M Gharib - PhD Candidate, Department of Watershed Management, Science and Research Branch, Islamic Azad University, Tehran, Iran
B Motamedvaziri - Assistant Professor, Department of Watershed Management, Science and Research Branch, Islamic Azad University, Tehran, Iran
B Ghermezcheshmeh - Assistant Professor, Soil Conservation and Watershed management institute, Agricultural Research, Education and ExtensionOrganization (AREEO), Tehran, Iran
H Ahmadi - Full Professor, Department of Watershed Management, Science and Research Branch, Islamic Azad University, Tehran, Iran

Increased flooding in recent years indicates that most parts of the country are subjected to periodic and destructive floodattacks. Therefore, the identification of high-risk areas with potential runoff production within a watershed area is one ofthe most important measures in flood control and reduction of the damage caused by it. In this study, the quasi-distributionalModClark method was employed to simulate the hydrograph of flooding, and the unit flood response method was appliedto determine the intensity of flooding of different areas of the Tangrah watershed, Iran. For this purpose, the ModClarkmodel was first calibrated and verified. Thereafter, the design of rainfall with 50 and 100-year return periods (Tr) wasextracted at the Tangrah station and the design flood was calculated with the above-mentioned return periods. Bycombining the curve number layers, slope, precipitation, and flow distance, homogeneous units were obtained in terms ofthe flood. The effect of each homogeneous unit on the total watershed output was obtained by the removal of each unit andimplementation of the rainfall-runoff model. According to the 100-year return runoff production potential, homogeneousunits of 116 with a fi (0.54 m3/ s. km2) were identified as the most effective cell in the Tangrah watershed area, whichcould be explained by the soil type, vegetation, and other physical factors of these units.

ArcGIS; Distributed Model; Flooding Map; ModClark Model; Unit Flood Response