Conceptualization of recharge processes in the world most populous megacity in the past three decades using WetSpass-M Model: lessons and opportunities for Managed Aquifer Recharge (MAR)

Current demographics have projected that Lagos will become the world’s most populated megacity by the year 2100. This rapidly increasing human population has led to rapid depletion of groundwater resources of its highly productive coastal aquifers. The recharge processes and its drivers are yet to be quantified and understood. This challenge prompt the need to estimate the past and present recharge rate and understand the recharge processes in the megacity using WetSpass-M model. Input data such as land cover, DEM, slope, water depth, soil, temperature, precipitation, evapotranspiration, windspeed representing the past three decades (1990 to 2020) were inputted into the model. The findings established the two contrasting trends with recharge rates decreasing from 761mm/yr to 563mm/yr and runoff increasing from 292mm/yr to 400mm/yr. Similar spatial patterns of land use, simulated recharge and runoff were observed in the central area of Lagos. This supports the pressures from urbanization activities in the reduction of infiltrating water expected to recharge the aquifers and increasing runoff waters with potential of creating environmental hazards. The increasing runoff amount at the places near the water bodies serves as source water for Fiver Bank Filtration takeoff of Managed Aquifer Recharge (MAR) that can be captured, treated and stored in aquifers for later use. This when used will reduce the water availability crisis reported and projected in city of Lagos.