Prioritizing Flooding Potential of Watershed Using HEC-HMS Model in Comparison with Franko- Roodier Method (Case Study: Nazloochay Watershed)

The flood peak is one of the most important subjects in flood control projects. Because of lack of gauging stations in the outlet of all sub watersheds, this study based on simulating rainfall-runoff in the watershed by Hydrologic Models. HEC-HMS is designed for simulating rainfall-runoff. In this study all the essential information about watershed as Hydrologic soil groups, Land use, Flood hydrograph and Physical Properties were determined. Then the Model was run by the chosen events, and then was optimized and calibrated. Next flood hydrographs for 2-100 return periods were simulated for computing peak Flow. The “specific Discharge” method was used for determining the most flood active area. The results showed that, five sub watershed in the Upstream and middle of Nazloochay as B11, A21, A112, N, L112 with the specific discharge of 0.95,0.94,0.81,0.77 for 25 return period and with highest CN of 80, 75, 72, 75, 75 and the area of 52.6,35,43,42.7,45 had the highest impact on the flood peak and ranked from 1-5 and were determined as the most critical sub watershed.