Pragmatic approach for prioritization of flood and sedimentation hazard potential of watersheds

Abstract

Flood is one of the natural disasters that generates a lot of damages every year in different points of the world. Also, soil erosion is among the processes that threats the soil and water resources of the country. The performance of a small watershed is not same as the hydrologic response of a large watershed. Determining the amount of participation and prioritizing the sub-basins in terms of flood generation in the outlet of the basin can be a large help in correct locating the flood control and soil and water conservation projects and leads to decreasing the negative impacts of the flood control operations at unnecessary regions or at the regions with lower priority and also it prevents personal tastes. Therefore, determining the flood generator regions and prioritizing the sub-basins in terms of flooding and sedimentation potential is essential for better management of the watersheds. For this purpose, the aim of this research is to determine the amount of participation of the eastern sub-basins of the Gorganrud River Basin of Golestan province, Iran in flooding and sedimentation and their prioritization in terms of flooding and sedimentation potential using the multi-criteria decision-making methods. In this present study, we used area estimation indices, gravel coefficient, drainage density, basin average slope, basin average height, curve number, cover percentage, sediment yield, sediment delivery ratio, runoff height and concentration time. Indicators are considered to be important indicators affecting water permeability, runoff production and, consequently, the potential for flooding and sedimentation. Following the formation of decision matrix with 13 options (sub-basins) and 11 criteria (evaluation index), Technique For order Preference by Similarity to ideal Solution (TOPSIS), Simple Additive Weighting (SAW), Elimination Et Choice Translation Reality (ELECTRE) and Vise Kriterijumska Optimizacija Kompromisno Resenje (VIKOR) techniques were used to prioritize sub-basins. Borda and Copland methods were used to combine the rank of proposed techniques. Also, in order to validate the models, we estimated the percentage change and the intensity of the changes. The results showed that the highest runoff height index (0.179) and the average height index of the basin had the lowest weight (0.031), according to experts. Considering the results of the combined ranking of the proposed techniques, sub-basins 12, 1 and 2 are in first to third priority, respectively, and have a more critical situation than the rest of the sub-basins. Field studies clearly show the results of the research, because sub-basins 12 and 1 exhibit the highest erosion, poor soil and gradient. Also, zones with flood and sedimentation potential in the area showed that 49/31% of the area in high and very high risk. This study proves that multi-criteria decision-making methods and RS and GIS techniques are very suitable, precise, economically and temporally advantageous, and helpful tools to evaluate and prioritize the sub-basins in the soil erosion and soil and water conservation topics. Therefore, considering the multiple objective functions and the costly watershed management operations, it can be said that multi-criteria decision-making methods can be used for better management of watersheds in terms of biological and structural flood control operations. So, prioritization can be done based on a mathematical logic. The proposed method in this research is very suitable for watersheds without sufficient data. Hence, such researches which are low cost as well as quick can be used and watersheds can be prioritized for management and conservative acts.