Dan Forster, Murray Gillon
A robust and defensible dam surveillance process is considered to be the ‘front-line of defence’ in ensuring dams do not present an unacceptable risk to people, property and the environment. The concept of a ‘Quality Chain of Dam Surveillance’ describes the surveillance process as a multi-linked chain where each step in the process forms a critical link. Without rigorous attention given to quality assurance links in the chain can become tenuous or broken and thus compromise the integrity of the whole chain. Hydro Tasmania is currently re-engineering its existing surveillance process using the Quality Chain of Dam Surveillance as a basis.
This paper presents the concept of the quality chain and uses the Hydro Tasmania improvement initiative as an example application of the concept. The paper is intended to provide a fresh perspective on what is sometimes considered a stale topic and reinforces the need for a considered approach to dam surveillance.
2011 – The Quality Chain of Dam Surveillance
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
Rory Nathan, Peter Hill
This paper provides an overview of the different simulation frameworks used for the estimation of design floods.. For small events the behaviour of many flood modifying factors is highly variable and chaotic, whereas as the magnitude of the event increases so does the organising influence of the dominant meteorologic conditions. The approach to design flood estimation will depend upon the availability of data and the exceedance probabilities of interest. The techniques can vary from frequency analysis of the data recorded at a site to rainfall-runoff modelling with design rainfall inputs derived from regional frequency analysis. For extreme floods, which are of relevance for assessing flood loadings for dams and the assessment of spillway adequacy, the stochastic (Monte Carlo) approach offers a number of advantages over the traditional deterministic approach. Although there has been significant progress in design flood estimation practice in Australia over the last couple of decades there remains many significant research and training needs.
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
The application of maintenance to mechanical assets is a mature and well understood discipline. Although techniques and methods differ from industry to industry, the experiences and knowledge of practitioners should be transferable, but are they?
A challenge faced by all engineers is finding the appropriate balance between obtaining detailed physical evidence of asset condition through invasive disassembly and inspection against assessing condition based on monitoring and past performance.
This paper describes the experiences of the author in applying mechanical maintenance skills in the dams environment and shares some important lessons learned along the way.
2011 – If it ain’t broke don’t fix it – or should you? Lessons learned from relying on past performance of mechanical assets.
G. Hadzilacos, ML. Ng, K. Taske, A. Small and B. Loney
Alteration of flow patterns by constructing a dam may have an irreversible impact on ecosystems depending on the timing, duration and frequency of these flows. As part of an Environmental Impact Study, carried out for a proposed mining operation in Australia that included an earth dam on a pristine ephemeral creek, an appropriate waterway management scheme was proposed that required the establishment of measurable instream flow requirements. This paper describes an environmental flow analysis (EFA) carried out to identify flow regimes that achieve the desired ecological outcomes for the affected waterways. The EFA methodology was based on the range-of-variability approach using a calibrated rainfall-runoff model to form the hydrologic basis. The study established a relationship between flow components and ecological variables based upon which the flow requirements were estimated using a simple methodology.
2011 – A case study of an initial Environmental Flows Assessment for an earth dam on a pristine stream in Cape York