Title

Groundwater Recharge Estimation Using Chloride Mass Balance Dry Creek Experimental Watershed

Publication Date

12-2006

Type of Culminating Activity

Thesis

Degree Title

Masters of Science in Hydrologic Sciences

Department

Geosciences

Major Advisor

Dr. James P. McNamara

Abstract

Estimates of groundwater recharge conducted via chloride mass balance application at multiple catchment scales within Dry Creek Experimental Watershed delineate both a percentage of annual precipitation partitioned to recharge and spatial variability within the recharge. Inclusion of stream flow discharge in the chloride mass balance equation further qualifies the recharge estimates as net groundwater recharge values representing water available to deeper mountain block groundwater flow paths. The estimate of annual precipitation partitioned to net groundwater recharge for the entire catchment, water year July 2004 through June 2005, is zero to 11%. However, application at multiple catchment scales within Dry Creek Experimental Watershed indicates as much as 22% of annual precipitation being partitioned to net groundwater recharge in higher elevation subcatchments during the same period. Results for the second study year, July 2005 through June 2006, were predominantly assessed as invalid due to mobilization of inter-annually stored unsaturated zone chloride. Spring and stream chloride concentration time-series data applied to hydro graph separation were utilized to determine the timing of unsaturated zone chloride mobilization and concurrent vertical and lateral transport toward bedrock infiltration and stream channels. Additionally, gain/loss analyses conducted using the stream chloride concentration time-series data provide evidence of stream flow loss to groundwater recharge. The contrasting results for water year 2004-2005 versus 2005-2006 emphasize caution necessary in addressing assumptions underlying application of chloride mass balance to recharge estimation and the need for careful delineation of an appropriate multi-annual period of integration toward an estimate of average annual groundwater recharge.

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