Development of an Original Integrated Mine Water Balance Model for Complex Tropical Open-Pit Operations in Nigeria

Accurate mine water balance modelling is a fundamental prerequisite for environmental compliance, water resource planning, and flood risk management at open-pit mine sites, yet existing mine water balance frameworks are largely derived from temperate and semi-arid climatic contexts and perform poorly when applied to complex Nigerian tropical settings. This dissertation develops an original integrated mine water balance model specifically designed for complex tropical open-pit mining conditions in Nigeria. The modelling framework integrates high-resolution rainfall-runoff modelling using SWAT, pit groundwater inflow simulation using MODFLOW-SURFACT, and process water consumption modelling using dynamic systems simulation. Model development drew on comprehensive hydrological, hydrogeological, and operational monitoring datasets collected over two years from three contrasting open-pit mine types: an iron ore operation in Kogi State, a granite quarry complex in Ogun State, and an artisanal gold operation in Niger State. The integrated model is the first to simultaneously resolve inter-seasonal variability, orographic rainfall effects, and rapid land use change driven by expanding pit footprints in a Nigerian tropical setting. Validation against independent monitoring data achieves Nash-Sutcliffe efficiency coefficients above 0.82 for all three test sites. Application of the model to evaluate proposed mine expansion scenarios at the Kogi iron ore operation reveals a 340 percent increase in peak dewatering pumping requirements, with significant downstream stream flow depletion during dry season months. The dissertation delivers an open-source implementation and guidance manual for mine water practitioners in West Africa. Keywords: mine water balance, tropical open-pit mining, hydrogeological modelling, Nigeria, water management.