Cotter Dam, Australia17 February 2014
The Cotter Dam enlargement project in the Australian Capital Territory (ACT) has been named by IWP&DC as its Australasian Project of the Year. Completed in October 2013, the project will play a key role in helping secure the water supply for the ACT and surrounding region well into the future.
In October 2013, Australian Capital Territory (ACT) Chief Minister Katy Gallagher officially launched the Cotter Dam, marking the end of a four-year construction project that will help to relieve the burden of harsh water restrictions on the Canberra community for future generations to come.
The ACT Government gave the go ahead for the construction of the enlarged Cotter dam in 2007 following nearly a decade of severe drought.
The project consisted of the design and construction of a new dam roller compacted concrete (RCC) dam immediately downstream of the existing Cotter Dam that increased the storage capacity of the existing reservoir from 4ML to 78ML. The project includes the following components:
- 80m high RCC gravity dam, with a crest length of 330m, RCC Volume 380,000m3.
- 60m high dry intake tower incorporated into the upstream face of the dam.
- Reinforced concrete stilling basin and outlet works at the toe of the dam.
- Two zoned earth and rockfill embankment dams, 19m and 23m high, on the ridge forming the right abutment of the main dam to retain the enlarged storage.
Four years of construction
Construction commenced in November 2009 and the dam was officially launched on 14 October 2013. The new Cotter dam is the tallest RCC dam in Australia. Its increased capacity will add an extra 35% to total water storage for Canberra and the surrounding region.
The dam has been constructed through the Bulk Water Alliance which is comprised of ACTEW Water, John Holland, Abigroup and GHD. It will be operated by ACTEW Water.
As the design partner for the BWA, GHD was responsible for the following activities:
- Review of previous studies and optimisation of preferred arrangement.
- Detailed geotechnical and geological investigations of the main dam site, saddle dam sites, quarry and borrow areas.
- Detailed aggregate and RCC mix design investigations.
- Borrow area investigations for the embankment saddle dams.
- Computational fluid dynamic and scale physical modelling of the spillway.
- Detailed design of RCC dam and appurtenant works.
- Detailed design of the saddle dams.
- Full time site role, providing design advice and review on an ongoing basis.
The dam will support the economic growth and development of Canberra and the ACT through its next hundred years, providing long-term water security.
"A project of this scale has had significant economic benefits for the ACT economy through an active construction sector and the creation of hundreds of jobs," commented Minister Gallagher. "This major infrastructure project is evidence that Canberra is a 21st century city where investments made now will pay off for the future benefit of the city"
ACT environment groups welcomed the completion of the new Cotter Dam as they said that, in delivering the project, the Bulk Water Alliance joint venture through planning approvals and design incorporated the history and heritage of the Cotter River into the construction philosophy.
"The community has always been very much at the heart of this project and in delivering water security for future generations of Canberrans we have considered many, many facets of the environment, our heritage and our history," said Ray Hezkial, ACTEW's Project Manager on the construction program. While much of this was instigated by the planning approval process, it has been the detail and enthusiasm with which the project team has entered into these many aspects and in particular the partnership with Parks and Recreation, who will be the custodians of this area once we have handed the river back to the community."
ACT Parks & Recreation has played an important role throughout the construction program, guiding the construction team, through a shared vision, on many areas of environmental construction and planning, and in maintaining and enhancing the Cotter Reserve for future generations.
ACT Parks & Conservation Service's Brett McNamara said: "I can recall early conversation based on the premise of ensuring that post Dam construction, we would have an enduring and lasting legacy. Today as you stroll down the majestic tree lined Cotter Avenue we have collectively achieved that vision."
There have been numerous environmental considerations of the project throughout the design, planning and construction phases. These include:
- Around a million tonnes of foundation bedrock was quarried and retained on site to be crushed and used in the construction of the dam wall.
- Processing and crushing this bedrock onsite into aggregate for RCC use saved a potential 2.8M km of construction vehicle journeys.
- Management and rehabilitation of 420ha of native land in the Cotter Dam catchment area to offset the biodiversity impact of constructing the new dam.
- Commitment to offset all carbon emissions associated with the construction and operation of the project.
- Relocation of more than 120 Grass Trees (Xanthorrea) from the inundation zone. These were replanted on the Discovery Trail, at the Australian National Botanic Gardens Canberra, at the National Arboretum and in rehabilitated areas of the Cotter catchment.
- In consultation with the Yurung Dhaura Indigenous work group, a nursery of bush medicine and traditional food species was planted.
Supporting local wildlife
The new Cotter Dam construction program has also supported local wildlife, with the habitat of the endangered Macquarie Perch a key component of the design and planning. The team has been working with experts from the University of Canberra to develop a world first in rock reef technology to provide a safe and sustainable environment for this rare indigenous fish to thrive.
The intricate pattern of rocks used to create this specialist habitat has been a fundamental feature of the wider dam program. The habitat will continue to support the universities research well beyond the construction period.
Senior Research Fellow in Freshwater Fisheries Ecology and Management for the University of Canberra Mark Lintermans said: "The fish research and management program associated with the ECD is world class, and has provided opportunities for fish conservation that otherwise would not have been available.
"The genuine interest in fish conservation by ACTEW and the BWA has facilitated a strong partnership approach with the University of Canberra that has delivered security of water supply along with improved outcomes for threatened fish species."
Full details of the Cotter Dam Enlargement project can be found on the ACTEW website at: www.actew.com.au
An indepth article looking at the safety features of the dam construction was published in the May 2013 issue of IWP&DC (p26-28). Click here to subscribe now.