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Simulated Water Budgets and Ground-Water/Surface-Water Interactions in Bushkill and Parts of Monocacy Creek Watersheds, Northampton County, Pennsylvania--A Preliminary Study with Identification of Data Needs

U.S. Geological Survey Open-File Report 2006-1143

By Dennis W. Risser


This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

View the full report in PDF 5.5 MB

ABSTRACT

This report, prepared in cooperation with the Department of Environmental Protection, Office of Mineral Resources Management, provides a preliminary analysis of water budgets and generalized ground-water/surface-water interactions for Bushkill and parts of Monocacy Creek watersheds in Northampton County, Pa., by use of a ground-water flow model. Bushkill Creek watershed was selected for study because it has areas of rapid growth, ground-water withdrawals from a quarry, and proposed stream-channel modifications, all of which have the potential for altering ground-water budgets and the interaction between ground water and streams.

Preliminary 2-dimensional, steady-state simulations of ground-water flow by the use of MODFLOW are presented to show the status of work through September 2005 and help guide ongoing data collection in Bushkill Creek watershed. Simulations were conducted for (1) predevelopment conditions, (2) a water table lowered for quarry operations, and (3) anthropogenic changes in hydraulic conductivity of the streambed and aquifer. Preliminary results indicated under predevelopment conditions, the divide between the Bushkill and Monocacy Creek ground-water basins may not have been coincident with the topographic divide and as much as 14 percent of the ground-water discharge to Bushkill Creek may have originated from recharge in the Monocacy Creek watershed. For simulated predevelopment conditions, Schoeneck Creek and parts of Monocacy Creek were dry, but Bushkill Creek was gaining throughout all reaches.

Simulated lowering of the deepest quarry sump to an altitude of 147 feet for quarry operations caused ground-water recharge and streamflow leakage to be diverted to the quarry throughout about 14 square miles and caused reaches of Bushkill and Little Bushkill Creeks to change from gaining to losing streams. Lowering the deepest quarry sump to an altitude of 100 feet caused simulated ground-water discharge to the quarry to increase about 4 cubic feet per second. Raising the deepest sump to an altitude of 200 feet caused the simulated discharge to the quarry to decrease about 14 cubic feet per second.Decreasing the hydraulic conductivity of the streambed of Bushkill Creek in the reach of large losses of flow caused simulated ground-water levels to decline and ground-water discharge to a quarry to decrease from 74 to 45 cubic feet per second.

Decreasing the hydraulic conductivity of a hypothesized highly transmissive zone with a plug of relatively impermeable material caused ground-water levels to increase east of the plug and decline west of the plug, and decreased the discharge to a quarry from 74 to 53 cubic feet per second. Preliminary results of the study have significant limitations, which need to be recognized by the user. The results demonstrated the usefulness of ground-water modeling with available data sets, but as more data become available through field studies, a more complete evaluation could be conducted of the preliminary assumptions in the conceptual model, model sensitivity, and effects of boundary conditions. Additional streamflow and ground-water-level measurements would be needed to better quantify recharge and aquifer properties, particularly the anisotropy of carbonate rocks. Measurements of streamflow losses at average, steady-state hydrologic conditions could provide a more accurate estimate of ground-water recharge from this source, which directly affects water budgets and contributing areas simulated by the model.

Table of Contents

Abstract
Introduction
     Purpose and Scope
     Previous Investigations
     Hydrogeologic Setting
     Available Data
          Water-Level Measurements
          Discharge Measurements
Simulated Water Budgets and Ground-Water/Surface-Water Interactions
     Conceptual Model
     Model Development
          Computer Code and Grid
          Boundary Conditions
               Recharge from Precipitation
               Streams
               Quarry
               Wells
          Aquifer Properties
     Model Adjustments
          Weighting of Measurements
          Adjusted Model Parameters
     Preliminary Results of Model Simulations
          Predevelopment Conditions
          Effects of a Water Table Lowered for Quarry Operations
          Effects of Changes in Hydraulic Conductivity
               Streambed Hydraulic Conductivity
               Highly Transmissive Zone
               Horizontal Anisotropy Ratio
     Assumptions and Limitations of the Preliminary Model
Suggestions for Future Data Collection
Summary
References Cited

This report is available online in Portable Document Format (PDF). If you do not have the Adobe Acrobat PDF Reader, it is available for free download from Adobe Systems Incorporated.

View the full report in PDF 5.5 MB

For more information about USGS activities in Pennsylvania contact:
Director
USGS Pennsylvania Water Science Center
215 Limekiln Road
New Cumberland, Pennsylvania 17070
Telephone: (717) 730-6960
Fax: (717) 730-6997
or access the USGS Water Resources of Pennsylvania home page at:
http://pa.water.usgs.gov/.



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