A survey on spatial and temporal variations of groundwater quality and quantity in Sarayan plain in south Khorasan province

Nowadays, due to water scarcity in the country, especially in arid and semi-arid areas, optimal management of groundwater resources is necessary. This study investigates the quality and quantity of underground water of the Sarayan plain in the northwest of South Khorasan Province in a 14-year period (1998-2012) using statistical methods. The number of samples studied included 20 wells, six qanats and three springs. Then, using GS software, appropriate statistical methods were selected. Results showed that Kriging method was suitable for zoning of the factors. Using interpolation methods, appropriate spatial maps for each of the groundwater quality parameters (EC, TDS, and SAR) were obtained in three years (beginning, middle and end of the fourteen-year period). The results of the spatial variations of the TDS and SAR showed that the reduction of these two parameters was more severe in the middle and southern parts of the study area. To evaluate changes in groundwater depth in the plains, the depth maps of the ground water resources were prepared during the study period by the use of the results of measuring the depth of water in each of the observation wells. Results showed that in 1998, in the eastern and southern plains, the water was at a closer distance to the ground and with the advance toward the West and especially to the north, water was available in deeper parts of the ground. In the study area, the average amount of rainfall is less than the average amount of the whole of Iran and groundwater resources in agricultural water supply plays a fundamental role. Therefore, the sustainability of water resources is affected by sustainable management of underground water resources in the agricultural sector.