Flash flood risk assessment and sanitation infrastructure vulnerability in unplanned urban areas: A GIS-based analysis of the Sinza River catchment, Dar es Salaam

In rapidly urbanizing African cities, the combination of poor sanitation and growing climate risks remains underexplored. This study examines the combined flood risk and vulnerability of faecal sludge management (FSM) systems in the flood-prone Tandale Ward within the Sinza River catchment, Dar es Salaam. A multi-criteria GIS method integrated five weighted factors: precipitation (0.25), proximity to rivers (0.30), elevation (0.20), slope (0.15), and land use (0.10) to produce flood hazard maps. High and very high-risk zones were identified based on composite index thresholds from the weighted overlay. Validation involved household surveys (n = 308), interviews with pit emptiers, and field observations, which confirmed frequent flooding and sanitation failures in identified hotspots. Results indicate that over 90% of Tandale falls within high to very high flood risk zones, with significant dependence on pit latrines near rivers and low-lying areas. These findings highlight the urgent need for tailored, climate-resilient sanitation strategies in informal settlements.