Seaham Weir Refurbishment and Modification
Abergeldie was engaged by Hunter Water to deliver the Seaham Weir Refurbishment and Modification project. Located on the lower Williams River, Seaham Weir is a crucial part of the Grahamstown Dam scheme, which supplies 40% of the drinking water for Hunter Water customers. The project involved installing new low-flow weir gates to improve the weir's operational efficiency, enabling more frequent and controlled water releases as needed. The refurbishment and modification were necessary to enhance water flow management, maintain the weir pool's water level, and improve fish passage along the river.
Scope of works
The scope of works included:
- Refurbishment of the existing weir gates to meet safety and compliance standards.
- Installation of four new low-flow weir gates on the eastern side of the weir for controlled water releases.
- Excavation works.
- Dewatering and installation of permanent sheet piles to reinforce the weir structure.
- Construction of a cofferdam.
- Construction of a new fishway for improved fish passage up and down the river.
Complexities associated with working in water and poor weather conditions
Working within a river environment required meticulous planning and execution, with constant attention to the river's dynamics and environmental impact. Our team worked closely with the Hunter Water capital works and operational teams to refine the design, ensuring it met operational needs while optimising the temporary works design for safe and efficient delivery of flow controls and gateways. Throughout the construction period, the team ensured at least one of the existing weir gates was operational and that the fishway had no impact on water levels, upstream or downstream.
At every stage of the project, careful consideration was given to the river’s natural flow, implementing stringent measures to manage stormwater runoff and erosion. Numerous government approvals were secured to validate these solutions and the impact on local fisheries
The La Niña weather conditions experienced in New South Wales, marked by multiple major floods, added significant challenges to the project. These conditions demanded heightened vigilance and adaptive strategies to ensure continued progress while protecting the surrounding ecosystem.
Sustainable environmental practices
Prior to the commencement of construction works, the team first spread the material on-site to allow it to dry, then sifted it bucket by bucket using an excavator and a sieve to separate and reuse the rock. Sustainable materials including low-carbon concrete and eco-friendly ash felt were also utilised, ensuring the project achieved the environmental goals from both Hunter Water and Abergeldie.
Long term benefits
The project achieved excellent ecological and engineering outcomes, restoring the site to a more natural state. The upgraded weir now more accurately mimics natural flows from the catchment area, facilitating water progression into the saline region and the Hunter River. This improvement has led to a thriving local ecosystem, including fish and birds, while the new integrated fishway further enhances fish movement both upstream and downstream. The installation of new low-flow weir gates allows for more controlled and frequent water releases, reducing large or sudden fluctuations in weir pool water levels.