Spatial evaluation of appropriate areas to collect runoff using Analytic Hierarchy Process (AHP) and Geographical Information System (GIS) (case study: the catchment "Kasef" in Bardaskan

Collecting runoff is used to minimize losses and strengthening water reserves (water resources) in the system of catchments. Identifying suitable locations to collect runoff is an important step towards maximizing water availability and optimal utilization of agricultural land in semi-arid areas. Collecting rainwater and runoff is of measures that can be effective in proper utilization of water available in arid areas. Using traditional Knowledge, constructional skills, and local resources and due to geographical and climate conditions, water collection systems are expanded as a means of extant water supply in different areas. Nevertheless, regardless of indirect impacts on downstream hydrological and ecological systems, methods of collecting runoff are needed to understand better the environmental and hydrological effects of catchment system. For the purpose of spatial evaluation of suitable areas to collect runoff in the catchment "Kasef" in Bardaskan, runoff values are first calculated using the model of curve number and the maps of land use, hydrologic groups of soil, runoff production potential, the distance from both the arable lands and residential area are thereafter prepared in the environment of Arc-GIS 9.3 software. Then, they are weighted using Analytical Hierarchy process (AHP) based on the questionnaire forms and the expert choice 11 software and the relative importance of each of the main criteria and their classes are calculated. So the maps are finally combined in Arc-GIS software to determine the convenient localities of collecting runoff. The results showed that, amongst several criteria, according to expert opinions the criterion of runoff potential has allocated the utmost relative importance to assess susceptible areas for collecting runoff. Also, 2.35 % and 114.68 hectares of the catchment area "Kasf'' has a very high potential for runoff production and 12.27 % and 598.11 hectares of this catchment has a high potential and 48.66 % and 2371.62 hectares has a very low potential. It was also noticed that 12.39 % and 603.78 hectares of the catchment area "Kasef'' has a very high proportion and 0.41 % and 20.14 hectares has a high proportion and 6.89 % and 335.8 hectares has a very low proportion for the susceptible areas to collect runoff. We can finally say that spatial evaluation and identification of suitable areas to collect runoff is an important and necessary step in applying and developing runoff collecting systems in each system of catchments.