Effects of land-use changes and ground-water withdrawals on stream base flow, Pocono Creek watershed, Monroe County, Pennsylvania

Dates

Year: 2007

Citation

Sloto, Ronald A. , 2007, Effects of land-use changes and ground-water withdrawals on stream base flow, Pocono Creek watershed, Monroe County, Pennsylvania: "Pennsylvania Water Science Center , GGENLL0000".

Summary

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 [...]

Summary

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.

Contacts

Author :: Sloto, Ronald A.
Publisher :: "Pennsylvania Water Science Center , GGENLL0000"

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Web Link	http://pubs.usgs.gov/sir/2008/5030/

Effects of land-use changes and ground-water withdrawals on stream base flow, Pocono Creek watershed, Monroe County, Pennsylvania

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