Flood risk on arid alluvial fans: a case study in the Joghatay Mountains, Northeast Iran

Among the common hazards related to alluvial fans, flooding is one of the most important. Nonetheless, in populated alluvial fans, not only the natural processes are effective in floods, but the artificial structures and modifications can change the behavior of flooding and its potential risks. This study aims to indicate the flood-prone landforms in a set of populated alluvial fans in an arid region and investigate the role of anthropogenic activities in controlling/exacerbating flooding in alluvial fans. To achieve this goal, 15 Ground Range Detected in High resolution (GRDH) SAR Sentinel-1 images, covering a total of 24 alluvial fans, were acquired. Pre-processing and post-processing steps were applied to all images to identify flood-prone sections of the studied alluvial fans. The results showed that feeder channels, spreading sites, and wide interfluves are the most flood-prone landforms of alluvial fans. In terms of anthropogenic modifications to mitigate flooding, a rampart system is distributed in the study area. Ramparts are levee like structures formed from the fan material. They aim to mitigate flood hazard on residential areas, infrastructures, and agricultural lands of the study area. Results show that the rampart system can reduce the danger of floods, but it cannot be considered a long-term solution. Therefore, a comprehensive flood protection system distributed throughout the whole alluvial fan system is needed. Results also reveal that in regions where flood monitoring is challenging, SAR images can be used as a freely available data set to monitor and identify flooding hotspots.