Tony McCormick, John Grimston, Robin Dawson
Project Aqua is a proposed hydroelectric and irrigation resource sharing development on the Lower Waitaki River in New Zealand’s South Island. The NZ $1 billion project aims to deliver approximately 540 MW peak power at an economically viable price, while minimising environmental and social impacts. Application of traditional hydro concepts in historical studies for the same reach has not provided an economic solution. The current proposal challenges conventional thinking in many areas with innovative concepts allowing a significantly lower cost while not sacrificing safety or flexibility.
Development of storage may involve high social and environmental impacts. No significant storage is needed for Project Aqua as the operation of existing upstream dams can be modified to provide for peaking demand and maintenance of minimum flows. The river intake offers innovative features with its very low profile structure. The concept allows a departure from the traditional barrage or dam diversion and maintains an open braid for jet boat and fish passage. This concept has proven to be a major feature in the overall project progression to the current stage.
The largest impact component of the scheme is the eight canals designed to carry 340 cumecs over 63 km through six power stations. Cuts and fills form the canals with locally derived materials used for the embankments and lining. Expensive lining has been minimised by balancing flow exchange with groundwater through the cut and fill sections.
Feasibility design has been completed and resource consents are currently being sought. This paper will cover the significant design features and impacts.
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Tom Ryan, Charles Todd and Simon Nicol
The potential impacts of cold water releases on the downstream thermal regime include: reducing the seasonal temperature range (lowering of the maximum and raising the minimum); reducing the diurnal temperature variation; rapid temperature changes; and delaying the seasonal warming of stream temperatures. Recent investigations have identified at least 20 large dams within Victoria, that have the potential to release cold water from below the hypolimnium. A monitoring program is currently being implemented in Victoria to identify the occurrence of cold water releases and to estimate the extent of the downstream impacts.
Cold water releases have been shown to impact the biological processes within aquatic ecosystems and consequently reduce the natural productivity. The physiological development of native freshwater fish can be impacted in a number of ways. Growth and reproductive development of adult fish is impacted while the survival of eggs and larvae can also be retarded. As a result, the sustainability and viability of native fish populations are greatly compromised.
Using stream temperature data from the Mitta Mitta River downstream of Dartmouth Dam, the decline of the native fish populations, due to cold water releases, can be demonstrated under current operating conditions. The decline in population numbers can be further demonstrated with the use of a simple age-based population model for Murray Cod. The spawning opportunity and survival of egg and larvae can be improved for Murray Cod by increasing the overall spring release temperatures by 2, 4, 6 and 8 oC. The population model adjusted for these thermal improvements, results in increased survival prospects for the Murray Cod population.
Paul W. Heinrichs & John Bosler
Spring Creek Dam is a 16m high zoned earthfill dam with a central vertical concrete core wall storing 4700 ML for Orange City Council’s water supply. It was a 14.5m high dam constructed in 1931 and in 1947 was raised by 1.0m. In 1966 after a week of heavy rain following a long dry spell, an 80m section of the downstream face slumped but the dam fortuitously survived. In 1969 the dam was re-constructed but no internal drain/filter was installed.
Following the 1994 dam surveillance report, piezometers were installed in the downstream fill. Drilling for these revealed that a substantial portion of the zone downstream of the core wall was saturated. The piezometers recorded piezometric elevations that closely and rapidly followed the reservoir level. Subsequent site investigations identified pockets of very low strength fill immediately downstream of the core wall. It was concluded that the core wall was seriously compromised and the storage level was subsequently, significantly lowered, as an interim dam safety measure.
Dambreak studies indicated the dam is a high hazard and hydrological studies found that the spillway capacity was inadequate.
This paper details the problems involved, their analyses, and the remedial measures proposed at the concept design stage. These include a chimney filter/drain, a stabilising fill combined with embankment crest raising and the construction of a 3-bay fuse plug auxiliary spillway.
David J. Walland, Jeanette Meighen, Catherine Beesley, Karin Xuereb
The method for estimating Probable Maximum Precipitation in areas of Australia affected by tropical storms has been revised. The method that it replaces, designed in the 1970s is considered outdated and based on limited data.
The entire Bureau rainfall record has been examined objectively for the largest rainfall events. These events have been analysed and modified to enable storm transposition across a large region. The modifications are based on local topography, moisture and location. Once the storm data is transposed to a single location it can be meaningfully compared and used to construct an upper estimate on the possible rainfall. This estimate can then be used in conjunction with information about a specific catchment in order to estimate Probable Maximum Precipitation at that location.
Richard R. Davidson, Shane McGrath, Adrian Bowden, Andrew Reynolds
Goulburn-Murray Water (G-MW) manages thirteen major dams for the State of Victoria. As part of its Dam Improvement Program (DIP), five priority dams were identified for detailed safety and performance evaluation. Over the last three years, the design reviews have been completed and a series of dam safety issues have been identified which pose societal and financial risk. Substantial financial resources will be required to be applied over a considerable period to bring these dams into compliance with established international and Australian standards. Which of these dam safety issues should be addressed first? In what sequence and with what urgency should the actions be implemented? Can cost-effective interim targets be set? How can the remaining eight
dams, which could also pose societal and financial risk, be prioritised for future detailed investigation? To answer these questions a quantitative risk assessment approach was used. The approach utilised expert engineering and consequence panels and included input to and review of the process and outcomes by a stakeholder reference panel reporting directly to the Board of G-MW. The implementation of a strategic risk management process has now begun to progressively and systematically reduce the dam safety risk across the entire dams portfolio. This process recognises that available funding for risk reduction measures is very limited, so the highest risks are reduced in an incremental fashion to achieve interim risk targets and eventually meet contemporary dam safety standards.
J. Matthews, A. Crichton, G. Gibson
Glenmaggie Dam is a 37m high concrete gravity dam, which was constructed from 1919 to 1927. A
design review, which was carried out in line with ANCOLD Guidelines, (SMEC 1999) indicated that the dam did not meet the ANCOLD Guidelines for earthquake. This was despite the fact that the dam was stabilised in 1989 by the addition of 70 post-tensioned ground anchors. Faced with the possibility of having to perform a major upgrade to the dam, Southern Rural Water opted to undertake a more detailed assessment of the seismic loads and to carry out further analysis of the dam using the time history method. The time history method uses an accelerogram to model the forces acting on the structure throughout the earthquake and takes into account the continually changing direction of these forces. It can also be used to determine the size of any permanent
displacements caused by the earthquake, which can then be compared to the maximum allowable permanent deformation of the dam to determine if they are acceptable. The study was carried out by GHD Pty Ltd and also utilised updated seismic information for the dam site provided by the Seismology Research Centre and a geological assessment of the local faults by the URS Corporation. This paper discusses the methods used to determine the seismic loads; the techniques used in the study and the outcomes and follows the process from a dam owner’s perspective.