Bill Hakin, Peter Buchanan, Doug Connors, Darren Loidl
To allow greater flexibility in their generation and hence a better response to the peaks in electricity demand, Southern Hydro decided to increase the Full Supply Level of Dartmouth Regulatory Dam by 3.5m using labyrinth Fusegates.
The Regulating Dam is located on the Mitta Mitta River, approximately 8 km downstream of Dartmouth Dam. It is a 23 m high concrete gravity structure with a 60 m long central spillway section. The dam forms the storage required for regulating releases from the Dartmouth Power Station back to the Mitta Mitta River, so as to satisfy environmental requirements.
Although this is the second Fusegate project in Australia it is unique in that difficult access conditions determined that construction in mild steel would be the most appropriate. Initial civil works involved construction of a flat sill to replace the Ogee spillway crest so that it could support the Fusegates. The installation contractor devised an ingenious method for installing the huge structures over the top of the gate-house which blocks direct access to the spillway. Design was very much undertaken with the installation method in mind to ensure a high quality project with minimum contractual risk.
This paper discusses the construction stage of this very interesting spillway modification.
There is a widespread perception among dam engineers that tree root invasion occasions a very serious threat to embankment dams by virtue of its potential to initiate piping failure, with appropriate action invariably recommended. Remedial works can, on occasions, be extensive.
While the principle is ostensibly plausible and scarcely challenged, there has never been, to the Author’s knowledge, a satisfactory investigation to establish any credible scientific basis for it. One case that has attracted some attention in literature (by virtue of the extent of the investigation undertaken), viz a piping accident at Yan Yean Dam, is critically reviewed to show that the accepted view on the role of tree roots in this incident is less than satisfactory. In the course of this review, two physical Laws of Piping are proposed, and applied both to this case and to another nearby Melbourne Water dam that also has a history of piping.
Whilst the consequences of piping in a major dam are such that risk from this source must be kept to a very low level, it is concluded here that piping risk arising from tree root invasion has been considerably overstated and that a more balanced assessment is necessary before determining what, if any, action is required.
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.
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.
Phillip Jordan, Rory Nathan, L. Mittiga1 M. Pearse, and Brian Taylor
There are many important dams and other structures on catchments smaller than 1000 km² with response times less than 24 hours, however these catchments have been largely overlooked in previous research into large and extreme floods. This paper is an initial step in “catching up” design practice for short duration rainfall events to the current best practice that is available for estimation of floods from rainfall events with durations of 24 hours and greater.
Two issues are specifically addressed in this paper. Firstly, a regional analysis of short duration rainfall depths is conducted to extend the frequency curve beyond an AEP of 1 in 100. Rainfall frequency curves are estimated for durations between 0.5 and 12 hours, using data from ten pluviograph sites around Australia. Secondly, sets of temporal patterns are derived that could be useful in joint probability analysis of short duration rainfall events. The effects of these new rainfall depths and temporal patterns on flood frequency curves are tested by applying them to rainfall-runoff routing models for three dams with small catchment areas.
Hydro Tasmania has recently developed a Dam Safety Emergency Plan, which covers 54 referable dams throughout Tasmania. A major contribution was the development of the Pieman River flood warning system. The flood warning system is a computer-based model that forecasts the hydrological situation of the catchment up to 48 hours into the future and alarms the appropriate personnel when a flood event is imminent. The Pieman River catchment experiences some of the highest average annual rainfalls in Tasmania and contains dams in the High Hazard category. The flood warning system was developed using Hydstra Modelling™ (formerly TimeStudio), which links directly to the Hydstra TSM™ database. This package offers powerful automation tools that enable the Pieman River flood warning system to operate, alert personnel and display results on Hydro Tasmania’s internal website with no manual involvement. With its maintenance free operation and user-friendly interfaces, the Pieman River flood warning system is an effective contribution towards the overall risk management package of the Pieman River Power Development.