Mapping flood hazard in Driouch region (north-eastern of Morocco) using AHP and numerical approaches

Abstract

Driouch City situated in the northeastern of Morocco, has been historically prone to flooding due to its geomorphological and anthropogenic factors. The main objective of this study is to conduct a comparative analysis of the flood hazard in this region using two different approaches. The first approach combined GIS with the multi-criteria decision analysis AHP to create flood hazard maps, using nine static key parameters, which are elevation, slope, flow accumulation, distance from the river, drainage density, runoff, land use, Topographical Wetness Index (TWI), and Normalized Difference Vegetation Index (NDVI). Then, weights are assigned to these factors based on their impact on flooding in the Driouch City. The results indicate that the distance from the river significantly affect areas surrounding the mainstream of Kert basin and its two tributaries. The next step involves comparing the AHP-GIS results with the outputs from the numerical method commonly used as a validation approach for static methods. In this study, it consists of conducting a hydraulic simulation using Iber, a 2D model based on the Saint-Venant equations for flood area distribution. The key input parameters of the simulation are Digital Elevation Model (DEM), land use, runoff and rainfall data. The post-process of the simulation shows how water depths and velocities are distributed along the rivers, noting the high vulnerability to flooding of Oued Kert and Oued Hammam with values exceeding 1m and 1m/s, respectively. By overlaying these two parameters using the GIS, the second flood hazard map is obtained. The comparison of the two resulting maps shows a clear similarity for areas classified as having higher-order flood hazards, which confirms the findings of each other and correlating with historical data; AHP classifying and weighting flood causative factors, and Iber modeling the behavior of the flood. This study concludes the importance of considering the two approaches to assess flood hazards. Most vulnerable areas to sudden floods are residential areas in this case, requiring the redevelopment of watercourses and hydraulic structures and developing a risk prevention plan.