D.S. Bowles and Loren R Anderson
Starting a quarrel is like breaching a dam; so drop the matter before a dispute breaks out. Proverbs 17:14 (NIV)
An approach is summarised for presenting the outcomes of traditional engineering assessments and risk assessments to inform non-technical decision makers. The decision justification approach can be adapted to any dam owner’s unique decision context. It includes rating systems for presenting the outcomes from engineering assessments and from applying tolerable risk criteria, including ALARP. Three decision types are addressed: setting tolerable risk goals for individual dams, identifying a risk reduction pathway for a portfolio of dams, and managing residual risk on an on-going basis
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Tim Waldron, K D Murray and Allan Crichton
The City of Hervey Bay is a growing tourist community that is located a comfortable 3½ hour drive north of Brisbane. To meet the growing water demands of the community, Wide Bay Water Corporation required the raising of its sole water supply – Lenthalls Dam.
At the time of the option study, Queensland dam owners were aware of their obligation to manage their dams to minimise adverse environmental impacts but detailed Environmental Flow Objectives were still being developed.
This required a solution for the raising of Lenthalls Dam that provided maximum flexibility while, at the same time, being cost effective.
A range of solutions and new technologies were investigated. Using a Risk Management methodology, the Crest Gate system developed in South Africa was adopted.
Subsequently, draft Environmental Flow Objectives have been set and the use of a gated system has been beneficial in meeting post-winter flow objectives.
Paul W. Heinrichs & John Bosler
Spring Creek Dam is a 16m high zoned earthfill dam with a central vertical concrete core wall storing 4700 ML for Orange City Council’s water supply. It was a 14.5m high dam constructed in 1931 and in 1947 was raised by 1.0m. In 1966 after a week of heavy rain following a long dry spell, an 80m section of the downstream face slumped but the dam fortuitously survived. In 1969 the dam was re-constructed but no internal drain/filter was installed.
Following the 1994 dam surveillance report, piezometers were installed in the downstream fill. Drilling for these revealed that a substantial portion of the zone downstream of the core wall was saturated. The piezometers recorded piezometric elevations that closely and rapidly followed the reservoir level. Subsequent site investigations identified pockets of very low strength fill immediately downstream of the core wall. It was concluded that the core wall was seriously compromised and the storage level was subsequently, significantly lowered, as an interim dam safety measure.
Dambreak studies indicated the dam is a high hazard and hydrological studies found that the spillway capacity was inadequate.
This paper details the problems involved, their analyses, and the remedial measures proposed at the concept design stage. These include a chimney filter/drain, a stabilising fill combined with embankment crest raising and the construction of a 3-bay fuse plug auxiliary spillway.
R.I. Herweynen and A.M. Hughes
Hydro Tasmania has a number of dams which were designed and constructed in the 1950-70s
with fully grouted, post-tensioned anchors. The method used was leading edge in its day,
however, it does not achieve the cable protection of modern methods which provide two barriers
against corrosion and are monitorable. Hydro Tasmania has developed and employed an
innovative program to ascertain the integrity and remaining life of the cables and to prepare
long term management plans for its cabled dams.
An international panel was set-up to provide guidance on the overall issue, assist in developing
a sound methodology for assessing the corrosion of the anchors and advise on long-term
monitoring. To focus the efforts, Catagunya Dam was adopted as the pilot dam, as the stability
of this dam is very much dependent on the integrity of the anchors. This paper will provide a
brief overview of the project to date but will focus in detail on the main components of the
corrosion assessment of the anchors, namely:
The paper also provides a brief summary of the instrumentation installed at Catagunya Dam to
assist with the long-term monitoring of the dam.
David J. Walland, Jeanette Meighen, Catherine Beesley, Karin Xuereb
The method for estimating Probable Maximum Precipitation in areas of Australia affected by tropical storms has been revised. The method that it replaces, designed in the 1970s is considered outdated and based on limited data.
The entire Bureau rainfall record has been examined objectively for the largest rainfall events. These events have been analysed and modified to enable storm transposition across a large region. The modifications are based on local topography, moisture and location. Once the storm data is transposed to a single location it can be meaningfully compared and used to construct an upper estimate on the possible rainfall. This estimate can then be used in conjunction with information about a specific catchment in order to estimate Probable Maximum Precipitation at that location.
Tony McCormick, John Grimston, Robin Dawson
Project Aqua is a proposed hydroelectric and irrigation resource sharing development on the Lower Waitaki River in New Zealand’s South Island. The NZ $1 billion project aims to deliver approximately 540 MW peak power at an economically viable price, while minimising environmental and social impacts. Application of traditional hydro concepts in historical studies for the same reach has not provided an economic solution. The current proposal challenges conventional thinking in many areas with innovative concepts allowing a significantly lower cost while not sacrificing safety or flexibility.
Development of storage may involve high social and environmental impacts. No significant storage is needed for Project Aqua as the operation of existing upstream dams can be modified to provide for peaking demand and maintenance of minimum flows. The river intake offers innovative features with its very low profile structure. The concept allows a departure from the traditional barrage or dam diversion and maintains an open braid for jet boat and fish passage. This concept has proven to be a major feature in the overall project progression to the current stage.
The largest impact component of the scheme is the eight canals designed to carry 340 cumecs over 63 km through six power stations. Cuts and fills form the canals with locally derived materials used for the embankments and lining. Expensive lining has been minimised by balancing flow exchange with groundwater through the cut and fill sections.
Feasibility design has been completed and resource consents are currently being sought. This paper will cover the significant design features and impacts.