Nearly all mining operations depend on the availability of a raw water supply source for various uses on site, ranging from minerals processing to dust suppression, and providing hydraulic power to longwall equipment.

Water presents challenges for many organisations in the mining sector. In the last decade, the extremes of the Australian climate have highlighted the risks of both water scarcity and abundance. Maintaining the right balance of water is critical to the success of all mining operations.

The continued operation of and planning for new mining operations in Australia has historically relied on recorded rainfall and evaporation data to assess the climatic variation, and therefore, the extremes in water availability. However, recent climatic events within the Bowen Basin in Queensland highlighted deficiencies and the potential vulnerability mining operations as a result of inadequate mine water management both on site and off site when challenged by the extremes of a variable climate.

Managing climatic risk

Water issues as a result of climatic variability cannot be managed until they are characterised and understood. The first step in understanding vulnerability of an operation to climate variability is to have a robust understanding of the site water management. This includes knowing the water movements on site, including demands, pump movements, storage volumes and water quality. Coupled with this is the need to understand future mine planning in terms of production and mining sequence, and how it will affect the water management of the site.

Characterising the risk to the operations can be addressed through a portfolio risk management approach, using an integrated stochastic climate analysis with advanced water modelling software. The development and application of stochastic climate series allows mining companies to quantify the risk of future climate variability. This can be enhanced using water modelling software to link individual site water balances across several operations to water supply storages and delivery infrastructure. The stochastic assessment simulates climate variability and allows the impacts to a range of outcomes to be quantified, including uncontrolled releases, pit flooding and lost production.

Coupling stochastic climate analysis with water balance modelling across an entire portfolio of assets and operations provides a versatile, risk-based assessment and decision-making tool to support the organisation’s operations. The tool has a customised interface to allow the user to independently and directly test the implications of changes to their operating scenario as their planning evolves.

This approach enables mining companies to understand the manner in which different sites will respond to a particular water strategy, and respond accordingly. Ultimately, it enables them to:

• Identify opportunities to move water between sites 
• Manage the draw-down on site water storages to use site water more efficiently 
• Identify the impact of risks to third party infrastructure (government-owned raw water infrastructure) on their operations 
• Conduct trade-off studies to identify and prioritise operational activities during climate extremes 
• Identify a different security of supply or acceptable risk level at each operation based on the economics of each operation 
• Prioritise and justify capital spending for supporting infrastructure such as raw water pipelines and on site water management infrastructure

The portfolio risk management tool provides valuable input to cost benefit assessments, which enables the value proposition on an infrastructure investment decision to be understood. The capital expenditure on infrastructure for risk mitigation is best justified by calculating the value of the lost production. This is particularly valuable during the strategic planning for expansion projects, where significant capital costs are required to provide or upgrade infrastructure.

Risks to operations

The greatest risk to operations is due to insufficient raw water for the various activities on site, but particularly for processing coal. The greatest risk is not just the supply risks; it is the limited understanding of climatic variability, their risk to and impacts on operations, and a lack of planning to mitigate these risks.

High rainfall generally has a more immediate, operationally-focused management and compliance issues, associated with discharging the water off site, and less long-term, production-related impacts. However, droughts present sustained and prolonged risk to operations which could shut down production for periods ranging from a month to years.

Although climatic extremes always present a risk to operations and production, advanced planning and an understanding of climatic variability can mitigate the potential impact of climatic extremes. If the peaks in raw water demand are utilised as the design basis for external water supply, this results in oversizing and under-utilisation of the external water supply infrastructure (pipelines and pump stations). This is an ineffective use of capital. Peak water demand, and therefore infrastructure required, can be reduced and appropriately managed through continued supply of raw water from external sources over a longer period. This reduces the peak demand whilst maintaining operations.

Critical to the ability to draw raw water via infrastructure during these periods are large on-site storages. Existing mines are advantaged by generally having large storages from previous mining operations. However, new mines do not, and therefore, are more dependent on external infrastructure (pipelines and pump stations) and more susceptible to variable climatic conditions. New mines can also be at risk when raw water supply is unavailable due to infrastructure outages. As they are dependent on continued supply, any disruption to supply during climatic extremes can place them at elevated levels of operational risk, and therefore, risk of lost production.

Application to mining operations

Risk management and mitigation is an ever-present component of mining. Climatic conditions are an element of risk, however, it is more unpredictable and can present greater challenges to manage. However, there are a range of opportunities available to minimise the risk for existing and new operations.

The best method for managing the potential risk to operations is by understanding the extremes of climatic variability for operations and the mitigating triggers for action when challenged with climatic extremes.

Secondarily, the continuous review of operations and the prevailing and long-term forecast environmental conditions enables on-site water uses to be adjusted or modified at the earliest possible opportunity. This helps mitigate the potential impacts of prolonged periods of low rainfall and run-off.

By taking a balanced, statistical view of the potential climatic extremes, planning can be undertaken to minimise the production risk. In addition, modifying the mine water management system and providing sufficient flexibility in its operation can mitigate the potential risk and allow for rapid response to changing conditions, particularly for periods of excessive rainfall.

Through advanced planning for climatic variability, the mining operation (and its owner) can proactively manage the risks and plan for potential solutions. Infrastructure planning plays an important role in minimising the potential timeframes required to implement solutions.

Fundamental to the management of water on site is understanding the demands and volumes of water required under a range of climatic conditions. Whilst this understanding will be limited for new mines (where no historic data is available), water use data at existing mines is invaluable for informing the demands and options for on-site management. Data collection for all water uses is critical to the success of all mine water strategies. Coupled with the continuous review of operations, this can aid in managing the risk.

The key to overcoming these challenges is having a detailed understanding of current and proposed operations, and their associated demands. Coupled with a stochastic assessment of the local climatic system, the specific risk to operations can be determined and appropriate, cost-effective water management measures identified, planned and implemented as required to minimise the risk of lost production.

Elements of this article were presented by Tim Saxby at the 2011 International Mine Water Association (AMWA) Congress held in Aachen, Germany.

References

National Climate Centre (2011), Special Climate Statement 24, http://www.bom.gov.au/climate/current/statements/scs24b.pdf, Australian Bureau of Meteorology 2011.

National Climate Centre (2007), Special Climate Statement 14, http://www.bom.gov.au/climate/current/statements/scs14.pdf, Australian Bureau of Meteorology 2007.

Finch J (2011), Queensland Mining Devasted by ‘Worst Flooding on Record’. QLD Mining and Energy Bulletin Winter 2011.

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