Dambreak & Consequences (September 2013) – MODULES 1 to 5
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:
$0.00 - $80.00
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.
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.
Peter Hill and Rory Nathan
The ANCOLD Acceptable Flood Capacity (AFC) guidelines were published in 2000 and provide guidance on the selection of design flood capacities for dams and specifically a deterministic fallback provision for spillway capacities. Since the guideline was published, there has been a continual evolution in dam safety management practices and related guidelines, including the 2003 ANCOLD guidelines on risk assessment and the current revision of Australian Rainfall and Runoff by Engineers Australia. This paper describes the scope of the current AFC guidelines and perceived opportunities for refinement. A survey of users was used to test and identify issues and gauge the need for the guideline to be updated. A number of topics were identified that would benefit from clarification or further guidance. These topics include consistency with other ANCOLD guidelines, clarity on the selection of the AFC, definition of the dam crest flood, freeboard and application to gated structures.
Tommie Conway, Katherine Miller, Peter Hill
The ‘Black Saturday’ fires of the 7th of February 2009 and the continuation of fires over the following weeks had devastating human, environmental and financial costs for Victoria. Many of Melbourne’s water supply catchments and assets were burnt and the major harvesting catchments were seriously threatened. This paper highlights the need for owners and managers of catchments, dams and associated infrastructure to better understand and plan for the potential impacts of fire, given its predicted increased likelihood and severity due to climate change.
The paper will share Melbourne Water’s recent experiences of the fire, the scale of the impact to the business in terms of assets damaged and catchments affected, the extent of the burn and the threat that was faced. It will describe Melbourne Water’s experience with the United States Burnt Area Emergency Response (BAER) team to expediently map the severity of the fires, to identify areas of concern and prioritise fire recovery works. Of interest to those involved in risk management will be the discussion of the construction flood risk analysis at Tarago Reservoir which was revisited due to severe fire damage to the catchment.
Keywords: fire impact, Melbourne’s water catchments, BAER team, hydrology, Tarago, construction flood risk analysis
Many Australian and international dam owners use risk assessments to understand and manage the societal risks posed by their dams. This requires estimates of dam failure consequences, particularly the potential loss of life (PLL). The methods used to assess PLL have become more varied and sophisticated in recent times. This paper summarises the current status of the methods most relevant to the Australian dams industry (i.e. RCEM, HEC-LifeSim, the Life Safety Model), and comments on their applicability for Australian PLL assessments. This commentary is based on material presented by dam owners, regulators, researchers and consultants from the United States, Canada, United Kingdom and the Netherlands, at workshops on estimating dam failure consequences held in Denver in 2016 and Toronto in 2018.