EFFECTS OF DROUGHT AND GROUND-WATER PUMPING ON GROUND WATER AND STREAM BASEFLOW IN THE FRENCH CREEK BASIN, CHESTER COUNTY, PENNSYLVANIA

This project is being done in cooperation with the Delaware River Commission.




NEED FOR THE PROJECT

The Delaware River Basin is a 13,500-square-mile watershed comprised of parts of Delaware, New Jersey, New York, and Pennsylvania. The Delaware River Basin Commission (DRBC) is a federal/interstate agency with regulatory authority over water resources in the basin. The DRBC reviews water resource projects and issues permits for withdrawals of surface and ground water. In response to concerns over increasing use of ground water in an area with limited ground-water resources, the DRBC established in 1980 the Southeastern Pennsylvania Ground Water Protected Area (GWPA), which covers about 1,250 square miles. Special regulations were issued by the DRBC for the GWPA to provide for the effective management of ground-water resources, protect the rights of present and future water users, and acquire additional information to more accurately plan and manage water resources. As demand for use of limited water resources increases in the near future, water allocations may be subject to conjunctive use and conservation requirements established in the GWPA. The permitting process will become more involved at that point, requiring analyses of the combined impacts of withdrawals on surface water and ground water.

The effects of pumping ground water on ground-water availability and streamflow during low-flow conditions have not been quantified; hence, management decisions can be based on only simple comparisons between pumping rates and estimated baseflow. Questions such as the impact of drought duration and antecedent hydrologic conditions on recession during drought cannot be addressed. Furthermore, the effect of proposed expansion of ground-water pumping cannot be adequately predicted using available information.

PROJECT OBJECTIVES

The objective of this study is to develop a quantitative understanding of the relationship between ground water and surface water. To accomplish this, a numerical model of ground-water flow will be developed for the French Creek Basin in Chester County, Pennsylvania. The two-dimensional flow model will be capable of simulating current conditions and potential long-term ground-water pumping and will quantify the impact of pumping on water levels, ground-water availability, and stream baseflow. The model also will simulate the impact of reduced recharge caused by drought on ground-water levels and baseflow.



APPROACH USGS will construct, calibrate, and document application of a two-dimensional ground-water-flow model that will simulate surface-water baseflow in the French Creek Basin. The model area will extend beyond the surface-water basin of French Creek to account for ground-water flow between adjacent subbasins. The model will be constructed using available Geographic Information Systems (GIS) datasets through a model preprocessor with shapefile import capabilities.

Model calibration will be based on long-term steady-state conditions approximated by available water budgets, water-table maps, and results of aquifer tests, where available. Streamflow data from the streamflow-measurement station, French Creek near Phoenixville (USGS station 014725157, drainage area 59.1 square miles, period of record October 1968 to current date), also will be used in constraining the transient hydraulic properties of the aquifer system. Calibration will use a stepwise procedure that minimizes the sum of model errors by changing model parameters such as hydraulic conductivity and recharge based on measured water levels and streamflow at multiple locations in the basin.

The calibrated model will be used to simulate long-term hydrologic characteristics of the basin including a water budget and spatial distribution of streamflow. Transient simulations will be used to illustrate the long-term response of stream baseflow and ground-water levels to modified recharge conditions representing drought. The model will be used to illustrate the effects of new or increased ground-water pumping on stream baseflow and ground-water levels for a limited number of hypothetical well locations.

Available information for the French Creek Basin will be compiled, reviewed, and summarized. These data include streamflow data, water-level data, and hydraulic testing results. Some additional data will be necessary for an analysis of the response of the streams to potential ground-water pumping. These additional data include:

• Stream gains and losses. Streamflow-discharge measurements (seepage investigations) at two separate times (one at high baseflow, one at low baseflow) are necessary to provide information on ground-water discharge to streams in specific subbasins.
  
• Water levels. At the same time the seepage investigations are made, water levels in selected wells in the French Creek Basin will be measured.
  

Return to the USGS Chester County Water Resources Page

Return to the Water Resources of Pennsylvania Home Page
or go directly to:





The URL for this page is http://pa.water.usgs.gov/malvern/french_creek.html

Please note our privacy statement and disclaimer
Accessibility