History, heritage and the environment are as important as the bricks and mortar (figuratively speaking) of this new generation of roller compacted concrete dams.
Just as the original dam formed a firm foundation around which to build our national capital a hundred years ago, so too will the new dam provide a foundation on which to build Canberra’s second century of development. At nearly twenty-times the capacity of its predecessor, the new dam will boast a storage capacity of more than 78 Gigalitres, boosting the ACT’s overall water storage capability by 35 per cent. In a community ravaged by ten years of drought at the start of the millennium, this will provide long-term water security for future generations, and the basis on which to continue the territory’s rapid growth.
Years of debate gave way to years of planning – it was important to get it right from the start. While the original dam had, at just 18 metres, little impact on the vast valley, the new dam would tower over the Cotter reserve at 80 metres – the height of a 26 storey building. Its impressive stature would be visible for miles. Environmental aspects had to be carefully considered and the wealthy heritage of the area further enriched.
Garrett Cotter’s legacy is preserved in the Cotter Dam Discovery Trail, a 1.4 kilometre walking trail which has now reminded more than 200,000 visitors of the area’s heritage and rich natural history. Preserving the plant and wildlife of the area was always a fundamental aspect of the project team’s work. Around 200 indigenous Grass Trees (xanthorrhoea) were preserved, taken from the construction site and carefully moved to the National Botanic Gardens and the fledgling National Arboretum. But it is perhaps the protection of the endangered Macquarie Perch that is the project’s greatest environmental achievement, building the world’s first freshwater rock reef, a 7 kilometre weaving wall of giant boulders, carefully placed one-by-one into position to create a safe environment for the indigenous species, protecting the slim population from marauding cormorants.
The project team worked closely with the University of Canberra’s Dr Mark Lintermans, a Senior Research Fellow in Freshwater Fisheries Ecology and Management, with some 30 years’ experience. Lintermans helped design the infrastructure and his studies on the perch population provided the evidence on which to base what he described as a ground-breaking project. “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.”
The research is going well and early signs indicate that the population is thriving, with tests on the stomach contents of the perch revealing a healthy diet of earth worms picked off as they rise to the surface investigating the impounding waters of the Cotter Reservoir.
Like most of the construction aggregate used on site, the rock reef boulders were quarried from the walls of the abutments. Sourcing a million tonnes of construction material in this way, to be ground down and turned into concrete at the site’s batch plant, would save the project 2.8 million construction kilometres, enough to circumnavigate the earth 71 times, making a huge saving in the dam’s carbon footprint. ACTEW and its Bulk Water Alliance construction partners John Holland, GHD and Abigroup, committed to offsetting all carbon emissions associated with the construction. A large part of that is the rehabilitation of 420 hectares of native land in the dam’s catchment area.
‘Sourcing locally’ was very much the mantra in sourcing the project team and contractors. In consultation with groups like the Master Builders Association and civil construction companies, the project team was able to better understand local business needs and reach an acceptable balance within the industry. At its peak, around 400 employees were working on the construction of the dam. The project team was comprised of around 61% local employment, with about 34% of all contractor businesses and suppliers sourced locally. This helped to inject around $88million into the local economy.
Furthermore, the very purpose of the dam is to provide long-term water security to the community, helping Canberra to avoid the more severe water restrictions which might have affected the city in the past. According to research from the Centre of International Economics (CIE), Stage 3 water restrictions could cost the ACT economy in the region of $180million each year.
David Pearce, CIE’s Executive Director said: “While most costs accrue to households, some also arise for commercial activities and water intensive businesses. In addition, the tourism sector is affected by restrictions. The magnitude of these costs can be measured by observing the effects of restrictions on particular activities. These latest estimates suggest that, for example, the total cost of spending per year in stage 3 restrictions, is around $180 million. The potential cost of a year spent on higher levels of restrictions (stage 4, which does not allow any outside use) is much higher still at around $540 million.”
Preserving the history of the area was fundamental to the construction team and particularly the indigenous heritage. In consultation with the Yurung Dhaura Indigenous work group, a nursery of bush medicine and traditional food species was planted. A new trail network was formed from the project’s haul roads, the largest of which was named after the young indigenous leader Honyong, who first led Irish convict drover Garrett Cotter to the banks of the river, abundant in pure, fresh water. Also preserving the history of the modern-day settlers was the modernisation of Cotter Avenue, a popular picnic area for generations of Canberrans. New barbecue, picnic and toilet facilities were introduced. This initiative doubled with the redevelopment of Casuarina Sands, as an alternative while the avenue was renovated.
Engaging the ACT Government’s Parks and Conservation Services’ Brett McNamara as an adviser, and a key component on the environmental and heritage aspects of construction, was fundamental to the success of the project. Brett believes the shared vision was what made the project so successful, “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.”
With Canberra’s centenary approaching, it was important that the construction was recorded for future generations. Just as the building of the original Cotter Dam and associated pump house was photographed for posterity, and used to mark 100 years of engineering in the capital, so too our contemporary engineers used digital technology to record the building of this modern engineering feat. The project and its people were recorded by local documentary maker Richard Snashall, who has so far produced around 60 short films. Renowned Canberra landscape photographer, Col Ellis has documented the land and the construction through a series of 50 events producing a library of images that will mark the construction for future generations.
Preserving the construction and the history of the area for future generations and inspiring young people to create their own engineering stories is something that has always been important to the construction team. The Cotter Dam’s associated education program has engaged with more than 1600 young people, teaching them about the role the River Cotter played in the location of our nation’s capital. It also promotes the importance of protecting the water catchment, and following a decade of drought, water’s role as a vital natural resource.
The Enlarged Cotter Dam project was part of a wider program of major water security projects which also included the construction of the Murrumbidgee to Googong (M2G) pipeline, the upgrade of the Googong Dam Spillway (GDS) and the Murrumbidgee to Cotter upgrade of the 100-year old Cotter pump station. Together, these projects would provide water security for future generations of Canberrans. The M2G project would replicate the environmental elements of the Cotter Dam enlargement. Working with the Australian National Botanic Gardens the construction team endeavoured to preserve the endangered small purple pea, Swainsona recta. Seeds were collected and germinated before seedlings were planted around the Williamsdale region. The plants are now flowering profusely, producing healthy seeds that have been collected and deposited safely in the National Seed Bank.
The Cotter dam construction project has had its fair share of hurdles to jump over. A geological fault that was only discovered during the excavation phase of the project set work back by a number of weeks and added millions of dollars to the budget. But while the project team did everything to protect nature, nature would strike back with awesome force. Just two days after the completion of the nearby Googong Dam Spillway upgrade project, the clouds that had been gathering over 10 years of drought burst and the spillway did the job it was designed to do admirably. In March 2012 nature exacted vengeance with a flood so intense that it threw scaffolding about like sticks. Tree trunks left ravaged by the bushfires years previously were left scattered across the construction site. The damage would take weeks to clear and cost the project tens of millions of dollars. Had the wall been complete, the inundating waters would have filled the dam twice over.
The dam, and indeed the wider Cotter Reserve was returned to the community in October 2013. Launched by Chief Minister Katy Gallagher, Canberra came out in force to celebrate the achievement. Just as enthusiasts had clamored a few short months before to walk along the crest, so too they headed to the Cotter to walk through a million tonnes of concrete and celebrate the opening with the unique experience of walking through the maintenance gallery area of the dam wall. Thousands enjoyed the family festivities and counted the 296 stairs from bottom to top.
The project has grabbed the imagination of the community, with Dam Cam – the strategically positioned web camera recording every minute of construction – being eagerly followed by thousands of enthusiasts. It has been among the most viewed pages on the ACTEW website. It has inspired future generations of engineers as young boys and girls learned about the construction, environmental engineering and the importance of water as a raw natural resource. Families have returned to the Cotter in droves, with the project team and its partners delivering modern facilities for a traditional picnic venue under the project’s heritage banner.
The construction has always looked to the future, in developing innovative building methods, new environmental thinking and working in partnership with numerous stakeholders. However, first and foremost it looked to provide essential water security for future generations of Canberrans and support the economic growth and development of our capital, regardless of what population growth or our changing climate might throw our way – it has been and always will be a little Aussie battler.
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