A model on investigation on flood hazard over watersheds of Iran

Flood is a hydrologic process whose dimensions change under different natural and artificial conditions of the earth surfaces as well as climatic conditions. Flood can be taken as a natural disaster and will bring about damages and casualties, if this phenomenon is not well recognized enough, or if it is not controlled or stopped. Appropriate planning can be taken into account to reduce the financial damages and civilian casualties caused by floods, by recognizing flood hazard and its spatial distribution. In this research, a method was suggested to determine flood hazards, based on main factors affecting hazard, and then applied for Hendijan-Jarrahi basin in the southwest of Iran. The results show that seven factors, including the intensity of flood potential, flood frequency, flood damage, flood casualties, the population exposed to the flood, residential places and lands exposed to the flood, were recognized as the main parameters to control flood hazard. Afterwards, the matric of hazard factors were identified by weighting to each of them and determining their domains based on data of floods during the last 50 years in second order basins of the country. Flooding areas also were recognized by using the Landsat TM 2002. In addition, the intensity of flooding potential were estimated with different return periods by applying the data of hydrometery stations and using regional analysis of daily and instantaneous peak flow for applying to ungaged basin. the layer of flood hazard were prepared based on 5 factors including flood frequency, flood damage, civilian casualties, the population and residential areas exposed to flooding. Then after, the flood hazard zoning were recognized and mapping, by combining and overlaying the layer of flood hazard with the layers of flooding areas and flooding intensity. By applying the model in Hendijan-Jarrahi basin, it was inferred that in this basin the maximum flooding took place in a fourth order Khairabad basin, following by Zohreh basin in Hendijan, otherwise, downstream Hendijan basin had the order of sever flood hazard. Moreover, Allah basin located in the upstream of Jarrahi had the maximum specific flood discharge yet the flood hazard in this basin was low risk. Also, the flood hazard is in the mean level of risk in Maroon and downstream of Jarrahi. Therefore, flood intensity and flood hazard do not much in one area, so it should be into account the basins which are flood prone to control the flood and reduce the flood risk.