FY 1999 Progress Report on: Potential Groundwater Recharge from the Infiltration of Surface Runoff in Cold and Dry Creeks

Abstract

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

Potential Groundwater Recharge from the Infiltration of Surface Runoff in Cold and Dry Creeks, Phase 2

“…The first value is the "probable maximum precipitation" from Skaggs and Walters (1981), and the latter three values from Wigmosta and Guensch (2005) correspond to a return period of 100 years. For comparison, the largest rainfall event during January 1995 was 1.02 inches over approximately 3 days.…”

“…For comparison, these recharge volumes are 7 to 14 times the average annual recharge rate for surface runoff estimated by Dinicola (1997), and fall between two estimates of direct recharge from infiltrating rainfall and snowmelt for the entire Hanford Site: 6,680 ac-ft/y (Fayer and Walters 1995) and 14,467 ac-ft/y (Jacobsen and Freshley 1990). The recharge volumes estimated here are less than half of those by Wigmosta and Guensch (2005) because that study used the entire Cold Creek basin down to the Yakima River as the area basis for computing runoff. Here, the focus was on recharge that originates tens of kilometers away and infiltrates in a relatively concentrated area on the Hanford Site.…”

“…Four hypothetical rainfall events were simulated: 6-hour probable maximum precipitation (PMP) from Skaggs and Walters (1981) and 100-year 24-hour, 100-year 3-day, and 100-year 7-day precipitation from Wigmosta and Guensch (2005). The PMP value is by far the largest, at 4.6 inches.…”

“…This source of groundwater recharge is of particular interest because of its role in maintaining the west-east hydraulic gradient in the unconfined aquifer between runoff events and temporarily increasing the gradient immediately after such events. In Phase 1 of this study, Wigmosta and Guensch (2005) estimated potential runoff from the Cold and Dry Creek basins using two hypothetical precipitation events and the Soil Conservation Service (SCS) curve number approach (Soil Conservation Service 1972). For the probable maximum precipitation over 6 hours (4.6 inches, [Skaggs and Walters 1981]), they estimated a runoff volume of 7 to 11 times the annual recharge, depending on assumed curve number.…”

“…The purpose of this phase 2 study was to extend the work of Wigmosta and Guensch (2005). First, weather and high-resolution runoff data from storm events during January 1995 were analyzed in greater detail.…”