Detection of Areas Associated with Flash Floods and Erosion Caused by Rainfall Storm Using Topographic Attributes, Hydrologic Indices, and GIS

Abstract

Storm floods are the most common of natural disasters that can affect infrastructure and cause human casualties, environmental destruction, and economical losses. Increased storm frequency and intensity related to climate change are aggravated by several factors, such as the growing occupation of floodplains, increased runoff from hard surfaces, inadequate management policy, and silted up drainage. The objective of this research is the integration of topographic attributes (elevation, slope, curvature, and water catchment), topographic profiles, and hydrologic indices derived from Digital elevation model (DEM) in a geographic information system (GIS) environment to detect areas associated with flash floods and erosion caused by rainfall storm and sediment transport and accumulation. The selected study area is the region of Guelmim city in Morocco. This region has been flooded several times over the past 30 years and was declared a “disaster area” in December 2014 after violent rainfall storms killed many people and caused significant damage to the infrastructure. GIS was used to extract topographic profiles and attributes as well as for the implementation of the stream power index (SPI), sediment transport index (STI), and compound topographic index (CTI). Moreover, it was used for spatial data management and manipulation whereas the PCI-Geomatica image processing system was used for fuzzy k-means unsupervised classification for topographic attributes and hydrologic indices. The obtained results show that hydrologic indices demonstrated that the rainfall and the topographic morphology are the major contributing factors for flash flooding and catastrophic inundation in the study area. The runoff water power delivers vulnerable topsoil and contributes strongly to the erosion and land degradation process, and then transports soil material and sediment to the plain areas through natural action, i.e. water power and gravity. The unsupervised classification leads to three homogeneous units of dynamic response to hydrologic processes. The high levels of aggressiveness are encountered in the valleys and over areas with steeper slopes. The valleys are zones of flow accumulation receiving the contribution of large upslope drainage areas, thus allowing high rates of erosion. Conversely, low runoff aggressiveness is connected with areas of low slopes. Likewise, the role of the lithology associated with the terrain morphology is decisive in the erosion risk and land degradation in this region.