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WASHINGTON STATE UNIVERSITY (2010)

ESTIMATING GROUNDWATER RECHARGE VIA SURFACE INFILTRATION IN COLD SEMI-ARID REGIONS

DEAN GARCIA LAURA

Titre : ESTIMATING GROUNDWATER RECHARGE VIA SURFACE INFILTRATION IN COLD SEMI-ARID REGIONS

Auteur : LAURA DEAN GARCIA

Université de soutenance : WASHINGTON STATE UNIVERSITY

Grade : MASTER OF SCIENCE IN ENVIRONMENTAL ENGINEERING 2010

Résumé
Aquifer recharge from infiltration of precipitation and snowmelt runoff is a key component of the overall subsurface water balance. Movement of water through the unsaturated zone down to the water table is considered to be governed by factors such as existing site conditions (including soils, topography, and vegetation cover), geology, and climate. Predicting the movement of water in cold, semi-arid regions prove more complex due to the strong differences in seasonal precipitation and sub-freezing top soil temperatures. Such climate can be observed in the Spokane Valley- Rathdrum Prairie (SVRP) aquifer, which is the region examined in this study. Numerical modeling of the Richards’ Equation with the UNSAT-H model is the method used to estimate flow through unsaturated soil, ultimately predicting groundwater recharge. UNSAT-H employs soil-water retention functions such as Brooks-Corey and van Genuchten to predict soil hydraulic properties needed to measure the recharge flux. This study compares candidate soil-water retention functions with field data collected at four SVRP watershed locations, determines the influence of variables in the soil-water retention functions for cold, semi-arid conditions, examines the climatological parameters and soil characteristics on vertical soil moisture distribution, and analyzes the spatial variation of recharge around the SVRP aquifer. The preferred method for modeling infiltration in cold, semi-arid conditions was determined to be the van Genuchten function. Results helped validate selection of the candidate soil-water retention function. The associated van Genuchten parameters determined for cold, semiarid conditions were found to be lower than that of normal conditions. Results also estimated the four watershed locations to have a ratio of recharge from precipitation within a range of 27%-50%. Three of the four watershed sites slightly overestimated recharge, particularly in the fall, exhibiting the difficulty in measuring the recharge flux in cold, semi-arid regions. The prediction of the recharge flux will ultimately help to understand and properly manage groundwater resources for current and future uses

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Page publiée le 12 décembre 2011, mise à jour le 6 mars 2019