The establishment of the Sendai Framework for Disaster Risk Reduction 2015‒2030 prompted local governments to prepare flood risk assessments. However, within the rural contexts of low- and middle-income countries, such tools do not account for the details necessary for risk management. Limited data availability is the most frequently reported reason for such deficiencies. Moreover, flood exposure is particularly uncertain. This study aimed to overcome this obstacle through the use of fine-grained open-access information, local datasets, and ground truth data. Its novelty is the identification of flood-prone assets and the formulation of risk reduction measures. This approach was applied to a 58-km section of the Niger River upstream of Niamey. Notably, risk is considered the product of hazard and damage, expressed in monetary terms. On the basis of five hazard scenarios, hydraulic modelling was employed to determine the floodplain, which was then validated against Sentinel-2 satellite images. Buildings and crops were identified through visual interpretation of Google Earth satellite images and verified on the ground. Wells were located according to statistics from the Ministry of Hydraulics and Sanitation. The potential damage resulting from a flood with a 10-year return period was partitioned, with 57% attributed to crops and 43% to buildings. Horticulture alone accounted for 43% of the total damage. Half of the damage to buildings is concentrated in 13 settlements. Nine structural measures are recommended on the basis of the expected inundation depth.
M. Tiepolo, M. Housseini, Giorgio Cannella et al.· Natural Hazards· 0 citations
Culverts are widely used to provide crossings over small rivers and can strongly influence flood hydraulics by controlling upstream water levels. During high flows, insufficient conveyance may cause pressurization and overtopping, with important implications for flood hazard assessment. Although computational fluid dynamics (CFD) is increasingly applied to investigate these complex hydraulic processes, systematic evaluations of its performance remain limited. This study addresses this gap by validating a three-dimensional CFD model against previously published laboratory experiments for culvert-only, weir-only and combined culvert–weir configurations under both steady (rising and receding discharge sequences) and unsteady flow conditions. Beyond benchmark validation, diagnostic analyses examined inlet region mesh resolution, inflow ramp history and turbulence closure, together with the associated outlet ventilation and attachment mechanisms. The model reproduced upstream water levels with mean absolute relative error (MARE) values ranging from 0.90% to 5.42% and captured the main stage–discharge relationships across the tested configurations. However, the experimentally observed transition from partially full to pressurized flow in the combined culvert–weir configuration was not reproduced consistently. The diagnostic analyses showed that inlet resolution influences entrance losses and post-submergence headwater, inflow history alters outlet attachment and ventilation and turbulence closure affects barrel filling and air-pocket morphology. The results indicate that CFD can reproduce water level and overtopping responses well when carefully configured, while regime transition prediction remains more uncertain because of its sensitivity to ventilation and discharge history effects.
Yacine Bouyousfi, R. Vesipa, P. Claps· Water· 0 citations
