The enlargement of the Cotter Dam is being undertaken by ACTEW to provide a greater security of water supply to Canberra. The project involves constructing a larger, higher new dam wall immediately downstream of the existing Cotter Dam, to allow the present dam to continue functioning and supplying water while construction is underway. The project raised a number of environmental issues partly because the Cotter Dam currently supports a self-sustaining population of (endangered) Macquarie Perch, and because the Bendora Dam, upstream of Cotter Dam, contains a breeding population of (endangered) Trout Cod. Bendora Dam will not be physically affected by the works on Cotter Dam, but its operations may be altered. An ecological risk analysis was conducted to identify critical environmental risks that would need to be investigated and managed or ameliorated and management strategies were put in place to reduce risks. ACTEW have adopted an adaptive management approach to the project, but in order to implement that approach it is necessary to conduct effective monitoring of the fish populations of concern. These potentially include the two endangered species, as well as potential predators (such as cormorants) and competitors (such as trout). Power analysis has been used as a tool to evaluate whether it is feasible to monitor key populations sufficiently rigorously to be able to confidently detect a change (either an increase or decrease in a population). For Macquarie Perch and trout it should be possible to detect population changes statistically with a logistically feasible monitoring program.
2011 – Using risk analysis, power analysis and adaptive management to minimise ecological impacts of the Cotter Dam enlargement
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Rob Campbell, Tom Kolbe, Ron Fleming, Christopher Dann
Hinze Dam is an Extreme hazard category water supply dam situated in the Queensland Gold Coast hinterland, owned and operated by Seqwater (formerly owned by Gold Coast City Council). The Hinze Dam Stage 3 works involved raising the previously 65m high central core earth and rockfill embankment approximately 15m to a maximum height of approximately 80m.
The Stage 3 works included a program of foundation curtain grouting, consisting of six discrete grout panels, five of those beneath areas where the embankment was extended and one beneath part of the spillway enhancement works. Five of the six grout panels were essentially single row panels, with one or more partial rows added in specific areas of high grout take. The remaining grout panel (Panel 4) was constructed as a triple row panel.
A number of challenges were encountered and overcome during the Stage 3 foundation grouting works due to highly variable foundation conditions, ranging from extremely low strength residual soil to highly fractured and permeable high strength rock.
The grouting works were undertaken using downstage grouting techniques, with manual recording of data, manual control of grout pressures and injection rates and use of predominantly neat cement grout mixes.
A key issue in the execution of the foundation grouting works was the maximum grout pressures applied to the foundation and this was discussed in detail between the project design team and external review panel. This paper presents the results from project specific grout trials and production grouting to demonstrate that closure of the foundation was consistently achieved (with one exception discussed herein), which supports the grouting approach employed and the adopted grout pressures.
This paper presents a case study description of the Stage 3 foundation curtain grouting works, including a summary of key learnings which may be of benefit to future dam foundation curtain grouting projects.
Lesa Delaere, Ivor Stuart, Thomas Ewing, David Marsh
As part of Wide Bay Water’s commitment to minimising environmental impacts of its water supply weirs, a “Nature Like” Fishway is under development for the Burrum No 1 Weir. This project is a fishway offset provision for the raising of Lenthalls Dam in the upper reaches of the Burrum River in Hervey Bay. The Burrum No 1 weir forms the primary pumping pool for the Hervey Bay water supply and is located at the tidal limit of the Burrum River. Understanding fish biology and behaviour is critical to the effectiveness of the design of a fishway as much as the balance between the goals of maximising fish passage versus cost, construction and operational difficulties that a fish passage solution may present.
This paper presents the aquatic ecology of the project and the inter-relationship of fish biology and river flow frequency. It discusses the fish species of the Burrum River, their behaviour, seasonal migration and criteria for successful passage. It presents the analysis of river flows with respect to frequency and headwater/tailwater relationships to weir drownout, which was complicated by the tidal flow regimes downstream of the weir. These aspects were also applied in consideration of river behaviour; low flow characteristics for fishway operation during dry seasons and drought, and high flow characteristics during the wet season and floods.
The biological needs for successful fish passage for two very different river flow characteristics were analysed. This allowed targeted design criteria and fishway solution to be developed to provide maximum benefit without causing undue cost to the project.
Burrum Weir Fishway – Fish Biology and River Flows: Two Faces
M. A. Hariri Ardebili, M. Akbari and H. Mirzabozorg
This paper presents a study on the effects of incoherence (considering the Harichandran and Vanmarcke coherency model) and wave-passage (considering various wave velocities) on the nonlinear responses of concrete arch dams . A double curvature arch dam was selected as numerical example, the reservoir was modeled as incompressible material and the foundation was modeled as a mass-less medium. Ground motion time-histories were artificially generated based on a Monte Carlo simulation approach. Four different models were considered in the generation of ground motions; Uniform excitation; Just incoherence effect; Just wave passage effect; and finally take into account both incoherence and wave passage effects. It was revealed that modeling incoherency can have significant effect on the structural response of the dam by modifying the dynamic response of uniform excitation and inducing pseudo-static response. Also, it was concluded that incoherency effect overshadow wave passage effect and results caused by wave passage effect are close to the results of uniform excitation.
2011 – Comparison of wave passage and incoherence effects on nonlinear non-uniform excitation of concrete arch dams
Bob Wark, Alex Gower, Paul Hurstand Sofia Vargas-Pedroza
ANCOLD has been working towards setting up guidelines for outlet works and has a standing committee that is addressing this issue. Recent papers have addressed the issues of current technical practice. However the authors believe that there is a sufficient body of experience available from recent incidents to provide a valuable tool that the guidelines can use to address the issues that are important. The authors have identified almost 40 incidents with outlet works that have occurred over the last 40 years, many of them within the last 20 years and have tabulated them as part of this paper. These range from the interesting to those that can and have threatened worker safety and life. The paper outlines the most significant of these and summarises the causes and corrective action necessary.
Horror Stories with Outlet Works
Kirsty Carroll, Kelly Maslin, Richard Rodd
Melbourne Water manages over 210 retarding basins across Greater Melbourne ranging in size from 4ML to 4700 ML with embankment heights from 0.3m to 10m. Over the years the basins have been designed and constructed by a range of different owners and authorities. Varying design and construction standards with the majority of retarding basins generally being located in highly urbanised areas, has resulted in Melbourne Water having a large portfolio of assets that have potential to pose a significant risk to the downstream communities they are designed to protect.
High level hazard category assessments completed over the last10 years identified that approximately 90 structures were either High or Extreme hazard categories based on the ANCOLD Guidelines on Assessment of the Consequences of Dam Failure.
In an attempt to identify retarding basins requiring priority consideration for remedial works Melbourne Water embarked on a process of completing a dam safety risk assessment for five of the retarding basins in accordance with the ANCOLD Guidelines on Risk Assessment. The objective of the risk assessment was to develop an understanding of the key risk issues that might affect retarding basins as distinct from water supply storages, identify potential remedial works and develop a prioritised risk management strategy for the five basins considered. In completing the risk assessment there was also significant discussion about ways to streamline the process to allow assessment of the remaining basins.
This paper details the results obtained from the risk assessment, investigates the application of the base safety condition and implementation of a risk management strategy. It also looks at similarities between sites to enable common upgrades to be implemented across the range of retarding basins. This paper also discusses the need for guidelines specific to retarding basins to be developed.
How do you solve a problem like retarding basins? An asset owner’s perspective