Siting Improvement Operations for Rainwater Conservation Schemes in Natural Areas (A Case study of Nazluchai Basin, Urmia)

Proper siting of rainwater conservation systems is an important step to ensure water supply in a watershed. The present study was carried out to identify the factors involved in rainwater infiltration and storage and to determine suitable locations for the construction of rainwater conservation systems in Nazluchai Basin, Urmia. For this purpose, slope, rainfall, land use, soil texture, and soil depth were selected as the parameters affecting rainwater storage and subsequently subjected to AHP analysis in order to determine the weight of each in the different improvement operations studied. In a second step, the TOPSIS model was used to prioritize the sub-basins with regard to the improvement operations of pitting, contour trenching, terracing, and contour furrowing. Based on the results, pitting was found superior to the other improvement operations in the study area as evidenced by the Ci values of 0.94, 0.28, 0.20, 0.31, 0.08, 0.02, and 0.01% obtained from the TOPSIS model for pitting in sub-basins 1 to 7, respectively, indicating the higher priority of sub-basin 1 for performing the pitting improvement operation. According to the same results, sub-basins 3, 2, and 4 were identified as the priority ones for contour trenching, terracing, and contour furrowing, respectively. It was found that while the costly rainwater harvesting schemes cannot be economically justified for the study area, the alternative rainwater conservation schemes may be of priority on economic grounds.  A final finding of the study indicated that not only the criteria but also the combined AHP-TOPSIS model used in this study may help state executive departments to select appropriate improvement operations in other watersheds.