Link to USGS home page
Thumbnail of cover

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

By Leslie A. DeSimone

Scientific Investigations Report 2004-5114

ABSTRACT

Water-supply withdrawals and wastewater disposal in the Assabet River Basin in eastern Massachusetts alter the flow and water quality in the basin. Wastewater discharges and stream-flow depletion from ground-water withdrawals adversely affect water quality in the Assabet River, especially during low-flow months (late summer) and in headwater areas. Streamflow depletion also contributes to loss of aquatic habitat in tributaries to the river. In 1997–2001, water-supply withdrawals averaged 9.9 million gallons per day (Mgal/d). Wastewater discharges to the Assabet River averaged 11 Mgal/d and included about 5.4 Mgal/d that originated from sources outside of the basin. The effects of current (2004) and future withdrawals and discharges on water resources in the basin were investigated in this study.

Steady-state and transient ground-water-flow models were developed, by using MODFLOW-2000, to simulate flow in the surficial glacial deposits and underlying crystalline bedrock in the basin. The transient model simulated the average annual cycle at dynamic equilibrium in monthly intervals. The models were calibrated to 1997–2001 conditions of water withdrawals, wastewater discharges, water levels, and nonstorm streamflow (base flow plus wastewater discharges). Total flow through the simulated hydrologic system averaged 195 Mgal/d annually. Recharge from precipitation and ground-water discharge to streams were the dominant inflow and outflow, respectively. Evapotranspiration of ground water from wetlands and non-wetland areas also were important losses from the hydrologic system. Water-supply withdrawals and infiltration to sewers averaged 5 and 1.3 percent, respectively, of total annual out-flows and were larger components (12 percent in September) of the hydrologic system during low-flow months. Water budgets for individual tributary and main stem subbasins identified areas, such as the Fort Meadow Brook and the Assabet Main Stem Upper subbasins, where flows resulting from anthropo-genic activities were relatively large percentages, compared to other subbasins, (more than 20 percent in September) of total out-flows. Wastewater flows in the Assabet River accounted for 55, 32, and 20 percent of total nonstorm streamflow (base flow plus wastewater discharge) out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September.

The ground-water-flow models were used to evaluate water-management alternatives by simulating hypothetical scenarios of altered withdrawals and discharges. A scenario that included no water management quantified nonstorm stream-flows that would result without withdrawals, discharges, septic-system return flow, or consumptive use. Tributary flows in this scenario increased in most subbasins by 2 to 44 percent relative to 1997–2001 conditions. The increases resulted mostly from variable combinations of decreased withdrawals and decreased infiltration to sewers. Average annual nonstorm streamflow in the Assabet River decreased slightly in this scenario, by 2 to 3 percent annually, because gains in ground-water discharge were offset by the elimination of wastewater discharges.

A second scenario quantified the effects of increasing withdrawals and discharges to currently permitted levels. In this simulation, average annual tributary flows decreased in most subbasins, by less than 1 to 10 percent relative to 1997–2001 conditions. In the Assabet River, flows increased slightly, 1 to 5 percent annually, and the percentage of wastewater in the river increased to 69, 42, and 27 percent of total nonstorm streamflow out of the Assabet Main Stem Upper, Middle, and Lower subbasins, respectively, in an average September.

A third set of scenarios quantified the effects of ground-water discharge of wastewater at four hypothetical sites, while maintaining 1997–2000 wastewater discharges to the Assabet River. Wastewater, discharged at a constant rate that varied among sites from 0.3 to 1.5 Mgal/d, increased nonstorm streamflow in the tributaries adjacent to the sites and in down-stream reaches of the Assabet River. During low-flow months, flow increases in tributaries were less than the constant dis-charge rate because of storage effects and increased ground-water evapotranspiration. Average September flows, however, more than doubled in these scenarios relative to simulated 1997–2001 conditions in Fort Meadow, Taylor, Cold Harbor, and Stirrup Brooks. Increases in Assabet River flows were small, with reductions in the wastewater component of flow in September of 5 percent or less.

Simulation-optimization analysis was applied to the upper part of the basin to determine whether streamflow depletion could be reduced, relative to 1997–2001 conditions, by management of monthly withdrawals, with and without ground-water discharge. The analysis included existing supply wells, one new well (in use since 2001), and a hypothetical discharge site in the town of Westborough. Without ground-water discharge, simulated nonstorm streamflow in September in the Assabet River about doubled at the outlet of the Main Stem Headwaters subbasin and increased by about 4 percent at the outlet of the Main Stem Upper subbasin. These increases were obtained by using water-supply sources upstream of lakes, which appeared to buffer the temporal effect of withdrawals, in low-flow months, and by using water-supply sources adjacent to streams, which immediately affected flows, in high-flow months. With ground-water discharge, simulated flows nearly tripled at the outlet of the Assabet Main Stem Headwaters subbasin, increased by 18 percent at the outlet of the main stem Upper subbasin, and more than doubled in a tributary stream. The general principles illustrated in the simulation-optimization analysis could be applied in other areas of the basin where streamflow depletion is of concern.

CONTENTS

Abstract

Introduction

Purpose and Scope

Description of the Study Area

Previous Studies

Ground- and Surface-Water Resources

Geologic Setting

Hydraulic Properties

Ground-Water Flow

Recharge

Water Levels

Surface Water

Streamflow

Ponds and Wetlands

Water Use and Management

Water Supply and Consumptive Use

Wastewater Discharge and Return Flow

Simulation of Ground-Water Flow

Steady-State Numerical Model

Spatial Discretization

Boundary Conditions

Stresses

Recharge and Evapotranspiration

Water Withdrawals and Discharges

Hydraulic Properties

Model Calibration

Model-Calculated Water Budgets and Flows

Transient Numerical Model

Temporal Discretization and Initial Conditions

Boundary Conditions and Stresses

Hydraulic Properties

Model Calibration

Model-Calculated Water Budgets and Flows

Model Limitations

Evaluation of Ground-Water-Management Alternatives

Simulation of Altered Withdrawals and Discharges

Simulation of No Water Management

Simulation of Increased Withdrawals and Discharges

Simulation of Ground-Water Discharge of Wastewater

Hypothetical Discharge Site in the Fort Meadow Brook Subbasin

Hypothetical Discharge Site in the Taylor Brook Subbasin

Hypothetical Discharge Site in the Cold Harbor and Howard Brooks Subbasins

Hypothetical Discharge Site in the Stirrup Brook Subbasin

Summary of Scenarios of Ground-Water Discharge of Wastewater

Simulation-Optimization of Withdrawals, Discharges, and Streamflow Depletion

Methods

Simulation-Optimization of Withdrawals and Discharges in Westborough

Response Coefficients

Management-Model Application

Summary

Acknowledgments

References

Appendix 1: Estimated Average Monthly Streamflow, Nonstorm Streamflow, and Model-Calculated Average Monthly Nonstorm Streamflow at Measurement Sites in the Assabet River Basin, Eastern Massachusetts

Appendix 2: Model-Calculated Average Annual, March, and September Hydrologic Budgets for Subbasins in the Assabet River Basin, Eastern Massachusetts

Appendix 3: Average Monthly Withdrawals and Discharges at Permitted Municipal and Nonmunicipal Water-Supply Sources and Wastewater-Treatment Facilities used in the Calibrated Transient Model to Simulate Average 1997–2001 Conditions and in a Scenario of Increased Withdrawals and Discharges in the Assabet River Basin, Eastern Massachusetts

FIGURES

1–3.Maps showing:

1.The Assabet River Basin, subbasins, streamflow-gaging stations, and long-term observation well, eastern Massachusetts

2.Surficial geology of the Assabet River Basin

3.Depth-weighted hydraulic conductivity from well logs and transmissivity zones in stratified glacial deposits in the Assabet River Basin

4, 5.Graphs showing:

4.Monthly mean precipitation for long-term average conditions and for 1997–2002 at National Oceanic and Atmospheric Administration weather stations in Bedford and West Medway

5.Monthly recharge rates estimated from A, streamflow records at the Assabet River streamflow-gaging station in Maynard; B, streamflow records at the Nashoba Brook streamflow-gaging station; and C, climate data from Bedford and West Medway weather stations, for long-term average conditions and 1997–2001

6.Map showing streamflow-measurement sites, observation wells, and pond- measurement sites in the Assabet River Basin

7–12.Graphs showing:

7.Monthly and daily average water levels at long-term observation well ACW158, Assabet River Basin

8.Measured water levels, September 2001 through December 2002, and estimated average monthly water levels, 1997–2001, at selected observation wells in the Assabet River Basin

9.Monthly mean streamflow for long-term average conditions and daily mean streamflow, 1997–2001: A, Assabet River streamflow-gaging station at Maynard; B, Nashoba Brook streamflow-gaging station near Acton

10.Instantaneous streamflow measurements, June 2001 through December 2002, and estimated mean monthly streamflow and nonstorm streamflow at selected flow-measurement sites in the Assabet River Basin

11.Measured water levels, September 2001 through December 2002, at selected ponds and impoundments in the Assabet River Basin

12.Schematic diagram showing water use and return flows in the Assabet River Basin

13, 14.Maps showing:

13.Public-water and sewer systems in the Assabet River Basin

14.Permitted water-supply withdrawals and wastewater discharges in the Assabet River Basin

15.Graph showing monthly average permitted withdrawals, wastewater discharges, and imported water for public supply, 1997–2001, in the Assabet River Basin

16, 17.Maps showing:

16.Areas of private-water supply with consumptive water use and areas of public-water supply with septic-system return flow in the Assabet River Basin

17.Model area, grid, hydraulic conductivity zones, and simulated ponds, streams, water withdrawals and surface-water inflows for ground-water-flow models of the Assabet River Basin

18.Diagram showing vertical discretization for ground-water-flow models of the Assabet River Basin

19.Relation between observed and model-calculated A, ground-water levels; and B, nonstorm streamflow for average conditions, 1997–2001, for the steady-state ground-water-flow model of the Assabet River Basin

20.Map showing model-calculated steady-state water table in the Assabet River Basin

21.Graph showing model-calculated average annual inflows to and outflows from the surficial layer of the simulated ground-water-flow system in subbasins of the Assabet River Main Stem and tributary subbasins, 1997–2001, Assabet River Basin

22.Map showing anthropogenic outflows relative to total model-calculated average A, annual; and B, September outflows from the simulated ground-water-flow system in subbasins of the Assabet River Basin

23, 34.Graphs showing:

23.Model-calculated components of average annual nonstorm streamflow in subbasins of the Assabet River Main Stem, 1997–2001

24. Model-calculated average annual total nonstorm streamflow and the component of flow that originated as wastewater, for existing conditions and two hypothetical scenarios of altered withdrawals and discharges in the Assabet River Basin

25.Monthly average recharge rates and rates of evaporative loss of ground water for the transient ground-water-flow model of the Assabet River Basin

26.Model-calculated and observed water-level fluctuations during the average annual cycle for selected observation wells and ponds in the Assabet River Basin

27.Model-calculated and observed mean monthly nonstorm streamflow at the A, Assabet River at Maynard; and B, Nashoba Brook near Acton streamflow-gaging stations on the Assabet River, Assabet River Basin

28.Model-calculated and observed mean monthly nonstorm streamflow at flow- measurement sites on the A, Assabet River; and B, tributaries, Assabet River Basin

29.Observed and model-calculated monthly nonstorm streamflow for the calibrated transient model and for several alternative model parameters at the Assabet River at Maynard and a selected tributary site in the Assabet River Basin. Horizontal and vertical hydraulic conductivity of stratified glacial deposits multiplied and divided by 2 for the A, Assabet River at Maynard and B, Cold Harbor Brook; horizontal and vertical hydraulic conductivity of till multiplied and divided by 2 for the C, Assabet River at Maynard and D, Cold Harbor Brook; storage property of stratified glacial deposits increased and decreased by 50 percent for the E, Assabet River at Maynard and F, Cold Harbor Brook; recharge fluctuations during the annual cycle and evapotranspiration rate in wetlands and nonwetland areas decreased by 50 percent for the G, Assabet River at Maynard and H, Cold Harbor Brook

30.Model-calculated average A, March; and B, September inflows to and outflows from the surficial layer of the simulated ground-water-flow system in subbasins of the Assabet River Main Stem and tributary subbasins, 1997–2001, Assabet River Basin

31.Model-calculated components of average A, March; and B, September nonstorm streamflow in subbasins of the Assabet River Main Stem

32.Model-calculated average A, March and B, September total nonstorm streamflow and the component of streamflow that originated as wastewater, for existing conditions and two hypothetical scenarios of altered withdrawals and discharges in the Assabet River Basin

33.Model-calculated average A, annual; B, March; and C, September nonstorm streamflow from subbasins of the Assabet River Main Stem and tributaries for comparison with minimum streamflow requirements for the protection of aquatic habitat

34.Model-calculated changes, relative to simulated 1997–2001 conditions, in average annual inflows to and outflows from the surficial layer of the simulated ground- water-flow system in subbasins of the A, Assabet River Main Stem; and B, tributary subbasins, in a hypothetical scenario of no anthropogenic water management in the Assabet River Basin

35.Map showing changes in sewer lines and areas of septic-system return flow simulated in a hypothetical scenario of increased withdrawals and discharges in the Assabet River Basin

36, 37.Graphs showing:

36.Model-calculated changes, relative to simulated 1997–2001 conditions, in average annual inflows to and outflows from the surficial layer of the simulated ground-water-flow system in subbasins of the A, Assabet River Main Stem; and B, tributary subbasins, in a hypothetical scenario of increased withdrawals and discharges in the Assabet River Basin

37.Model-calculated components of average A, March; and B, September nonstorm streamflow in subbasins of the Assabet River Main Stem, in a hypothetical scenario of increased withdrawals and discharges in the Assabet River Basin

38.Map showing hypothetical ground-water discharge sites for wastewater used in simulations in the Assabet River Basin: A, Fort Meadow Brook subbasin in Hudson; B, Taylor Brook subbasin in Maynard; C, Cold Harbor and Howard Brooks subbasin in Northborough; and D, Stirrup Brook subbasin in Westborough

39, 40.Graphs showing:

39.Model-calculated average annual, March, and September nonstorm streamflow in tributaries to the Assabet River for existing conditions and scenarios of hypothetical ground-water discharge of wastewater at four sites in the Assabet River Basin: A, Fort Meadow Brook ; B, Taylor Brook; C, Cold Harbor Brook; and D, Stirrup Brook

40.Monthly withdrawal and discharge rates for 1997–2001 and for the management-model applications for decreased streamflow depletion in the Assabet River and tributaries in low-flow months in the upper part of the Assabet River Basin: A. OPT1; B, OPT2; C, OPT3; D, OPT4; E, OPT5; F, OPT6; and G, 1997–2001

TABLES

1.Hydraulic properties of stratified glacial deposits as determined by analysis of aquifer tests at public-supply wells in the Assabet River Basin, eastern Massachusetts

2.Average annual recharge rates and precipitation for the Assabet River Basin

3.Characteristics and water levels at observation wells and ponds in the Assabet River Basin

4.Characteristics and water levels at long-term observation wells near the Assabet River Basin

5.Drainage-area characteristics and mean annual flows at streamflow-gaging stations in and near the Assabet River Basin

6.Drainage-area characteristics and mean annual flows at streamflow-measurement sites in the Assabet River Basin

7.Population on public water and sewer and per capita water use in the Assabet River Basin, 2000

8.Permitted water-supply withdrawals and wastewater discharges in the Assabet River Basin

9.Existing (1997-2001) and permitted withdrawals for municipal public-water systems in the Assabet, Sudbury, and Concord River Basins

10.Simulated water withdrawals and discharges in calibrated models (1997–2001) and in scenario 2 for permitted withdrawals and wastewater discharges and unpermitted golf-course withdrawals in the Assabet River Basin

11.Steady-state model-calculated average annual water levels and observed water levels at observation wells and ponds in the Assabet River Basin

12.Steady-state model-calculated average annual nonstorm streamflow and observed nonstorm streamflow at measurement sites in the Assabet River Basin

13.Steady-state model-calculated average annual water budget for the Assabet River Basin

14.Water-level-fluctuation residuals and mean absolute-flow residuals for the calibrated transient model and model runs that use alternative model parameters, Assabet River Basin

15.Transient model-calculated average March and September water budgets for the Assabet River Basin

16.Model-calculated mean monthly nonstorm streamflows for August and September at sites for comparison with minimum streamflow requirements for habitat protection, Assabet River Basin

17.Model-calculated nonstorm streamflow from subbasins in the Assabet River Basin for existing conditions (1997-2001) and two scenarios of altered water-management practices

18.Hypothetical ground-water discharge sites for wastewater used in simulations in the Assabet River Basin

19.Hydrologic response coefficients for the public-supply wells and a hypothetical ground-water-discharge site in the upper Assabet River Basin

20.Model-calculated average monthly nonstorm streamflow, 1997-2001, and changes in monthly average nonstorm streamflow determined by solutions to management models in the upper Assabet River Basin


AVAILABILITY

This report is presented in Portable Document Format (PDF).

To view and print report you will need to use PDF Viewer or Adobe Acrobat Reader (available as freeware)

Users with visual disabilities can visit this site for conversion tools and information to help make PDF files more accessible

 

Printable tabloid cover (21.4 MB)--1 page

Left inside cover (14 KB)--1 page

Right inside cover (22 KB)--1 page

Table of contents (317 KB)--8 pages

Report's main body (17 MB)--94 pages

Appendixies (4.28 MB)--40 pages

Whole report (10.4 MB)--142 pages

Errata

 

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

DeSimone, L.A., 2004, Simulation of ground-water flow and evaluation of water-management alternatives in the Assabet River Basin, eastern Massachusetts: U.S. Geological Survey Scientific Investigations Report 2004-5114, 133 p.


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


U.S. Department of the Interior, U.S. Geological Survey
Persistent URL: http://pubs.water.usgs.gov/sir20045114
Page Contact Information: GS Pubs Web Contact
Last modified: Thursday, January 10 2013, 06:31:52 PM
FirstGov button  Take Pride in America button