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.
Investigations of damaging blowback incidents at the headrace tunnel intake to Rangipo Power Station in the Central North Island of New Zealand are described. The blowback phenomenon is explained theoretically based on evaluation of the evidence available from the incidents and information obtained from the literature. A physical hydraulic model study is described in which this explanation of the blowback phenomenon was verified. The model was also used to devise a solution for the blowback problem.
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.
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.
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
This paper provides an insight into the management of reservoirs under drought conditions within the new water management frameworks established under the Council of Australian Governments (COAG) Water Reforms. Traditional approaches to the sharing of available supplies during drought are no longer appropriate as the roles of the resource regulator, infrastructure operator, and Government have been separated in the interests of providing certainty for water users and the environment. Recent experiences during drought in the Upper Mary River system near Gympie in Queensland has demonstrated the need to ensure the robustness of water sharing rules for reservoirs under the new framework if certainty is to be delivered.