Flood Inundation Modeling in the Gourou Watershed of Côte d’Ivoire, West Africa

Abstract

Nowadys, floods and droughts are becoming more and more frequent all other the world. According to the Emergency Events Database, Africa is the third continent most affected by flood events in terms of occurrence, total deaths, injured, affected and homeless. This report showed that since 1989, Côte d’Ivoire has experienced floods in 1996, 2007, 2008, 2010, 2014, 2015, 2016, and recently in 2017 and 2018. Those floods caused 169 deaths and around 40000 affected people. Floods occur principally in Abidjan. Their occurrences and amplitudes will increase due to climate change and the increasing urban population. The study was conducted to construct hydrological and hydrodynamics models couple with GIS for flood inundation mapping in Gourou watershed in Côte d’Ivoire. HEC-HMS and HEC-RAS models were used to achieve the specified objective. The result of hydrological modeling showed that the HEC-HMS model simulated fairly well the peak discharges. A sensitivity analysis of the HEC-HMS model parameters used in this study showed that the model outputs are more sensitive to Curve Number compared to the percentage of impervious area and lag time. From the result of hydrodynamics model, it was obvious that the floodplain inundated areas increase with the magnitude of flow within the modeled network confirming the high flood hazard level for settlements and activities near the main canal in Gourou watershed. The WSE profile showed a great variability as water is moving from upstream toward downstream. The obtained flood inundation map for 5-, 10-, 20-, 50-, 100-years illustrated that most of the inundated areas are built-up areas. Thus, flood inundation maps developed in this study can be used for decision making, along with strategies for flood preparedness