Expression of Interest Seaham Weir Refurbishment and Modification

⁠⁠⁠Seaham Weir was constructed on the Williams River in 1967 to improve the yield of the Grahamstown Water Supply Scheme, with addition of the mechanical gates commencing in the late 1970's and commissioned in the early 1980's. Hunter Water extracts water from Seaham Weir Pool for storage in Grahamstown Dam.

The Principal owns, maintains and operates the Weir, the associated gate and fishway structures.

Seaham Weir is a critical component of the Grahamstown Water Supply Scheme which supplies drinking water to approximately 400,000 people in the Lower Hunter. Seaham Weir performs several critical functions including holding water in Seaham Weir Pool for transfer to Grahamstown Dam, releasing flood flows to mitigate flooding of surrounding lands, and preventing saline intrusion into Seaham Weir Pool by limiting upstream movement of tidal saltwater. Water is released, or flows past Seaham Weir by three main mechanisms, largely depending on the flow rate of water that is entering the Weir Pool. Water can be released through flow under two large gates, over the weir wall (during floods) and through the fishway. Without the Seaham Weir Pool transfers, the Principal would not be able to meet supply obligations.

Condition assessment of the existing Seaham Weir gates indicates significant deterioration and an increasing risk of functional failures (component faults) including the gates becoming stuck in either the up or down position. Without intervention, the asset condition and associated risk of functional failures will continue to deteriorate.

Seaham Weir in its current form has restricted fish passage and poor flow control at low river flows. Modifications to Seaham Weir are required to comply with environmental objectives agreed to by the Principal and included in the cabinet endorsed 2014 LHWP. The environmental objectives developed as part of the 2014 LWHP aim to help protect aquatic health by providing a share of water for the downstream environment, and include Seaham Weir performing the following functions:
Releasing a 500 ML 'flood' flow approximately once per year;