Impacts of urbanization and rainfall variability on the drainage of a small urban watershed in Dakar, Senegal

Residents around the outlet of the Grand Yoff basin are exposed to periodic flooding and unsanitary conditions that degrade their living environment during the rainy season. Indeed, urbanization and rainfall variability are key environmental factors in the neighbourhoods within the Grand Yoff watershed. To understand these natural and human influences in a 5.8 km² watershed, we analysed rainfall and socioeconomic data. Rainfall variability was assessed using the Standardized Precipitation Index (SPI). Based on annual rainfall totals and the watershed area, the volume of rainwater input was estimated. Similarly, wastewater discharges were calculated based on population size and the proportion of water discharged. The analysis showed that water inputs during the recent wet phase (2005–2023) amounted to 75,718,080 m³ per year. At the same time, wastewater discharges are estimated at 5,505,302 m³ per year. This highlighted the harmful impact of urbanization on water flows. Both the quantity and quality of water are affected by rainfall variability and population growth within the watershed. The implications for neighbourhoods located in the watershed should encourage a better integration of rainfall variability and sanitation in flood control strategies. Moreover, nature-based solutions deserve to be tested within the watershed. Key words: Watershed, rainfall, wastewater, urbanization, Dakar.