COMPARISON OF DIFFERENT GEOSTATISTICAL METHODS TO ESTIMATE GROUNDWATER LEVEL AT DIFFERENT CLIMATIC PERIODS

S. M. Sadat Noori, K. Ebrahimi, A. M. Liaghat, University of Tehran, Iran

Abstract

The main aim of this study has been to assess the spatially variability of groundwater level at different climatic periods. The study area is Saveh-Nobaran aquifer in IRAN. Firstly using two drought indices, different climatic periods in the region including wet, normal and dry during 1993-2003 were recognized. The standardized precipitation index (SPI) which is one of the most high used drought indices, and the standard index of annual precipitation (SIAP) which has been proposed the best index for assessing drought in IRAN region have been compared. Secondly, with the use of measured elevations of the water table, experimental semivariograms were constructed that characterizes the spatial variability of the measured groundwater levels. Spherical, exponential and gaussian semivariogram models were fitted to the experimental semivariograms and it was found that the gaussian model was the best. Groundwater levels were interpolated by Kriging, Cokriging, TPSS and Inverse Distance Weighted (IDW) methods and with calculating RMSE, MAE and R2 it was found that Kriging, TPSS and IDW methods resulted in higher errors as compared to Cokriging method. The R2 coefficient obtained from Kriging, Cokriging, TPSS and IDW methods were 0.95, 0.97, 0.89, and 0.83, respectively. Finally, the Cokriging method was used to create groundwater level maps, including maximum, average and minimum water levels for each climatic period (wet, normal and dry). Results obtained from geostatistical analysis showed that groundwater depth varies spatially in different climatic conditions. The proposed method can be very helpful for decision makers in water resources management section to allocate groundwater resources in different climatic conditions.