Flood Risk Zonation Using Compilation CN Model and AHP Via GIS (Case Study: River Basin Balekhlo)

In this research the runoff coefficient and effective elements that affect the floods risk of Balekhlo basin were estimated and studied. In this area (Balekhlo River basin) to estimate the amount of runoff the curve number method (CN) were used. This method is the most common method to predict runoff volume. For this purpose, the data and information required includes: the maximum daily rainfall statistics, maps Density of vegetation, soil and Hydrologic Soil Groups were prepared and entered into Geographic Information System (GIS) environment. Combining these data with the model (SCS), maps (CN) basin, the amount of precipitation (S) and runoff (Q) was prepared. Finally, the hierarchical analytical process was used and six factors include: runoff, hydrological soil groups, slope, vegetation density, land use and drainage density were weighted using AHP method. Finally, the zonation map of flood potential produced with different return periods (5, 15, 25 and 50 years) by weighed layers. Results showed that about 40 to 47 percent of watershed areas, during periods of 5 to 50 years have moderate flooding potential.