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Great Valley Water Resources Science Forum October 7, 2009

Understand watershed hydrologic processes, water availability, and climate links with the GSFLOW model. Simulate flow rates, storage volumes, and hydrologic responses to land use change and climate conditions. Enhance modeling capabilities for groundwater and surface water interactions.

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Great Valley Water Resources Science Forum October 7, 2009

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  1. GSFLOW Coupled Groundwater/Surface-Water Model: Background and Possible Applications in the Great Valley Great Valley Water Resources Science Forum October 7, 2009

  2. Why was GSFLOW developed? • To improve our ability to simulate and understand • Watershed hydrologic processes and water availability • Links between hydrologic processes and climate, vegetation, land uses, water-supply development, and ecology

  3. Uses of GSFLOW • Determine flow rates and storage volumes of water throughout a watershed—from the tree canopy to deep aquifers: • Evaporation and plant transpiration • Soil infiltration and interflow • Snowpack generation and depletion • Groundwater recharge • Streamflow generation

  4. Components of Streamflow for a Year of Below-Average Precipitation, Sagehen Creek, Truckee, CA

  5. Uses of GSFLOW • Simulate both low-flow (baseflow and drought) and high-flow (storm) conditions within a watershed

  6. 28 25 Maximum Temperature, degrees C 22 19 16 2019 2025 2031 2037 2043 2049 2055 2061 2067 2073 2001 2007 2013 2079 2085 2091 2097 Uses of GSFLOW • Simulate hydrologic response to changing land uses, population growth, and possible future climate conditions Projected average maximum daily temperature, Tahoe Basin, California and Nevada

  7. What is GSFLOW?A Basin-Scale Model Based on the USGS PRMS Watershed Model and MODFLOW Groundwater Flow Model

  8. Enhanced Modeling Capabilities Developed for GSFLOW • Unsaturated-zone flow below soils, streams, and lakes Flow, storage, and ET in the unsaturated zone and recharge to the water table in response to infiltration at land surface

  9. Enhanced Modeling Capabilities Developed for GSFLOW • Enhanced soil-zone dynamics (capillary, gravity-flow, and preferential-flow reservoirs) • Enhanced streamflow simulation

  10. Some of the Hydrologic Processes Simulated • Potential ET • Canopy interception • Snowpack accumulation, melting, sublimation • Surface-water runoff • Interflow • Infiltration to soil zone • ET within soil zone • 1-D Unsaturated-zone flow, storage, and ET • 3-D Groundwater flow • Streamflow • Lakes

  11. Climatic and Hydrologic Drivers • Precipitation • Air Temperature • Solar radiation • Groundwater withdrawals • Groundwater flow and water-level conditions along boundary of simulated area

  12. Spatial Discretization—PRMS hydrologic response units (HRUs) are intersected with MODFLOW finite-difference cells Sagehen Creek watershed, Truckee, CA

  13. Some Important Design Criteria for GSFLOW Development • Calculate and provide detailed water-budget information for the various hydrologic processes in both space and time • Ensure that the model conserves mass • Allow simulations using only PRMS or MODFLOW to facilitate initial calibration of model parameters prior to a full GSFLOW (coupled-model) simulation

  14. Initial GSFLOW Applications by the USGS • Trout Lake Watershed, WI • Black Earth Creek Watershed, WI • Spring Creek Watershed, PA • Incline Basin near Lake Tahoe, Nevada • Walker Lake Watershed, NV • Santa Rosa Plain, northern CA • Rialto-Colton Basin, southern CA

  15. Possible Applications in the Great Valley

  16. Opequon Creek Watershed Link the transient groundwater-flow model of Opequon Creek watershed with a PRMS model Opequon Creek

  17. Benefits • Improved representation of hydrologic processes in the watershed and links among land-surface, subsurface, and surface-water hydrologic systems • Improved water budgets throughout all hydrologic components of the watershed

  18. Data Considerations • Climate inputs: • Daily precipitation and air-temperature data • Land-surface processes: • Evapotranspiration • Canopy interception • Snowpack dynamics • Surface runoff • Soil-zone processes

  19. Data Considerations • Streamflow and Springs • Subsurface processes: • Unsaturated-zone flow • Groundwater flow, including wells

  20. Discretization of Watershed:PRMS HRUs could be coincident with MODFLOW cells, but not required

  21. Calibration Considerations • A multistep process: • PRMS transient (daily) calibration • MODFLOW steady-state calibration • Coupled GSFLOW transient (daily) calibration • Calibration data: • Streamflow • Groundwater levels

  22. GSFLOW Code and Documentation Report Available online: • USGS Water Resources Groundwater Software webpage • http://water.usgs.gov/software/lists/groundwater/

  23. Questions?

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