William Ziegler and Heather Middleton
This paper presents the collation of over 20 years of data on vertical and horizontal movements around Cataract Dam in the Southern Coalfield of New South Wales, reporting subsidence that continues 25 years after extraction in the area ceased. The occurrence of increased vertical movement over old goaf areas as the result of extraction in the same seam at greater than 1km distance has been observed. Together with a change in the behaviour of measured head of water 6 years after extraction ceased in the area. These points raise the question, how long should subsidence monitoring continue after extraction has ceased in areas of important infrastructure?
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This paper presents the methods used to apply a Flood Operation Simulation Model, and the methods used to present results of thousands of flood simulations in a way that different operational options could be compared. The approach was found to be valuable to understand the capacity of the dams to mitigate floods. The study identified shortcomings for the conventional design event approach to flood estimation. A broader range of stochastic floods was an advantage to assess flood mitigation performance and extreme floods of interest to dam safety.
A C Mostert, D J Hagen, P C Blersch
The changes in flood operations since the 2006 flood, covering weather monitoring, hydrological flood station monitoring, and downstream monitoring, are discussed in detail in the paper.
Dr Andy Hughes, Tom Wanner and Ben Jones
Hampstead Heath is one of London’s most popular open spaces, situated just 6 kilometres north of Trafalgar Square. ‘The Heath’ covers over 300 hectares and contains open countryside, an abundance of wildlife, sporting facilities and two chains of ornamental and fresh water swimming lakes, which date back to the 18th Century. The Heath is covered by its own Act of Parliament, of 1871, which protects its historic and environmental importance for the City of London.
In 2011 it was assessed that failure of one or more of the earthfill dams, that retain the ornamental and swimming lakes, could cause failure of downstream dams and subsequent release of floodwaters into the London Borough of Camden and the London Underground, with the potential for a high loss of life. As a result a study was carried out to better understand the scale of the works required to upgrade the dams to prevent their failure, and the associated environmental, social and political impacts.
This paper will present the ideas formulated to safely pass the design floods for ten dams within this sensitive environment, which include the installation of new spillways and/or the raising of dam crests, whilst taking in to account the site constraints and the age of the dams, some of which are up to 300 years old. The risk assessment carried out to quantify the overall risk of the dam failures will also be discussed including the breach inundation flood modelling of central London.
The paper will focus on the engineering and environmental constraints of the project in relation to the highly urbanised area, and the challenges faced when trying to accommodate the needs of many government and high profile stakeholder bodies, and pieces of legislation, in one of the most politically sensitive parts of the country
Damon Miller and Grant Jones
Mt Buller Alpine Resort has significant constraints on its capacity to store and supply potable water during times of peak demand, which impacts the ability to sustain and grow visitation to the resort, limiting optimal functioning and future development of the resort.
A proposed new 100 megalitre dam would primarily supply the resident and visitor populations with a reliable potable water source while also maintaining through snowmaking, the Resort’s amenity and functionality during winter for skiing and snow-play.
Standard dam engineering criteria of technical feasibility and environmental impact influenced the site selection and design of the new off-stream storage whilst additional key drivers unique to an alpine resort, framed around impact to existing skiable terrain and resort functionality, were critical to satisfy the resort stakeholders. The need to minimise the visual impact of the dam and integrate with the resort environment was also of high importance.
Dennis C. Green
Current good practice for risk management as represented in ANCOLD guidelines emphasises risk reduction beyond tolerable risk levels to As Low As Reasonably Practicable (ALARP). Risk reduction reflected in key design parameters such as the spillway design flood is monitored on a quantitative basis, while the guidelines also draw attention to a number of non-quantifiable measures.
Recent work health and safety legislation in Australia does not at first appear to relate to dam safety, but it mandates elimination of risk, and, if that is not possible, then it mandates reduction of risk So Far As Is Reasonably Practicable (SFAIRP). It is tempting to believe that this is equivalent to ANCOLD’s approach to ALARP, but the devil is in the detail of the legislation. This paper argues for a change to a more systematic presentation of recording of decisions on dam safety risk management, lest the legislation expose dam owners unwittingly to liability when they thought they were following good practice. In particular, the re-focussing of ANCOLD Guidelines to align more recognisably with the new legal paradigm, including preparation and adoption of a Safety Case, is recommended.