Yamba/Iluka Ebb Tide Release Detailed Concept Design

Client: Clarence Valley Council (via Department of Commerce)
Year: 2008-Ongoing
Project Reference: 08069
WRL Technical Report: Detailed Concept Design of Yamba-Iluka Ebb Tide Release (2008/28)

Clarence Valley Council is currently upgrading the sewage treatment systems for the townships of Iluka and Yamba. These towns are located at the mouth of the Clarence River, with Iluka to the north and Yamba to the south of the river entrance. In 1997, the NSW Coastal Policy stated that “new ocean outfalls will be embargoed until a full investigation of alternative wastewater strategies has been undertaken and considered by the Government”.

Detailed discussions have been undertaken to determine a socially acceptable location for the recycled water releases. These discussions have involved a range of stakeholders including representatives from local recreational fishing groups, local commercial fishing cooperatives, the NSW Maritime Authority, the NSW Department of Lands, the NSW Department of Primary Industries (including NSW Fisheries), the NSW Department of the Environment and Climate Change, local Aboriginal Land Claimants and local community working groups.

Upon acceptance of a potential release location, fieldwork was undertaken to: survey the lower Clarence estuary, determine potential effluent flow paths and measure ebb tide discharges and velocities. This was used to develop a hydrodynamic model that was calibrated and verified for the lower Clarence River. The model was shown to adequately describe the hydrodynamics in the vicinity of the proposed ebb tide release and is fit for the intended purpose of providing base data and analysis for the release designs. A range of model simulations were tested to optimise the design of the ebb tide release. Exit velocity and head loss calculations were used to develop optimal configurations for Yamba and Iluka. Water quality modelling in the near-field zone was then employed to calculate the dilutions that would be achieved with these diffuser configurations under different ambient flow regimes.

A subsequent post-flood survey by WRL in May 2009 has increased the hydrosurvey dataset for the lower Clarence River, providing increased confidence in determining the design of the ebb tide release. Work on this study is presently ongoing.