C.F. Wan, R. Fell, M.A. Foster
This paper presents the findings of experimental investigation of the rate of piping erosion of soils conducted at the University of New South Wales.
Two tests, namely the Slot Erosion Test and the Hole Erosion Test, have been developed to study the erosion characteristics of a soil. The erosion characteristics are described by the Erosion Rate Index, which indicates the rate of erosion due to fluid traction, and the Critical Shear Stress, which represents the minimum shear stress when erosion starts. Results of the two laboratory erosion tests are strongly correlated. Values of the Erosion Rate Index span from 0 to 6, indicating that two soils can differ in their rates of erosion by up to 106 times. Coarse-grained soils, in general, are less erosion-resistant than fine-grained soils. The Erosion Rate Indices of coarse-grained cohesionless soils show good correlation with the fines and clay contents, and the degree of saturation of the soils, whereas the Erosion Rate Indices of fine-grained cohesive soils show moderately good correlation with the degree of saturation. The absence of smectites and vermiculites, and apparently the presence of cementing materials, such as iron oxides, improves the erosion resistance of a fine-grained soil.
The Hole Erosion Test is proposed as a simple index test for quantifying the rate of piping erosion in a soil, and for finding the approximate Critical Shear Stress corresponding to initiation of piping erosion. Knowledge of these erosion characteristics of the core soil of an embankment dam aids assessment of the likelihood of dam failure due to piping erosion in a risk assessment process.
M. Shirley, P. Hill, S. Hannon, B. Abernethy, H. Griffith and S. Gatti
There is an ever increasing focus on the impact of water resource infrastructure, and particularly dams, on downstream hydrology and hence ecology. Over the last few years this focus has led to the rapd development in the philosophy and techniques for estimating the requirements of water dependent ecosystems.
This paper outlines the application of a new framework for estimating environmental water requirements which results in a range of flows, rather than a single recommended flow. Furthermore, a range of strategies for providing this water to the environment will be explored.
The paper uses the current environmental flows study on the Onkaparinga River Catchment for the Onkaparinga Catchment Water Management Board to illustrate the issues and application of the methodology. The natural hydrology of this catchment has been impacted by pumping of water from the River Murray, a major dam (Mt Bold) and the diversion of flow at Clarendon Weir. This substantial multi-disciplinary study over 3 years is estimating environmental water requirements and the strategies for providing this water to the environment.
H. Morrison, J. Leckie, P. Richardson, R Paton
Awoonga Dam is a 40 metre high concrete faced rockfill dam on the Boyne River near Gladstone in Central Queensland. The dam supplies domestic and industrial water to the Gladstone region and the Callide Power Station. Stage 1 will increase FSL by 10 metres to EL 40, which increases storage capacity from 289,000 ML to 777,000 ML. To provide for future industrial growth in the region, the dam design facilitates future raising up to a nominated FSL of EL 62, in a number of stages.
The project consists of:
Significant savings were realised by adopting the alliances project delivery method, resulting in completion 5 months ahead of program and more than 10% under budget.
This paper details development of the project under the alliance and outlines some of the lessons learnt.
Pieter van Breda, Alison White, and Greg Carmody
Site works on the $150 million Warragamba Dam Auxiliary Spillway project commenced in March 1999 and were completed in June 2002. Successful interaction with the local community, to achieve an equitable outcome, has been a feature of the communications strategy for the project.
The Auxiliary Spillway is located close to the village of Warragamba, a township of approximately 2,000 residents. The closest residence is about 200 metres from the site. The EIS and subsequent planning documents identified key localised environmental impacts that the project would impose. The main concern of local residents, including a local action group, was the impact on their amenity during construction of the Auxiliary Spillway, particularly in relation to noise, vibration, dust and traffic.
The conditions of approval for the project included a range of communication activities, of which the formation of a Community Liaison Committee (CLC) with an independent Chairperson was a key component. When the membership of the CLC was established the Sydney Catchment Authority (SCA) and chairperson agreed that it needed to fully represent the local community – and therefore included community representatives from Warragamba and two nearby villages, the Chamber of Commerce, the local action group, the local school, local council, the dam owner (SCA) and the project manager (AWT P/L).
The establishment of the CLC has proven to be very successful. It has been the voice of the community, with responsibility to act on behalf of the community and to keep them informed of progress on the project. When issues arose during the construction, the CLC were briefed on the particular matter. The CLC was instrumental in resolving these community issues and has allowed this $150 million civil project to proceed without community attributed delays.
P. H. Southcott, R. Herweynen and R. Fell
Hydro Tasmania is in the process of undertaking a Portfolio Risk Assessment of its 54 referable dams, of which 14 are concrete faced rockfill dams. One of the potential failure modes identified during the study so far is a concentrated leak developing in the face slab or joints of the slab, leading to failure of the dam. Current methodologies for assessment of piping failures through embankment dams are considered inadequate for this failure mode. This paper discusses an event tree methodology developed from the work of Foster and Fell (1999) and Foster et al (2001) to address this failure mode. The key aspect of this method is identifying the factors that influence the likelihood of initiating a concentrated leak through the perimetric, vertical and crest wall joints and through the face slab concrete. It is concluded that for the vast majority of well designed and constructed concrete faced rockfill dams that a concentrated leak leading to failure is very unlikely.
R.A. Ayre and T. L. McGrath
The regulatory environment of Queensland’s water resources has changed significantly within the last few years as a consequence of the passing of the Water Act 2000. SunWater, as the owner of referable dams and the operator of water infrastructure, is required to observe the provisions of the new Act.
SunWater has undertaken dam failure analyses of a number of its dams in accordance with the new guidelines prepared by the Department of Natural Resources and Mines. The results of these assessments are being used as part of a portfolio risk assessment of its assets to help prioritise refurbishment activities. Aspects within the guidelines relate to various ANCOLD publications, with a focus on the consequence of failure for determining incremental hazard categories and appropriate design standards for spillway adequacy.
SunWater also operates its schemes under the provisions of Interim Resource Operation Licenses (IROLs). As part of Government’s water planning process, SunWater is required to submit proposed water management arrangements for its schemes. SunWater develops these arrangements, which include operation, water trading, and monitoring rules, to meet its business objectives and the objectives of government. With government approval, these proposed arrangements will translate to the provisions of Resource Operation Licenses when the Resource Operation Planning (ROP) process is completed.
This paper describes SunWater’s experience and approach to meeting regulatory requirements in the above areas.