Dynamic assessment of flood inundation based on a spatiotemporal hydrological model feed by a dynamic representation of human activities

Floods are one of the most recurrent and damaging natural disasters in cities in developing countries today. The city of Abidjan (economic capital of Côte d'Ivoire) is not immune to these disasters. Indeed, according to the ONPC (2014), floods have killed an average of 13 people each year since 2009. One of the causes of the worsening and recurrence of these disasters is the urbanization experienced by the city of Abidjan in recent years. This urbanization has resulted in an increase in waterproofed areas and at the same time an increase in the volume of runoff water. The main objective of this research is to study the dynamics of floods and to see the impact of human activities on the hydrological functioning of the Gourou and Bonoumin watersheds in order to anticipate the risks of flooding. To do this, several specific objectives have been assigned in this study. These are: (1) the morphometric characterization of each watershed ; (2) the cartographic and diagnostic of stormwater management works and the dynamics of land use as well as the study of the variability of rainfall relative to the resurgence of floods in each basin ; (3) the establishment of a geographic information system for the study of floods; and (4) the prospective study of the evolution of land use and the future hydrological functioning of the watersheds studied using scenarios in order to take measures to fight against floods. The equipment used is composed of rain gauges (for measuring the spatial variation of rainfall in each sub-basin), limnimetric scales (to measure the heights of water in rivers), a double-ring infiltrometer (to measure the infiltration capacity on the basins) and software (Goldsim for simulating the behavior of watersheds). The data used consist of climatic data (temperature, rain), historical data on the floods in Abidjan, land use data (satellite images), physical characterization data of the watersheds (slope, hydrographic network, sanitation network , rainwater management works, morphometric parameters of the basins. The methodology adopted consisted of (1) collecting historical data on past floods in Abidjan; (2) description of the environment during rainy events; (3) studying the morphometric parameters of the watersheds studied and also (4) the study of the evolution of rainfall. Thus, the results obtained made it possible to show that the Gourou and Bonoumin basins cover respectively an area of 27.42 km² and 46.37 km² and the Gravelius indices of the two basins are respectively 4.89 and 5.51. Each year, the risk of a flood occurring is 75% with an average of more than 500 million property damage. The level reached in flooded areas of about 1 meter and according to historical data about inundations in Abidjan, on average 16 people lose their lives each year.