Steven Fox, Garry Fyfe
This paper describes some key details of the construction of the Lake Eppalock Main Embankment Remedial Works Project. This $8.25 million earthworks project was completed on a “live” storage to an accelerated program. As the dam owner Goulburn-Murray Water took the decision to directly manage the construction of these works with resultant benefits in timing, risk management and project management costs.
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Pieter van Breda, Peter Walton, Kate Lenertz and Tim Sheridan
The Warragamba Dam Auxiliary Spillway Project, designed to manage floodwaters up to a Probable Maximum Flood event, was approved by the NSW Minister for Urban Affairs and Planning on February 12, 1998. An Environmental Impact Statement prepared for this project predicted that noise, dust (suspended and deposited), blasting, vibration, water quality and revegetation would be the significant environmental issues requiring management throughout the construction phase.
The closest residents are approximately 200m from the construction activity. The works must not interfere with the operation of the Dam, which stores 80% of Sydney’s drinking water and the integrity of the existing infrastructure must be maintained at all times. The approved proposal was to emplace the 2.2Mm3 of spoil excavated to create the spillway in an area 25 ha by 20m high on top of a ridge on the left bank adjoining the Blue Mountains National Park. This created visual impact and rehabilitation challenges.
Although the contract for this project was primarily performance based, strict environmental clauses were incorporated to manage these priority issues. Noise and dust modelling were required from each pre-qualified Tenderer, to demonstrate capability of compliance with NSW Environment Protection Authority requirements. This formed part of the tender assessment. Criteria were also developed for revegetation, specifying numbers of endemic trees, shrubs and grasses per 400m2 of spoil emplacement in order to create a floral community similar to the existing adjacent National Park.
The implementation of these requirements and the development of a site Environmental Management Plan by the Sydney Catchment Authority, Australian Water Technologies and Abigroup Contractors, whilst maintaining productivity, has proven to be a working example of the benefits of Partnering.
This paper describes the use of a high strength woven geotextile and preloading to stabilise the surface of a very low strength tailings pond, and the incorporation of a geosynthetic clay liner (GCL) within the final capping design to complete closure. The pond, which contains tin and copper tailings, formed the lower tailings containment area of a three-tiered tailings storage, located directly above the Wild River in North Queensland. Stabilising the lower pond (area 2,500 m2), which contained tailings of “zero strength” in the central area involved the placement of a woven geotextile over the surface, which was anchored around the perimeter. The placement of finger berms (preloading fill) on the geotextile was successful without exceeding the bearing capacity of the tailings overall. Settlements of the berms were closely monitored to allow the system to support construction plant. After the finger berms were joined, they were widened until the area was covered. A sand layer was then placed over the area followed by a GCL to form an impermeable barrier prior to the placement of clay and topsoil.
B. S. Sherman
Many large Australian dams currently lack selective withdrawal capabilities and release water mainly from deep within the hypolimnion. Deep-water releases coupled with the strong thermal stratification typical of Australian reservoirs results in discharge temperatures 10 °C or more colder than would normally be expected. Cold water pollution has impacted more than 1000 km of river habitat in Australia where it is known to impair spawning, feeding and survival of many native fishes.
This report reviews alternative approaches for the mitigation of cold water pollution below dams. The underlying theory and practical limitations of operation as well as field experience (including cost) with each of the methods are discussed. Two methods in particular, suface pumps and submerged curtains, appear to offer cost-effective alternatives to the expensive retrofitting of dams with multi-level outlet structures (estimated to cost $5-35m per dam for major dams in NSW). These methods are predicted to be capable of increasing discharge temperatures by 4-10 ° throughout the range of irrigation releases without any redirection of flows, i.e. hydropower releases can be maintained at present levels. This holds the promise of restoring more desirable temperatures over hundreds of kilometres of river.
The entire historical record of rainfall archives held by the Bureau of Meteorology over the region of Australia affected by tropical storms has been examined and the extreme storms have been extracted. From this database, we account for site specific effects (moisture and topography) from each of the storms, allowing us to compare storms amongst each other. This then allows us to construct a theoretical maximum precipitation in a generalised sense. By then returning the site specific information for a particular region, we can infer the probable maximum precipitation at this location.
The use of risk analysis for dam safety is becoming more widespread. Dam owners are increasingly aware of the need for information on current and emerging practices from the world scene to determine how to proceed with the use of risk assessment. The paper summarises the findings of a Churchill Fellowship study into risk assessment for dam safety management. Dam owners, regulators and consultants from the United Kingdom, France, the Netherlands, Norway, Sweden, the United States and Canada were consulted for the study. Conclusions are drawn from the findings and recommendations made for future development.