Seasonal Rainfall Effects on Mine Water Balance and Production Reliability: Evidence from an Open-Pit Gold Mine in Southwestern Nigeria

Effective water management is essential for maintaining safe and efficient open-pit mining operations, particularly in tropical regions where seasonal rainfall can significantly influence mine water inflow and dewatering requirements. This study evaluates the impact of seasonal rainfall variability on dewatering performance and production efficiency in an operational open-pit gold mine in Southwestern Nigeria. The research utilised rainfall records, pit water inflow measurements, dewatering performance data, and monthly production reports collected from mine operational records and supplemented with meteorological data. The datasets were processed and analysed using descriptive statistics, Pearson correlation, regression modelling, independent sample t-tests, and analysis of variance to establish relationships between rainfall variability, water accumulation, dewatering response, and production performance. Results revealed a moderate positive and statistically significant relationship between rainfall and surface water inflow (r = 0.577, p = 0.001), indicating that increased rainfall directly contributes to pit water accumulation through surface runoff. Regression analysis showed that rainfall explained 33.3% of the variation in surface inflow, with each additional millimetre of rainfall increasing surface water inflow by approximately 12.98 m³. In contrast, groundwater inflow showed a weak and statistically insignificant relationship with rainfall (R² = 0.007, p = 0.677), suggesting that subsurface hydrogeological characteristics have greater influence on borehole inflow behaviour. The relationship between rainfall and production output was also statistically insignificant (r = 0.132, p = 0.503), demonstrating that effective dewatering systems and operational planning reduced the direct impact of rainfall on mine productivity. The study concludes that rainfall primarily affects open-pit mining operations through increased surface water inflow rather than direct production losses. The existing dewatering system was found adequate for managing seasonal water challenges; however, improved borehole utilisation, real-time water monitoring, energy-efficient pumping strategies, and enhanced runoff control are recommended to optimise future mine water management.

Seasonal rainfall; Open-pit mining; Mine dewatering; Surface water inflow; Groundwater inflow; Production efficiency; Gold mining.

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