Following the catastrophic failure of the bottom outlet conduits of the Massingir Dam, a rehabilitation project was launched involving the installation of steel liners and the rehabilitation of the hydromechanical equipment. This paper describes the testing of an emergency gates for possible use as a control gate to maintain supply to downstream water users. It further describes the innovative use of alternative access for concreting and other services, the use and benefits of self-compacting concrete for infill concreting between the steel liner and existing concrete and the programme and cost benefits of pressurising the steel conduit prior to concrete encasement.
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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.
This paper will explore the differences in pore pressures resulting from saturated and unsaturated seepage (pore pressure) analysis. It will also evaluate some conventional recommendations, such as the inclusion of essential components of the embankment dam and omission of inessential components. In addition, the identification of inessential components will be discussed.
Finally, pore pressures obtained from these analyses will be compared to monitoring data in order to identify the most appropriate seepage (pore pressure) model.
In conclusion, advantages and disadvantages of each method will be discussed and recommendations will be provided in order to gain the most appropriate results.
The results of this paper can be used for designing new embankment dams or safety reviews of existing dams, particularly when there is lack of reliable monitoring data.
Population at Risk (PAR) estimation involves quantification of people who could be exposed to flooding in the event of a dam failure. Conventionally, estimates of PAR involve manual and subjective assessment of individual structures located downstream of dams. To reduce the reliance on subjective judgement and better leverage publicly available population datasets, an automated method of PAR assessment was developed. This approach used the Geoscape dataset of building representations to disaggregate Australian Bureau of Statistics 2016 Census data for a study area around Gawler, South Australia.
Representative day and night spatial distributions of PAR were constructed to characterise the diurnal movement of people between homes and workplaces or other day activities. Flows of people were directly quantified to reduce reliance on high level assumptions regarding exposure. A Random Forest model was used to filter sheds and other unpopulated structures from the Geoscape dataset.
The largest deficiency in this approach is the lack of high detail data to classify building usage. It is recommended that the potential for automation of PAR assessment be continually revisited as more datasets become available.
Earthquakes are a well-known threat to the safety of dams. While this threat is subdued for Australian Dams, the potential for earthquake induced failure of a dam requires risk minimisation in the downstream community through monitoring and emergency response procedures. This paper details WaterNSW’s approach to their development of a Seismic Monitoring Strategy which was to align the business and ensure an appropriate post-seismic response.
The strategy also identifies that a proactive approach to seismic instrumentation can be taken to reduce business risk by aiding decision making should a dam be in a damaged post-seismic state.
The interim outcome of implementing the Seismic Monitoring Strategy resulted in a fast emergency
response time and less overreaction/distraction of dam safety resources in insignificant seismic events. There is opportunity for other Australian dam owners to implement similar systems to = WaterNSW and achieve similar results.
Yarrawonga and Torrumbarry Weirs; located on the Murray River bordering Victoria and New South
Wales, are operated by Goulburn Murray Water on behalf of the Murray Darling Basin Authority.
The electrical and control systems that operate both structures were nearing 20 years of age, resulting in risk associated with equipment nearing the end of its useful working life and hardware obsolescence, driving this upgrade program. These control systems are critical in the monitoring and management of river levels and flows that extensively affect Victorian and New South Wales irrigation supplies and recreational users on the Murray River and Lake Mulwala.
Considerable effort was required to update and develop the control philosophy before proceeding to the design phase of the projects. The requirement to work on these brownfield sites, while maintaining operational ability and minimising dam safety and water delivery risks, resulted in a significant implementation and commissioning process. During the course of these works, the opportunity was also taken to enhance and update remote monitoring capability.
The lessons learnt on these projects are being incorporated into current Electrical and Control System Upgrade projects at Cairn Curran Reservoir and Dartmouth Dam.