Loss of life estimates in dam breach circumstances are a key determining input in establishing the appropriate risk profile for these assets. They can also be useful in identifying the most effective emergency management responses. While there are a range of approaches described in the literature for assessing loss of life for concentrated population centres, there is little specific guidance on approaches to be taken when there is only a small number of properties or where itinerant loss of life has the potential to be the dominant risk element. Itinerants are most commonly considered to be road users, although, they can alternatively be any temporary users of the floodplain. The literature on flood fatalities indicates that the largest number of deaths occurs at vehicle crossings or otherwise when individuals voluntarily enter waterways. An approach has been developed for identifying the cases where itinerant loss of life has the potential to be the dominant vector for flood fatalities. In addition, the available flood fatality literature and associated databases have been reviewed to establish the precursors to fatalities.
A simple stepped procedure is presented which allows the user to identify cases where itinerant risk to life on roads should be considered with a separate procedure and a method presented by which itinerant life loss may be identified.
Vietnam has many embankment dams to supply water to the agricultural sector. Most of these dams were built between 1970 and 2000 but have degraded significantly since their construction due to a number of different reasons. Identifying the main potential failure modes for these dams aims to improve their dam safety management systems as well as help to target dam safety rehabilitation works. The research was conducted by analysing 207 Dam Safety Reports and Feasibility Studies published by the Vietnamese Ministry for Agricultural and Rural Development between 2017 and 2019. The priority level of rehabilitation required to these dams was assessed by analysing whether overtopping, seepage and slope stability related potential failure modes were likely to occur. The results revealed the main potential failure modes of embankment dams in Vietnam and the possible reasons for these are discussed. The approaches to rehabilitate the dams that are outlined in the Feasibility Studies were also analysed and are discussed in general terms. The results provide valuable insight into commonly encountered dam safety issues with embankment dams in Vietnam.
International emergency agencies such as the Federal Emergency Management Authority (FEMA) in the U.S. highlight a lack of public awareness of hazards relating to dams (FEMA, 2012). This is an issue faced by emergency management agencies around the world, including in Australia and New Zealand. Without hazard awareness, communities who live downstream of large dams are potentially more vulnerable to possible risks, and are likely to be less resilient when hazards arise. One way to address this knowledge gap is risk communication or the meaningful and purposeful exchange of information about risk among relevant parties (Covello, von Winterfeldt, & Slovic, 1984).
This study adopted a mental models approach (see Lazrus et al., 2016) to identify community members’ knowledge of dam failure by comparing their views with those of experts. Data were collected via depth interviews with dam safety experts (n=5) from across Australia, and community members (n=26) living downstream of dams in South East Queensland in Australia. Participants were asked to discuss knowledge about dam failure and to evaluate a dam safety message taken from a U.S. dam authority that was verbally read to them. Interviews were transcribed and analysed to identify the gaps between expert and community member knowledge.
Analysis showed some convergence on general dam operations but, less comprehensive community understanding of the causes of dam failure and dam safety management. Response to the U.S. dam safety message was mixed, with some participants believing it delivered the message appropriately, and others feeling it overstated risk or that its intended use was primarily to protect dam operators. Notably, these varied responses were often related to participants’ level of knowledge of dams. Combined, the findings highlight an opportunity to close the gap in knowledge. These findings will inform the strategies and materials for the South East Queensland bulk water authority Seqwater in engaging with communities downstream of their 26 dams. The research will guide the approach in conveying knowledge with an appropriate tone to support ongoing community engagement activities and increase resilience.
Earthquake design of a dam and associated appurtenant structures is a key aspect of dam design in the modern era. This paper outlines the design process undertaken to address potential earthquake loading for the 32m high outlet tower to be constructed as part of the new Eurobodalla Southern Storage project on the NSW South Coast. The driver for the project is to provide increased water supply security to communities on the South Coast, an area that is currently serviced by a single reservoir and is subject to frequent water restrictions. Construction is planned to commence for the project in early 2021.
This paper presents the design methodology undertaken to meet the requirements for earthquake design and presents a novel defensive design solution to improve the reliability of the outlet works for post-earthquake operation. The Authors contend that utilising this approach in design of future outlet towers will provide a greater level of confidence in the ability to undertake intervening measures following a severe earthquake. Moreover, the technology has the potential to serve as a relatively inexpensive interim upgrade measure for existing outlet towers expected to sustain an unacceptable degree of damage under earthquake loading.
Sedimentation of reservoirs is acknowledged as a global issue and likely impacts water storage capacity in Australia. This major challenge to our future water supply is a highly complex process with deposition leading to infilling of the reservoir of course sediments in headwaters following major inflows, progressively to finer fractions towards dam walls. Wave action and catchment inflows during drawdown conditions will further transport and redistribute sediments into the main body of the reservoir.
Managing reservoir sedimentation requires an understanding of the sediment types and deposition patterns across the reservoir. Once the location and type of sediment is known, strategies to mitigate the effects on the reservoir can be determined. Methods typically used for determining sedimentation of a reservoir are empirical or modeling techniques that rely on detailed data from inflow events, suspended solids loads and flow rates. In the absence of this data, more direct measurements to quantify the amount of sediment present can be used. Direct measurements are more robust than modelling approaches that utilise rating curves that can result in over estimations of the sediment present. This study combined several measurement techniques to produce high spatial coverage of the reservoir floor. Detailed validation of this approach was undertaken in one representative reservoir prior to adopting this approach across multiple reservoirs.
Failure modes of seepage and internal erosion have been identified as one of the key issues for the
ongoing safety of dams and canals in New Zealand. Accordingly, many dams and canals have had
improvement works carried out to mitigate this issue. This paper examines the long-term performance of these measures including three case studies. It is concluded that the performance of these measures has been variable, but ongoing monitoring and periodic review has identified deterioration in performance. There are a number of technical areas where uncertainties on long-term performance may still remain, such as geotextiles in important filter functions and waterstops of various types.