Groundwater is the main source for domestic and agricultural uses in Eghlid, a city in Fars province, southern Iran. In this study, the spatial and temporal changes of groundwater depth in 41 observation wells in Eghlid for wet and dry seasons during 1997, 2003 and 2010 were investigated using geostatistical approaches. The experimental semivariograms were calculated and modeled using GS+ software and the groundwater depth was interpolated by ordinary kriging (OK), simple kriging (SK) and inverse distance weighting (IDW) methods, within the GIS environment. Moreover, the fluctuation in groundwater depth during 13 years (from 1997 to 2010) in both wet and dry periods was calculated and mapped. Results showed that the depth to groundwater in Eghlid aquifer has a strong spatial correlation and the spatial structure follows a spherical model for three years. However, the spatial correlation distance is larger for both seasons in 1997 (greater than 27 Km) than 2003 (22 to 27 Km) and 2010 (23 to 25 km).
The cross-validation results indicated that OK having the lowest root mean square error (RMSE) and mean error (ME) was the most appropriate method for interpolating groundwater depth. Therefore OK was used to map the spatial distribution of depth to groundwater over the study area. The generated maps showed more spatial variability of groundwater depth for wet season than dry season for three years. Besides, depth to groundwater slower for wet seasons than dry seasons. Also the results indicated that the ground water depth is decreased slightly from 1997 to 2003; however there is a considerable drop (2-13m) from 2003 to 2010. Moreover the drop in groundwater is more obvious in the central toward west and southern parts of the aquifer. These regions are more critical and should be carefully managed for an optimum exploitation of the groundwater resources.
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