Nerida Bartlett, David Scriven, Peter Richardson
The failure of a number of consecutive wet seasons has resulted in storage levels in Eungella Dam being at dangerously low levels such that supply could be exhausted by June 2007. Eungella Dam supplies bulk water to the Bowen Basin coal fields as well as the Collinsville power station and the Collinsville township.
The Collinsville township, power station and coal mine as well as the Newlands mines take water from the Bowen River Weir which is supplied from Eungella Dam some 95 kilometres upstream. Transmission losses of the order of 25 to 50% have been experienced for releases from Eungella Dam to Bowen River Weir.
The Eungella Dam catchment area is 142 square kilometres. Significant flows occur in the Bowen River downstream of Eungella Dam, the catchment area above Bowen River Weir being 4,520 square kilometres. The topography in the surrounding area (near Collinsville) is not suitable for dam construction.
The opportunity existed for the construction of an offstream storage adjacent to the Bowen River Weir so that the downstream flows could be captured reducing the demand on Eungella Dam thus making more water available for upstream users.
A 5,200 ML offstream storage, associated pump station and rising main was designed, constructed and filled within a period of 12 months.
Foundations at the site are highly permeable sands. Marginally suitable clay for a seal was in short supply as was suitable rock for slope protection. A fixed price budget had been set by the contributing customers.
This paper describes the hydrology, site conditions, design and construction of the project.
Karen Riddette, David Ho & Julie Edwards
Over the last five years in Australia, the use of computational fluid dynamics for the investigation of waterflows through hydraulic structures has been steadily rising. This modelling technique has been successfully applied to a range of dam upgrade projects, helping to assess spillway discharge capacity and structural integrity, and giving insight into flow behaviours including orifice flow, shock wave formation and chute overtopping (Ho et al, 2006). Innovative and cost effective upgrade solutions have been implemented from numerical model studies including baffle plates (Maher and Rodd, 2005) and locking arrangements to protect radial gates from extreme floods.
This paper will begin with a review of recent dam engineering applications, including outlet flow through a fish screen, the performance of a fishway against hydraulic and environmental criteria and pipe flow in a large pumping station. Some of the difficulties and limitations of the modelling technique will be examined together with current research being conducted to address these issues and further validate the numerical results against published data. Some interesting results to date will be reported on elliptical crest discharge, boundary geometry, and model/prototype correlation.
With increasing computing power and software enhancements, the potential applications for numerical simulation in dam engineering continue to grow. This paper will also examine the future outlook and highlight some recent advances such as the thermal simulation of cold water pollution, air entraining flows and combined free-surface and pipe flow in a morning glory spillway.
Janice H. Green and Jeanette Meighen
The Probable Maximum Precipitation (PMP) is defined as ‘the theoretical greatest depth of
precipitation that is physically possible over a particular catchment’. The PMP depths provided by
the Bureau of Meteorology are described as ‘operational estimates of the PMP’ as they represent the best estimate of the PMP depth that can be made, based on the relatively small number of large events that have been observed and our limited knowledge of the causative mechanisms of extreme rainfalls.
Nevertheless, the magnitudes of the PMP depths provided by the Bureau are often met with scepticism concerning their accuracy when compared to large rainfall events which have been observed within catchments and which are, typically, only 20% to 25% of the PMP estimates. The recent increases in the PMP depths, resulting from the revision of the Generalised Tropical Storm Method (GTSMR), have served only to entrench this cynicism.
However, analyses of the magnitudes of the storms in the databases adopted for deriving PMP depths show that these observed storms constituted up to 76% of the corresponding GTSMR PMP depths and up to 80% of the Generalised Southeast Australia Method PMPs for the storm location. Further, comparisons of the PMP depths to large storms observed in similar climatic regions around the world indicate that the PMPs are not outliers.
The results of these analyses are presented for a range of catchment locations and sizes and storm durations and demonstrate that the PMP estimates provided by the Bureau of Meteorology are reasonable and are not unduly large.
David M. Schaaf, P.E., Jeff Schaefer, Ph.D., P.E., P.G
The United States Army Corps of Engineers (USACE) has an inventory of over 600 dams. The main purpose of many of these dams is for flood control, but there are a significant number of dams primarily used for navigation. Additional benefits at many of these projects are provided through hydropower generation, recreation, and irrigation for farmers. Many of the dams are quite old and represent an aging infrastructure across the inventory. In addition, leaner budgets relative to the need for repairs across the aging system require that USACE invest wisely in order to efficiently use available funds to reduce the greatest risks across the inventory. Previously, individual projects with perceived deficiencies were evaluated separately by the responsible district. This evaluation was not compared in any programmatic way to other USACE dams being evaluated for deficiencies.
In order to improve the process of making risk-based decisions across the entire spectrum of USACE dams, the Screening for Portfolio Risk Assessment (SPRA) for the USACE Dam Safety Program was initiated during the summer of 2005. This effort represents the first level of a multiple phased effort to bring full scale risk assessment to the decision-making regarding making investment decisions associated with dam safety by linking engineering reliability with economic and life loss impacts on a relative scale. The SPRA effort involved the development of a tool for evaluating the relative life and economic risk of dam failures for a variety of deficiencies across the inventory of USACE dams. This paper will focus on the basic aspects of the evaluation tool as well as the process by which the screening was completed.
G. Hunter, R. Fell, S. McGrath
The main embankment at Tullaroop Reservoir is a 42m high zoned earth and rockfill dam that was constructed in the late 1950s. The constructed embankment has a very broad, well compacted clay earthfill zone with dumped rockfill on the mid to lower upstream and downstream shoulders.
Over a two week period in April 2004 a diagonal crack of 60mm width and greater than 2m depth developed on the downstream shoulder of the main embankment. The crack was located on the left abutment and extended from the crest to the toe of the embankment. The diagonal crack terminated at the downstream edge of the crest. A continuous longitudinal crack extended along the downstream edge of the crest from the diagonal crack almost to the left abutment. Since April 2004 no further widening of the diagonal crack has been observed.
This paper presents the findings of a series of site investigations and analysis to understand the mechanism for formation of the diagonal crack, and the risk assessment process that culminated in the eventual construction of a full height filter buttress on the left abutment of the main embankment. Factors that influenced the cracking included the change in slope in the foundation profile, the temporary diversion channel on the left abutment, residual stresses in the dam abutment due to differential settlement during construction, a complex foundation geology and presence of shear surfaces in a Tertiary alluvial sequence that formed due to valley formation, an historic dry period and a prolonged period of drawdown. The presence of the crack and its assessed mechanism of formation presented a dam safety risk of piping through the embankment. The risk evaluation process was worked through with URS, Goulburn-Murray Water (G-MW), and G-MW’s expert panel, and eventuated in construction of the localised filter buttress in February – March 2006 to address the dam safety deficiency.
The Water Act 2003 established a new role for the Environment Agency, that of the Enforcement Authority for the Reservoirs Act 1975 in England and Wales. The transfer of this regulatory role from 136 Local Authorities has had a significant impact on the regulated community. Further change is heralded with the forthcoming introduction of Reservoir Flood Plans, Post-Incident Reporting and a review of current regulations. The improvements sought in reservoir safety may be at risk due to a growing skills shortage and increasing financial constraints imposed by owners.
This paper highlights the issues impacting on the reservoir industry in England and Wales and in recognising developments made by ANCOLD members the author seeks to understand how they are being responded to in Australia.