Spatial and Temporal Analysis of Groundwater Level Fluctuations in deep and shallow aquifers of Golestan province using nonparametric statistical tests in GIS environment

Groundwater as one of the valuable resources all over the world is unfortunately facing a great decline of aquifer level during past decades cused by its overexploitation beside the decrease of precipitation. This reduction is more in arid and semi-arid climatic zones where the most part of irrigation requirement is supplied through wells. Therefore, the monitoring of the spatio-temporal variation of aquifer water table would be necessary. In this study, shallow and deep aquifers of Golestan province were considered as case study. Non-parametric tests including Mann-Kendall, Sen’s slope and Pitite were used for analysis of recorded time series between years of 1990 to 2016 in 277 piezometric stations. The results were interpolated in GIS enviroment. In this study, the pattern and trends of groundwater level data were investigated. Results showed the aquifer groundwater level has a decreasing trend in most of the areas but in shallow aquifers along with the decreasing trend, an increasing trend has been observed in some places. In shallow aquifers, the slope of the trend line is in accordance with groundwater flow direction but there is no regular pattern in deep aquifer. The decreasing trendline of groundwater variation in deep aquifer is more than 8 percent. This aquifer has worst conditions about groundwater depletion than the shallow aquifer and this may be due to overexploitation of the aquifer and the failure of fast replacement. Also result showed that all three nonparametric tests were highlighted these variations and are following the same pattern.