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Uncontrolled draw off  of groundwater resources has caused a severe drop at water table levels. However, loss of runoff from rainfall in the world and especially in our country is very high and significant. Therefore the tendency toward the optimum use of surface water runoffs and uncontrolled, instead of uncontrolled draw off of groundwater resources is necessary. In this paper, two different methods for determining the areas suitable for  rainwater collecting  in two decision support systems (DSS) based on the GIS is presented which helps decision makers for selecting appropriate sites for collecting  rain water in Birjand plain, Southern Khorasan province. In this study, Six criteria including rainfall, catchment area's slope, soil's depth and texture, the plain water course  and land uses were applied. In the first method,  different characteristics of the basin is directly involved in decision making and the second one acts  based on the capacity of the area for production of runoff and also social -economical factors. The results obtained of each method, in terms of capacity of Rain Water collection, classifies the area  in 4 groups: low, medium, good and  very good. Comparing the two methods shows that in Birjand plain, using the first method is more suitable and generally from the West part  to the East part of the plain ,  its ability to collect Rain Water will increase.