Matthew Pollard, John Vitkovsky, Richard Priman
Abstract: South East Queensland (SEQ) currently has severe (Target 140) restrictions imposed to help secure supplies during the current drought which is the worst on record. Additionally, a $9 billion water infrastructure program is being fast-tracked to increase the climate resilience of the region and provide for long term sustainable growth.
The Draft South East Queensland Water Strategy (SEQWS) released in March 2008 was prepared by the Queensland Water Commission to reduce the likelihood of ever experiencing such severe restrictions again and to ensure water security into the future. The Strategy includes a Water Supply Guarantee underpinned by advanced analytical techniques for estimating the system yield from surface water, groundwater and manufactured water supplies connected by the SEQ Water Grid. This approach builds on the Level of Service (LOS) Objectives methodology, originally promulgated by the Water Services Association of Australia in their June 2005 paper entitled “Framework for Urban Water Resource Planning”. The approach has led to a significant improvement in our understanding of water supply risks and the associated planning implications for assessed yields/water availability.
To assess yield using the LOS objective methodology and to determine the benefits of the new water infrastructure, a regional water balance model for the connected SEQ Water Grid simulating the water sharing arrangements of all of the SEQ water sources was established. The model uses a logic tree to allocate water using a “proportional storage rule” from multiple sources to meet competing demands. This approach enabled quantification of the increase in system yield resulting from the construction of the SEQ water grid which allows demands from previously disconnected areas to be met by more efficient allocation of water from supply sources. Stochastically generated dam inflow data was used to facilitate a more comprehensive assessment of climate variability and water supply risk than is possible with historic data alone.
The paper discusses the managed hydrologic risk approach adopted in developing the regional water balance model which implements the LOS Objectives approach and improves the understanding of the relationship between the level of service, supply yield and risks associated with climate variability. The result is a far more thorough approach to planning for future water service delivery and water infrastructure.
Keywords: level of service objectives, South East Queensland Water Strategy, SEQ Water Grid, yield, water security, regional water balance model, stochastic modelling, climate variability.
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Abstract: A number of SunWater’s dams are in the process of being upgraded to the acceptable flood capacity (AFC) to ensure the highest level of safety. The Fred Haigh Dam upgrade was completed in September 2006 and the Bjelke Petersen Dam upgrade was completed in October 2007. Borumba Dam is the latest upgrade being undertaken with construction commencing in April 2008 and is expected to be completed by December 2008. Each dam underwent a comprehensive risk assessment to identify and evaluate all risks with respect to the ANCOLD tolerability limits to ensure risks satisfied ALARP. The assessment identified the most cost effective upgrade solutions for detailed design.
The upgrade at Fred Haigh, Bjelke Petersen and Borumba Dams will enable them to pass an extreme flood equivalent to 50% of the Acceptable Flood Capacity (AFC). This is Stage 1 of a two stage upgrade to ultimately achieve 100% of the ANCOLD “Fallback” AFC which is the standard SunWater has adopted for its major dams. SunWater has prioritised spillway capacity upgrades to achieve a minimum dam portfolio standard of passing 50% Acceptable Flood Capacity inflow by 2015 and full Acceptable Flood Capacity inflow by 2025.
The most economic Stage 1 upgrade option for Fred Haigh, Bjelke Petersen and Borumba Dams was to maintain the existing spillway width and to raise the dam crest with a concrete parapet wall. For the Bjelke Petersen and Borumba Dams the spillway training wall heights were raised to allow for increased flow though the spillway. From the hydraulic model studies and flood routing a height of each different dam crest wall was obtained.
This paper will describe the different methods and considerations used for upgrading Fred Haigh, Bjelke Petersen and Borumba Dams to the 50% AFC.
Keywords: dam safety, spillway, Fred Haigh Dam, Bjelke Petersen Dam, Borumba Dam, SunWater, Queensland.
Mark Hore, Joseph Matthews
Abstract: Substantial flooding occurred in the Gippsland region in late June 2007, following the severe bushfires experienced during the previous summer. Major damage was sustained to the regions infrastructure, which included the gated storages at Glenmaggie Dam and Cowwarr Weir, located in the neighbouring Macalister and Thomson river catchments respectively. The flood event at Glenmaggie Dam produced a record peak inflow of well over 250,000 ML/day, which was more than twice the previous record.
The magnitude and intensity of the flood event created a number of issues for the staff at Southern Rural Water (SRW), who are engaged in the safe operation of the facilities. The event tested the organisations emergency management systems and the ability of the organisation to effectively manage events at multiple sites. Some of challenges faced included: a rapid rise in storage volumes; the loss of upstream warning gauges; the accumulation of large volumes of debris; the development of suitable release strategies and the communication and engagement with the local community.
The event caused a significant amount of damage to key infrastructure at both sites, with the Cowwarr Weir storage being the worst affected. A number of high priority projects have been completed since the event, with spending to date totalling $3 million. The unusual nature of the flood event provided the opportunity to review previous flood assessments and to identify deficiencies with elements of the existing infrastructure. Of particular interest was the subsequent hydrology review which provided a comparison with previous modelling assessments. The review included a flood frequency assessment which showed that the magnitude of the Glenmaggie flood was in the order of a 1:200 AEP(Annual Exceedance Probability) event, which was disproportionate to the rainfall event frequency assessed as having a 1:50 AEP, when averaged across the catchment. The aim of the paper is provide a case study for other dam engineers who may be preparing for future flood events in similarly affected catchments.
Keywords: flood, gated storage, dam performance, remedial works.
Steven O’Brien, Brent Mefford, John Harris
Abstract: The Hinze Dam Stage 3 Upgrade required ‘Waterway Barrier Works Approval’, including fish-passage assessments. The dam, sited in the Nerang River catchment, has relatively undisturbed riverine habitat upstream which, together with the reservoir’s recreational fishery, was a key driver for inclusion of a fishway. Low outflows from the dam and impacts of development on the river downstream contrast starkly with upstream environments.
The Hinze Dam Alliance (HDA) assessed that upstream transfer of fish will have significant environmental benefits but downstream passage, beyond that achieved during spill events, could not be justified.
Constraints at the site for upstream passage include unvarying 7.25ML/d releases from the reservoir and a distance of nearly 300m between the reservoir and the downstream river pool. HDA has developed an innovative trap-and-haul system to collect upstream-migrating fish near the spillway and transport them by tanker to upstream release areas. This system is the first of its kind designed for Australia. It provides flexibility to accommodate varying fish biomass, the ability to operate over a range of flows up to 20-year ARI events, facilities for data collection and removal of pest species, and capacity to manage predation with small-fish refuges during trapping and transfer and by releasing fish at several protected sites in the reservoir.
Keywords: fishway, trap and haul System, fish passage
Brunner Wolfgang G, Bi Arthur, Chang William, Zong Dung Feng
ABSTRACT: In the South of the Sichuan province the 240 MW Yeleh hydroelectric power project is under construction by Sichuan Nanya River Basin Hydraulic Power Development Company Limited, a state-owned enterprise, and China Gezhou Ba Water & Power Group Company Ltd.. This project sets out to develop the mountain cascade of the Nanya river, a tributary of the Dadu River, provide superior electricity and adjust flood peak and frequency. The specialist contractor Foundation Engineering Company of China Water Resource and Hydropower (FEC) was awarded the contract of foundation treatment at the right bank, which included the construction of a 75 m deep concrete cut-off wall inside a 6.0 m x 6.5 m tunnel. The requirement for 19 317 m3 cut-off wall to be constructed in permeable and very dense gravel/cobble formations and a demanding project program led FEC to adopt the BAUER Low Headroom Cutter CBC25/MBC30 in conjunction with the overlap cutter joint.
Keywords: hydroelectric project, dam, dam tunnel, cut-off wall, trench cutter
Francisco Lopez, John Bosler
Abstract: A study has been undertaken to determine the structural adequacy of the Intake Tower for the Dartmouth Dam Low Level Outlet Works under the Maximum Design Earthquake (MDE). The tower is a reinforced concrete frame structure. The study included the definition of appropriate seismic inputs and nonlinear time-history analyses for different levels of ground shaking.
The behaviour of the tower was assessed in terms of material strains. The seismic acceleration-time history was applied to the model and the nonlinear analysis identified the locations in the structure which reached the following performance thresholds: cracking of core concrete, yielding of reinforcing steel, fracture of reinforcing steel and crushing of core concrete.
The results of the study showed that the tower was able to resist, without collapse, the loadings imposed by three different MDE acceleration time-histories. The predicted level of damage consisted of generalised yielding of reinforcement, formation of numerous plastic hinges at different locations in the tower and generalised spalling of cover concrete.
Overall, the structural response of the tower under the MDE events was considered satisfactory and met the performance requirement that structural collapse should not occur.
Keywords: intake tower, nonlinear, inelastic, time-history, seismic analysis.