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Summary of full report
by Dr John D Pisaniello and Prof Jennifer M McKay
October 2004
RIRDC Publication No 04/051 RIRDC Project No USA-10A and USA-12A
Executive Summary
Up until now, the cost of accessing professional advice about dam design
and safety has resulted in it being out of the reach of many landholders.
In order to help address this problem, a more affordable process to assist
those seeking professional advice has been developed and is presented here.
This report describes the process used and results obtained in the development
of a cost-effective spillway design/review procedure for small dams in
Southeastern Australia.
The development process primarily involved deriving regionalised Dam Crest Flood capability prediction relationships for reservoirs on small rural-type catchments using the RORB engineering model in line with modern best practice. Such relationships had already been developed for South Australia (Pisaniello PhD Thesis), and preliminary relationships only had been developed for Victoria as a result of previous research undertaken at the University of South Australia. The current study has significantly progressed the Victorian relationships and also well established preliminary relationships for NSW.
In total, 12 “representative” catchments in NSW and 6 catchments in Victoria have been hydrologically modelled, and extended flood studies of hypothetical dams placed on the same catchments have then been conducted. The hypothetical dams represent a wide range of reservoir conditions and spillway capacities up to the Probable Maximum Flood (PMF). Appropriate analysis has led successfully to the derivation of regionalised relationships based on simple hydrological/hydraulic variables, for predicting reservoir flood capability as either Annual Exceedance Probability (AEP) or %PMF. It is this output which is checked by an engineer against modern bestpractice safety criteria in order to either determine the adequacy of an existing spillway and/or the necessary size of an appropriate spillway.
This establishes a reliable and credible procedure that will encourage better and more uniform private dam design and safety management in both NSW and Victoria. The procedure is applicable to dams on small catchments up to 100 km2 in size in NSW and up to 20 km2 in size in Victoria: this will usually cater for most private dam cases in each State.
In essence, applying the procedure in “review mode” merely requires (1) a short site visit by an engineer in order to measure a few simple necessary parameters (for example, spillway width and heights, embankment height and reservoir and catchment area), (2) input of these parameters into the developed regionalised prediction relationships in order to determine the spillway flood capability of the dam and then (3) checking this result against current best-practice safety criteria which is incorporated in the prediction relationships. When used in “design mode”, the same basic parameters are related to a proposed reservoir, or upgrade of an existing reservoir. The parameters are varied iteratively in the same regional prediction relationships until the best-practice safety criteria together with the owner’s storage needs are satisfied. Therefore, the process can be applied either in the checking of existing dams, the re-design of existing dams or the design of new structures. Both spillway and storage designs can be tailored to suit the surrounding landscape and the storage requirements of the landholder. The resulting design information is presented graphically for both landholders and construction contractors.
The regional relationships upon which the procedure is based are being developed. by an Australian Research Council (ARC) Discovery project, which will further extend this research via a “community partnerships” approach. While the catchments utilised in both NSW and Victoria represent reasonable “State-wide” spread, it will be appropriate for future studies to undertake works on additional catchments within each region in order to increase confidence in the developed design/review relationships applying to the entire area within each region. The Discovery project is entitled ‘cost-effective integrated engineering and “community partnerships” solution to a latent water policy issue: private dam management and flood safety’ and is due for completion by the Water Policy and Law Group at the University of South Australia in 2005. Nevertheless, as they stand here, all relationships display excellent predictive accuracies, therefore enabling them to be used in practice with confidence.
The main benefit of the procedure is it reduces the effort and resources that are normally required by an engineer for conducting a “state of the art” reservoir flood capability study. The procedure provides a basis for quick yet accurate review and/or design of private dam spillways against any design flood standards. At the same time, it is in line with modern acceptable practice which is of critical importance in a court of law to satisfy the requisite duty of care, that is: to avoid negligent liability in the event of dam failure and subsequent litigation.
Often landholders hire contractors to construct their dams, who are not properly trained or skilled in designing and constructing of dams, nor in taking account of the recent changes in engineering practices and upward revisions of rainfall and flood data. Thus, many dams have not been built to an adequate standard: this is currently a worldwide problem. Hence, a clear need has developed for dam owners to review the spillway flood capabilities of their dams, and upgrade if necessary, in order to meet their duty of care and avoid liability for possible failure consequences.
The commercial potential of the procedure is significant in regions where spillway safety review is mandatory by legislation, and the demand for the procedure becomes somewhat assured. In Victoria alone there are some 800 farm dams which have been identified as requiring review. Therefore, the key details of the design/review relationships as developed in this study have been kept confidential in order to avoid any persons using the relationships and charging unreasonable fees before they are even finalised by the future ARC research. Once the relationships are finalised, various options will be assessed as to how best ensure that the cost-effective benefits of the procedure are not abused, but rather passed on to the farming community. For example, licencing the procedure to a number of engineering firms and then relying on market forces to ensure that the savings are passed on, or perhaps establishing a new “farmer-friendly” company that will deliver the spillway service at a costeffective price. In the meantime, any landholders requiring the cost-effective service based on the “useable” procedure presented here can contact Dr John Pisaniello at the University of South Australia (ph: +61 8 8302 0031), and an interim review can be organised via the University’s “controlled” business services.
Overall, bringing the curves together here from each of the three States, NSW, VIC and SA, has successfully established a mechanism applicable to the whole of Southeastern Australia. The project has gone a long way in establishing a scientifically acceptable procedure that will promote consistency and uniform standards and strongly encourage better private dam design and safety management in Southeastern Australia. This will set a precedent for the remaining States to follow so as to ultimately develop a mechanism applicable Australia-wide.
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