Applications of Precipitation-Runoff Modeling System (PRMS) in Groundwater Studies

Georgina King gave this presentation at the Groundwater Resources Association of California 21st Annual Conference and Meeting October 4, 2012.

Applications of Precipitation-Runoff Modeling System (PRMS) in Groundwater Studies

Georgina King, PG, CHg, and Cameron Tana, PE

Water purveyors in the Soquel-Aptos basin, Santa Cruz County, California need recharge estimates to assist them making groundwater management decisions. Specific decisions are related to pumping curtailments during low rainfall periods, planning for recharge impacts due to future land use changes, and effects of shifting pumping closer to recharge areas. The USGS’s Precipitation-Runoff Modeling System (PRMS) was selected as the tool to determine the rainfall-recharge relationship for the basin, and thus be used to estimate the amount of recharge likely from available rainfall data. The model can also be used to identify or map areas of recharge.

PRMS simulates streamflow from precipitation, after evapotranspiration, and groundwater recharge are accounted for. Model input is daily climatic data: precipitation and temperature. Hydrologic and physical characteristics are assigned to the model area. Calibration using average monthly solar radiation, potential evapotranspiration, and daily streamflow as targets improved model credibility.

The deep recharge results from the PRMS model are also being used as the recharge input to a MODFLOW model for Central Water District, which pumps from the Aromas area of the Soquel-Aptos basin. The MODFLOW model will be used to evaluate shifting pumping inland closer to recharge areas in order to address water quality issues. MODFLOW estimates of stream percolation will be used to evaluate the uncertainty introduced by using PRMS and MODFLOW in sequence as opposed to coupling PRMS and MODFLOW in a GSFLOW model.

Leave a Reply