Search

Floods, especially large floods, are one of the most important factors affecting river morphology and ecosystems. Due to the effects of floods on landforms, the analysis of the geomorphological consequences of floods is important. In this study, the effects of an extreme flood that happened on April 1, 2019, in the Khorramabad River Basin located in western Iran are investigated. This research aims to investigate the effects of floods on channel changes as well as estimating the amount of flood-related erosion and sedimentation of the Khorramabad River. To do so, Sentinel-2 satellite images, Google Earth images, geological and topographic maps, and field investigations have been used in this research. First, the river channel was extracted from cloud-free multispectral Sentinel-2 images taken before (March 22, 2019) and after (April 21, 2019) the flood. Then, the amounts of erosion, sedimentation, and also unchanged areas were calculated using the Union tool in ArcGIS. Furthermore, using Google Earth images, cross-sectional profiles were prepared in two sections of the river, and changes in the depth and width of the riverbed were studied. The results show that the flood has significantly affected the width and depth of the channel, and the most prominent impacts of the flood were shifts of the riverbed and severe bank erosion in the meandering areas. According to the field surveys, floodwater occupied floodplains around the river channel and destroyed the adjacent agricultural lands and gardens. The analysis of river channel maps (before and after the flood) indicates that the greatest changes in the river channel (46.4% of the total changes) occurred as riverbed widening in the downstream and midstream areas due to riverbank erosion as well as river channel shifts. The changes caused by sedimentation account for 18.6% of the total changes, and the remaining 35% of the river channel area did not change at all.