Runoff Production Potential Zoning Using Fuzzy GIS-MCDA Models (Case Study: Tajan River Basin)

Because in Iran, flood phenomenon has the highest financial losses and death tolls among the natural disasters, thus reducing the damage caused by it has been considered for a long time and it is regarded essential. The most urgent action to deal with this natural disaster is to make preparations and take measures to reduce its harmful effects. One of the basic measures in this regard is the recognition of flood-stricken areas and the zoning of these areas in terms of the risk of flooding or runoff production. As a result, it is possible to decide on the use of land and various applications, such as agriculture, urban, industrial, etc., and minimize flood damages. In this study, first the factors affecting flood formation such as geology, precipitation, drainage density, distance from the waterway, concentration time, slope, aspect, soil material and land use were identified. Then, using the GIS capabilities and the fuzzy hierarchical analytical method, the zoning map of flood gas potential of the Tajan basin was prepared in five classes of very low, low, moderate, high and very high floodwater potential. Accordingly, 0.51% of the basin areas have very high runoff potential, 5.48% of the regions are with low runoff potential, 29.09% are with medium run runoff potential, 52.4% are with high runoff potential and 12.52% are with very high runoff production potential. Also, the range of Sari city is in the range from medium to high runoff potential, and 87 of the 441 villages in the studied area have very high runoff potential and are in the danger zone. In general, the situation of the roads in the basin is not suitable for the runoff production potential, and the main parts of the roads in the catchment area, including the main roads such as the parts of the Sari-Semnan axis, have very high run runoff production potential. Flood Damage alleviation both by structural or Non-Structural measures firstly requires accurate identification of study area in terms of flood risk or runoff production potential. This is more important due to financial limitations and the lack of an integrated management perspective. The presence of a zoning map of runoff production potential in Tajan basin is more important as it is located in border of Mazandaran and Semnan provinces and since some of the flood-prone areas are located in Shirin Rood tributaries at Chashm district of Semnan province and its floods impose substantial damage to downstream areas in Mazandaran province. Hence, this zonation map and its results, i.e. identifying runoff prone areas, assist us to define, complete and develop watershed project at   upstream of flood-prone areas with high runoff potential with holistic view as well as proper prioritization in management decisions. Also through management of the financial and human resources, roads prone to flooding can be secured and it helps to prevent the establishment of industries and population centers and the implementation of civil constructions and projects in the high risk areas. At the same time   in credit and budget allocation for flood and education areas with high runoff generation potential are prioritized. It is also possible to consider the zoning map of runoff production potential in the selection of plowing and furrow methods, tillage and flood protection and flood control measures.