Assessment of the Impacts of Sand Mining on River Morphology in the Osun River Basin, South West Nigeria

Commercial sand mining from riverbeds has intensified across South West Nigeria in response to construction demand, with documented consequences for river morphology, aquatic habitats, and downstream water supply. This study assesses the impacts of sand mining on river morphology in selected reaches of the Osun River Basin in Osun State. Cross-sectional surveys of river channel geometry were conducted at eight sites, comparing morphological parameters including channel width, depth, bed elevation, and bank slope between actively mined and unmined control reaches. Historical satellite imagery spanning 2015 to 2024 was analysed to document channel planform changes. Water samples collected upstream and downstream of mining sites were analysed for turbidity, total suspended sediments, and selected heavy metals. Interviews with 80 sand miners, 60 fisherfolk, and 10 water utility operators captured perceptions of change and operational concerns. Findings demonstrate that mined reaches exhibit significantly higher channel incision, bed armour development, and bank instability compared to control sites. Downstream propagation of turbidity pulses during dredging operations impairs water treatment performance at Osun State Water Corporation intake points. Fisherfolk report acute loss of spawning grounds and 35 to 50 percent declines in catch in mined sections. The study recommends establishment of mining exclusion zones around critical river sections, enforcement of environmental impact assessment requirements for extraction operations, and restoration of degraded reaches. Keywords: sand mining, river morphology, Osun River, channel incision, aquatic impacts.