The impact of resolution DEM and Manning roughness coefficient of performance of the model HEC-RAS-WMS In determining flood risk areas (Kashkan River)

The flood phenomenon as a hydro-climatic event and one of the most important natural hazards in Iran, the preparation of maps of areas vulnerable to this danger in urban areas is one of the most important concerns of environmental crisis planners. To achieve this goal, researchers must use appropriate data and hydrology models with the best efficiency. In fact, one of the most important issues affecting the results of various hydrological models that determine the risk areas of floods is the role of digital elevation model and roughness factor. Roughness factor coefficient is one of the important characteristics in studying the characteristics of river flow, and determining the appropriate roughness coefficient that represents the real conditions of the river is of special importance. In this study, the HEC-RAS model was used in WMS software, which used the most practical hydrological models. In this model, the effect of digital elevation model with different resolution and sensitivity of the model to determine the Manning roughness coefficient in the exact area of flooded areas (flooding levels) in the model output has been investigated. The study area of this study is the Kashkan River watershed with an area of 9276 km, part of which has been studied. The results of this study show that increasing the resolution of the digital elevation model in determining the vulnerable areas of flooding is very effective in the accuracy of this model, reducing the accuracy of the range is very low so that it does not correspond to environmental reality. The HEC-RAS-WMS model was also sensitive to changes in the Manning roughness factor and in order to determine the flood zones in this model, the changes in the roughness factor must be carefully adjusted. the importance of this issue, researchers in this field should be careful enough to use the data used in such topics to have the results of appropriate application in urban and regional planning.