Edgar Dam Upgrade

Client: Hydro Tasmania 
Location: Tasmania, Australia
Date: 2010 - 2026

Providing specialist engineering and technical support for a major dam upgrade in a remote, sensitive location

Services

• Geotechnical investigations
• Surveying
• GIS mapping
• Hydraulic assessment
• Flood mapping
• Risk assessment
• Dam engineering concept design and detailed design
• Environmental and planning studies and documentation
• Principal’s Engineer services

Background

Edgar Dam is located in the south-west of Tasmania, in a Wilderness World Heritage area. It was constructed in 1972 and is part of the Gordon-Pedder hydropower scheme, which includes the largest water storage in Australia and provides up to 13% of Tasmania’s power.

The dam is located adjacent to the Lake Edgar fault (previously thought to be inactive) and its upstream and downstream shoulders are founded on fluvioglacial sandy gravels potentially subject to liquefaction. With updated seismic knowledge, Hydro Tasmania initiated a dam safety review to quantify the dam’s seismic risk and develop risk mitigation measures. This led to an upgrade project to increase the dam’s seismic resilience as well as reduce risk associated with piping through the embankment.

The dam upgrade is the culmination of many years of investigation, risk assessment, design, approvals and planning by Hydro Tasmania, Entura and contractors, working collaboratively to achieve an efficient, resilient outcome.

Solution

In 2010, Entura was engaged to undertake a dam safety review of Edgar Dam in accordance with the Guidelines on Dam Safety Management (ANCOLD, August 2003). The dam safety review included:

• site inspection and technical scoping
• scoping and supervision of geotechnical investigations
• structural and stability analyses, including post-liquefaction analyses
• risk assessment
• development of risk mitigation measures and upgrade concept options.

Entura worked collaboratively with Hydro Tasmania colleagues during the development of the scope and specification and the implementation of the geotechnical investigations. Geotechnical investigations included sonic drilling, standard penetration testing, permeability testing and down-hole shear wave testing.

Entura provided expertise in hydrology and hydraulics, dambreak modelling and consequence assessment, surveying and GIS mapping, and civil and structural engineering to support Hydro Tasmania’s understanding of the site’s conditions, potential risks and possible solutions.

Following the dam safety review, Entura was engaged to develop concepts and detailed design for upgrading the dam to meet modern design standards. The design proposed removing the downstream concrete face, excavating to bedrock, and then adding a rockfill filter buttress and crest wall.

During the construction phase, Entura’s geotechnical specialists worked closely with colleagues in Hydro Tasmania and with the contractor to inspect and map the excavations. Their responsiveness ensured that the contractor could progress the excavation works and rockfill placement without unnecessary delay.

Entura provided ongoing design support throughout the construction phase, including reviewing work method statements, responding to requests for information and design changes, and conducting regular engineering and geotechnical inspections - all of which contributed to ensuring that the works proceeded in accordance with the design intent.

Outcome

The Edgar Dam upgrade was successfully completed by the principal contractor (Hall Earthmoving) four months ahead of schedule in 2026. The upgrade significantly reduces risk associated with a major earthquake on the nearby Lake Edgar Fault, enhancing the safety, reliability and resilience of Hydro Tasmania’s renewable energy infrastructure.