Topographic indices and two-dimensional hydrodynamic modelling for flood hazard mapping in a data-scarce plain area: a case study of Oued Laou catchment (Northern of Morocco)

Abstract

This article aims to assess flood hazard in the Oued Laou basin. It is a catchment on the Mediterranean coast (Northern part of Morocco) potentially periled by flash floods and accelerated development of anthropogenic activities. In this study, two complementary methodologies were applied; the first one introduces a new topographic wetness index (TWI-Ks) that aims to identify flood prone-areas executed on the basin scale. Then were validated using sentinel-1 images. The second one is a two-dimensional (2D) hydrodynamic model applied on a locale scale (plain of Oued Laou), to describe and calculate the flood parameters and mapping flow indicators based on a high grid resolution (DTM) generated using Arial photogrammetry. The results highlight that the new approach of TWI-Ks model provides more reliable results than the classic TWI in terms of delineating areas at potential risk. Even though, both of them provide reliable susceptibility mapping. The analyses of the 200-year flood event simulated by 2D hydrodynamic HEC-RAS model, revealed that the flood inundation extent consequently affected almost all floodplain assets. Especially, crop fields and road N16, as tends to present danger even on buildings as a result.