Eleyele Dam Reservoir, Ibadan, Southwestern Nigeria: A Review of Historical Studies, Sedimentation Investigations, Catchment Changes and Research Gaps for Sustainable Management

Abstract

Eleyele Dam Reservoir, which was impounded on the Ona River in Ibadan, Southwestern Nigeria, in the 1940s, is one of the city’s oldest water-supply infrastructures and has attracted a substantial, though thematically fragmented, body of research over the past two decades. This paper reviews that literature, organised around the reservoir’s historical research record, its sedimentation-specific investigations, the catchment changes driving sediment inflow, the methods previously applied to study it, and the major findings, limitations and research gaps that emerge from this body of work. Thirty studies met the review’s inclusion criteria. Historical studies span hydrological assessment, geochemical and pollution investigations, and physico-chemical water-quality monitoring, alongside more recent land use/land cover (LULC) change analyses. Two studies have attempted to quantify sedimentation at Eleyele Dam directly: a satellite-derived bathymetric estimate, and a field echo-sounder bathymetric survey covering 2021-2023, which recorded a decline in minimum depth from 1.78 m to 0.69 m and a broadly stable maximum depth (10.39 m to 9.99 m) over the three-year period, with a statistically significant change in bed morphology attributed to both catchment land-use pressure and sedimentation. This field survey, however, covered only a portion of the reservoir over a short three-year window, leaving the reservoir’s longer-term, full-extent sedimentation trend unresolved. Catchment change—principally rapid built-up expansion and forest decline between 1984 and 2019, compounded by a rising and increasingly variable rainfall regime—provides a well-documented basis for the observed depth decline, though it has not yet been linked quantitatively to it. Methods applied in comparable Nigerian and African reservoirs, including the Revised Universal Soil Loss Equation (RUSLE) and the Soil and Water Assessment Tool (SWAT), have not yet been applied to the Eleyele catchment. The review identifies the limited spatial and temporal coverage of existing bathymetric data, the lack of locally calibrated erosion/sediment-yield models, and the disconnection between water-quality, LULC and sedimentation research strands as the principal research gaps constraining sustainable management of Eleyele Dam, and sets out a corresponding agenda for future research.