Sensitivity analysis of flood parameters to roughness variation

Roughness estimation is one of error sources in flood simulation. In this study the flood was simulated in Atrak Olya, Chaylogh, Gelian and a part of Atrak river with different roughness coefficient using HEC-RAS ،GIS and HEC-GEO RAS and the effect of roughness coefficient on flood area, flood depth and velocity in different return period were studied. Results showed that for 100-year flood, the flood area and depth increased 1.1% and the flood velocity decreased around 4% for each 10 % increment of roughness coefficient. In addition, for each 10% decline in roughness coefficient, the depth variation was not considerable but the flood area decreased 1.1% and the flood velocity increased about 8.3%. The flood velocity to roughness variation was more sensitive than flood depth and area. Depth flood had the less dependence to roughness and it changes very low with more than 10% change in roughness coefficient. This trend is almost similar for all return periods