Assessment of flood risk of Nekarood basin using multi-criteria decision based on intuitive reasoning Dempster- Shafer

  Among the natural disasters, flood causes heavy losses on the agriculture, fishery, housing and infrastructures. It also strongly affects the economic and social activities. the use of modern science, especially remote sensing and GIS techniques helps the planners to assess the risk map of natural hazards such as floods for a region in the least possible time. Multi-Criteria Decision Analysis (MCDA) provides methods and techniques required to analyze complex decision problems which often includes non-comparable data and metrics. Nekarood watershed due to its special properties is Prone to serious and subversive floods. the aim of this study is to assess the risk map of Nekarood Basin caused by floods using multi-criteria decision and based on intuitive reasoning. According to the opinion of experts the two sets of effective criteria on flood risk and vulnerability has been used for the study area. Hydro-climatologic, topographic, land cover and geological factors as effective criteria on flood risk and population density, yields and distance from the road network factors as effective criteria on flood risk were determined for study area. Primary data used in this study included digital elevation model, 8 Satellite LANDSAT 8 images for different months of 1395 to 1393 years to provide vegetation maps, land use map, Geological map, isorain shapefile, road network shapefile, waterways network shapefile, demographic statistics and information relating to agriculture lands and gardens. to dispel uncertainty in the experts opinions about the importance of different criteria on flood risk, Intuitive reasoning theory and Dempster-Shafer model was has been used and final weight of each criterion is obtained. Then, by using the multi-criteria decision method the flood risk map has been made. using the mean and standard deviation, risk map was normalized and the study area In terms of risk was classified to five classes; very low, low, medium, high and very high. Finally, the state of sub-basins and land uses in terms of risk was assessed, compared and analyzed. The results show that topographic factors and population density have the highest degree of importance on risk and vulnerability Caused by floods respectively. to prepare flood risk map for the study area, the number 0.701 was considered for weight of risk factors and 0.299 for vulnerability weight factors. The results of the different risk classes study show that downstream sub-basin of Neka watershed contains the most area of high and very high risk classes and upstream of Neka include the lowest area of high and very high risk classes. Generally; 87 percent of high and very high-risk areas are in downstream sub-basin of Neka. also for dense forest, thin forest and rangeland the area ratio of low and very low risk classes, is greater than area ratio of high and very high risk classes. But for made and agriculture land uses area ratio of high and very high risk classes are more than area ratio of low and very low risk calsses. Results indicate that 59% of the made land use of Nekarood watershed Located in high and very high Risk classes. Flood risk for Neka city in very high and 67% of it located in very high risk class while 90% of Neka city is located in high and very high classes. Nekarood river enters the city of Neka with a considerable amount of water discharge after passing a very long way, approximately 130 km. this route has mounainous topography, steep slopes and high altitude. this amount of water passes Neka city through a single channel and finally empties into the sea. Since this channel has limitted capacity ,during flood time, water spreads into the city and consequently dangerous flood occurs. The results indicate that the use of new technologies such as remote sensing and GIS for mapping natural disasters such as flood Risk is very efficient and useful. In the meantime using multi-criteria decision based on intuitive reasoning is very useful to assess flood Risk of Nekarood watershaed. The use of this model in the study according to consider many criteria, well-calculated the degree of hazard, vulnerability and finally risk for the study area. Neka city due to their particular position has very high potential for flood risk and vulnerability. The results indicate the necessity of the managers and planners attention in various agencies related to floods in the study area