INVESTIGATION OF SUB-BASINS CONTRIBUTION LEVEL ON BASINS FLOODING INTENSITY USING GIS (CASE STUDY: QARASO, KERMANSHAH, IRAN)Armin Bani Bayat and Zakaria Zoorasna
In the current situation, flood prone areas in Iran are estimated about 91 million hectares. In other words, 55% of Iran areas contribute in producing direct and rapid runoff which about 45% of them have flooding intensity of moderate to high and according to being flood prone of the Qaraso Basin, determining flooding zones is an essential issue. In this research a method was provided that using hydrological models determines flood prone and risky regions within a basin and in other hand prioritizes flooding intensity in each sub basin or hydrological units. The model performance calculations show that contribution of the sub-basins in the output flood does not depend on the sub-basin size and discharge and sub-basins with larger discharges do net contribute in the output flood essentially. In other words, the sub-basins show a type of non-linear behavior. It should be noted that all the mentioned stages were performed regarding various return periods and finally no changes made in the sub-basins priority. In this regard, Sub-basin S6 is more critical among the sub-basins in terms of impact on the basin output flood. On the other hand, among the factors affecting the watershed outlet in all basins, the most important and at the same time the simplest factor in terms of control and effect on the basin output flood, the CN factor was determined. For example, if using the flood control operation in the critical sub-basin stream path, its slope reduces to 40% of the initial slope, only about 11% of the output peak discharge will be reduced and such operation requires huge costs. But in sub basins, if the CN value reduces to 10% of the initial value, about 40% of the peak discharge will be reduced.
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