Grahamstown Dam Stage 2 Augmentation

NSW
Hunter Water
2004 - 2005

Abergeldie collaborated with Hunter Water to deliver the Grahamstown Dam Stage 2 Augmentation project, which included the construction of a new spillway and embankment. Abergeldie built a new embankment dam, spillway, and outlet works to accommodate the increasing demand. This project raised the reservoir water level to RL 12.8, resulting in a 50% increase in storage capacity.

Scope of works

The scope of work included:

  • Construction of a cofferdam and completion of diversion works.
  • Construction of a reinforced concrete spillway, including rock anchors and a mass concrete abutment.
  • Construction of the dam embankment, including foundation grouting, zoned construction, and drainage.
  • Construction of the outlet works, including the control structure and all associated equipment.
  • Demolition of the interim wall and temporary bund and completed the discharge culvert.
  • Installation of instrumentation and provided power.
  • Construction of roads and restoration works.

Preserving the local ecosystem

With a commitment to protecting the local ecosystem, the team constructed frog ponds north of the site to accommodate a local frog species. The new embankment construction required dewatering a significant portion of the lake. To ensure the preservation of aquatic life, fish and turtles were carefully relocated to the main body of the lake before these works began.

Resource recycling

Abergeldie strategically planned to ensure that all water transfers were conscientiously managed, with 180,000,000L of water pumped back into Grahamstown Lake instead of being released through the existing spillway gates. A further 80,000,000L of acidic, low-pH water was treated and pumped into Grahamstown Lake.

The team effectively managed resources by repurposing materials throughout the project. They used 30,000m³ of surplus material to backfill an existing borrow pit near residents. Additionally, approximately 50,000m³ of acid sulphate soil was treated on-site and stockpiled for future use by Hunter Water in constructing a levee downstream of the new spillway. 

Flood management 

A key objective of this project was the construction of a new spillway, designed to safely discharge flood flows from the dam. This critical infrastructure upgrade not only enhances the dam's capacity to manage excess water during heavy rainfall but also significantly improves overall safety and flood risk management for the surrounding communities.