Geostatistical Assessment of spatial and temporal variations of ground water quality parameters in Qorveh and Dehgolan SouthPlain

In recent years, overuse of ground waters has led to a significant decrease in water levels and has also reduced groundwater quality. Therefore, qualitative analysis of ground water reservoirs is deemed necessary to manage exploitation of these resources and determine the most optimal and economic cropping patterns. Geostatistical methods are the most widely used and appropriate tools for monitoring qualitative variables. In this regard, the spatial variations of qualitative variables such as Na+, TH, EC, SAR, Cl-, SO42-, Mg2+, PH, TDS and K+driven from 70 wells on aquifers of Ghorveh and Dehgolan Plain located in Kurdistan province were studied. The statistical period of the data used in this study covers the years 1984-2012. After analyzing the variogram by GS+ software, data interpolation was performed using three methods of ordinary kriging, simple kriging, and inverse distance weighing with the powers of 1, 2 and 3, respectively. The results shows that the omni-directional semivariogram for all variables is nearly identical. The results also indicate that using ordinary kriging and simple kriging methodscause fewer errors in estimating most qualitative variables. The values of mean error (ME) statistics in the kriging method are close to zero, indicating the least bias in estimations. Also, water quality was classified in terms of Schuler and Will Cox terms methods, so that the results reveal that most of the wells are within an optimal range, yet a few are in medium and bad ranges. Zoning results demonstrated that groundwater quality in the western, southern, and southeastern zones is better than those of other sectors. Thus, it is necessary for management to reduce consumption and change cropping patterns to improve water quality in areas with poor water quality.