A. Ahmed-Zeki, G. Roads
South East Queensland Water Corporation (SEQWater) as owner and operator is proceeding with an upgrade of the flood capacity of Wivenhoe Dam. SEQWater has formed an Alliance with Leighton Contractors, Coffey Geosciences, Montgomery Watson Harza (MWH) and the Department of Commerce-NSW (formerly DPWS, NSW) to upgrade Wivenhoe Dam. This paper presents feasibility level investigation and design activities for an upgrade option, comprising a large labyrinth auxiliary spillway at the right abutment of the dam, for supplementing the existing gated spillway in handling the Probable Maximum Flood (PMF) event. This right abutment auxiliary spillway option incorporates Hydroplus type concrete fuse gates. The investigation so far has proved the technical viability of this option, however, ranking along with the other three options against various criteria will lead to the selection of the preferred upgrade option.
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Peter D Amos, Thomas G Newson, Murray D Gillon
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.
In 1998, ANCOLD Guidelines entitled “Guidelines for Design of Dams for Earthquake” was issued. The Guideline mainly deals with the seismic aspects of dams and only a basic reference is made to the seismic assessment of intake towers in Section 8.3. Although the much needed and pioneering step taken to introduce this Guideline is to be appreciated and it has covered the seismic aspects of dams, some confusion does exist amongst dam / structural engineers in assessing the seismic performance of concrete intake towers. This is mainly due to the fact the behaviour of reinforced concrete intakes towers is quite different from that of earth or concrete gravity dams. This confusion could potentially lead to gross overestimate of the inertia loads on concrete intake towers resulting in unnecessary expenditure in investigation and remedial works.
The energy dissipation due to inelastic hysteresis behaviour of concrete members results in a great reduction in the inertia loads compared with those calculated with traditional “elastic” analysis methods. This consequently results in significant reductions in bending moments and shear forces on the tower and its foundation. It is very important to understand the basic behaviour of reinforced concrete, considering the composite action of concrete, longitudinal & hoop reinforcing steel, before embarking in sophisticated dynamic analysis the outputs of which are highly dependent on the input parameters
The authors have developed a methodology in which the hysteresis energy dissipation due to the inelastic behaviour of concrete intake towers is considered. Various criteria were defined for serviceability and ultimate failure modes such as excessive deflection, spalling of concrete, buckling of reinforcing steel. The confinement effect of hoop steel on the core concrete is also considered.
This paper will present the fundamental aspects of seismic behaviour of reinforced concrete structures with practical cases as applied to intake towers. The results showed that the current methods adopted by various Dam Authorities in Australia are cursory and the energy dissipation aspect should be considered, in conjunction with expert advice, before undertaking any remedial works.
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.
John Grimston, Robin Dawson, Maurice Fraser
Water supply for irrigation of horticulture and agriculture in New Zealand has gained considerable momentum since the mid 1990’s. The rapid growth of the wine industry in areas such as Marlborough (located at the top of the South Island) and dairy conversions in many areas of South Canterbury are prime examples of the pressure being applied to existing water supplies and sources and the increasing need for new irrigation supplies and security of supply.
The larger irrigation projects of the past were implemented by the government – schemes such as the Rangitata Diversion race and the Lower Waitaki irrigation project both on the east coast of the South Island. The 1990’s and early 2000’s has seen a largely hands off government approach to potential irrigation projects with the shift towards leaving it to market forces to build irrigation schemes. The result has been that due to significant larger project risks and capital cost requirements with often multi party stakeholder groups, only relatively small schemes have been implemented – the Waimakariri irrigation scheme and Opuha irrigation dam are a few examples. However, in recent years with the value of water increasing several significant irrigation projects promoted by private enterprise or progressive district councils with farmer groups are being investigated and a few may be close to implementation.
The recent drought conditions have focussed attention on the need for storages to maintain security of supply and, together with the balance with sustainability, the consenting environment in New Zealand and existing river/aquifer allocations, significant challenges to development are presented.
Specific case examples include the proposed Delta dam near Blenheim being developed by a private group of irrigators and the Bankhouse development being implemented by a private owner in the same Marlborough region.
This paper provides a background to irrigation in the South Island and describes these two proposed schemes and associated storage dams, together with an insight into the key issues related to the proposed projects.