

Appendix Part 1

Appendix Part 2

Appendix Part 3

Appendix Part 4

Posted February 2011