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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There are many important dams and other structures on catchments smaller than 1000 km² with response times less than 24 hours, however these catchments have been largely overlooked in previous research into large and extreme floods. This paper is an initial step in “catching up” design practice for short duration rainfall events to the current best practice that is available for estimation of floods from rainfall events with durations of 24 hours and greater.
Two issues are specifically addressed in this paper. Firstly, a regional analysis of short duration rainfall depths is conducted to extend the frequency curve beyond an AEP of 1 in 100. Rainfall frequency curves are estimated for durations between 0.5 and 12 hours, using data from ten pluviograph sites around Australia. Secondly, sets of temporal patterns are derived that could be useful in joint probability analysis of short duration rainfall events. The effects of these new rainfall depths and temporal patterns on flood frequency curves are tested by applying them to rainfall-runoff routing models for three dams with small catchment areas.
Phillip Jordan, Rory Nathan, L. Mittiga1 M. Pearse, and Brian Taylor
Garth Barnbaum and Robert Bell
Hydro Tasmania has recently upgraded the control systems for the spillway gates of three of its dams, Clark Dam, Meadowbank Dam and Liapootah Dam. The upgrades followed internal reliability assessments that highlighted high reliance on operator attendance, single points of failure and operational difficulties on each of the three gate systems.
The three gates are of contrasting types. Clark Dam Spillway Gates are submerged orifice type radial gates, operated by wire rope hoists. Meadowbank Crest Gates are flap type gates, held by 10 hydraulic cylinders per gate, a design that has had a difficult operating history. Liapootah is a floating drum gate. The upgrades for each gate therefore required different solutions, albeit within a common basis of design framework. The solutions arrived at are innovative, and meet or exceed worlds best practice.
All three gates are now fully automatic, with PLC control. The use of PLC’s significantly enhances the reliability of the gates. Extensive use is also made of the PLC in monitoring key systems. For example, an impossibly rapid lake level rise detected by one transducer, but not its duplicate, will be alarmed but ignored to avoid unnecessary discharge. All systems incorporate appropriate redundancy. The PLC systems also provide some automatic functional testing functionality and enhance remote alarms and local fault finding.
Mechanical systems were modified to facilitate automation and increase reliability. Stand by power sources used include auto-start diesel genset, DC batteries and a micro hydro generator.
The design and implementation of each of the upgrades was carried out by the Electrical and Mechanical Group of Hydro Tasmania’s Consulting Division, in conjunction with Generation Division’s Project Management Group.
John Phillips, Yu Sheng, Jennifer Henderson
The main iron ore body at Cockatoo Island in the West Kimberleys forms a cliff face plunging steeply into the sea. It was mined by BHP down to low tide level, but the tidal range of 10 metres hampered operations. Being a very pure and sought after ore, various investigations were made to determine methods of extracting the ore below the sea. A coffer dam into the sea was investigated with the conclusion that the soft marine sediments and apparent artesian groundwater in the foundation posed a major risk and high costs.
The mine was sold to a smaller company who proceeded to win useful ore from the island. They also eyed off the undersea ore and approached GHD to use soft ground technology developed for the Derby Tidal Power Project. The soft marine sediments and apparent artesian groundwater conditions were investigated.
The paper describes the design processes involved to achieve dam stability in a space limited by lease boundaries and the desire to maximise the amount of ore that could be accessed. A key to the process was the development of construction techniques and core placement procedures that could cope with the tidal range. Timing aspects were crucial and were controlled by observations of an extensive array of instruments installed for control purposes.
Bellfield dam is a 78,500 ML drought reserve storage for the Wimmera-Mallee Stock and Domestic System. The 800m long by 57m high zoned earth and rockfill dam is located on Fyans Creek upstream of the Grampians tourist town of Halls Gap in north western Victoria. The dam was built in the period 1963-67. Later in 2002-03 as part of a flood security upgrading (FSU) program, had its rock chute spillway deepened by 3.4m and its embankment crest raised by 1.9m to withstand a PMF.
To manage the FSU’s likely construction constraints and risks, Wimmera Mallee Water’s Headworks Group successfully undertook the upgrading by a mix of schedule of rates contracts and direct management.
This paper complements a companion paper by WMW’s design consultants, URS and describes why and how direct management was used, plus unconventional aspects of spillway deepening and the raising of a narrow dam crest with earthworks and a pre-cast parapet wall.
Keywords: Drill and blast, pre-cast parapet wall, narrow embankment crest, direct management, construction.