A four-phased approach to mine dewatering design and implementation for surface and underground mines – 2026
Kym L Morton1, Wayne L Van Heerden2
1KLM Consulting Services Pty Ltd, 22 Central Road, Lanseria, 1748, South Africa, ORCID 0000-0002-5865-1979
2KLM Consulting Services Pty Ltd, 22 Central Road, Lanseria, 1748, South Africa.
Abstract
Mining requires penetrating the local and regional water table as well as disrupting the natural flow of water on surface and below ground. The excavation of voids creates inflows, which, when there are sufficient sources of water and the country rock is permeable, become a nuisance to operations and often a serious hazard that can result in fatalities. Water is the most frequent cause of mining insurance claims.
A detailed dewatering design and effective implementation of the design improves working conditions by reducing water risk, wear and tear on machinery and operational earth moving costs. A good design also increases safety factors in slope stability for open pits, thus improving overall safety. For underground mines, a detailed dewatering design, which is properly implemented, can reduce both Capex and Opex by over 10%. An accurate dewatering design, which intercepts water before it contacts the ore body, also reduces water treatment costs and protects the environment. The success of a dewatering strategy is dependent on a detailed understanding of the groundwater regime, observed through a comprehensive water level and flow monitoring network.
The application of the best strategy for mine dewatering can intercept the bulk of inflows. Dewatering options can be combinations of both passive and active strategies comprising precise storm water design, use of drainage trenches, construction of sumps, drilling of drain-holes, equipping of pit-perimeter pumping boreholes (wells), timeous installation of in-pit boreholes and the construction of dewatering galleries. A four-phased approach to dewatering design and implementation promotes logical management of relevant data, assembly of information, and creation of knowledge for use in all aspects of dewatering design and facilitates timeous implementation.
Mine dewatering design strategy is similar for both surface and underground mines, and can also be used when planning a transition from open pit to underground extraction. Impacts of groundwater inflows on mining operations are best assessed at the pre-feasibility stage of mine design, but can be done at any stage of mine life. This paper recommends a hydrogeological investigation be implemented in four phases. The first phase is typically a desktop study to identify and quantify the water management problem, collection of initial site data, construction of a detailed initial conceptual hydrogeological model, then use of the information to brainstorm and identify the most practical and pragmatic options for water control.
Phase 2 includes numerical modelling of the conceptualisation, supported by an accurate interpretation of updated and detailed monitoring data. The objective of Phase 2 is to use the initial conceptual model to drive predictive simulations of different dewatering options. This enables evaluation of the possible strategies and methods for accurate groundwater control. The next phase, Phase 3, uses detailed mine plans to set specific dewatering targets, including nominated water levels and pressures for all mine sectors for specific dates. These initial dewatering designs and layouts can be used to create a prototype installation, which can test the concept and measure the effectiveness of the method in dewatering or depressurising specific mining sectors. Success of the prototype and its evaluated results are used to improve the design. This improves efficiencies and assists with the creation of an updated design and strategy for full implementation of dewatering for all areas of the mine. Phase 4 includes optimisation, mine closure design and long-term water management.
A phased approach is iterative, requiring the conceptual and numerical models to be regularly scrutinised, updated using the most recent water level and flow rate monitoring information. The results are compared to the target water levels, and then the methodology can be improved and refined. In parallel, the monitoring network is continually upgraded to monitor specific metrics relevant to each stage and sector of the mine. The phased approach can be repeated annually, particularly if water inflows are seasonal, to ensure continuous improvement of water control. Dashboards can also be used to show relevant areas of water control in real time.
Keywords: phases, inrush, mudrush, mine dewatering design, water level targets, conceptualisation, dewatering methods, dewatering scenarios, dashboard.
This paper is an extended version of a paper presented at the IMWA 2024 annual conference called “A phased approach to mine dewatering design” Morton, K.L. (2024) ‘A phased approach to mine dewatering – Updated from IMWA 1993’, West Virginia Mine Drainage Task Force Symposium & 15th International Mine Water Association Congress, pp. 458–463.