Keirnan Fowler, Peter Hill, Phillip Jordan, Rory Nathan, Kristen Sih
Although there are considerable uncertainties in the science of climate change, there is a growing recognition of the importance of the issue. Incorporation of climate change impacts is now required in policy guidance from several government authorities and it is prudent risk management to consider the effects of climate change in planning for water resource infrastructure, including assessment and design of dam upgrades. This paper describes the potential impact of climate change on extreme flood estimates and provides a case study for Dartmouth Dam in south-eastern Australia. Three inputs to flood estimation were considered according to the projected impact of climate change; namely design rainfalls, modelled losses and initial reservoir level. The relative influence of each of these factors is explored. Rainfall and losses had a similar (and opposite) influence on results and for this dam the reservoir level prior to the flood event had the largest influence on results. This case study demonstrates that the insights of climate modellers and hydrologists need to be integrated in order to provide defensible estimates of the impact of climate change in flood hydrology studies. Credible projections of changes in design rainfall intensities are required for the full range of exceedance probabilities across Australia.
Application of Available Climate Science to Assess the Impact of Climate Change on Spillway Adequacy
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Kristen Sih, Peter Hill, Susan Ryan, Siraj Perera
Although ANCOLD provides guidance on good dam safety practices, in Australia it is the State and Territory Governments’ role to protect the public from dam safety incidents and in many cases these jurisdictions have legally binding regulations in place that dam owners must adhere to. This paper presents a comparative analysis of the dam safety regulations currently in place for Australian states, as well as selected international jurisdictions. The limit of applicability of the regulations, number of dams regulated, content of the regulations and powers and responsibilities of the regulator are all compared. It was found that there is a large range within each of these categories with regulatory approaches varying from light-handed and objective based, to highly prescriptive. The extent to which risk management principles are used in the regulations for each jurisdiction has also been investigated. It was found that in jurisdictions where higher hazard category dams account for a higher proportion of dams being regulated, risk analysis is included in the regulations. Finally, the ANCOLD societal risk criteria and ALARP considerations have been compared and contrasted with those from international jurisdictions and other hazardous industries.
Richard Herweynen, Colleen Stratford
Assessing the potential for erosion of foundation rock downstream of a spillway is a problem faced on many dams, whether new or existing. The problem is made particularly difficult not only due to the uncertainty in determining the erosion potential of the rock, but also due to the variable hydrologic characteristics of flood events.
The selected spillway option for Wyaralong Dam comprises a centrally located primary spillway with a secondary spillway located on the left abutment. A stilling basin energy dissipater is provided at the toe of the primary spillway. Downstream of the secondary spillway, an apron channel will direct flows back to the stilling basin. However, for flood events larger than the 1 in 2000 AEP event, the capacity of the secondary spillway apron is exceeded and flows spill out across the left abutment of the dam towards the river channel. Erosion of this left abutment was viewed to be a potential dam safety issue, and as such, careful consideration was required during the design stage to determine the acceptability of this spillway arrangement.
In order to provide structure to a problem which often relies solely on engineering judgment, a decision process was developed, taking into consideration some of the more definable aspects of the problem. These aspects included the geological characteristics, the initial hydraulic characteristics, the flood duration, the nature of erosion should it occur and the stability of the dam. This paper describes the decision process and methodology used at Wyaralong Dam to
determine the acceptability of erosion. This paper will present the process in a way that it can be used by others in future dam projects, both new and upgrades.
A Unique and Holistic Approach to the Erodibility Assessment of Dam Foundations
Gavan Hunter and James Toose
Hinze Dam, located on the Gold Coast in Queensland, is an Extreme hazard storage under the authority of Seqwater (Southeast Queensland). The Stage 3 works, which are coming to completion, require raising the existing 65 m high central core earth and rockfill embankment almost 15 m to a maximum height of 80 m. The reservoir has been near full supply level for the construction period.
Numerical modelling and empirical predictive methods were used to estimate the deformation at three key embankment sections during construction; the right abutment of the main embankment, the maximum section and the main to saddle embankment connection. The results of the analysis were incorporated into the dam safety management plan to provide a framework for evaluation of the monitored deformation during construction.
This paper summarises the numerical modelling and outlines the framework of the dam safety management plan. It then compares the actual deformation measured during construction against the predictions. Overall, the modelled deformation has compared very well in terms of trend and reasonably well in terms of magnitude with the actual deformation to date. On one occasion the deformation has exceeded the estimates and triggered a response to elevate the review to higher levels within the Alliance. Concluding comments are provided on the useful aspects and limitations of the numerical modelling at Hinze Dam.
David Ryan, Sean Fleming
The Connors River Dam and Pipeline Project comprises the construction of a 367,540 ML storage on the Connors River located in central Queensland and a 130 km pipeline capable of delivering annually 49,500 ML of high priority water to the rapidly expanding Central Queensland Coalfields. The dam also has the capacity to supply water for the downstream agricultural sector.
Key outcomes of SunWater’s recent business case investigations included the identification of a strategy that would deliver the project in parallel with the construction programs currently being developed by the coal mining sector, the delivery of a quality product with high certainty cost and the ability to supply water at a commercially attractive rate. Construction activity is currently scheduled to commence in mid 2011, with commissioning of the works early 2014.
The paper outlines the project details, the design features of the dam and pipeline and the contract strategy adopted in an attempt to deliver the project on time and within budget.
Keywords: Roller Compacted Concrete, Early Contractor Involvement, Design and Construction.
G.L. Vaschetti, C.A. Verani, J.W. Cowland
Geomembranes are an established technique for long-term waterproofing of hydraulic structures including all types of dams, canals, tunnels and reservoirs.
Three construction projects are presented that feature unique waterproofing solutions leading to faster construction programmes and granting safer and longer service life at lower costs: The 35 m high Paradise Dam (aka Burnett River), Australia’s largest volume Roller Compacted Concrete (RCC) dam waterproofed using a PolyVinylChloride (PVC) geomembrane sandwiched between prefabricated concrete panels and the RCC itself; The 50 m high multipurpose Meander Dam in Tasmania, designed as a RCC dam of the low cementitious content type whose imperviousness is provided by a PVC geomembrane installed in exposed position and mechanically anchored to the upstream face of the dam; And the Eidsvold Weir, a 115 m long 15.45 m high RCC structure used for water supply, waterproofed using an external PVC waterstop installed on the upstream face and able to accommodate the expected movements at the joints.
The paper will outline the technical details, installation and performance of the geomembranes.
Advantages gained from the use of a geomembrane waterproofing system on RCC dams – experiences from Australia