Due to the climatic conditions, topography and geomorphology, many parts of Iran are at risk of floods every year, so that studies have shown that more than 80% of Iran's area is at risk. In general, 32% of natural disasters in Iran are related to floods, so it is necessary to identify flood-prone areas, predict occurrence, zoning and assess flood damage. The HEC-FIA model is one of the models for measuring flood damages. In this study, Kasgan watershed has been investigated and flood damage in human, infrastruture and agriculture has been estimated using this model. In this research, many softwares have been used, the most important of which are HEC-RAS and HEC-GeoRAS and HEC-FIA. In HEC-RAS software, in order to simulate steady and unsteady flows, the cross sections of the main river channel and discharge rates in different return periods and real flood hydrographs are required. The required cross sections in the HEC-GeoRAS extension are obtained using the exact waterway DEM and transferred to the HEC-RAS and the maximum flow rates with different return periods were calculated using maximum instantaneous discharges and frequency analysis. The output of the steady-state simulation was transferred to HEC-GeoRAS to generate flood zones, and the flood zones were obtained with different return periods. Flood zoning maps were introduced into the HEC-FIA model along with the HEC-DSS file resulting from the unsteady current simulation. The collected infrastruture, human and agricultural information were also entered into the model and flood damage was estimated. The results of this research showed that in the flood that occurred in the region in 2006, 74.14868 billion Rials of damage was inflicted on the agricultural sector and the total damage to buildings, cars and other facilities was estimated as 12273800000 Rials. Also, in case of 1000 return period floods in this region, in the agricultural sector, 1835820 billion Rials damage is estimated and around 75706.2 billion Rials damage will be estimated forall buildings, cars and equipment inside the buildings. Keywords : Flood zoning, HEC-DSS, HEC-GeoRAS, HEC-RAS
