Peter F Foster and Peter K Silvester
Clyde Dam, the largest concrete gravity dam in New Zealand, was constructed in the 1980’s on the Clutha River in New Zealand. Lake Dunstan, which is the reservoir formed by the dam, reached its full operating level in 1993, some 21 years ago.
This paper summarises the performance of the dam over this period, the changes in operations that have been undertaken and looks to future challenges. The performance and management of the landslides around Lake Dunstan that were remediated prior to lake filling is outlined. The large floods experienced in the Clutha River in the 1990’s highlighted aspects of the flood management procedures that needed amending to capture lessons learned and some modifications to appurtenant structures have been completed. Changes to the environmental management in moving from water rights to consent conditions under the Resource Management Act are addressed.
Over the last 21 years a sediment delta has progressed down Lake Dunstan, as expected, and a long term sediment management plan has been developed for both Lake Dunstan and Lake Roxburgh which is downstream of Clyde Dam. A summary of the plan is discussed. The seismic hazard at the dam site is currently under study to update the seismic assessment parameters for the dam.
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Bronson McPherson, David Guest, Barton Maher, Ian Tanner and Amit Chanan
There is significant community interest in the potential for water supply dams to be adapted for flood mitigation, particularly for major dams located upstream of flood vulnerable populations. There may be a number of large dams which have the potential to provide significant flood mitigation benefits to Australian communities if they can be adapted for flood mitigation functionality. Other dams already provide significant flood mitigation benefits, however their limitations are not properly understood by the general public. Two major dams located near a large urban town centre prone to flooding are examined as a case study and some international cases are presented.
Flood mitigation often has a different funding source to water supply. The funding arrangements for flood mitigation dam works can be complex, considering the potential stakeholders and somewhat intangible benefits. If the community wants to use a water supply dam to provide flood mitigation then who provides the funding for the modification works?
This paper presents the methods used to apply a Flood Operation Simulation Model, and the methods used to present results of thousands of flood simulations in a way that different operational options could be compared. The approach was found to be valuable to understand the capacity of the dams to mitigate floods. The study identified shortcomings for the conventional design event approach to flood estimation. A broader range of stochastic floods was an advantage to assess flood mitigation performance and extreme floods of interest to dam safety.
Behrooz Ghahreman Nejad
In recent years, dam designers have become increasingly interested in application of the geomembrane sealing systems (GSS) in design of tailings storage facilities around the world. The main reasons for this have been the deformation characteristics, environmental aspects (ie seepage minimisation), speed of construction and constructability of geomembrane liners in most climatic conditions. This paper reports the design and application of two types of geomembrane sealing system in Angas Zinc (AZ) and Sarcheshmeh Copper (SC) tailings dams. The former is a 25m high zoned earthfill embankment with an HDPE liner system, located in an environmentally sensitive site in South Australia. The latter is a 94m high zoned rockfill embankment with a PVC liner system, located in a region of high seismicity in central Iran.
The designs of the AZ and SC geomembrane sealing systems including geomembrane liner, drainage layer, anchoring, leak detection system and drains, and instrumentations are discussed in detail. The performance of the liner systems during operation is also presented.
Wark, Bob; Thomas, Louise
This paper discusses the rating curves developed for several case studies from the Pilbara and Kimberley, including the Harding Dam, Moochalabra Dam and Ophthalmia Dam. The paper will discuss the impact of underestimated rating curves on the design of infrastructure. An example has occurred at Harding Dam where the pump station was designed to be inundated at a 1:100 AEP and this is now estimated to occur at a lower AEP. The paper will also discuss methods to improve the accuracy of rating curves and the challenges associated with determining accurate rating curves.
A C Mostert, D J Hagen, P C Blersch
The changes in flood operations since the 2006 flood, covering weather monitoring, hydrological flood station monitoring, and downstream monitoring, are discussed in detail in the paper.