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This paper presents a number of innovative hydrologic investigations undertaken for the recent
detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating
extreme floods in the tropics is the estimation of flood events of long critical durations. The
implication is that there is an increased focus on estimating the correct volume (not only the peak
flow). This paper describes the regional analysis of flow volumes that was used to validate the
estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial
reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works.

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2005 Papers

2005 – THE EXTREMES OF TROPICAL HYDROLOGY
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This paper presents a number of innovative hydrologic investigations undertaken for the recent
detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating
extreme floods in the tropics is the estimation of flood events of long critical durations. The
implication is that there is an increased focus on estimating the correct volume (not only the peak
flow). This paper describes the regional analysis of flow volumes that was used to validate the
estimated flood volumes.
Another issue of considerable importance is the assumed relationship between inflows and initial
reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works.
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2005 Papers

2005 – The Extremes of Tropical Hydrology
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Peter Hill, Kristen Sih, Rory Nathan, Phillip Jordan

This paper presents a number of innovative hydrologic investigations undertaken for the recent detailed design of upgrades for Ross River Dam in North Queensland. A key issue for estimating extreme floods in the tropics is the estimation of flood events of long critical durations. The implication is that there is an increased focus on estimating the correct volume (not only the peakflow). This paper describes the regional analysis of flow volumes that was used to validate the estimated flood volumes.

Another issue of considerable importance is the assumed relationship between inflows and initial reservoir level. The analyses described in this paper showed that inflows are independent of reservoir levels for the more frequent events but for more extreme events they are correlated. This has important implication on how the initial reservoir level is incorporated in the hydrologic analysis. The final aspect covered by the paper is the derivation of seasonal flood frequency curves. This is particularly important given the highly seasonal nature of rainfalls in the tropics and the results are important for assessing risks during construction and scheduling the upgrade works
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2006 Papers

2006 – Development and Application of a Risk Analysis and Prioritisation Tool (RAPT) for Dam Safety Management
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Peter Hill, Rory Nathan, Phillip Jordan, Mark Pearse

This paper outlines the development and application of the Risk Analysis Prioritisation Tool (RAPT) which has been developed as an interactive tool to aid dam safety risk management. RAPT allows the risk profile and prioritisation of upgrades to be incrementally updated as inputs are refined. The paper outlines some of the requirements of a risk management tool and the resulting functionality of RAPT and the lessons learnt from its application to more than 75 dams.

Issues covered include:
- importance of understanding and tracking the reliability of the inputs;
- requirements for incorporating staged upgrades and non-structural risk reduction measures;
- impact of different approaches to prioritising risk reduction measures; and
- approaches for summarising and conveying risk results
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2014 Papers

2014 – Stochastic Simulation of Inflow Hydrographs for Wivenhoe and Somerset Dams
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Phillip Jordan, Alan Seed, Rory Nathan, Peter Hill, Eva Kordomenidi, Clive Pierce, Michael Leonard

This paper discusses the stochastic framework that was used to generate the 5449 sets of inflow hydrographs, to develop and stress test a dam operations model. The stochastic simulations were driven by 600 different space-time patterns of rainfall generated using a stochastic space-time multiplicative cascade model. Eight significant storms were identified in the radar archive to identify parameter sets for the stochastic generation algorithm and 600 replicates of space-time rainfall were generated. The statistical properties of spatial patterns of 48-hour rainfall bursts on eight major subcatchments of the Brisbane River catchment from the 600 stochastic replicates were verified against the same statistics derived from 38 major flood causing rainfall events observed in the catchment. The hydrographs were generated using an URBS rainfall runoff routing model of the Brisbane River catchment, which was calibrated to 38 historical flood events (between 1955 and 2013) and tested on a further 10 historical flood events (between 1887 and 1947).

The stochastically simulated sets of inflow hydrographs were then used to assess the impact of variations in flood operation rules for Wivenhoe and Somerset dams. The stochastically generated events exhibit substantial variability in runoff hydrographs but with variability that is statistically consistent with observed events. The stochastically generated hydrographs provide a considerably more realistic basis for testing the outcomes for different flood operations strategies than the single design event approaches that have previously been adopted.

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2015 Papers

2015 – Towards consistency in potential loss of life estimates: Testing the new Reclamation Consequence Estimating Methodology
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Chriselyn Meneses, Simon Lang, Peter Hill, Mark Arnold

Risk is the product of likelihood and consequences. Much effort is put into the risk assessment process for large dams to ensure there is a consistent approach to estimating failure likelihoods across an owner’s portfolio. For example, the use of common peer review teams and methods like the ‘piping toolbox’ allow the risk assessment team to apply repeatable logic and processes when estimating failure likelihoods. However, the methods for estimating life safety consequences are often not applied consistently. This inconsistency leads to estimates of potential loss of life (PLL) that vary between dams in unexpected ways, because results from the most commonly applied method (Graham, 1999) are sensitive to threshold changes in flood severity and dam failure warning time.
The recently released Reclamation Consequence Estimating Methodology (RCEM) is intended to supersede Graham (1999). RCEM varies fatality rates continuously with DV, and is therefore less sensitive to changes in flood severity. In this paper, estimates of PLL from RCEM are compared with results from Graham (1999) for five dams. Results from the latest US Army Corps of Engineers model for estimating the consequences of dam failure (HEC-FIA 3.0) are also compared with RCEM and Graham (1999) for one dam. Comment is then made about the important considerations for applying RCEM consistently across a portfolio of dams.
Keywords: potential loss of life, dam safety, risk analysis
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2016 Papers

2016 – Benchmarking 2D Hydraulic Models for Dambreak and Consequence Assessments
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Chriselyn Kavanagh, David Stephens, Peter Hill

Two-dimensional hydraulic models are now widely used to simulate flooding downstream of dams as part of dambreak assessment studies. These models provide high resolution information on velocity distribution across the floodplain, which is of paramount importance to accurate estimation of the depth-velocity product required when undertaking loss of life assessments. In addition, the outputs from these models are much more readily presented as maps and animations, which can be an important tool in the dam safety emergency planning process.

Recently, the United States Army Corps of Engineers released a new version of the popular hydraulic model HEC-RAS which includes the ability to conduct two-dimensional simulations. Other widely used two-dimensional models include DHI’s MIKE suite and TUFLOW. This paper presents a review of the capability, functionality and useability of these models for the specific purpose of dambreak modelling. Key features considered as part of the review include model stability, run times, methods of simulating dam breaches, outputs and the ability to link to loss of life simulation models. A case study comparing the performance of three commonly applied models is presented and discussed, and advice is provided on model selection.
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2017 Papers

2017 – Observations from Five Australian Applications of HEC-LifeSim to Estimate Potential Loss of Life from Dam Failure
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Chriselyn Kavanagh, Simon Lang, Andrew Northfield, Peter Hill

The U.S. Army Corps of Engineers have recently releasedHEC-LifeSim1.0, a dynamic simulation model for estimating life loss from severe flooding (Fields, 2016). In contrast to the empirical models that are often used to estimate life loss from dam failure, HEC-LifeSim explicitly models the warning and mobilisation of the population at risk, and predicts the spatial distribution of fatalities across the structures and transport networks expected to be inundated. This capability provides additional insights to dam owners that can be used to better understand and reduce the life safety risks posed by large dams. In this paper, we demonstrate the use of HEC-LifeSim to model the potential loss of life from failure of five large Australian dams. Particular attention is paid to how the predicted life loss varies with warning time, in a manner that depends on human response and the transport network’s capacity for mass evacuations, and the modelled severity of flooding. We also examine how the HEC-LifeSim estimates of life loss compare with those from the empirical Reclamation Consequence Estimating Methodology (RCEM).
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2017 Papers

2017 – Tailoring Consequence Assessments for Retarding Basins
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Andrew Northfield, Simon Lang, Peter Hill

Melbourne Water currently manages more than230retarding basins (RBs). A large portion of these are less than 4 metres high, and traditionally structures of this size have not been subject to intermediate or detailed ANCOLD Consequence Assessments. However, the need to understand the failure consequences for smaller structures has increased over time, as risk based approaches to managing safety have expanded from large dams to other water retaining assets.

Undertaking detailed consequence assessments for all Melbourne Water’s RBs would not be practical, given the costs and time involved. Therefore, this paper describes a method for assessing the level of ANCOLD Consequence Assessment that is justified, based on the structure’s attributes. It also presents an equation that was used to estimate peak outflows from RB failure. The peak outflow estimates can be used to model approximate failure inundation extents downstream of small dams and RBs.

The paper draws on work that HARC have recently undertaken for Melbourne Water to assess the failure consequences for 88 RBs. The outcomes are relevant to other organisations that own or manage significant numbers of small water dams or RBs.
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2017 Papers

2017 – The Design Flood Frequencies for My Dam Have Changed – Why?
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Mark Pearse, Peter Hill

Risk assessments for large dams and the design of upgrades are often dependent on estimates of peak inflows and outflows well beyond those observed in the historic record. The flood frequencies are therefore simulated using rainfall-runoff models and design rainfalls. The recent update of Australian Rainfall and Runoff (ARR) has revised the design rainfalls used to model floods that are of interest to dam owners. This will change the best estimate of flood frequencies for some dams. However, for most dams the impact of revised design rainfalls on flood frequencies is small compared to other factors that can change (independent of dam upgrades). These include model re-calibrations to larger floods, changes to operating procedures that affect the drawdown distribution and improvements in how the joint probabilities of flood causing factors are simulated. In this paper, we look at how the design flood frequencies for some of Australia’s large dams have changed, the reasons for this and then identify five key questions for dam owners to ask to aid assessment of whether the hydrology for a dam should be reviewed
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2018 Papers

2018 – Using HEC-LifeSim to Better Understand and Reduce Dam Failure Consequences for Three Case Studies Around Australia
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Hench Wang, Andrew Northfield, Peter Hill

HEC-LifeSim modelling has been emerging in the industry over the last few years and is increasingly becoming the preferred method for detailed consequence and failure impact assessments. The increased adoption rate of HEC-LifeSim modelling is a result of advancements to computation power and hydraulic modelling techniques and allows dam owners to obtain more robust and consistent estimates of the potential loss of life (PLL) compared to the traditional Graham (1999) and RCEM (USBR, 2014) approaches.

This paper will demonstrate, through the use of three examples, how the inputs and outputs from HEC- LifeSim have been used to identify potential ways to better understand the consequences as a result of dambreak.
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2020 Papers

2020 – Demonstrating risk benefits of improved monitoring and surveillance
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Hench Wang, Peter Hill, Sam Banzi, Muhammad Hameed

Dam owners can often struggle to demonstrate the dam safety risk benefits that can be achieved through non-structural risk reduction measures, such as adoption of smart technological solutions that improve the timeliness and quality of decision making. WaterNSW collaborated with HARC to develop a novel way of demonstrating benefits from improved data management. This paper discusses the use of HEC-LifeSim to demonstrate the reduction in life safety risk from improved monitoring through DamGuard for a case study dam in Sydney. DamGuard is a real-time dam safety monitoring system implemented by WaterNSW. This case study was the first time in Australia where a simulation model such as HEC-LifeSim was applied to quantify the life safety risk benefits pre and post the implementation of DamGuard. The implementation of DamGuard to the sample dam was estimated to reduce the life safety risk by 15%.
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2020 Papers

2020 – Estimation of consequences for WaterNSW’s diverse portfolio of Greater Sydney dams
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Andrew Northfield, Peter Hill, Muhammad Hameed, Hench Wang, Sam Banzi

In 2018 WaterNSW undertook a Portfolio Risk Assessment (PRA) for 20 dams across the greater Sydney area.

This paper describes the estimation of consequences for this large and diverse portfolio of dams. For some dams the population at risk were greater than 100,000 people whereas for others there were no permanent PAR which required the careful consideration of itinerants. This diversity of the dams required that the approach for estimating the consequences be tailored to the specific characteristics. For example, the approaches for estimating the potential loss of life (PLL) varied from a detailed simulation model (HECLifeSim) to a simpler empirical approach (Reclamation Consequence Estimation Methodology (USBR, 2014) to bespoke consideration of itinerant campers and users of walking tracks. For some dams the economic costs were driven by direct infrastructure costs whereas for other the indirect costs dominated the total economic cost for failure.
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2020 Papers

2020 – Implications of NSW Dams Safety Regulation 2019 on dam safety risk management
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Mark Pearse, John Pisaniello, Sam Banzi, Peter Hill

A completely new dam safety regulation framework was introduced into NSW in November 2019. The new framework addresses all aspects of dam safety management. The implications for dam owners in respect of risk reduction measures (RRMs) that will need to be undertaken have been the matter of debate and are the focus of this paper. The Dams Safety Regulation 2019 requires that dam owners eliminate or reduce the risk posed by their dams but “only so far as is reasonably practicable” (SFAIRP). This is a change from the previous Dams Safety Committee requirement that risks should be reduced as low as reasonably practicable (ALARP). The previous guidance around the extent and timing of risk reduction has been removed and dam owners are now required to determine what is ‘reasonably practicable’. These changes were anticipated to save hundreds of millions of dollars from the reduced cost of risk reduction measures across the state of NSW. These savings appear unlikely to materialise given that dam owners are likely to be highly cognisant of the need to meet the common law expectation that RRMs should be implemented unless the costs associated with the RRMs are grossly disproportionate to the benefits gained. The key changes in the new regulatory framework are identified along with the legal and financial implications in regard to RRMs followed by next steps that should be considered by dam owners in NSW. Many of the implications are applicable to other dam owners who operate under common law (including all states of Australia and New Zealand).
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Video

Dambreak & Consequences (September 2013) – MODULES 1-5 – Individual Modules
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Dambreak & Consequences (September 2013) – MODULES 1 to 5

Full course

An understanding of the consequences of dam failure is essential in dam safety emergency planning and as an input to risk assessment. In recent years there has been significant advances in hydraulic modelling and access to high quality elevation data which has revolutionised dambreak modelling. The advent of risk based approaches has increased the focus on estimating the consequence of dam failure and particularly the potential loss of life. The method developed by the USBR in 1999 has had widespread application in Australia and in recent years a number of more sophisticated simulation approaches have been developed. This session will cover the latest developments in dambreak modelling and the estimation of potential loss of life from dam failure.

This course is designed to present the state of practice on these matters for dam safety risk management. The 2 days are designed for both experienced and less experienced dam owners, regulators and consultants.

Includes access to the following videos:
- Dambreak and Consequence Assessment Overview – Peter Hill 15:41
- Dam Breach Parameters – Grantley Smith 23:22
- Dambreak Modelling – Grantley Smith 38:04
- Concurrent Floods – Peter Hill 22:18
- Loss of Life Case Histories – Wayne Graham 1:25:39
- Guidance in Estimating Loss of Life – Wayne Graham 58:52
- Recent Developments in Estimating Loss of Life – Simon Lang 50:24
- Severity of Damage and Loss (Economic, Social and Environmental Consequences) – Simon Lang 16:09
- Severity of Damage and Loss (Economic, Social and Environmental Consequences) – Wayne Graham 18:31
- Welcome and Introductions – Robert James 10:35
- Summary and Close of Workshop – Robert James 10:25
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2014 Papers

2014 – Considerations for Flood Estimation of Water Retaining Structures in Urban Catchments
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Peter Hill, David Stephens, Kelly Maslin, Rachel Brown, Simon Lang, and Chriselyn Meneses

There has been a growing awareness of the potential dam safety risks associated with hydraulic structures in urban environments such as retarding basins, water quality detention basins and recreational lakes. This has required estimates of rare and extreme floods for urban catchments and there are a number of important characteristics of urban catchments which distinguish them from rural catchments such as impervious areas, lack of streamflow data, blockage of structures and complex hydraulics. This paper describes the key considerations for flood estimation in urban catchments and draws examples from a number of current flood studies for urban catchments in Canberra.
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2013 Papers

2013 – Development and application of a risk based approach to managing floods during construction
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Simon Lang, David Stephens, Peter Hill, Mark Arnold and Tommie Conway

Considerable thought has been given in recent years to managing the risks associated with floods during the construction of new dams and dam upgrades. Both ANCOLD and the NSW DSC provide some limited advice on how this risk should be managed, with many dam owners aiming for societal risk during construction to be no higher than pre-construction. One approach to do this is to draw down the reservoir such that sufficient airspace is created to reduce the probability of overtopping the construction works to be equal to that of overtopping the dam crest pre-construction. However, this frequently leads to very large releases of valuable water resource being required. This approach also fails to consider that the conditional probabilities of failure may be quite different during construction than during normal operation. A risk-based approach was applied for the recent upgrade of Tarago Reservoir. Existing event trees from a failure modes analysis were adjusted to reflect the construction conditions. In some cases, the event probabilities increased (for example as a result of excavation of the dam embankment), however some also decreased (for example as a result of more rapid means of detecting and intervening in breach formation during construction). The conditional probabilities of failure during construction were then used to estimate the overall seasonal probability of failure, and it was found that a limited draw down of the reservoir would be sufficient to ensure that risks were no higher during construction than pre-construction. To reinforce this, the cost-to-save-a-statistical life was estimated for further drawdown of the reservoir and used to demonstrate that the risks were as low as reasonably practicable.
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Search Results: “” — Page 1

Hench Wang, Andrew Northfield, Peter Hill

Choose the individual modules or purchase the discounted entire course here.