Mining the advantages of water balance modelling
Mining operations are critically dependent on water, which is typically in short supply in areas where minerals are found. For a mining project to be economic, the operator must ensure a sufficient supply to run the operation.
A reliable supply of surface water, and the possibility of water reuse, can translate to savings in both supply pipelines and water licences.
To investigate the possibility of surface water supply for the Hera Gold Mine Project in Nymagee, western New South Wales, mine owner YTC contracted Strategic Environmental and Engineering Consulting (SEEC) to undertake a water balance model for the project.
The Hera gold-lead-zinc deposit is projected to achieve gross revenue of $510 million over its seven year life-span, with a 94 per cent gold recovery rate – providing water can be managed effectively. A shortage of water for mining could carry a serious price tag in a region which receives an annual rainfall of just 406 mm, with long gaps between periods of rainfall.
To undertake the water balancing model SEEC used eWater’s urban stormwater modelling software, music (model for urban software improvements conceptualisation). music is one of the few software tools available that can accurately simulate real-time water sensitive design.
“A mine relies on water and often the cheapest supply of water is from harvesting surface runoff. However, relying solely on surface water might not be enough,” says Mark Passfield, Director at SEEC in Bowral. “I was contracted to determine what supply confidence there might be from surface water alone. I estimated how much surface water they have out there, and used music as a pre-development assessment tool.”
Since dam size is influenced by the amount of rain an area receives and the local coefficient of runoff, Passfield says he inputted rainfall data and evaporation data for the Cobar region from the Bureau of Meteorology into music to enable him to estimate catchment runoff and to model the performance of various dam sizes.
“music helped me optimise the size of the dams,” he says.
Passfield calibrated music to yield the estimated surface runoff.
“In the Nymagee region, two to three per cent of the rainfall is expected to become runoff and this can be harvested,” he says. “music enabled me to optimise the dam sizes, make an estimate of supply confidence and predict potential changes in stream flow. At the end of the model, I modelled the catchments with and without the supply dams. The results showed the primary steam would have about one and two per cent less mean annual flow with the dams in place. It was surprising to see how little effect the dams could have on the stream,” Passfield says.
“music enabled me to interrogate the models and dam sizes. I kept trialling different dam and catchments sizes until I got them optimised. I could also predict how much land was required.”
Passfield says the music interface is intuitive and is easy to use as a water balance modelling tool. For instance, for the same project, he modelled the difference between drawing water proportionally from four dams at once or from just one at a time until dry then moving to next. “It was interesting and showed that drawing water from four dams at once was slightly better than drawing water from just one at one time. I think, in that climate, evaporation plays a big part. This type of modelling can demonstrate how to use dams in an efficient way“.
Passfield says he has applied music for several water surface assessments for mines, often as part of Environmental Impact Statements. He exports the music data to MS Excel in order to present the findings and results in graphs.
music helps urban stormwater professionals visualise possible strategies to tackle urban stormwater hydrology and pollution impacts. Since first developed in 2001, the software has been used by thousands of professionals working in private practice and in state, regional and local government agencies throughout Australia.