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Simulation of Ground-Water Flow and Evaluation of Water-Management Alternatives in the Upper Charles River Basin, Eastern Massachusetts

Water-Resources Investigations Report 02-4234

By Leslie A. DeSimone, Donald A. Walter, John R. Eggleston, and Mark T. Nimroski

 

ABSTRACT

Ground water is the primary source of drinking water for towns in the upper Charles River Basin, an area of 105 square miles in eastern Massachusetts that is undergoing rapid growth. The stratified-glacial aquifers in the basin are high yield, but also are thin, discontinuous, and in close hydraulic connection with streams, ponds, and wetlands. Water withdrawals averaged 10.1 million gallons per day in 1989–98 and are likely to increase in response to rapid growth. These withdrawals deplete streamflow and lower pond levels. A study was conducted to develop tools for evaluating water-management alternatives at the regional scale in the basin. Geologic and hydrologic data were compiled and collected to characterize the ground- and surface-water systems. Numerical flow modeling techniques were applied to evaluate the effects of increased withdrawals and altered recharge on ground-water levels, pond levels, and stream base flow. Simulation-optimization methods also were applied to test their efficacy for management of multiple water-supply and water-resource needs.

Steady-state and transient ground-water-flow models were developed using the numerical modeling code MODFLOW-2000. The models were calibrated to 1989–98 average annual conditions of water withdrawals, water levels, and stream base flow. Model recharge rates were varied spatially, by land use, surficial geology, and septic-tank return flow. Recharge was changed during model calibration by means of parameter-estimation techniques to better match the estimated average annual base flow; area-weighted rates averaged 22.5 inches per year for the basin. Water withdrawals accounted for about 7 percent of total simulated flows through the stream-aquifer system and were about equal in magnitude to model-calculated rates of ground-water evapotranspiration from wetlands and ponds in aquifer areas. Water withdrawals as percentages of total flow varied spatially and temporally within an average year; maximum values were 12 to 13 percent of total annual flow in some subbasins and of total monthly flow throughout the basin in summer and early fall.

Water-management alternatives were evaluated by simulating hypothetical scenarios of increased withdrawals and altered recharge for average 1989–98 conditions with the flow models. Increased withdrawals to maximum State-permitted levels would result in withdrawals of about 15 million gallons per day, or about 50 percent more than current withdrawals. Model-calculated effects of these increased withdrawals included reductions in stream base flow that were greatest (as a percentage of total flow) in late summer and early fall. These reductions ranged from less than 5 percent to more than 60 percent of model-calculated 1989–98 base flow along reaches of the Charles River and major tributaries during low-flow periods. Reductions in base flow generally were comparable to upstream increases in withdrawals, but were slightly less than upstream withdrawals in areas where septic-system return flow was simulated. Increased withdrawals also increased the proportion of wastewater in the Charles River downstream of treatment facilities. The wastewater component increased downstream from a treatment facility in Milford from 80 percent of September base flow under 1989–98 conditions to 90 percent of base flow, and from 18 to 27 percent of September base flow downstream of a treatment facility in Medway. In another set of hypothetical scenarios, additional recharge equal to the transfer of water out of a typical subbasin by sewers was found to increase model-calculated base flows by about 12 percent of model-calculated base flows. Addition of recharge equal to that available from artificial recharge of residential rooftop runoff had smaller effects, augmenting simulated September base flow by about 3 percent.

Simulation-optimization methods were applied to an area near Populatic Pond and the confluence of the Mill and Charles Rivers in Franklin, Medway, and Norfolk. Water is withdrawn from six supply wells for three towns in this area. Management objectives in this analysis were to develop pumping schemes that (1) maximized water withdrawals while imposing specified constraints on streamflow depletion and (2) minimized streamflow depletion while meeting minimum requirements for water supply. Application of the optimization techniques indicated that hydrologic responses of pond levels and streamflow to pumping at different supply wells in the Populatic Pond area vary in time and duration. This variability suggests that water withdrawals could be managed to minimize the effects of increased withdrawals on streams and ponds. Simulation of several preliminary scenarios indicated the possibility that, with active management of water-supply sources, water withdrawals could be substantially increased from existing and proposed sources while base flow in the Charles and Mill Rivers was maintained above minimum average monthly flow requirements. Alternatively, base flow could be increased in the Charles River during low-flow periods while existing and proposed withdrawals were met. Finally, results from these scenarios indicated that collaborative management of water sources by towns could reduce the effect of withdrawals on stream base flow, and, by implication, would allow greater withdrawals from the Populatic Pond area without xceeding specified limits on streamflow depletion.

CONTENTS

Abstract

Introduction

Purpose and Scope

Description of the Study Area

Previous Studies

Acknowledgments

Upper Charles Stream-Aquifer System

Hydrogeology

Water Withdrawals and Return Flow

Streamflow and Water Levels

Water Balance

Simulation of Ground-Water Flow

Steady-State Numerical Models

Spatial Discretization

Boundary Conditions

Stresses

Recharge

Water Withdrawals and Discharges

Hydraulic Properties

Model Calibration

Recharge

Hydraulic Properties

Calibration Results

Transient Numerical Models

Temporal Discretization and Initial Conditions

Boundary Conditions and Stresses

Hydraulic Properties

Model Calibration

Model Limitations

Evaluation of Ground-Water-Management Alternatives

Simulation of Increased Water Withdrawals and Altered Recharge

Simulation of Increased Withdrawals

Simulation of Altered Recharge

Simulation-Optimization of Water Withdrawals and Stream Base Flow in the Populatic Pond Area

Theory and Methods of the Simulation-Optimization Approach

Application in the Populatic Pond Area

Hydrologic Stresses and Responses

Management Model Applications

Increase Withdrawals while Maintaining Stream Base Flow above Specified Minimum-Flow Requirements

Increase Withdrawals while Maintaining Stream Base Flow at Current Levels

Increase Stream Base Flow while Maintaining Existing and Proposed Withdrawals

Limitations of Management-Model Applications

Summary

References

To link to a list of figures and tables click here FIGURES and TABLES

AVAILABILITY

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The citation for this report, in USGS format, is as follows:

DeSimone, L.A., Walter, D.A., Eggleston, J.R., and Nimroski, M.T., 2002, Simulation of Ground-Water Flow and Evaluation of Water-Management Alternatives in the Upper Charles River Basin, Eastern Massachusetts: Water-Resources Investigations Report 02-4234, 94 p.

 For more information about USGS activities in Massachusetts-Rhode Island District, visit the USGS Massachusetts-Rhode Island Home Page.




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