Paul Southcott, Tony Harman
This paper addresses structural behaviour of the Rowallan spillway walls and the learning that can be derived from this in the design of critical retaining walls in dams and how this can be applied both to remedial works and new work. The authors propose design criteria suitable for retaining walls in high hazard dams.
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Andrew Richardson, Stephen Farrelly and Phil Farnik
In 2012 an update to the Portfolio Risk Analysis (PRA) was undertaken by State Water Corporation for its 18 major dams in New South Wales. The updated portfolio level risk analysis of all the dams has taken account of the completion of major components of the 2006 dam safety upgrade program, while also incorporating continued engineering research into dam safety performance. This paper will provide an overview of the approach, the challenges faced in the process and it will highlight the innovative advances made representing industry best practice. Some future implications and directions will also be discussed.
The three main components of the PRA update in 2012 have included a significant amount of dam break hydraulic modelling including revised hydrology and flood inundation mapping delivered in-house by State Water with consultant support. The Consequence Assessment was developed with a spatial link to natural flooding and dam failure consequences by Sinclair Knight Mertz (SKM), while the third element in producing the event trees, risk analysis and PRA reports was undertaken by consultants GHD. Peer review of the PRA process and reports and additional technical review of the failure modes and event trees by a panel of industry experts provided the necessary independent input and oversight required by the NSW Dams Safety Committee.
State Water’s PRA update builds on the large body of work undertaken for and since the last PRA in 2002. The update process has applied a systematic and quantitative approach across the Portfolio that provides a robust basis for managing dam safety risk. The results of the PRA have identified further work required to investigate and assess the need for dam safety upgrade options for non-compliant dams. State Water’s investment in the PRA has produced a risk-based position on each dam in the portfolio that can be used to identify a range of measures in a revised dam safety upgrade program for the future.
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
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.
S. Suter, G. Singh, and M. Britton
Today, many organisations rely on hydrodynamic modelling to assess the consequences of dam break failure on downstream populations and infrastructure. The availability of finite volume shock-capturing schemes and flexible mesh schematisations in widely used software platforms imply that dam break modelling projects will be carried out differently in the future: Finite volume based platforms allow widespread application of shock-capturing methods and flexible mesh platforms can represent features in the study area more realistically and are more flexible thanks to varying mesh resolutions. Furthermore, the recent adoption of Graphics Processing Unit (GPU) technology in mainstream scientific and engineering computing will also significantly decrease computation times at relatively low cost.
This paper examines the application of finite volume, flexible mesh and GPU technologies to dam break modelling. One-dimensional (1D) modelling results are compared to those from two-dimensional (2D) finite difference and finite volume approaches. The results demonstrate that there are differences between modelling approaches and that the computational speeds of 2D simulations can be significantly reduced by the use of GPU processors.
Gary Gibson and Vicki-Ann Dimas
Earthquake recurrence models are based on observed seismicity, geological data and geodetic motion. They are particularly difficult to define in regions of low seismicity where the average recurrence interval between moderate to large earthquakes greatly exceeds the duration of the known earthquake catalogue.
The earthquake process may be considered as ongoing long-term deformation due to plate movement in the region about the fault, resulting in stress build-up, and a significant number of small earthquakes through the deformed region. Larger earthquakes occur at irregular intervals, with ruptures on the larger faults that release elastic strain energy from the region. Most strain energy release is during the large fault rupture.
This gives a wider range in hazard estimates compared with extrapolation methods, increasing hazard in regions of active faulting and reducing hazard where long-term geological stability can be observed. As dams are usually in regions with recent uplift, this method will tend to increase hazard estimates.