Retention basins for Urban flood mitigation: Insights from Ouagadougou in Burkina Faso

In this study, we simulated and analyzed the impacts of a retention basin as a hydraulic structure for mitigating flood peaks at the inlet of a stormwater drainage canal using the Storage Indication Curve method for various return periods. The adopted methodology involved modeling the hydraulic behavior of the retention basin and its discharge relationship based on water levels. For initial water levels ranging from 1 to 3 meters in the basin, the effectiveness in reducing peak flows is evaluated by estimating attenuation rates and the temporal delay of flood peaks. The results showed that the performance of the retention basin performance is satisfactory for attenuating a 10-year flood, with attenuation rates ranging from 23% to 54% and a flood peak delay of 20 to 55 minutes. For a 100-year flood, the attenuation rates vary from 18% to 30%, with a peak delay ranging from 17 to 30 minutes, depending on the initial water level. However, for consecutive rainfall events or an initial water level in the basin exceeding 1.5 meters, the hydraulic performance appears limited. Finally, we highlight the limitations of solely relying on retention basins for urban stormwater management and emphasize the need to implement Nature-based Solutions (NbS) at the local level to further mitigate effectively surface runoff in urban settings.