Assessment of CN method in runoff Estemation using of GIS In Madarsu basin in Golestan province

Every year, due to the penetration of cyclone and different air masses and also local conditions, the resulting flood phenomena causes extreme damage to the natural and economical resources. Sometimes, due to the flood waves or high density of residual materials, hydrometric stations are damaged and consequently the recorded data do not match to real data. Considering the lack of hydrometrical stations in most of the small watersheds, determination of runoff and maximum flood discharge requires a suitable method to estimate runoff and peak flow which to be used in flood and erosion control management plans. In this study empirical CN method is used. In this study, a principle of work method is applying of statistical data ( statistics year of climatology stations Robate, Ghare bil, Cheshmekhan, Hagholkhaje, Dasht, Dashte shad, tangrah,Ghojmaz,Til abad, pishkamar, Galikesh and station hydrometric Tnagrah). Spatial data analysis and also using of satellite images for gaining CN map in SCS model with GIS, in the next stage recognized applying the SCS equation, CN map and precipitation layer which zones have the potential for creating of similar runoff. In this study, also due to assessment curve number CN choice several flood danger that the results shows the high correlation between curve number calculated and curve number observed and also resulted that use of weight model in curve number calculate provided to consider all of effective factors in runoff existing and at the result attain reliable estimate of runoff resulting the rainfall