Evaluation of Surface Water Harvesting Potential in Aq Emam Watershed System in the Golestan Province

Given its low and sparse precipitation both in spatial and temporal scales, Iran is nestled in an arid and semiarid part of the world. On the other hand, because of population growth, urbanization and the development of agriculture and industry sector is frequently encountered with increasing water demand. The increasing trend of water demand will widen the gap between water supply and demand in the future. This, in turn, necessitates urgent attention to the fundamentals of economic planning and allocation of water resources. Considering the limited resources and the declining water table and salinization of groundwater, especially in semi-arid areas forces us to exploit surface waters. When we evaluate the various methods of collecting rainwater, surface water that is the outcome of rainfall-runoff responses in a basin, is found to be a potential source of water and it can be useful to meet some of our water demand if managed properly. Water shortages in arid areas are critical, serious and persistent. Thus, water harvesting is an effective and economic goal. The most important step in the implementation of rain water harvesting systems is proper site selection that could cause significant savings in time and cost. In this study the potential of surface waters in the Aq Emam catchment in the east Golestan province was evaluated. The purpose of this study is to provide a framework for locating areas with water harvesting potential. For spatial evaluation of potential runoff, first, the amount of runoff is calculated using curve number and runoff potential maps were prepared with three classes: namely, the potential for low, medium and high levels. Finally, to identify suitable areas for rain water harvesting, rainfall maps, soil texture, slope and land use were weighted and multiplied based on their importance in order to determine the appropriate areas to collect runoff. The results of runoff production potential indicated that May and June accounted for the highest runoff and it can be inferred from these results that both of these months are characterized with storms which was confirmed by interviewing local residents and as range-land covers the largest land use in the basin as well as low vegetation density in the spring and summer due to overgrazing, much more runoff has been produced which is in line with the studies conducted by the Department of Natural Resources of the Golestan province in Aq Emam watershed (2003) as well as findings of Eftekhari et al. The results showed that the highest areas of the sub watershed 8, and 3 were suitable for rain water harvesting. Thus, the appropriate areas for rain water harvesting in the sub watersheds do not have a uniform spatial distribution according to the results. It can be argued that these sub basins are characterized by 4 criteria to be appropriate for rain water harvesting, which is in confirmation with Miliniai et al. Also according to the results, the areas suitable for rainwater harvesting in each sub-basin have heterogeneous spatial distribution as confirmed by the results of Eftekhari and Jin et al. Given the final map from integrating data layers, it was found that the central part of the study area has a good potential for rainwater harvesting and as results show, suitable area for water harvesting in the watershed coincides with range-lands that have a moderate crown cover as confirmed by the results reported by Tabatabaii et al. Finally it can be said that spatial evaluation and identification of proper areas for rain water harvesting is an important and necessary step in the application of rain water harvesting systems.