Flood forecasting for a safer dam upgrade

An effective flood forecasting system is a vital tool for managing the significant risks that floods pose to communities, infrastructure and the environment.

If you can clearly understand the likelihood and scale of potential flooding and get accurate and timely warnings, you can better manage water infrastructure and implement safety plans in time to protect assets and communities at risk.

For hydropower businesses such as Hydro Tasmania, flood forecasting is a critical part of managing dam risk. Specialist power and water consulting firm Entura provides real-time inflow and flood forecasting and data management solutions to help manage Hydro Tasmania’s extensive catchments and 55 major dams.

Our most recent example of the risk-reducing benefits of flood forecasting systems is the major upgrade in 2014–15 of the Rowallan Dam on the Mersey River in Tasmania’s north, first built in 1968. The 43m-high earth and rockfill dam needed total refurbishment to be sure of a long, safe future.

Significant work was needed to bring the dam up to modern engineering standards and to increase its capacity to withstand large floods. To complete the necessary upgrade works, Rowallan Dam had to be excavated from crest to foundation on both sides of the spillway walls, exposing the heart of the dam.

The Rowallan Dam flood forecasting system allowed operators to confidently manage the flood risk during construction, ensuring the safety of construction workers and the public downstream, and protecting infrastructure and the environment from major flood damage.

The need for flood and lake-level forecasting at Rowallan Dam

During the construction phase of the major upgrade, Rowallan Dam faced a higher than normal risk of exposure to floods. Overtopping of the temporarily lowered dam crest during construction would compromise dam safety.

Kim Robinson, Senior Hydrologist and Project Manager for the Rowallan Dam flood forecasting system, said “This work was unprecedented in Australia because it was undertaken on a live dam, holding back Lake Rowallan – with a capacity of 130 000 megalitres.”

Kim explained that forecasts of lake levels were needed so that Lake Rowallan could be kept at the appropriate target level during the major excavation and refurbishment works. For safe work, the lake level needed to be lowered significantly by periodically opening a bypass valve to release water from the lake.

“The lake level needed to be low enough for safety, while also not losing too much valuable water, and potential revenue, by releasing too much water through bypass valves rather than through the power station,” Kim said.

As well as the required forecast of lake levels, a flood forecast was needed to indicate when emergency backfilling of the dam crest may be needed.

“The sensitivity of when to trigger this kind of action was a particular challenge” said Kim. “If backfilling was not carried out in time and a flood breached the construction works, the dam would be at risk of failure, with serious consequences for the storage downstream and potential impacts on communities.”

On the other hand, triggering an emergency backfill would be likely to delay construction by a year, with large financial impacts. “Backfilling is expensive and would risk extending the construction period into the wet season and the following summer,” said Kim, “which would be very costly both in terms of construction and from losing water that could have been used to generate power”.

A robust, effective flood forecasting solution

The solution to maintaining optimum lake levels and flood preparations during the Rowallan Dam upgrade was to develop a best-practice flood forecasting system, combining measured data from sensors at key locations with rainfall forecasts from weather forecasting agencies into a hydrologic model of the catchment.

“The modelling predicted lake levels and the time it would take for water to reach critical levels that could jeopardise the dam, always ensuring sufficient time for emergency backfilling,” Kim Robinson said. “The critical level varied depending on the depth of construction works, and maintained the same level of flood risk at all times.”

The entire modelling process ran automatically and provided an updated forecast every two hours during the construction period. Plots were developed showing the best-estimate forecast of inflow and lake level and rainfall over the catchment. The operators and construction managers used these plots to guide the operation of the valves to keep the lake at appropriate levels and to ensure appropriate preparation for emergencies.

Kim Robinson explained that alerts were set to trigger if the forecast exceeded the critical level. Plots were disseminated continually via email and a website. In an emergency, SMS and SCADA flood alerts would be sent out to relevant parties. If a flood alert was issued, the dam safety emergency plan would be activated.

“The system was made more robust by building in redundancies in the modelling and developing a stand-alone system at the dam site that did not require continuous connection to the database. This could be used if communications with the dam site were lost,” said Kim.

Striving for accuracy and certainty

For users to have confidence in the outputs of the flood forecasting system, it was important that the input data and hydrologic modelling were as accurate as possible, and that the level of certainty of the forecasts was clear.

“A plan was put in place to ensure that critical rainfall and flow gauges for the modelling were operational and that any maintenance required was undertaken within strict timeframes,” Kim Robinson said. “We developed routines to automatically check all input data for errors or missing data, and send alerts if inconsistencies were detected.”

Kim explained that the flood forecasting outputs included indications for operators of the uncertainty of both the rainfall forecasts and the modelling. “We developed the rainfall forecast uncertainty measures by comparing forecast rainfall to rain-gauge data over a historical period. The model uncertainty was estimated by running the model over a historical period with historical rainfall as input, and comparing outputs with measured lake levels,” he said.

The model has permanent ongoing value to the business and is being transitioned into the ongoing inflow and flood forecasting system which is used by Hydro Tasmania to manage power generation and dam safety risk. Learnings from this project are also being rolled out across the rest of a forecasting system which produces forecasts for 31 storages across  Hydro Tasmania’s portfolio.

To discuss how Entura can partner with you to develop a best-practice flood forecasting system to help you better manage your flood-related risks, contact David Fuller on +61 438 559 763, Phillip Ellerton on +61 439 010 172 or Shekhar Prince on +61 412 402 110.

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How can the grid survive distributed generation and storage?

A lot of the talk about the ‘death spiral’ in the demand for electricity from the grid in Australia has centred on the distribution end of the equation and the downside or asset risk associated with ‘disruptive’ technologies such as solar PV and storage.

I’ve suggested before that talk of the death of the grid may be premature. But how can the electricity industry respond to the advent of distributed generation and storage to embrace its potential benefits?

The grid is still required in some form

Historically, we have moved from a decentralised or local model of electricity generation and consumption to a more centralised generation model through the development of large-scale synchronous machines (hydro and thermal).  This was driven by efficiencies and the high energy demands, both in volume and reliability, of industry.

The reduction in cost of distributed generation and storage is changing the efficiency equation for smaller users.  But distributed generation and storage is not a viable alternative for all energy users, so the grid must remain in some form.

Balancing the value and cost of grid connection

All connected parties benefit to some extent from being connected to the grid.  Generators get a delivery mechanism for their product.  Industry gets an important input to production with high levels of reliability.  Small businesses and homes get access to controllable and comparatively inexpensive energy.  Customers with distributed generation and storage get access to a sink or source that can increase the value of their investment and cap their exposure to resource or equipment failure.

The network adds value to each of these transactions since without it the individual parties must all become self-sufficient. But this added value is not always perceived as adequate compensation for the cost of grid access.  This distortion will ultimately lead to an over-investment in distributed generation and storage to go with an existing over-investment in the grid.

Reaping the benefits of distributed generation and storage

I think two changes could foster more efficient co-development of network infrastructure and distributed generation and storage:

1. developing a real-time communication and control protocol with customer loads and storage
2. re-evaluating the worth of the network, basing value not on sunk cost but on utility.

Developing a real-time communication and control protocol

To enhance the synergies between distributed generation and storage and the wider network, real-time status and control of loads and storage must be available to whoever needs it.  The mechanics of this are not difficult unless response must be rapid.  The sooner a standard or an accepted architecture can be adopted, the more efficient the transition and the faster the realisation of benefits.

One of the great challenges of distributed generation and storage for network operators is that it fundamentally changes the assumptions that can be made about the predictability of system demand in the minute-by-minute operation of the grid.

Linking available generation more directly to that demand alleviates some of the risk associated with the increased volatility on the demand side.  It turns a looming risk into a relatively benign outcome, perhaps even a beneficial one.

For instance, if the decision to store is based on price and there is a small variation in this price setpoint across the storage fleet, then the amount of variation within one dispatch interval could be quite high, requiring larger amounts of regulation reserve to be dispatched for a larger percentage of dispatch intervals.

For large-scale renewable generators, linking to loads and storage may provide a way to increase demand to better utilise high potential yields that would otherwise be constrained in the market. The simplest example of this is a wind farm in a region where the interconnector to a larger region is at its limit.  The wind farm output will be constrained even if more wind is available, unless additional demand can be found on the same side of the constraint as the wind farm.

Re-evaluating the worth of the network

Distributed generation and storage decreases some customers’ reliance on the grid. Those customers may value the grid less, but still pay the same amount to access it. And those customers are now saying this doesn’t make sense.

We know the grid does offer value. In capability terms (reliability and security), the grid is very valuable to most customers, even if they don’t appreciate it. But the grid is over-built in capacity terms for a market awash in distributed generation and storage. For many consumers, it is no longer a choice of whether to invest in distributed generation and storage, but rather a choice of what rating of inverter or storage.

Network charges cannot continue to be based purely on the sunk cost of the development and provision of the network. This worked when there was little alternative.  But now that distributed generation and storage is viable for many, it is up to the network to improve its perceived value to keep its customers.

If customers’ willingness to pay is capped by a credible alternative, there is an easy choice for the rational customer with distributed generation and storage, and there is a hard choice for the electricity industry – change your pricing and enhance your product, or lose your customers.  This reality is better dealt with sooner than later.

The grid of the future must be developed by considering distributed generation and storage, and comparing the relative costs of network development against distributed generation and storage developments.

It is critical that we ensure the grid is right-sized for the future.  This will lead to any number of on-grid, hybrid or fully off-grid arrangements.  For an efficient outcome, the flexibility and agility of grid design and operation must complement rather than duplicate the capability provided by distributed generation and storage.

It’s not the fall that kills you …

The grid has a role to play in the future delivery and consumption of electricity.  But unless clear and correct signals are given to customers, the network will not follow an efficient trajectory to a new and suitable steady state, a soft landing.

A number of changes will help us create a bridge between where we are now (a grid that is increasingly unappealing to customers with distributed generation and storage) and where we need to be (a market with a seamless grid efficiently linking generators and loads).  These changes centre on standardising technology and being open to adaptive network pricing and planning.

Accommodating the growing competitiveness of distribution and storage is essential to the long-term wellbeing not only of the electricity industry but also the economies it has nurtured and that sustain us all.

If you would like to find out more about how Entura can help you adapt successfully to the rapidly changing market for electricity generation and energy services, contact Donald Vaughan on +61 3 6245 4279.

About the author

Donald Vaughan is Entura’s Technical Director, Power. He has more than 25 years of experience providing advice on regulatory and technical requirements for generators, substations and transmission systems. Donald specialises in the performance of power systems. His experience with generating units, governors and excitation systems provides a helpful perspective on how the physical electrical network behaves and how it can support the transition to a high renewables environment.

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Breathing new life into ageing assets: asset management in practice in PNG

The remote Ok Menga hydropower station in the Western Province of Papua New Guinea is vital to the operation of the Ok Tedi mine (OTML). It offers an example of just how expensive it can be when ageing power stations deteriorate and become increasingly unreliable.

The Ok Menga hydropower station provides almost three-quarters of the power needed to operate the mine, with the remaining power generated using expensive diesel fuel. The local power network is isolated and not connected to any of the country’s electricity grids, so any failure of the Ok Menga power station is costly.

If one of Ok Menga’s two generating sets is out of action, replacing that amount of hydropower (about 30 MW) with diesel-generated power could cost around AUD$650 000 a day in fuel alone. Worse still, a full outage of the power station could cause the mine to shut down, losing copper, silver and gold production worth around AUD$4 million per day!

The Ok Tedi mine had been scheduled to close in 2015, so preventative maintenance had not been a high priority for its owners, and the Ok Menga power station had become run down. When the mine’s proposed closure was delayed to 2025, a new operational strategy was needed to wring at least another ten years of useful and reliable life out of the more-than-30-year-old Ok Menga power station.

OTML needed the help of skilled asset management experts to extend the life of the Ok Menga power station, so it engaged specialist power and water consulting firm Entura to conduct an extensive condition assessment and come up with a risk mitigation plan to get the best out of the station in a cost-effective way. This also included building the skills and knowledge of OTML staff who had not had any formal training for years.

Ok Menga’s unique challenges

Although Ok Menga had many of the same asset management issues as any other hydro plant, it also presented some unique challenges in terms of risks and maintenance strategies. Its isolation and association with a large mining operation challenged many of the conventional rules fundamental to asset management in larger power utilities.

Leigh Smith, specialist consultant in asset management at Entura, explained: “In our asset management approach, we needed to take into account how the particular characteristics and circumstances at Ok Menga created differences for aspects such as the design life, planning outages, access to the plant, the holdings of critical spare parts, and the consequences of faults. For example, because outages at Ok Menga incur such high costs, we needed to replace rather than refurbish machinery, because they couldn’t have the machines offline for long.”

Bringing risks under control

Entura applied its best-practice asset management approach at Ok Menga by thoroughly assessing the condition, performance and remaining useful life of all aspects of the station, and developing a risk mitigation plan including urgent actions to remedy serious risks, and ‘quick wins’ to improve the state of the station quickly, cheaply and effectively.

As Leigh explained, “We report the condition of the plant in terms of business risk, and the mitigation strategies we propose are all about reducing risk to a level that’s acceptable to the business in cost-effective and practical ways”.

Quick wins and priority actions

At Ok Menga, two ‘quick win’ projects were identified to mitigate critical risks. The main inlet valves were difficult to access and in poor condition with no critical spare parts on site, and the original analogue turbine governors installed in the 1980s needed replacing but no governor spare parts were available.

“A failure in either or both of these areas was seen as likely in the foreseeable future and would create serious consequences of a prolonged forced outage for one unit or even the complete station,” said Leigh.

Replacements for the main inlet valves would take more than 18 months to deliver, so an emergency repair kit containing critical spares was ordered immediately. Replacement of the governor controllers with newer digital technology was also rapidly initiated to quickly reverse declining reliability.

Leigh said, “Getting these ‘quick win’ projects going straightaway was imperative and immediately reduced very significant risks.”

As well, at Ok Menga, three priority asset risk mitigations were identified relating to the station’s rock trap, unit 1 turbine and the dewatering and drainage system. The rock trap was found to be full, and cleaning it out was initiated quickly. Ok Menga’s unit 1 turbine was worn so the unit 1 runner and cassette were replaced. The security of the dewatering and drainage system had been degraded and it was at risk of failure so Entura recommended that it be upgraded to a system with greater reliability and redundancy.

“Because these priority actions minimised damage to turbines, avoided possible turbine malfunction, and reduced the risk of the powerhouse being flooded, they made a big contribution to reducing the owner’s overall risk exposure,” said Leigh.

Building capacity

To fill skill gaps at the Ok Menga power station, Entura developed an Australian-accredited program to train new and existing hydro operators. Local staff were included in the asset management process and have now had first-hand exposure to best-practice techniques.

“The owner of this power station is very committed to a sustainable future, and this extends to its staff.  The platform is now set for local staff to build on their newfound knowledge and continue to improve their understanding and skills in asset management,” explained Leigh.

Entura has developed its knowledge of asset management through our involvement over the past 100 years with the extensive power and water assets of Hydro Tasmania, Australia’s largest renewable energy producer. Our approach to asset management is recognised as best practice.

“We have spent considerable time learning and developing our systems and knowledge, and this enables us to deliver cutting-edge asset management techniques to our clients without the expense they’d incur if they started from first principles,” said Leigh.

Entura’s holistic best-practice asset management approach at the Ok Menga power station delivered a range of benefits including reducing immediate and longer term risks, and increasing the knowledge and skills of local staff – saving OTML the time and cost of developing its own in-house programs.

If you would like to discuss how Entura can assist you with assessing your hydropower plants or other power or water assets to minimise risk and maximise efficiency and useful life, please contact Leigh Smith on +61 419 884 318 or Shekhar Prince on +61 412 402 110.

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Less risk, more benefit: managing assets for long-term gains

Hydropower stations, like all technology or infrastructure, won’t stay efficient, reliable or safe without regular and ongoing attention.

Outages and failures caused by ageing or deteriorating infrastructure can be extremely expensive and serious, and far outweigh the costs of a well-targeted asset management plan. The costs of unreliability are even more significant for hydropower stations in isolated locations or where the power is relied on to run industrial or commercial operations.

But asset management isn’t only about avoiding disasters … It’s also about getting the most out of asset life or ‘getting more bang for your buck’. Owners and operators stand to reap rewards from improved performance and greater reliability if they protect and extend the lives of their investments using best-practice asset management techniques.

From basic to best practice

In today’s industry, significant amounts of time, energy and effort are invested in achieving desired plant performance at the lowest possible cost without exposing the business to unacceptable risk. Truly sustainable and successful businesses have found ways to balance these priorities, and have strategies in place to adjust the balance as needed when facing changing conditions.

Besides the large financial consequences of outages, failures of systems and equipment can also place the lives of workers at risk. Repairing and upgrading equipment and systems only after they fail is an extremely costly and dangerous way to manage assets. This kind of basic ‘breakdown-oriented’ or reactive asset management is likely to result in unreliable plant and increased human and financial risks.

As businesses mature in their approach to asset management, they progress from a breakdown-oriented approach, through reactive and corrective approaches, towards preventive, predictive and proactive approaches.

Best-practice asset management focuses on reducing risks and improving condition and performance to get the best results. It is driven by strategy and responds to the market, empowers the workforce and makes workers accountable, and always puts safety first. It also needs to be flexible enough to accommodate the individual characteristics of different hydropower stations.

Save time, save money, save lives

Specialist power and water consulting firm Entura thoroughly understands the complexities and benefits of asset refurbishment, upgrade, modernisation and extension of life.  As part of Hydro Tasmania, Australia’s largest renewable energy producer and water manager, Entura has day-to-day experience of the challenges of maintaining and upgrading assets to get the best performance, reliability and economy over the long term, through dealing with 30 hydropower stations built and maintained over the past 100 years.

Entura’s asset management techniques are based on condition, performance and risk – designed to save companies time and money. This approach is underpinned by an optimised system that combines reliability-centred maintenance (RCM) and failure modes and effects analysis (FMEA) using generic failure mode databases that can be applied to various different assets with quick results.

Entura’s asset management approach has helped other asset owners across Australia, New Zealand, Papua New Guinea and Malaysia to reduce their costs, reverse declining reliability, obtain better returns through increased performance and improved technology, increase personnel safety, decrease fire and flooding risk and other hazards, increase skills of their staff, and ensure the long-term viability of their valuable infrastructure.

Three steps to best-practice asset management

Entura’s approach to best-practice asset management has three steps that fully consider your assets’ past, improve their present operation and risk profile, and position them for their best possible futures.

Step one: Assessing assets

To fully assess an asset, we undertake detailed inspections and consider the four parameters of:

• condition (observed and measured condition, and maintainability, which takes into account the availability of spare parts, technical ability, and industry compliance)
• performance (both capability and reliability)
• confidence (the level of detail or rigour of the assessment)
• remaining useful life (an estimate of the rate of deterioration of the asset, indicating where the particular asset is on its lifecycle curve, and whether a refurbishment or upgrade can improve its position on this curve, even effectively returning it to as-new condition).

We present a high-level ‘water-to-wire’ summary of the condition and performance assessment results that quickly and graphically displays the known asset condition and remaining useful life, and identifies components for which the condition is not adequately known.

Step two: Developing a risk and mitigation plan

Once an asset has been fully assessed, we develop a risk and mitigation plan.

First, we gather and review a comprehensive set of information on the operation, design and construction of the station and its assets. We explore both the asset history and generic databases to determine probable failure modes.

Once we’ve gathered this information and analysed it against the requirements of the power station, we report the known condition of the plant in terms of business risk and develop practical and cost-effective mitigation strategies to reduce risk to a level that is both achievable and acceptable for the business.

We identify and undertake mitigation actions including ‘quick wins’ (actions that can be undertaken quickly and easily to achieve major improvements) and immediate priority activities to reduce risks. We also detect assets or components that need further investigation.

Step three: Optimising future performance (tailoring the balance)

Best-practice asset management takes a broad view of the life and operation of an asset, not only reducing immediate risks, but also promoting long-term efficient performance and sustainability. Our approach optimises the capital and operational costs over the remaining life of the asset.

A valued part of Entura’s asset management approach is our ability to offer a review of likely efficiency and capacity gains, and other general suggestions for improving performance and systems.

An important step in our holistic approach to achieving long-term safety, reliability and efficiency is training local hydro operators to fill any identified skill gaps and better safeguard the maintenance of assets. We build the capacity of our clients through on-site or formalised training through our Entura clean energy and water institute.

If you would like to discuss how Entura can assist you with assessing your hydropower plants or other power or water assets to minimise risk and maximise efficiency and useful life, please contact Ambrose Canning on +61 3 6245 4212 or Shekhar Prince on +61 412 402 110.

About the author

Ambrose Canning is Entura’s Principal Consultant, Mechanical Engineering. He has more than 30 years’ experience working on hydropower and water infrastructure projects in Australia, New Zealand, Malaysia, Papua New Guinea, India, Nepal, Philippines and Indonesia. He specialises in all aspects of hydropower development and redevelopment, upgrade and rehabilitation. He also has expertise in aspects of water infrastructure, such as dam electro-mechanical and hydro-mechanical equipment, pipelines, valves, pumps, screens, gates, valves and bulkheads.

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Dam safety: protecting lives and driving efficiencies

Humans have been damming rivers since 3000 BC for water retention and supply.

People can fish in the lakes formed by dams, sail on them, swim in them. They are important to life, providing water supply, irrigation for crops and power generation. But if a dam fails, causing devastating flooding downstream, the results can be catastrophic.

The worst dam failure in history occurred in China in 1975 when the Banqiao Reservoir Dam and other dams in Henan province failed, killing an estimated 171 000 people, with 11 million people losing their homes.

Safety is the key

Dam safety is a crucial aspect of modern dam building. Ensuring the safety of existing dams is a key concern of any dam owner, whether the dam is for generating power, protecting a nearby population from potential flooding or for the age-old reason of water supply.

Specialist power and water consulting firm Entura provides dam safety programs for Gordon Dam, the largest concrete arch dam in Australia, and other assets owned by Entura’s parent company, Hydro Tasmania, and for government and corporate clients around Australia, south-east Asia and southern Africa.

Hydro Tasmania is Australia’s largest water manager, so it needs to ensure that the risk of a failure across the portfolio is very, very small. With 55 large dams and many smaller ones, Hydro Tasmania needs to be able to identify the highest risk dams, so it is able to prioritise work on maintenance and refurbishment.  This is achieved using a process undertaken by Entura called a portfolio risk assessment (PRA).

Hydro Tasmania is committed to the safety of its assets for the people of Tasmania and its PRA enables the business to prioritise where it focus its financial resources, management and dam safety efforts.

What’s the level of risk?

Energy and water asset owners are increasingly choosing to implement a dam safety program to quantify and manage operational risks, evaluate high risks and find solutions for identified risks or deficiencies. Entura believes that a risk-based framework like a PRA is the best way to achieve an efficient and effective dam safety program.

Older dams or dams located upstream from populated areas are often high risk. The inspection regime for high-risk dams is understandably more robust and rigid than for low risk dams. However, it’s not just ageing that creates risks for dams. In Australia, the methods used to predict and anticipate floods are equally important, as is the increased knowledge that we’ve gained of the various causes and mechanisms through which dams can fail.

Entura’s PRA reviews the consequences of failure of a dam by looking at the impact that it may have on downstream populations, and also looks at the chance of failure occurring by considering extreme events such as floods and earthquakes, taking into account the specific site conditions.  It is the combination of the chance of failure with the resulting consequence that determines the level of risk.

A world-wide issue

A number of dam owners across the Asia-Pacific region are now looking at Entura’s PRA program, especially when they have a significant dam portfolio already developed. Our clients in the region are exploring how they can best use their resources and how to prioritise expenditure on their assets.

Having undertaken safety reviews and dam safety work in the Philippines, China, Indonesia, Malaysia, New Zealand, Papua New Guinea, Fiji and India, Entura understands the typical safety needs and drivers of dam owners across the world.

Australia has well-developed dam safety legislation in which Malaysia, for example, with its increasing number of dams, is very interested. Malaysia has experienced the tragic results of a dam safety incident, with the death of a number of people due to water releases through the spillway gates of Sultan Abu Bakar Dam.

On behalf of the Ministry of Public Utilities, Sarawak, Malaysia, Entura used its dam risk framework, similar to that used in a PRA, to assess whether the Bakun and Murum dams were ready to be impounded as construction reached conclusion. This dam risk framework looked at the potential scenarios that could lead to the sudden release of reservoir water, the likelihood of these scenarios occurring, and the corresponding consequences. Through this process the key dam safety risks were identified, and actions were determined to either eliminate or reduce the risks to an acceptable level.  These actions needed to be addressed prior to impoundment.

Dam safety is an ongoing concern

The safety and risk-level of a dam can change with time.  As dams or assets age, the way they are managed needs to change and they often need upgrading to ensure continued safe operation and desired life expectancy. But undertaking upgrades can potentially increase the risk of the dam during the construction phase – due to the removal of shoulder material from an embankment, or restricting the discharge capacity in a spillway chute. To contain the risks during the construction phase, operational practices might need modification, for example, operating a dam at a lower lake level during the period of construction to ensure the overall risk is not significantly increased.   This is why it is so important to have a plan to manage the safety of the dam during its entire lifecycle.

Five steps to assess dam safety risks

Risks can be reduced in a range of ways and, in many cases, a number of risk treatment options are used together:

• reducing the likelihood of the risk occurring (e.g. strengthen a dam)
• reducing the consequences if the risk does occur (e.g. upgrade emergency planning)
• staging risk treatments (e.g. address most cost-effective risk mitigation works first)
• balancing the resources required to treat a risk with the benefits of reducing the risk (e.g. examine various levels of investment and their respective risk reductions).

Entura’s portfolio risk assessment approach has five key steps:

Resource levelling

All businesses need to share resources across many activities besides risk mitigation works. For a hydropower company, a significant reinvestment in generating plant is required to both manage risk and maintain asset capability. Resources are also needed for investment for growth and diversification.

Within the dam portfolio, it is important to ensure that resources, both human and financial, are not applied to risk mitigation projects at the expense of the fundamentally important surveillance and monitoring activities. A balance is needed between reducing risk and maintaining and enhancing surveillance and monitoring instrumentation.

An ongoing effort

Finally, it is important to realise that the capital works program for dam safety risk reduction is not a static program, locked in and then implemented without change. Rather, it is an active program that is reviewed regularly, actively managed and needs to remain responsive to new or changed risks, developing understanding of dams engineering, shifts in business priorities, delays to projects, and new developments in risk management processes.

The same process can be applied to other assets

The PRA process can also be used for other assets that have a low chance of failure but high consequences if failure were to occur.  At Entura, we have successfully applied our PRA process to penstocks and pipelines, and to canal systems, identifying key risks and prioritising the actions needed in a way that most effectively manages resources.

If you would like to discuss how we can assist you with assessing your dam risks or developing a resource-effective and comprehensive dam safety program, or apply the same PRA process to other key assets, please contact Richard Herweynen on +61 3 6245 4130.

About the author

Richard Herweynen is Entura’s Technical Director, Water. Richard has three decades of experience in dam and hydropower engineering, and has worked throughout the Indo-Pacific region on both dam and hydropower projects, covering all aspects including investigations, feasibility studies, detailed design, construction liaison, operation and maintenance and risk assessment for both new and existing projects. Richard has been part of a number of recent expert review panels for major water projects. He participated in the ANCOLD working group for concrete gravity dams and is the Chairman of the ICOLD technical committee on engineering activities in the planning process for water resources projects. Richard has won many engineering excellence and innovation awards (including Engineers Australia’s Professional Engineer of the Year 2012 – Tasmanian Division), and has published more than 30 technical papers on dam engineering.

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