Zonation of flood hazard probability in Gamasiab river banks from Sahneh to Bisetoon - Kermanshah province

Flood is the most common natural hazard in the world that affects many people every year. This study aimed to assess the probability of flood hazard in Gamasiab River of Kermanshah using Multi Criteria Decision Making Approach (MCDA). So, four factors such as height, slope, distance from river, and land use were prepared and each factor was subdivided into 9 classes in the form of descending valuation. Then Normalized Weight Index (NWI) was calculated according to the effect of each factor on the probability of flood and Weighted Linear Combination (WLC) method was used to provide the final map of the flood hazard risk zonation. The results of flood risk zonation showed that about 61 square kilometers (12%) on both sides of the Gamasiab River had high and very high vulnerability. The Bistoon City and the lower reaches of the Gamasiab River have the high and very high-risk probability due to the decreasing of slope and height downstream of the Gamasiab basin. According to the results, Multi Criteria Decision Making Approach is a powerful, fast and low cost method in basins without hydrometric information for preparing flood risk maps.