Producing Curve Number Map (CN) of Hasanso Watershed using GIS

The different methods used to estimate flooding in watersheds that the major difference between them is maximum flood discharge. The Curve number of each watershed shows its hydrological behavior and water regime during precipitations. This study was carried out on Hasanso watershed, Khorasan province and its main object was produce the curve number map for the study area. Using GIS, the average weighted curve number of the watershed was 80 in humidity level of grade II and major part of the watershed area had curve number of 80. Results revealed that, the maximum number of curves during mean humidity reaches up to 91 and the minimum number to 60. Accordingly, high number of weighted average curve number could be an evident of low infiltration rate of watershed and increasing probability of flood occurrence owing to loess soil. In order to reduce water resources loss, it is necessary to implement basic practices at watershed in line with increasing of water infiltration rate and establishing water harvesting systems including pitting and contour furrow, combined with vegetation increasing projects such as seeding and shrub planting.