Khanh (Ken) Nguyen, Peter Allen
There is community concern regarding the potential for dams to fail and threaten lives. In Queensland, the Water Supply (Security and Reliability) Act 2008 provides for the regulation of dams whose failure could cause loss of life. Other consequences of dam failure such as interruption of services, economic loss and damage to the environment would also be of paramount importance for the safety management of our dams in the current climates of change.
In 2003, the Bureau of Meteorology (BoM) revised the Probable Maximum Precipitation (PMP) estimates for both short and long durations of extreme rainfalls for northern Australia. As a consequence, the majority of cases resulted in a significant increase of extreme flood estimates for many river catchments in Queensland. Subsequent studies by the BoM have investigated the potential impact that climate change might have on PMP estimation.
This paper examines the current progress of the Queensland Spillway Upgrade Program, by discussing the current regulatory environment and identifying a number of hydrological issues which may require further investigation for Queensland conditions.
Keywords: Spillway Upgrade, Acceptable Flood Capacity, Flood Discharge Capacity.
Tariq I.H. Rahiman, Amanda Barrett, Greg Dryden, Mike Marley, Cecile Coll
In this study we present the engineering geology of complex Late Carboniferous to Early Permian silicic volcanic rocks underlying the Connors River dam site located on the Connors River, at Adopted Middle Thread Distance (AMTD) 97.7 km. The initial investigation of the site by SMEC in 1976 characterised the bedrock as simple laterally continuous layers of rhyolite and pyroclastic rocks. Engaged by SunWater Limited since October 2007, Golder Associates have utilised a range of modern investigative techniques to reveal a more intricate bedrock geological model.
Geological mapping, targeted vertical and angle geotechnical drilling and trenching reveal that the dam site foundation consists of complexly laid felsic crystalline volcanic flow deposits, volcaniclastic (pyroclastic) deposits, and mafic intrusives. Petrographical tests depict a broad range of rock types that includes rhyolite, rhyodacite, dacite, basalt, volcanic breccia, lapilli tuff and tuff. Surface structural mapping and downhole acoustic televiewer profiling reveal that defects of varying orientations have developed in the rocks mainly as a result of tectonism. The rock defects are predominantly open joints and faults, and minor bedding, flow bands, decomposed seams and veins. The permeability of the bedrock, which appears to be primarily controlled by rock defects, was assessed using the results of Lugeon tests.
Rock stratigraphy, mineralogy and texture combined with high resolution seismic tomographic imaging were used to delineate three main engineering rock units. Unit 1, the oldest, occurs on the right abutment and consists mainly of slightly weathered to fresh, high to very high strength dacites and rhyodacites. Unit 2 occupies the central area of the dam foundation and overlies Unit 1. It comprises weakly bedded, slightly weathered to fresh, high to very high strength volcaniclastic rocks. Unit 3, consisting of variably weathered, high to very high strength flow banded and autobrecciated rhyolite, is the youngest unit and it overlies and partially intrudes Unit 2. All three rock units are intruded by slightly weathered to fresh and very high strength basalt, either as dykes or sills. The rock mass properties of the rock units were evaluated based on rock strength tests and the geological strength index (GSI).
Keywords: engineering geology, dam foundation, volcanic rocks, Connors River, dam site
Russell Paton, Peter MacTaggart, Lee Benson
The Nathan Dam project has been identified by the State Government of Queensland as a potential water supply option to facilitate future growth in central Queensland. The proposed storage is located approximately 69 km downstream of the township of Taroom and would have a storage capacity of 1,080,000 ML which would make it Queensland’s fourth largest storage.
The proposed dam arrangement includes a central concrete gated spillway section across the river in order to maximise the storage volume and limit the flood rise upstream such that flood levels at Taroom are not increased during major flood events. A high level fixed crest spillway, to assist in the passage of rare flood events, forms the right abutment portion of the dam wall. It is proposed that the bulk of the concrete sections of the dam be constructed using roller compacted concrete (RCC).
The investigations to progress Nathan Dam are complicated by the existence of the Boggomoss Snail (Adclarkia dawsonensis) within the proposed inundation area. The snail is listed as a critically endangered species under the Environment Protection and Biodiversity Conservation Act 1999 (EPBC Act), and a proportion of the snail’s known population is located on a Boggomoss (the colloquial name for an artesian spring) that will be inundated should the project proceed.
SunWater has engaged Australia’s foremost expert on land snails to design a translocation process aimed at relocating the species to alternative habitat outside the inundation area. The process will seek to not only protect the snail from the dam development, but to increase both its numbers and distribution thereby reducing risks to the currently isolated population from threats such as fire and predation. It is the first time in Australia that such a trial has been attempted, and SunWater is working closely with the Federal Department of Environment, Water, Heritage and the Arts (DEWHA) to ensure that the process is consistent with their policies and guidelines.
The paper will discuss the engineering and environmental challenges of the dam and how the Environmental Impact Study process can influence the delivery of a project.
Keywords: Nathan Dam, Environment, Engineering
Dr Azan Khan, Ahmad Nasir, Kumud Kandel, Jaya Kandasamy, Hadi Khabbaz, Mahub Ilahee
Cracking in the clay core of embankment dams is important to dam safety because it can cause seepage through transverse cracks and with excessive seepage cracks may begin to erode the soil on the sides of the crack. If there are no filters to control this erosion, the erosion may progress to form a pipe, eventually leading to breach of the dam. Recent climate change has resulted in long term drought conditions in various parts of Australia, especially west of the Dividing Range. The prolonged drought conditions can lead to the loss of moisture content in the clay core causing cracking of the core material. The current research is investigating a relationship between long term drought condition and loss of moisture content in the clay core. This paper presents the loss of moisture content in the clay core of three dams in Australia due to global warming. A rigorous finite element modelling has been conducted to capture the moisture content changes in a typical large clay core dam.
Keywords: clay core, dams, climate change, moisture content
Alice Lecocq, Bob Wark, Paul Hurst, Michael Somerford
The justification for dam safety remedial works is often based on an assessment of life safety risk and financial losses defined at a discrete point in time. However these parameters are likely to change over time with demographic growth, land and industrial development. The Water Corporation has a number of dams upstream of major growth areas and an understanding of the future direct and indirect economic consequences of dam failure are required in order to define the change in risk profile over time.
This paper outlines the study framework adopted by the Water Corporation to review its capital expenditure on its remedial works programme. Dam failure consequence assessments for Wellington, Serpentine and Samson Brook Dams are presented and the paper describes the methodology adopted to forecast the likely development within the inundation areas. A framework to consistently estimate future changes to life safety and economic consequences is also presented.
Keywords: demographic growth, land and industry development, monetary assessment, future trends, consequence assessment.
M. Amghar, A. Watt, C. Thorstensen
The future effects of climate change on water resources in the southeast Queensland and other parts of Australia will depend on trends in both climatic and non-climatic factors. Evaluating these impacts is challenging because water availability, quality and streamflow are sensitive to changes in temperature and precipitation. Other important factors include increased demand for water caused by population growth, changes in the economy, development of new technologies, changes in catchment characteristics and water management decisions. In Southeast Queensland, concern for climate change has increased in recent years with research on global climate change applied to part of Southeast Queensland and it has become apparent that the region’s climate has changed in recent times. Studies have shown that Southeast Queensland’s climate has been variable over history and in the present, is experiencing continuing sea level rise, and may experience
significant climate warming. The potential effects of climate change on coastal erosion, water availability, flood control, and general water management issues have been raised and widely discussed from a variety of perspectives.
This paper presents results of an integrated economic-engineering resource assessment optimisation model of Seqwater’s water supply system illustrating the value of optimisation modelling for providing an integrated approach needed to manage a complex multipurpose water system. Overall, the approach has its own limitations, but provides useful insights on the potential for operating the current or proposed infrastructure for different future conditions.
Keywords: Brisbane Water supply, Moreton, water resource plan, optimisation, environmental flows.