M. Barker, T. Burt, K. McCallum-Gaul, Dr M. Barry
The disused Stapylton quarry is located in the suburbs of the Queensland Gold Coast. Gold Coast City Council, as part of the Northern Wastewater Strategy, has included the use of the quarry for storage and re-distribution of reclaimed water from the Beenleigh Water Reclamation Facility (WRF) to the downstream cane farmlands. A comprehensive EIS has been produced, which has strict water quality requirements for the quarry environs as well as the reservoir and outflow. This paper presents the background to the Northern Wastewater Strategy, the requirements for the Stapylton reservoir and the analysis performed for the detailed design of the embankment dam and the inlet bubble plume destratification system. The modelling of the destratification system was undertaken using the programme DYnamic REservoir Simulation Model (DYRESM) coupled with Computational Aquatic Ecosystems DYnamics Model (CAEDYM). The outcomes and implications of the modelling for the design and system operation including environmental monitoring are discussed.
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.
Assessment of dam safety requires estimates of extreme rainfall together with the temporal and spatial distributions of extreme rainfall. In order to satisfy dam safety requirements for dams in the west coast of Tasmania, the Bureau of Meteorology has developed the method of storm transposition and maximisation for application in this region.
Daily, as well as continuously recorded rainfall data for all Bureau of Meteorology and Hydro Tasmania sites in western Tasmania have been analysed and the most outstanding rainfall events over one, two and three-day durations in the region have been identified. Meteorological analysis of these events reveals that the most significant rainfall events in the west coast of Tasmania are caused by the passage of fronts, which are sometimes associated with an intense extratropical cyclone, with a westerly or southwesterly airstream.
A database of isohyetal analyses of the most significant rainfall events in western Tasmania has been established. These can be used either ‘in situ’ or transposed to estimate mean catchment rainfall. Storm dewpoint temperatures for the purpose of moisture maximisation have been determined.
Cumulative and incremental three-hourly temporal distributions for sites having continuous rainfall data or three-hourly meteorological observations have been constructed and design temporal distributions of extreme rainfall have been derived.
An objective method for adjusting for differences in the topography between the storm and target locations is proposed
Richard Olive John Wonnacott, Stefan Schwank
The Diavik Dyke was constructed in 2001/2 in a major sub-Arctic lake in Canada’s Northwest Territories, to permit an open-pit diamond mining operation. The dyke, 3.9km long, was built in water up to 20 metres deep in a period of 17 months. For ten months of this period the lake was frozen. The project was notable for the extreme climate, discontinuous permafrost in the dyke foundations, very difficult logistics and the exceptional environmental constraints.
Project economics dictated a short construction period to permit the early generation of revenue from the mine. To confidently deliver a secure dyke within the time frame, the world’s most technologically advanced cut-off wall equipment was designed and fabricated in Germany.
This paper provides an overview of the dyke and focuses in more detail on the specialty equipment used for the cut-off wall and foundation treatment.
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.
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.