Portfolio risk assessment takes dam safety programs to the next level

A portfolio risk assessment allows owners of dams and other water assets to see the bigger picture of how to prioritise their efforts and resources to achieve the best safety result across their whole portfolio.

Constraints on budgets and resources remain key challenges for owners of dams and water assets, especially those with a large asset portfolio, as they attempt to reduce the risk to communities to an ‘as-low-as-reasonably-practicable’ level. Without a tool to prioritise safety works, it is impossible to use limited resources most effectively.

Dam owners have often overlooked the importance of prioritising their dam safety activities, resulting in resources being allocated equally to all dams or allocated randomly to selected dams.

For example, the traditional indexing method, which uses a standards-based deterministic approach to review deficiencies at a dam, does not look at the consequences of those deficiencies, so it fails to inform the dam owner of the associated dam safety risk.

Using a method such as this can often lead to defensive design, cost-ineffectiveness, blind upgrade, or a generic surveillance and monitoring program across all dams, and does not greatly assist the dam owner in managing the dam safety risk. Ultimately, resources may be wasted on low-risk dams, rather than used appropriately on dams with high safety risks.

Current best practice involves a risk-based probabilistic approach and takes into account the risk of failure of each dam to prioritise dam safety works. However, for a large dam portfolio, a full detailed risk assessment for all dams can be very costly and time consuming.

So, how can an owner of a portfolio of dam assets assess safety and prioritise investment without unnecessary effort or expense? The answer is portfolio risk assessment.

How portfolio risk assessment works

A portfolio risk assessment (PRA) is often a starting point for an effective dam safety program. It is not a detailed risk assessment of any particular dam, but an affordable high-level assessment at the portfolio level that presents to the dam owner the relative risk position of all dams. This enables the dam owner to better prioritise ongoing dam safety works and develop investment strategies.

In a PRA, the safety risk posed by each dam in the portfolio is usually assessed based on historically available information as well as information gathered in a workshop-type environment by an expert team of various disciplines. Key failure modes of each dam are identified, and the risks are quantified based on available information.

The key objective as a first step is to determine the first-pass risk position of the dams, followed by identifying any information gaps, strategy and priority to close these gaps. Output from a PRA can be tailored to suit organisational requirements, with risk positions determined in terms of societal, financial and political risks.

Flow-on benefits of the PRA process

PRA has proven to be a cost-effective tool in revolutionising an effective dam safety program for many dam owners in Australia and worldwide. It provides flow-on benefits to dam owners in managing their dam assets. In particular:

• Providing high-level focus and ease of reporting: A PRA provides an overview and high-level visibility and understanding of the current risk profile of the dam assets. This allows the dam owner to better focus on key dam safety issues, and makes reporting to senior management easier.
• Understanding relative risk and prioritising action: Establishing the risk profiles of all dams in a single risk plot not only informs whether the risk position of each dam is tolerable in accordance with industry best practice and guidelines, but also allows an understanding of the risk position of each dam relative to the others. This provides an opportunity for the high safety risk dams to be targeted first for dam safety activities, and allows prioritisation of dam safety recommendations.
• Best use of resources and identifying quick wins: Understanding the relevant dam safety risk profile provides clear direction for appropriately using resources to target mitigation of key risk items rather than attempting to implement all recommended actions at once, which is often not achievable. This also provides the opportunity to identify ‘quick win’ remedial works which may be less expensive yet significantly reduce risk.
• Ensuring key documentation is in place: Understanding the relevant safety risks of the dams also obliges the dam owner to ensure key documentation is in place, particularly for high safety risk dams. This may include dam safety emergency plans, operations and maintenance manuals, dam data books, hydraulic data, dam break inundation maps, and geotechnical reports.
• Reviewing surveillance and monitoring practices: A PRA provides an opportunity to review the existing dam surveillance and monitoring practice, and adopt a cost-effective risk-based approach to target the key failure modes rather than a blanket approach. As an example, a dam with a high risk of piping may require telemetered V-notches, whereas one without a high risk of piping may only require manually read V-notches or visual observations. In addition, the inspection frequency for dams with relatively low risk positions may be reduced, freeing up resources for use on dams with high safety risk.
• Improving dam safety emergency planning: An understanding of a dam’s key failure modes and failure consequences also allows improvement of critical dam safety information (e.g. event triggers, emergency evacuation), resulting in improved emergency planning.

Updating the PRA for continuous improvement

The outcome of a PRA would inform the knowledge gaps for any particular dams, and the necessary future works and investigations required to close those gaps. Following additional investigations, studies, remedial or upgrade works as a result of the initial PRA, it is good practice to update the PRA to review the portfolio risk and adjust the dam safety management strategy to achieve continuous improvement.

This will not only help dam owners to plan and prioritise their resources appropriately, but will also demonstrate to the regulator that an effective dam safety program is being implemented, which meets compliance requirements as well as industry best practices.

If you would like to discuss how Entura can assist you with assessing your dam risks through a portfolio risk assessment program, or apply the same PRA process to other key assets, please contact Shao Ng on +61 3 6245 4141 or Phillip Ellerton on +61 439 010 172.

About the authors

Shao Ng is a Senior Civil Engineer at Entura and has more than 16 years of experience in civil and dam engineering in Australia and overseas. Shao has considerable experience in project management, dam design and construction, geotechnical investigations, inspections and surveillance reviews, emergency planning, and dam operation and maintenance, and is familiar with national and international dam safety standards, guidelines and local regulatory requirements. Shao also has extensive experience in dam PRA.

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Managing risks for successful, sustainable projects

All power and water projects involve risks. The key to project success and sustainability is being able to anticipate, monitor and manage the full range of risks throughout the project lifecycle.

For power and water asset developers, sustainability is increasingly recognised as a key marker of project success and corporate reputation. Whether you’re building a hydropower station, a dam, a wind farm or a solar farm, achieving sustainability means ensuring that projects appropriately balance technical, environmental, social and economic considerations to deliver benefits and minimise risks across all these areas.

Power projects, especially in developing countries, hold great potential to contribute to the greater good by increasing prosperity and alleviating poverty, but growth must be balanced against any current and future impacts on communities or the environment. Sustainability is therefore a key concern for responsible developers, and for international financing organisations such as the Asian Development Bank, the International Finance Corporation and the World Bank.

Managing risks carefully, ethically and transparently can improve the financial and technical viability of the project, the ability to secure finance, the ability of key stakeholders to make informed decisions about the project’s future, the likelihood of community acceptance or ‘social licence to operate’, and the overall project outcomes, both now and for long-term success and sustainability.

What are the risks?

Some of the key risks to be considered throughout the design, development and operation of a power or water asset include factors such as the need or market for the project, the future energy or water demand, the best technology or design for the project, and the current and future availability of the resource.

It is also critical to consider the project’s stakeholders and broader community, particularly whether the project could involve potential social or environmental impacts and how these could be avoided, mitigated, offset or compensated, not just during development of the project but also during operation. Safety is also a key issue to be managed throughout a project’s life, including that of employees as well as the broader community.

Although not all risks will necessarily be able to be fully predicted, businesses are likely to gain substantial benefits from making structured and systematic efforts to foresee risks across the spectrum of financial, technical, stakeholder, community and environmental issues.

Assess risks early and often

Many project risks can be minimised or mitigated if they are properly anticipated early in the project, and progressively monitored and evaluated throughout the design, development, construction and operational phases.

Identifying key risks early allows companies to manage these risks throughout the project, minimising corporate, technical, environmental and social impacts and their associated costs, including damage to corporate reputation should an unmanaged risk develop into a crisis.

Assessing the risks progressively or in stages can minimise not only the cost of formal evaluation, but also save significant time and costs that could be wasted if a project were to be judged unviable during development.

Sustainability assessment, both formal and informal

Being able to formally or informally assess and comprehensively document risks and actions towards project sustainability offers significant advantages. While it can help guide a comprehensive review of risks, it can also help to identify further opportunities to increase positive outcomes. As well, it provides an easy way to regularly assess progress towards sustainability goals against established baselines, and offers a format for clear reporting both internally and to external funding bodies and stakeholders.  In other words, sustainability assessment and reporting is a valuable step in demonstrating a genuine commitment and responsible approach to achieving greater sustainability.

Entura uses a unique, tailored self-assessment tool to help power and water companies and developers understand the risks and opportunities facing their projects and build their capacity to assess, monitor and report on those projects. This tool is based on the assessment criteria identified in internationally recognised guidelines and standards such as the Hydropower Sustainability Assessment Protocol and those used by the International Finance Corporation.

The sustainability scanning tool can be used by an organisation to self-assess a project to identify whether key issues, risks and opportunities have been fully considered and to identify potential gaps needing further attention. This can be done internally following training on how to assess the criteria or undertaken by Entura’s trained assessors.

In addition, Entura’s sustainability scanning tool can be adapted to include other standards relevant to a project or client, or to assess compliance with criteria relevant to a client’s requirements or obligations (such as internal policies and/or permit or concession conditions). It can be used at any stage, or multiple stages, of a project, and for any level of sustainability goal (i.e. good practice or best practice). It can also be repeated over time for the same project to assess ongoing improvement, or to compare projects across a client’s portfolio.

The potential benefits to power and water asset developers of a systematic and thorough identification and management of the full range of project risks include easier access to finance, reduced corporate risks and costs, greater ability to anticipate and respond to stakeholder concerns, and avoidance of delays and problems through the project’s life.

This holds promise for delivering power and water infrastructure projects that are more likely to contribute positively to social, environmental and economic goals both now and into the future.

If you would like to discuss how Entura can assist you with assessing the sustainability of your project or support you to assess and track your own progress towards minimising risks and increasing sustainability, please contact Dr Eleni Taylor-Wood on +61 3 6245 4582 or Shekhar Prince on +61 412 402 110.

About the author

Dr Eleni Taylor-Wood is Entura’s Principal Consultant, Environmental and Social Science. Eleni has 20 years’ experience successfully managing large-scale, complex projects, as well as providing expert advice and independent review for a range of infrastructure and planning projects. She has worked on projects around the world including in Australia, Mozambique, South Africa, Iceland, Colombia, India, Malaysia, China, Solomon Islands, Fiji and Papua New Guinea. Her experience includes environmental and social impact assessment and management, strategic management of wetlands and waterways, feasibility and approvals for new hydropower projects, environmental flow determination and assessment, and sustainability assessments. Eleni is currently one of eleven accredited assessors worldwide under the Hydropower Sustainability Assessment Protocol.

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Using risk assessment to guide dam safety upgrades

Whether your focus is on a single dam or a whole portfolio, a risk assessment process helps you decide how best to intervene, and when, to get the maximum improvement in safety from your investment.

Using a risk assessment process to assess a whole portfolio of dams helps asset owners prioritise their limited resources for safety upgrades. Richard Herweynen, Entura’s Principal Civil Engineering, introduced our portfolio risk assessment program in his article ‘Dam safety: protecting lives and driving efficiencies’. Now we explore how a similar process can be used for a single dam to guide investigations, prioritise the order of a staged upgrade, and manage safety risks during construction, using the example of Hydro Tasmania’s Rowallan Dam.

The challenges of an ageing dam

Rowallan Dam is a 43m-high earth and rockfill dam built in the late 1960s, with two embankments on either side of a spillway located on a knob of very hard quartzite. The reservoir plays a key role in Hydro Tasmania’s hydropower system: it is a large storage at the top of the catchment and operates over a large range of water levels, capturing the high winter flows and then releasing them over the summer months through a cascade of five power stations downstream.

A dam portfolio risk assessment (PRA) completed by Entura in 2006 had identified Rowallan Dam as one of the potentially higher risk dams in Hydro Tasmania’s portfolio, with a number of suspected but not confirmed deficiencies. The potential deficiencies included a relatively high probability of a piping failure (internal erosion of the earthfill) as the filters were suspected to not meet modern standards and the dam had suffered a piping incident adjacent to the spillway walls when it was first filled.

As well, the PRA identified other potential deficiencies including questions regarding the spillway capacity, liquefiable foundations, potential for landslide hazards at the reservoir rim, structurally deficient spillway walls, and a limited capacity for dewatering.

With multiple potential deficiencies such as these, a range of challenges arise: Which deficiencies do we tackle first? Do we need to address all the deficiencies? To what level do they need to be addressed? How quickly should we address the deficiencies? And how do we justify to the business a large capital expenditure that will not generate any additional returns?

Reducing uncertainty

The original scope of the PRA was to assess the dam portfolio based only on the existing available information with the exception of preliminary dam-break modelling and consequence assessment. To allow the PRA to be completed within a reasonable timeframe and budget, this inevitably meant that significant gaps in our knowledge of the dams were filled with assumptions and best estimates.

A very targeted investigation program was then required to fill the gaps in our knowledge of Rowallan Dam’s particular possible failure modes and to prepare a fully justifiable business case. Entura led the investigation and concept development phase, working closely with external parties. The necessary investigations included:

• geological mapping of the potential landslide features (to determine whether they were in fact glacial features and not of concern)
• investigation into the core, filters and rockfill of the embankment (to confirm their properties)
• more detailed dam-break modelling (to confirm whether the original estimates of consequences of failure were correct)
• drilling of the left embankment foundation (to demonstrate whether liquefaction was a significant concern)
• full modelling of the flood hydrology (to confirm the flood risk)
• structural analysis of the spillway walls supporting the embankment on either side of the spillway chute

The spillway wall failure mode had not been identified in the PRA and was included in the investigation program to demonstrate that it was not a concern; however, it turned out to be the failure mode with the highest probability, and became the highest priority of the upgrade program.

Developing the upgrade program

When the specific investigations for Rowallan Dam were complete, the risk assessment for the dam was revised. The revised risk assessment determined the potential failure modes (in order of probability) to be failure of the spillway walls; piping along the spillway walls; piping through the upper part of the embankments; piping through the lower part of the right embankment; and overtopping of the dam during an extremely rare flood (rarer than a 1 in 10 000 year flood).

Developing an integrated, effective and progressively implemented solution that would not increase the dam safety risks during construction was a major challenge. Many alternatives for the outlet works, spillway augmentation and spillway walls were developed by Entura for resolving each dam safety risk while considering the construction flood risks and overall project risks.  This allowed Entura to find the right package of solutions to minimise the risks as well as the capital outlay. The ultimate solution included:

• increasing the monitoring of the spillway walls: To provide early warning of a possible failure, inclinometers were telemetered and alarmed. Monitoring picked up a possible deterioration in one wall, which was temporarily propped until a permanent solution could be implemented.
• increasing the dewatering capability of the dam: The riparian valve was replaced with one of greater diameter, and the controls of the turbine relief valve were modified to allow emergency bypass. This increased dewatering capacity was critical to managing flood risks during the later stages of construction and improved the ability to control any potential piping failure.
• strengthening the spillway walls on the inside of the existing walls: This approach incurred less risk of overtopping during construction than if the walls were strengthened on the embankment side. The replacement walls were designed to accommodate higher future discharges.
• installing modern, compliant embankment core filters: Installing these filters would protect the embankment from piping, but required major localised excavation adjacent to the spillway walls, including from the embankment crest to foundation, and reconstruction of the top seven metres of the embankment.

Lower risks, greater compliance

The major upgrades at Rowallan Dam have now reduced the dam’s safety risks. By considering a wide range of upgrade options and demonstrating that the selected option would significantly reduce the risk of failure through very targeted capital works, the Rowallan Dam risk assessment played a key role in developing a sound business case to demonstrate that the capital investment was both necessary and efficient – for a safer dam, both now and long into the future.

To find out more about how Entura can work with you to assess and remedy the safety risks of your dams or other water infrastructure assets, please contact Paul Southcott on +61 3 6245 4145, Phillip Ellerton on +61 439 010 172 or Shekhar Prince on +61 412 402 110.

About the author

Paul Southcott is a specialist civil engineer at Entura. He has more than 28 years of professional expertise in civil and dam engineering, as well as expertise in geotechnical, foundation, structural, hydraulic and hydropower engineering. Paul’s dam engineering experience spans geotechnical and hydrological investigation; feasibility and options studies; concept, preliminary and detailed design; engineering assessment, consequence assessment and risk assessment; safety reviews; monitoring and surveillance; and emergency planning. He has particular expertise in dam risk assessment and project managed the Hydro Tasmania portfolio risk assessment of 55 large dams, Southern Water’s 18 dams and most recently SA Water’s 18 large dams.  He was the technical leader for the Rowallan Dam upgrade project overseeing all aspects of the project including the detailed design of the spillway wall upgrades.

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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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What is the best dam type for my dam site?

Asking ‘what is the best dam type for my dam site?’ is a key question in the early stages of planning a dam project.

A number of dam types are being used around the world, such as concrete-faced rockfill dams (CFRD), roller-compacted concrete (RCC) dams, and asphalt-core rockfill dams, amongst others. Consultants that specialise in a particular dam type may offer a biased answer to the question, which is not in the best interests of the project.

The most appropriate response is that the best dam will depend on the unique characteristics of the dam site – available materials, climate, geology, topography, river flows, seismic risk – just to name a few.  This may sound obvious, yet it is surprisingly often ignored.

Although it is important that we take our experience and learnings from other projects and apply them to any new dam project, it is equally important that we do not force a past solution to fit a new dam site without considering that particular site’s uniqueness.

So, for any dam site, it is important to undertake an unbiased dam-type assessment that takes into account the range of site-specific conditions balanced against the broader project constraints (such as cost optimisation, and the availability of local design and construction expertise).

The following examples of dams with which I’ve been involved show how particular characteristics of each dam site determine the appropriate dam type.

Responding to local climate, geology and materials in Tasmania

On the west coast of Tasmania, Australia, where the rainfall is around four metres per year, Hydro Tasmania, Australia’s largest renewable energy producer and water manager, has constructed nine CFRDs.  Good rockfill was available at all of these sites.  Key reasons why CFRDs were used at these sites, rather than central-core earth and rockfill dams, included both the lack of quality clay material and the high rainfall in this region. High rainfall would significantly disrupt and delay the construction of clay-core dams due to issues with the compaction of the clay material, whereas construction of CFRDs could continue during rain. Asphalt-core dams might also have been possible in these local climate conditions, but would have presented different challenges for river diversion.

One of these CFRDs, the 82m-high Crotty Dam, faced potential instability should a traditional side-channel spillway be cut into the abutment slope, due to the steep abutment slopes and identified geological defects.  As a result, for the first time in the world, a spillway was created over the top of a high CFRD wall, combined with a large-capacity bottom outlet gate installed in the diversion tunnel.  This solution included an articulated concrete slab that would allow the spillway to move without cracking as the rockfill settled over time.

The solution at Crotty Dam was unique, but it was heavily influenced by the characteristics of the dam site and the construction materials available, which allowed a very stiff rockfill to be constructed, minimising the amount of settlement. The solution has proven a good choice, operating well for more than 20 years.

However, the particular solution that was successful for Crotty Dam may not be appropriate for other dam sites, where the dam might be significantly higher, where rockfill may be of poorer quality, or at a site with greater flood discharge or higher seismic risk.

A process of elimination in Papua New Guinea

In 2012, Entura undertook a detailed dam-type assessment for a site in Papua New Guinea, and in this case, the ultimate decision about the best dam type emerged from considering many site characteristics and then eliminating inappropriate dam types to reach a subset of viable possibilities.

The site was in an extremely high rainfall area (with approximately ten meters of rain each year), the rock foundation had relatively low strength and low stiffness, river flows were consistently high, there was deep alluvial material that would need to be removed or sealed, and the site was in a region with relatively high seismic risk.  Sources for concrete aggregate and rockfill were available.  However, due to the lack of strength and stiffness of the foundation rock, a conventional concrete gravity dam was not possible; and the extremely high rainfall posed significant challenges for a central clay core and rockfill dam.

As a result, the choices narrowed to a CFRD, an asphalt-core rockfill dam or a thick, trapezoidal RCC (or hard-fill) dam.  Ultimately, an asphalt-core rockfill dam was chosen as the preferred solution, as the core could be placed during high rainfall, the load would be adequately spread over the foundation, and it was considered a resilient design for the seismic loading.

Another important factor influencing the choice was that an asphalt-core rockfill dam would minimise problems and delays should the upstream temporary cofferdam overtop, because asphalt-core rockfill dams are always complete up to the current height of construction with no further work required below this level. Some other dam types require further work on the dam’s upstream face after the dam wall is constructed to its full height, requiring flood water to be pumped away to enable final-stage activities to proceed.

Challenges influencing RCC dam design and construction  

Many design and construction decisions for RCC dams can be significantly influenced by specific site conditions – for example, should the proportion of cementitious material (cement and fly-ash) in the RCC mix be low or high? Should one use conventional facing concrete, grout-enriched RCC or a PVC upstream membrane? Is RCC best delivered by truck or conveyor?

A significant influence on the design of the Wyaralong Dam in Queensland was the benefit of using an onsite, but inferior, sandstone aggregate for the RCC aggregate.  Using the onsite aggregate would reduce costs and benefit the local community through avoiding major aggregate haulage on public roads.

Using the onsite aggregate also influenced the investigations that occurred as part of the normal trial program used to develop an appropriate RCC mix. This in turn influenced the design of the dam because the trial mix program identified an issue with the surface durability of the RCC. Grout enrichment of the facing RCC was not suitable, so a conventional concrete using a high-quality basalt aggregate was used to provide the necessary durability.

The topography of the left abutment provided a natural ramp for an articulated truck delivery system.  This delivery system proved to be very flexible, but it was important to develop a suitable RCC mix for truck delivery.

One size doesn’t fit all

There is no easy or immediate answer to the question posed at the start of this article.  No single dam type offers the best solution for every dam site.  Although lessons learnt from other dam sites can help to rapidly narrow down a set of preferred dam types to consider in more detail, the appropriate dam type must be influenced by the unique conditions of the dam site.

Specialist power and water consulting firm Entura has significant experience with a wide range of dam types across the Asia-Pacific and southern African regions, particularly CFRDs and RCC dams.

You can read more about the way in which we responded to specific site characteristics for three RCC dams and the reasoning underpinning our design decisions in my 2012 ICOLD Conference paper “Unique challenges influencing the design and construction of three recent Australian RCC dams”.

If you would like to discuss how we can assist you with selecting the most appropriate dam type for your dam site, please contact Richard Herweynen on +61 3 6245 4130 or Shekhar Prince on +61 412 402 110.

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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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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