Determining Vulnerability of the Rozeh Chay Aquifer in the Urmia Plain, Using the Combination Method of DRASTIC, SINSTAC and SI Indexes

The Rozeh Chay Plain is located on the western margin of the Urmia Lake. The shallow groundwater table, agricultural activities, and particularly the use of fertilizers and pesticides may lead to the groundwater contamination. Therefore, assessing the vulnerability can play a vital role in protecting and benefiting from this aquifer. Various data, including: DEM, land use, operation and observation wells and nitrate concentration of water samples analyses in May 2016 were used. Using the ArcGIS, the raster layers of groundwater depth, net recharge, hydraulic conductivity, topography, land use, unsaturated zones, aquifer and soil media were determined using the kriging interpolation method. These layers were integrated by ranking and weighting with the overlapping functions and the layers of DRASTIC, SINTACS and SI methods were determined. The final map of the vulnerable areas was prepared using a weighted combination method. In order to evaluate the performance of each DRASTIC, SINTACS and SI method, the correlation coefficients (r) were calculated between the nitrate values and vulnerability indices were: 0.43, 0.37 and 0.30, respectively, and the correlation indices (CI) were 28, 27 and 25 respectively. The results showed that combination methods had higher values of the r (0.60) and CI (35) than the individual methods. The combined index presented in this study can combine both the intrinsic vulnerability and the actual and timely vulnerability risk, and in fact shows the comprehensive vulnerability. Based on the combined method, about 30, 45, and 25 percent of the area of the Rozeh Chay Plain are located in the low, medium and high vulnerability range, respectively.