Hydrogeological modelling for future scenarios in the Far West Rand

Abstract

The Far West Rand (FWR) characterised by its karstified dolomites and dewatering related gold mining activities, extends along the Witwatersrand mining region. These mining activities have directly impacted the characteristics of the dolomites, altering the groundwater flow pathways, accelerating sinkhole development and causing the regional high yielding springs to dry up. Subsequently changing the natural flow regime and hydrogeological characteristics of the dolomitic aquifer. This study implements a simplified water budget method to model future rewatering scenarios for the karstified dolomitic compartments of the FWR. The Saturated Volume Fluctuation (SVF) method was selected based on its adaptiveness for estimating present-day aquifer conditions as well as simulating recovery scenarios solely based on the average groundwater levels from monitoring boreholes, unlike similar water budget models. Due to the general lack in present-day monitoring data, the SVF’s lumped parameter approach provided easy calibration based on simulated water level response. Six SVF implemented equations each representing a separate compartment was calibrated over an 11-month period. Aquifer parameters were adjusted to simulate groundwater level responses within the compartments to best approximate the observed values over the same time period based on the historical rainfall sequence. To simulate recovery scenarios for each of the dewatered dolomitic compartments, SVF models were created based on the calibrated model parameters. The recovery scenarios were based on forecasted rainfall sequences created from historical data. Each of the compartments rewatered to near initial groundwater levels with inter-compartmental groundwater flow (IGF) having little effect on the overall rewatering. This resulted in spring reactivation with spring flow volumes lower than historical records. The model has demonstrated that a water budget model can simulate water level recovery in a post-mining scenario.