Determining the floodway and flood fringe of the Dinevar River using one-dimensional HEC-RAS model

Flooding is one of the most destructive natural disasters that causes loss of life and financial problems in urban and rural areas. In addition, this risk is a concern worldwide, and Iran, like many countries, faces flooding problems in urban and rural areas. Protecting people's lives and property from floods is a duty assigned to governments, and countries have enacted specific laws to manage floods and protect riverbeds and riverbanks. This research aims to determine the flood limit and flood margin of the Dinevar River using the one-dimensional HEC-RAS model. First, geometric data was prepared with the help of HEC-GEORAS extension in GIS software. To estimate the instantaneous peak discharge, the instantaneous peak discharge was calculated using the Hyfran software and the flood zone was simulated with different return periods. Then, based on 130 cross-sections, the area adjacent to the river was divided into two parts: the floodway and flood fringe zones, based on the 100-year flood level increase of 1 foot. Method 4 (the user specifies target water level increase) was used to determine the floodplain limit. The results of this study showed that in the first reach, the floodplain limit coincided with the old terraces of the Dinevar River. In the second and third reaches of the Dinevar River, due to the reduction of topographic restrictions, the riverbed has expanded and reached to an average of 300 and 500 meters in the second and third reaches respectively.