Estimation of groundwater recharge by rainfall and irrigation using inverse method (Case study: Tavabe-e Arsanjan, Fars province, Iran)

Groundwater is one of the important water resources in Iran. Groundwater resources supply the main part of fresh water in many region of Iran, so it should be taken into account. In this study, inverse method is used to estimate the fraction of rainfall and irrigation which infiltrate and recharge the groundwater. The objective of this study was estimation of aquifer parameters based on considering unsaturated zone (vadose zone). This objective was examined by writing and developing an inverse code in C++ programming language along with forward model (HydroGeoSphere) as a numerical model for two observation wells of Tavabe-e-Arsanjan, Iran. The model was used to address two specific issues. First, it was used to estimate the hydraulic conductivity, porosity, fraction of rainfall and fraction of irrigation that recharge groundwater which were unknown parameters in the Tavabe-e-Arsanjan area, Fars provance. Second, the model was used for prediction of water table elevation. Results of automatic calibration showed that estimated parameters were in reasonable range. Statistical analysis showed that calibration was sensitive to all four parameters besides that the estimated parameters are not perfectly correlated which implies that the models were not over-parameterized. Comparison of predicted and measured water table elevation showed that estimated parameters work well.