Australasia | Activities in Australasia IWP&DC reflects on recent developments across Australia and New Zealand
Above: The Warragamba Dam on the Nepean river in the Greater Sydney area of Australia. Proposals for raising the project to enhance flood protection have been on public exhibition
TO ENSURE THE LOCAL community and stakeholders “have full awareness of what is proposed and an opportunity to make submissions”, WaterNSW has extended public exhibition of the Warragamba Dam environmental impact statement focused on raising the structure. Constructed between 1948-60, the 142m high and 350m wide mass gravity concrete dam provides around 80% of Sydney’s water supply. Currently it is not designed for flood mitigation but the Hawkesbury- Nepean Valley in western Sydney has a long history of flooding and is considered to be the region with the highest flood risk exposure in New South Wales, if not Australia. In 2012, extensive flooding across south- eastern Australia saw Warragamba Dam spill for the first time in 14 years and raised awareness about the potential impacts of flooding in major urban areas. NSW Government established the Hawkesbury- Nepean Valley Flood Management Taskforce in 2014 to identify, develop and assess potential alternatives and options for reducing flood impacts and risks in the valley. The taskforce found that the most effective and efficient infrastructure option to reduce significant risks to people’s lives and property from regional flooding is to raise Warragamba Dam for flood mitigation. This proposal does not change the permanent full
water supply level of the dam or lead to permanent upstream inundation. It is solely to provide flood mitigation for downstream communities through temporary storage and controlled release of inflows from a flood mitigation zone airspace created by the raised dam; reducing risk to life and damages downstream by about 75%. The project includes:
● Raising the level of the central spillway crest by around 12m and the auxiliary spillway crest by
12 | December 2021 |
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around 14m above the existing full supply level for temporary storage of inflows.
● Raising the dam side walls, including the dam access road by up to 17m providing resilience for future impacts to projected climate change.
● A designated area within the existing dam precinct of around 105 hectares for construction and laydown areas
● Infrastructure to allow for environmental flows to be released from Warragamba Dam. Construction is expected to be completed about five years from the start of construction and the EIS acknowledges that the project “would have impacts that cannot be avoided either through design, operation or mitigation measures. Offsets will be required to compensate for unavoidable environmental impacts”. Over 80 dams in Australia are reported to have been raised at some point after their original construction. The EIS states that “the proposed Warragamba Dam raising, while a major construction undertaking, is not a pioneering engineering project. The experience and lessons learned from other similar dam raising projects have been utilised for the design and will be leveraged for the construction. This will improve project outcomes in terms of safety and quality assurance”. WaterNSW is a state-owned corporation and the owner and operator of Warragamba Dam. The EIS for the Warragamba Dam Raising was prepared by SMEC for WaterNSW and dated 10 September 2021. On 30 October, NSW announced it would extend the public exhibition until 29 November.
Hydro Tasmania Despite another challenging year with ongoing impacts
from Covid-19, Hydro Tasmania says it has delivered significant achievements and a transformation of
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