Open pit mines often experience significant surface water inflow that adversely impacts the production profile. SRK India was recently engaged by a leading mining entity that experiences significant volumes of surface water inflow to its operating pits. The problem is further complicated by poor surface water disposal system that possibly promotes recycling of disposed water to the operating pits.
Considering the inadequacy of surface water management system, SRK explored the opportunities to (1) prevent surface water inflow to the operating pits, (2) to dispose pumped out water away from the pit and (3) to distribute additional water to nearby communities for agricultural purposes.
Unmanned Aerial Vehicle (UAV) were flown around the operating pits to collect photogrammetry, land use-land cover and topography data. Following this, a catchment rainfall-runoff model was developed to assess surface water flow pathways and likely runoff volumes using the SCS Curve Number and Weighted Runoff-coefficient methods. Different duration of extreme rainfall event and suitable return periods were considered based on the IDF graphs developed. This helped to quantify the likely volume of surface water inflow towards the pits and the probable pathways that may be used to divert water away from the operating pits. SRK undertook multiple walk over surveys to validate such derivations.
Utilizing such site-specific knowledge, SRK developed the following:
- A mine dewatering system including advisory on optimal pumping requirement, pumping arrangement and reticulation requirements.
- Surface water diversion structures to prevent inflow to the operating pits. These structures were designed to carry intercepted runoff and pumped out water from the pit sumps. Engineering designs were developed using Manning’s formulation that helped to empirically compute velocity of flow in the channels and estimate normal depths in a uniform channel. The free board and side slope of the drains were designed following Indian and international guidelines. Peak flows were used to assess dimensions of each drain stretch. Fine adjustments in alignment were undertaken to minimize earthworks.
- A water diversion plan to combine surface water flows to a treatment plant and finally to divert the treated water to designed disposal ponds. Ponded water is planned to meet the agricultural requirement of the nearby communities. This in turn will reduce the dependency on groundwater.
- In addition, SRK also proposed a plan for integrated monitoring and database management using a Real Time Data Acquisition System (RTDAS) that will be useful in effective data recording, data sharing, visualization and sustainability. This will definitely help to reduce problems associated with inundation to the operating pits.
