Estimation of the Effects of Land Use and Groundwater Withdrawals on Streamflow for the Pomperaug River, Connecticut
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Prepared in cooperation with the Pomperaug River Watershed Coalition and the Town of Woodbury, Connecticut Estimation of the Effects of Land Use and Groundwater Withdrawals on Streamflow for the Pomperaug River, Connecticut Scientific Investigations Report 2010–5114 U.S. Department of the Interior U.S. Geological Survey Cover. Photographs show views of the Pomperaug River in Southbury, Connecticut. (Photographs by Edward Edelson, Pomperaug River Watershed Coalition) Estimation of the Effects of Land Use and Groundwater Withdrawals on Streamflow for the Pomperaug River, Connecticut By David M. Bjerklie, J. Jeffrey Starn, and Claudia Tamayo Prepared in cooperation with the Pomperaug River Watershed Coalition and the Town of Woodbury, Connecticut Scientific Investigations Report 2010–5114 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2010 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment, visit http://www.usgs.gov or call 1-888-ASK-USGS For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Bjerklie, D.M., Starn, J.J., and Tamayo, Claudia, 2010, Estimation of the effects of land use and groundwater withdrawals on streamflow for the Pomperaug River, Connecticut: U.S. Geological Survey Scientific Investigations Report 2010–5114, 81 p., at http://pubs.usgs.gov/sir/2010/5114. iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................2 Purpose and Scope ..............................................................................................................................2 Description of the Watershed ......................................................................................................................3 Climate ....................................................................................................................................................5 Streamflow .............................................................................................................................................5 Groundwater ..........................................................................................................................................5 Land Use and Land Cover ....................................................................................................................6 Water Use ..............................................................................................................................................6 The Precipitation-Runoff Model ..................................................................................................................6 General Description of the Precipitation Runoff Modeling System (PRMS) ..............................9 Model Sensitivity and Uncertainty ...................................................................................................10 Representation of the Watershed—Hydrologic Response Units (HRUs) .................................10 Precipitation, Temperature, and Geographic Input Data .............................................................12 Parameterization and Calibration of the Model .............................................................................13 Water-Balance Considerations ...............................................................................................20 Climatic Variables—Precipitation, Temperature, and Evapotranspiration ......................21 Interception.................................................................................................................................22 Soil-Moisture Balance ..............................................................................................................23 Runoff .........................................................................................................................................23 Surface Runoff ..................................................................................................................23 Surface Runoff Generated from Variable-Source Areas ..................................23 Surface Runoff Generated from Impervious Surfaces ......................................24 Subsurface Runoff ............................................................................................................25 Groundwater Flow ............................................................................................................28 Channel Routing .........................................................................................................................29 Diversions....................................................................................................................................33 Calibration, Objective Functions, and Optimization ............................................................34 Model Results ......................................................................................................................................35 Streamflow and Water Balance ..............................................................................................35 Flow Components and Groundwater Recharge ...................................................................47 The Groundwater-Runoff Model (MODFLOW) ........................................................................................58 General Description of MODFLOW Developed for the Watershed ............................................58 Representation of the Watershed–Hydrogeology .........................................................................58 Streams, Transient Recharge, Pumping, and Diversions .............................................................59 Calibration and MODFLOW Simulation Results .............................................................................59 Base Flow to Streams ...............................................................................................................59 Losing Reaches ..........................................................................................................................62 Management Scenario Applications ........................................................................................................62 Effects of Land Use and Groundwater Withdrawal on Streamflow ...........................................62 Effects of Land Use and Groundwater Withdrawal on Recharge and Base Flow ...................69 Limitations .....................................................................................................................................................74 Summary and Conclusions .........................................................................................................................74 Acknowledgments .......................................................................................................................................75 References ....................................................................................................................................................76 iv Figures 1. Map showing location of the Pomperaug River watershed, Connecticut, showing weather stations and U.S. Geological Survey streamgages used in the study .................3 2. Map showing the Pomperaug River watershed, Connecticut, showing town boundaries, watershed boundaries of the two main tributaries (Weekeepeemee and Nonnewaug Rivers), streamgages, and location of coarse glacial stratified drift deposits in the watershed ...........................................................................................................4 3. Map showing the Pomperaug River watershed, Connecticut, showing hydrographic features and hydrologic response unit boundaries ..............................................................11 4. Bar graph showing annual precipitation totals for water years 1976 to 2005 spatially averaged from 12 surrounding National Weather Service coop stations ........................12 5. Maps showing (A) topographic relief (slope) of the watershed and (B) the mean topographic slope for each hydrologic response unit used in the Precipitation Runoff Modeling System model of the Pomperaug River watershed, Connecticut .....................14 6. Maps showing (A) distribution of coarse glacial stratified deposits in the watershed and (B) the fraction of coarse glacial stratified deposits in each hydrologic response unit used in the Precipitation Runoff Modeling System model of the Pomperaug River watershed, Connecticut ............................................................................................................15 7. Maps showing (A) the drainage