Tarraleah Upgrades Project

Client: Hydro Tasmania
Location: Tasmania / Australia
Date: 2023 - ongoing

Futureproofing water infrastructure for greater flexibility and capacity of the Tarraleah hydropower scheme

Background

Hydro Tasmania has investigated how the 80-year-old Tarraleah hydropower scheme, on the River Derwent in Tasmania’s central highlands, could be redeveloped to deliver more energy for Tasmanians and better suit the dynamics of the evolving electricity market.

Water is transported to the Tarraleah Power Station from Lake King William via a complex 30 km network of open canals, flumes, tunnels, pipelines and ponds. The Tarraleah scheme helps regulate water to 6 other hydropower stations downstream and supplies about 6.5% of Hydro Tasmania’s total annual generation.

To provide greater flexibility for the scheme's future, Hydro Tasmania has embarked on a staged program of upgrade works to the scheme, which has some components aged between 60 and 80 years old.

The Tarraleah Upgrade project consists of a staged program of upgrades, including excavation and construction of an approach channel, new intake excavation and concrete structure, a 1 km tunnel, and a downstream portal. This infrastructure will prepare for the future replacement of the existing No 1 canal and No 2 canal.

A rigorous analysis of upgrade options determined that the preferred redevelopment option was a new pressurised water conveyance replacing the existing infrastructure. This would allow water to be transferred more efficiently to the new higher capacity power station, achieving the greatest capacity, storage, flexibility and reliability for every dollar invested, while addressing environmental risk. 

Solution

Entura’s specialists have provided a range of skills and services to Hydro Tasmania on this project over a number of years, through the early concept stages and the subsequent feasibility stages and now the onsite upgrade construction works. Our contributions have included geotechnical investigations, surveying, design, environmental surveys, water monitoring, planning, mechanical and electrical inputs, project management, site supervision and contractor management.

Challenges have included responding dynamically to the evolving understanding of the geological conditions at the site. The team onsite has also had to endure working in some harsh weather conditions in the cold and wet central highlands area of Tasmania, and how that impacts on personnel safety, management of spoil, sediment and water quality, and timely progress. The team has demonstrated agility and resourcefulness to maintain progress when low temperatures constrain the ability to pour and set concrete and shotcrete.

Entura’s personnel have taken a meticulous approach to minimise environmental footprint and fauna/flora impacts in the sensitive alpine location. Effective management of contractors has built positive and productive relationships, while keeping the project moving without harm to people or environment.

Entura designed and oversaw the installation of an innovative ‘plastic’ concrete cut-off trench. The trench protects the deep excavation from the seepage waters of Lake King William. A plastic concrete core was used due to its versatility to create an effective seal if water is encountered in the foundation and allow post-construction grouting if leakage through the fractured rock foundation is deemed significant. Furthermore, the impermeable core can be constructed in any weather conditions, presenting significant benefits to the construction schedule compared to a clay core or liner options.

Outcome

Excavation at the site of the new water intake on Lake King William is well advanced. Entura will continue to support the next phases of construction. Our team are proud to be working alongside our Hydro Tasmania colleagues to contribute to the future of this iconic Tasmanian hydropower scheme, so that it can deliver more energy more efficiently for many generations of Tasmanians and advance Australia's clean energy transition.

We were also integral to the dam safety improvements made from 2021–23 at Mossy Marsh Dam, which is also part of the Tarraleah scheme.