2003 – COPING WITH PROBABLE MAXIMUM FLOOD – AN ALLIANCE PROJECT DELIVERY FOR WIVENHOE DAM

Categories: 2003, Papers Tags: 2003, B Maher, D. Gill, G.Roads, K. Chandler, S.Macnish

SEQWater is the major supplier of untreated water in bulk to Local Governments and industry in the South East Queensland region of Australia, through ownership of Wivenhoe, Somerset and North Pine Dams. Wivenhoe Dam (Lake Wivenhoe) is located on the Brisbane River in Esk Shire. The storage provides both flood mitigation and water supply storage to Brisbane and Ipswich. The water supply storage capacity at full supply level is 1,160 GL. An additional 1,450 GL of storage above full supply level is used for flood mitigation.

Changes to the estimation of extreme rainfall events has resulted in significant increases in the estimates of the PMF since the original design of Wivenhoe Dam. To upgrade the flood security of Wivenhoe Dam, SEQWater has formed an alliance with Leighton Contractors, Coffey Geosciences, MWH and the NSW Department of Commerce.

This paper details the alliance delivery method, the latest estimates of the PMF based on the GTSMR method and details of the two preferred options being finalised by the Alliance.

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Papers 2003

2003 – Data for Maintenance Management
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I. Sanders

The paper highlights the fundamental importance of correct data selection and storage for the quality of Asset Management demanded for today’s water industry infrastructure.

In developing this theme, the concept of Risk driven maintenance is introduced to focus attention on those issues that not only the identify the appropriate data to be collected and stored, but also, by way of illustrated examples, the direct relevance and application of reliability engineering principles in Risk Analysis.

The author’s principle objective is to demonstrate that the historical data on reliability, condition and performance must be supported with detailed costing information if any worthwhile outcomes are to be forthcoming from analysis.
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Papers 2003

2003 – POSITIVE COMMUNITY INVOLVEMENT SAVES TIME AND COSTS AT YARRAWONGA WEIR
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Yarrawonga Weir was constructed in the 1930’s and is located on the Victoria / New South Wales border, between the towns of Yarrawonga and Mulwala. Dam safety investigations revealed that the main embankment was founded on a very loose layer of sand that would be vulnerable to liquefaction even under the operating basis earthquake

This paper details the statutory approvals and community consultation processes that were employed and the benefits that they provided to the $13 million remedial works project.

Local communities can assist, be neutral or obstruct a project. By engaging the community in a positive manner it is possible to deliver excellent results without increasing costs.
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Papers 2003

2003 – “Spillway Gates a Survey of Operational and Reliability Issues” – Results of Preliminary Analysis
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Glen Hobbs

A survey of spillway gate systems and operations has recently been completed by dam organisations in Nth America, Australia and New Zealand. The survey sought to identify typical arrangements for spillway gate systems and common features pertaining to reliability such as system redundancy, actuation methods and back-up systems, gate and hoist types, remote and local operation, gate testing programmes, and human factors.

Sixteen organizations responded, covering sixty two dams and nearly four hundred gates. This Paper reports on the preliminary analysis of the data, providing an overview of the industries’ approach to spillway gate operation and control.
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Papers 2003

2003 – Use of Artificial Aeration to Control Iron and Manganese in Reservoirs.
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Frank L Burns

By 1976 head loss in the 23 km long 750/900 mm diameter CLMS pipeline from Eppalock Reservoir to Bendigo had increased from 45.7 m to 98.2 m (115%) after only 12 years service. The cause was identified as increased friction from soft voluminous iron and manganese bacterial slime building up on the pipe walls and increasing the friction. Inspection of the drained pipes in the dry gave little indication of the problem since the slime consolidated to an innocuous looking thin smooth coating as it dried.

1960 studies by Tyler and Mitchell at the University of Tasmania for the Hydro-Electric Commission had shown that the micro-organisms producing these slime growths were present in all pipelines. However they required the presence of iron and manganese in the water to flourish and produce flow reduction. Remobilisation from oxygen deficient bottom sediments was shown in the 1940’s by Pearsall and Mortimer in England to be a major source of iron and manganese in reservoir water and this could be controlled if sufficient dissolved oxygen could be provided to convert the reducing conditions at the sediments to oxidising conditions.

An experimental aeration system designed by the author was operated in the 180,000 ML Eppalock Reservoir for 19 days during March 1977. This mixed the reservoir to the depth of the aerators (24 m) increasing the low 10% saturation dissolved oxygen at this depth to a high 94% saturation thereby changing chemical conditions from reducing to oxidising. As a result the iron concentration in the surface water decreased from 2.04 mg/L to 0.54 mg/L but there was little change in the pre-aeration 0.03 mg/L manganese concentration with this short period of aeration. The iron concentration in the water flowing in the pipeline changed from 1.78 mg/l to 0.57 mg/l.

The problem of pipe flow reduction from bacterial slime growth on the pipe walls is discussed in this paper and examples are given of the use of automatic reservoir aeration to overcome the problem including costs and results.
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Papers 2003

2003 – INVESTIGATION OF A DETERIORATING SEEPAGE CONDITION IN ARAPUNI DAM FOUNDATION, NEW ZEALAND
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In September 2000, pressures being monitored in a geological fracture beneath Arapuni Dam were found to be rising significantly, indicating that a deteriorating condition was developing in the foundation. Two boreholes drilled in 1995 had intersected high water pressures within the fracture in an area close to the downstream face of the dam, posing a risk of major leakage developing from where the fracture day-lighted downstream of the dam. Lumps of clay, bitumen and lake biota, including snails and small fish, were identified discharging from the boreholes, indicating that a significant leakage path had developed. Detailed investigations, the subject of this paper, were carried out from September 2000 to confirm the extent and nature of the deterioration. A range of groundwater investigation techniques and tools were used, while the reservoir remained full, to identify the source of the leak and confirm the path it took. The investigations culminated in development of a groundwater model that described the seepage behaviour in the dam foundation. Based on the investigation information gathered, the foundation fracture bearing the high water pressure was successfully grouted in December 2001 without lowering the reservoir.
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