Assessing Groundwater Potential Using Aquifer Transmissivity: A Case Study of the Odudunka Erosion Site, Nanka Gully, Anambra State, Nigeria

The study area is situated within Nigeria’s humid tropical rainforest zone, specifically on a cuesta landscape in the Awka-Orlu uplands, underlain by the Nanka Formation (Early Eocene) and the Imo Shale Formation (Palaeocene). The geological, hydrogeological, geotechnical, and hydrogeochemical characteristics of the region—combined with human activities—have significantly contributed to the initiation and expansion of gully erosion. Numerous springs, streams, and lakes have been observed to drain the gully floodplains. The research revealed that an increase in hydraulic head during the rainy season accelerates subsurface flow, thereby enhancing gullying processes. Exposed lithologies were found to host perched aquifers and fully saturated zones, especially within the Nanka Formation, which are susceptible to erosion, landslides, and flooding. This paper evaluates the groundwater potential of selected gully sites within the Nanka region of Anambra State, Nigeria.