عنوان مقاله [English]
IntroductionFlood is a stream that is larger than the average volume of water along the river (Wool, 2000). Bowell (2007) estimated flood damage in the 2000s by about $ 21 billion. In Iran, floods are one of the most important natural hazards in most parts of the country. The study of natural features of the catchment area helps to understand hydrological and geomorphic issues such as flood, erosion and mass movement (Isa and Afyang, 2011).One of the most important tools in hydraulic analysis is the study of morphometric parameters of the basin, which makes it possible to assess the behavior of the hydrological systems of the basin (Anjeliliri, 2008).The hydrological response of the river basin is related to the physiographic characteristics of the drainage basin, such as size, shape, slope, drainage density and flow lengths (Kumar et al., 2000). Morphometric analysis and prioritization of basins are essential parameters for managing and evaluating flood risk (Yusuf et al., 2011). Sarpol Zahab Basin has heavy rainfall and its geological and geomorphological conditions are favorable for the formation of flood. Due to the passage of the Alvand River through the city of Sarpul Zahab and the location of the village and agricultural land and human facilities along the river's outskirts, flood risk zoning is necessary and necessary. The aim of this study is to zonate the potential of flood discharge of Sarpul Zahab basin and its sub-basins using morphometric parameters.Materials and methodsIn the first method, 9 parameters of morphometry area, Slope index, Relief ratio, Weighted mean bifurcation ratio, Stream frequency, Drainage density, Basin shape index, Ruggedness numberand Texture Ratio Basin of Sarpul Zahab and its sub-basins were calculated. The degree of risk of the parameters was calculated according to equations (1) and (2).equations (1) HD =equations (2) HD =The zoning of sub-basins is based on the sum total of nine parameters in terms of flood risk. The risk of flooding is divided into five areas of low risk, medium risk, high risk, very high risk and severe risk (Table 2), and each zone has a score of 1 to 5 (Fahan and Ayat, 2017).In the second method, 12 parameters Bifurcation ratio, Drainage texture, Compactness index, Form factor, Circularity ratio, Elongation ratio, Lemniscates ratio, Relief, Stream frequency, Drainage density, Ruggedness number and Relief ratio Which have a direct runoff ratio, were calculated for the Sarapul Zahab basin and its five sub-basins. For the values derived from each of the twelve parameters in each sub-area, the rank (rank) is allocated from 1 to 6 (Altaf et al., 2014). The higher values have the greatest impact on flooding and have the highest score (Batt et al., 2019).The index (Cv) is an average of 12 morphometric parameters (Batt et al., 2019, 53), and the sub-basins are zoned in terms of the potential of flood landslides.Discussion and Results The studied basin has five sub-basins, Rijab, Pathagh, Ghaleh Shahin, Sarabgarm and Qarawiz. The drainage network pattern in the Sarpul Zahab Basin and its sub-basins is dendritic and the main drainage of Sarpul Zahab basin is 6. Total sum of the degree of risk of nine morphometric parameters in the catchment area 27.21, which indicates the potential for severe flood risk in this basin. The submarine Rijab with a degree of risk of 26.65 has a very high potential flood risk potential. The sub-basins of the castle and Shahin castle with a hazard degree of 28.26 and 27.12 have a high risk, the sub-basin of the 22.03 range with a medium risk potential and a sub-basin of 20.87 degrees with a low risk of flood risk. Indicator values (Cv) for the Sulfol Basin 4.75, which has a high potential for flood risk. The 4.27 Ridge submarine has a high potential flood hazard potential. The sub-basins of the castle and Shahin Castle are respectively 3.08 and 3.16, respectively, with a medium-risk flood hazard potential, respectively. The sub-basins of Qarawis and Sarabag with 2.83 and 2.91 values, respectively, have a potential flood hazard potential.ConclusionIn the first method, 57.05% of the area of the Sarapul Zahab basin has a high risk, 32.67% has a potential hazard, 3.86% has a moderate risk potential and 6.41% has a low potential hazard. In fact, 89.72% of the area of the Sarpol Zahab Basin has a high and severe flood risk potential. The second method, 32.67% of the area of Sarpul-Zahab Basin has a high potential hazard, 57.05% has a moderate risk potential and 10.27% has a low potential hazard. The comparison of the results of the two methods with each other and the morphometric and geomorphological conditions of the Sarpol Zahab basin and its sub-basins indicate which results from the second method, which is based on 12 morphometric parameters, is more adapted to the natural conditions of the basin. The two small, fairly smooth slabs and low-slope sub-basins, which have low topographic slopes and are limited to the limited permeability of quaternary deposits, have low potential potentials. Submerged and long castles and castle fortifications, most of whose area is in the range of permeable quantum deposits, with low slope, has a medium risk potential. The Rijab sub-basin has sloping ranges because of its high ruggedness and is close to the circle, with a high potential hazard. The Sarpul Zahab basin is also high due to mountainous conditions and the presence of steep slopes in more than 65% of its area and the shape close to the circle has a high risk of flooding. The application of 12 morphometric parameters to 9 parameters of morphometry and more emphasis on parameters related to basin shape have made the second method more effective in potential flood hazard potential in Sarpul Zahab basin and its sub-basins.