The volume of water available for groundwater recharge through the infiltration of surface runoff in Cold and Dry Creeks was estimated for a 100-year storm and the Probable Maximum Precipitation (PMP) of Skaggs and Walters (1981). A 100-year, 7-day design storm was developed from 40 years of precipitation data measured at the Hanford Meteorological Station (HMS). Runoff measured in Upper Cold Creek was used with HMS precipitation data to calculate curve numbers for the Soil Conservation Service rainfall-runoff model. The estimated water available for recharge from surface runoff produced by the 100-year storm is 3-6 times the annual recharge rate from direct infiltration of precipitation over the Hanford Site. Potential recharge from the PMP is 7-11 times the annual volume of direct recharge.iii
SummaryThe rate of groundwater movement in the uppermost unconfined aquifer beneath the Hanford Site to the Columbia River is dictated by an east to west head gradient in the aquifer. This gradient is in turn influenced by the amount and spatial distribution of recharge. The purpose of this study was to estimate the volume of water available for groundwater recharge from infiltration of surface runoff in Cold and Dry Creeks resulting from a 100-year, 7-day storm.The approach used to estimate potential recharge was to construct numerical models to simulate rainfall-runoff and channel recharge processes and use these models with a 100-year design storm as input. Specific tasks addressed in FY1999 included: 1) constructing a digital elevation model of the study area, 2) gaining an understanding of runoff generation to guide development of the design storm and numerical models, 3) developing an appropriate design storm using 40 years of precipitation data from the Hanford Meteorological Station, and 4) constructing a numerical rainfall-runoff model of Cold and Dry Creeks.The estimated water available for recharge from surface runoff produced by the 100-year storm is 3-6 times the annual recharge rate from direct infiltration of precipitation over the Hanford Site. Potential recharge from the PMP is 7-11 times the annual volume of direct recharge.v