Evaluation of Methods for Determining the Aquifer Hydrodynamic Coefficients based on Pumping Test in Fars Province

Hydrodynamic coefficients of aquifer are essential parameters in water resources studies such as water budget calculations and groundwater modeling. A small error in calculation of these coefficients causes large errors in water resources studies. The conventional methods such as Theis and Cooper - Jacob are generally used to estimate the hydrodynamic coefficients while theoretically, application of these methods produce considerable errors. In addition, wellbore storage and skin effect are usually ignored. In this research, pumping tests conducted in some of karst and alluvial aquifers in Fars Province were used. Although 52 pumping and observation wells were available only with respect to the completeness of the pumping test data, 20 pumping and observation wells were selected after checking accuracy of the data using diagnostic plots for evaluation of the methods for determining the aquifer hydrodynamic coefficients. In order to eliminate the error of wellbore storage and skin effect, the corresponding time interval was removed from the original drawdown-time data. This time intervals were identified using diagnostic plots. The results revealed that the errors of traditional analytical models in calculation of the hydraulic conductivity in the karst and unconfined alluvial aquifers were 88.22% and 76.09%, respectively. These models were only suitable for confined alluvial aquifers. Also wellbore storage and skin effect were identifiable in the large diameter pumping wells and in the other wells were ignorable.