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| Publications— Scientific Investigations Report |
By Ronald A. Sloto
View the report in Portable Document Format (PDF) SIR 2008-5030 (2.63 MB)
The Pocono Creek watershed drains 46.5 square miles in eastern Monroe County, Pa. Between 2000 and 2020, the population
of Monroe County is expected to increase by 70 percent, which will result in substantial changes in land-use patterns. An
evaluation of the effect of reduced recharge from land-use changes and additional ground-water withdrawals on stream base
flow was done by the U.S. Geological Survey (USGS) in cooperation with the U.S. Environmental Protection Agency (USEPA)
and the Delaware River Basin Commission as part of the USEPA’s Framework for Sustainable Watershed Management Initiative.
Two models were used. A Soil and Water Assessment Tool (SWAT) model developed by the USEPA provided areal recharge values
for 2000 land use and projected full buildout land use. The USGS MODFLOW-2000 ground-water-flow model was used to estimate
the effect of reduced recharge from changes in land use and additional ground-water withdrawals on stream base flow.
This report describes the ground-water-flow-model simulations.
The Pocono Creek watershed is underlain by sedimentary rock of Devonian age, which is overlain by a veneer of glacial
deposits. All water-supply wells are cased into and derive water from the bedrock. In the ground-water-flow model, the
surficial geologic units were grouped into six categories: (1) moraine deposits, (2) stratified drift, (3) lake deposits,
(4) outwash, (5) swamp deposits, and (6) undifferentiated deposits. The unconsolidated surficial deposits are not used as
a source of water. The ground-water and surface-water systems are well connected in the Pocono Creek watershed. Base flow
measured on October 13, 2004, at 27 sites for model calibration showed that streams gained water between all sites measured
except in the lower reach of Pocono Creek.
The ground-water-flow model included the entire Pocono Creek watershed. Horizontally, the modeled area was divided into a
53 by 155 cell grid with 6,060 active cells. Vertically, the modeled area was discretized into four layers. Layers 1 and 2
represented the unconsolidated surficial deposits where they are present and bedrock where the surficial deposits are
absent. Layer 3 represented shallow bedrock and was 200 ft (feet) thick. Layer 4 represented deep bedrock and was 300 ft
thick. A total of 873 cells representing streams were assigned to layer 1.
Recharge rates for model calibration were provided by the USEPA SWAT model for 2000 land-use conditions. Recharge rates
for 2000 for the 29 subwatersheds in the SWAT model ranged from 6.11 to 22.66 inches per year. Because the ground-water-flow
model was calibrated to base-flow data collected on October 13, 2004, the 2000 recharge rates were multiplied by 1.18 so
the volume of recharge was equal to the volume of streamflow measured at the mouth of Pocono Creek. During model calibration,
adjustments were made to aquifer hydraulic conductivity and streambed conductance. Simulated base flows and hydraulic heads
were compared to measured base flows and hydraulic heads using the root mean squared error (RMSE) between measured and
simulated values. The RMSE of the calibrated model for base flow was 4.7 cubic feet per second for 27 locations, and the
RMSE for hydraulic heads for 15 locations was 35 ft.
The USEPA SWAT model was used to provide areal recharge values for 2000 and full buildout land-use conditions. The change
in recharge ranged from an increase of 37.8 percent to a decrease of 60.8 percent. The ground-water-flow model was used to
simulate base flow for 2000 and full buildout land-use conditions using steady-state simulations. The decrease in simulated
base flow ranged from 3.8 to 63 percent at the streamflow-measurement sites. Simulated base flow at streamflow-gaging
station Pocono Creek above Wigwam Run near Stroudsburg, Pa. (01441495), decreased 25 percent. This is in general agreement
with the SWAT model, which estimated a 30.6-percent loss in base flow at the streamflow-gaging station.
Additional ground-water withdrawals were simulated in the Scot Run and Cranberry Creek subwatersheds for 2000 and full
buildout land-use conditions. Hypothetical wells were added to each subwatershed to simulate additional ground-water
pumping. Combined simulated pumpage from the wells ranged from 50,000 to 1,000,000 gallons per day. All pumpage was
considered consumptive. In the Scot Run subwatershed, five hypothetical wells were placed close to the stream. With an
additional 1 Mgal/d (million gallons per day) of ground-water withdrawals, the simulated base flow of Scot Run decreased
35 percent under 2000 recharge conditions. Using the full buildout recharge rate, simulated base flow decreased 44 percent.
With this distribution of wells, the base flow of adjacent Transue Run was not be affected by ground-water withdrawals in
the Scot Run subwatershed.
In the Cranberry Creek subwatershed, three hypothetical wells were placed close to the surface-water divide between
Cranberry Creek and Bulgers Run, and three hypothetical wells were placed close to the surface-water divide between
Cranberry Creek and Laurel Lake Run. With an additional 1 Mgal/d of ground-water withdrawals, the simulated base flow of
Cranberry Creek decreased 14 percent, the simulated base flow of Bulgers Run decreased 15 percent, and the simulated base
flow of Laurel Lake Run decreased 48 percent under 2000 recharge conditions. Simulated pumping wells close to the
surface-water divide in the Cranberry Creek subwatershed had the least effect on the base flow of Cranberry Creek and the
greatest effect on the base flow of Bulgers Run. Using the full buildout recharge rate, the simulated base flow of
Cranberry Creek decreased 62 percent, the base flow of Bulgers Run decreased 61 percent, and the base flow of Laurel Lake
Run decreased 96 percent from 2000 levels.
Abstract
Introduction
Purpose and Scope
Description of Study Area
Previous Investigations
Geology
Bedrock Geology
Catskill Formation
Poplar Gap Member
Packerton Member
Long Run Member
Beaverdam Run Member
Walcksville Member
Towamensing Member
Trimmers Rock Formation
Mahantango Formation
Marcellus Formation
Surficial Geology
Outwash
Ice-Contact Stratified Drift
Lake Deposits
Swamp Deposits
Moraine Deposits
Hydrology
Water-Level Fluctuations
Ground-Water/Surface-Water Relations
Effect of Land-Use Changes and Ground-Water Withdrawals on Stream Base Flow
Surface-Water-Flow Model
Ground-Water-Flow Model
Model Description and Assumptions
Aquifer Hydraulic Conductivity
Recharge Rates
Pumping Rates
Simulation of Base Flow
Simulation of Hydraulic Head
Model Limitations
Effect of Land-Use Changes on Base Flow
Effect of Additional Ground-Water Withdrawals on Base Flow
Summary and Conclusions
Acknowledgments
References Cited
Suggested citation:
Sloto, R.A., 2008, Effects of land-use changes and ground-water withdrawals on stream base flow, Pocono Creek watershed,
Monroe County, Pennsylvania: U.S. Geological Survey Scientific Investigations Report 2008-5030, 38 p.
If you have Adobe® Acrobat® or Adobe® Acrobat®Reader® installed on your computer, you may view and print the PDF version of this report. Acrobat Reader, is a free download from Adobe Systems Incorporated.
View the report in Portable Document Format (PDF) SIR 2008-5030 (2.63 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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