Wellhead Protection Area Delineation Using the Analytic Element Method

Abstract

Wellhead protection areas (WHPAs) were delineated around three water supply wells in Urmia Plain, Urmia City, Iran. WhAEM2000 (V.2.1.0) computer model based on the analytic element method was used and two years time of travel WHPAs were delineated for pumping wells drilled in the basin of Shahr-Chai River located in Urmia Plain. The steady-state flow was applied for unconfined aquifer. This feature included the main surface water features (rivers and lake), recharge rate due to precipitation, irrigation and periodical tributaries, and inhomogeneity to represent the western area of the plain, having different characteristics. The model was subsequently calibrated by means of the observed piezometric heads as test points. In confined aquifer the groundwater does not have interaction with the surface waters and no recharge penetrates into the aquifer. Hence, uniform flow was applied to create a new model. In confined model two parameters (hydraulic gradient and direction of the flow) were then evaluated using three points method. To overcome uncertainties related to the aquifer parameters and lack of sufficient piezometric data, the parameters sensitivity analysis and the hypothesis testing method were used and the final WHPAs were reasonably delineated for the wells. Results showed that the shapes of the WHPAs for wells in unconfined aquifer are longer and narrower than those in confined aquifer.