Oral Presentation International Conference on River Connectivity (Fish Passage 2018)

Seaham Weir is located near the town of Seaham on the lower reaches of the Williams River. It is owned and operated by Hunter Water. The weir provides a separation between saline tidal water in the Hunter River Estuary and fresh water that flows down the Williams River. The existing components of Seaham Weir consist of a rock weir, two control gates and an orifice style fishway.

The requirement of the study was to develop an integrated fishway for both upstream and downstream migration of fish and flow control gates that could release environmental flows between 10 and 500ML/d.

The study involved:

• Assessing the types of fishway and gate type options;
• Identify options for the Integrated fishway and flow control gates:
  • Various site location and layouts; and
  • Various gate sizes and combinations.
• Carrying out physical modelling of the short-listed options to determine;
  • The preferred layout of the proposed gates and fishway;
  • The gate operation strategy across the design range of flows and downstream water levels; and
  • Look at improvements to the layout to optimised fish passage.

The design incorporated a fish retention weir primarily to limit fish being expelled from the fishway at low tailwater and also offer the chance for fish within the retention weir to remain near the fishway entrance at low tides.

Another innovative component of the design was to incorporate a submerged and removable weir within the stop board guides downstream of one of the gates to control turbulence within the fish retention weir pool.