Assessment of Water Quality of the Otamiri River Along Selected Reaches Using an Integrated UAV–GIS–Laboratory Framework for Environmental Decision Support

<title>Abstract</title> <p>This study assessed water quality along selected reaches of the Otamiri River, Imo State, Nigeria, through an integrated framework combining field sampling, laboratory analysis, unmanned aerial vehicle (UAV) imagery, geographic information system (GIS) analysis and predictive modelling. Five monitoring stations distributed along a 1,080 m river reach were evaluated for physicochemical, heavy-metal and microbiological indicators. Results showed acidic conditions (mean pH = 5.93), elevated chemical oxygen demand (mean COD = 23.73 mg/L), and widespread exceedances for lead, cadmium, total coliforms and faecal coliforms. Dissolved oxygen remained above 4 mg/L at all stations, indicating that some ecological assimilative capacity persisted despite substantial contamination. UAV–GIS analysis identified pollution hotspots associated with sand mining, refuse dumping, urban runoff, settlement encroachment and riverbank disturbance. A field-calibrated first-order BOD₅ attenuation model, BOD₅(L) = 8.46 exp[-(0.00106L)/0.19], was developed using measured flow velocity, reach distance and the full replicate dataset from the doctoral investigation. The model achieved a strong fit (R² &gt; 0.975) and was evaluated through calibration–validation partitioning, observed-versus-predicted comparison, residual and influence diagnostics, and comparative application to independent river observations. External evaluations for the Otamiri, Nworie, Ogun/Benue, Ganges and Thames Rivers produced predictions generally within 10% of reported observations. Complementary empirical relationships were developed for BOD₅ and selected water-quality variables; station-mean regressions are reported separately as exploratory summaries and should not be confused with the replicate-level predictive models. The integrated framework provides a practical decision-support tool for identifying pollution sources, estimating organic-pollutant attenuation and prioritising river-management interventions. The river remains unsuitable for direct drinking-water use without treatment. Priority actions include sanitation control, regulation of sand mining and effluent discharges, riparian-buffer restoration and repeated multi-season UAV–GIS-supported monitoring.</p>