Environmental Impact Assessment of Sand Dredging Operations on the Ogun River Ecosystem, Ogun State

Sand dredging along the Ogun River has intensified to meet construction material demands in Ogun State, raising concerns about riverbed destabilisation, turbidity, and aquatic habitat loss. This study conducted an environmental impact assessment of commercial sand dredging operations at three sites along the Ogun River, evaluating changes in water quality, benthic habitat, and riparian vegetation condition. Water samples were collected upstream and downstream of active dredging sites and at 200-metre intervals during and between dredging operations. Turbidity, total suspended solids, dissolved oxygen, and pH were monitored continuously over eight weeks. Benthic macroinvertebrate communities were sampled before and after dredging activities at each site. Riparian bank erosion was assessed using photographic documentation and bank recession measurement. Results showed turbidity spikes of up to eighteen-fold above background levels during active dredging, with cascading effects on benthic invertebrate abundance and dissolved oxygen depletion. Bank erosion rates at dredged reaches were significantly higher than at control sections. Riparian tree root exposure and bank collapse were observed at two sites. Benthic communities showed reduced taxonomic richness immediately post-dredging with partial recovery within six weeks. The study recommends introduction of mandatory environmental management plans for dredging operators, enforcement of setback distances from sensitive riparian zones, and real-time turbidity monitoring requirements as conditions of dredging licences in Ogun State. Keywords: sand dredging, environmental impact assessment, Ogun River, turbidity, benthic habitat.