Investigation of Qualitative Changes and Determination of Vulnerability Zone of Sari Plain Aquifer Using SI Model and Man-Kendall non-Parametric Test

Groundwater is one of the important sources of drinking water and agriculture in the northern regions of the country. Population increases and demand for agricultural products, especially rice, in the northern parts of the country have increased the utilization of water resources in the past decade. The aim of this study is investigation of Sari plain aquifer vulnerability using SI model and the qualitative changes of water resources using Mann-Kendall test and age slope diagram for the total cations and anions, TDS, EC, pH and SAR of 38 operation wells registered in Mazandaran province. Firstly, the changes of qualitative parameters were investigated from 2006 to 2018. Then, the maps of SI model parameters (groundwater depth, net recharge, aquifer media, topography and land use) rated and the weight map of each parameter was obtained. The results of Mann-Kendall test and age slope diagram showed that the P-value of SAR variable is significant but total cations and pH is less than 0.05. The coefficient of determination (R2) showed that the total cations, SAR and pH with values of 0.272, 0.249 and 0.235 have most related to the qualitative changes of groundwater resources in Sari plain. The age slope diagram also showed an ascending trend of the parameters. Finally, with the overlap of SI model parameters, most of the areas with moderate vulnerability risk (50.92) included the highest percentage of area. Validation results showed that, 57.19 percent and 0.67 percent of area has moderate and lowest overlap respectively.