Canal Entrance and Sand Trap Dredging (Port Geographe, WA)
Port Geographe marina is approximately 5 km east of Busselton, Western Australia. It is situated within Geographe Bay; a large shallow embayment that supports extensive seagrass beds.
Due to previous engineering design oversight, large quantities of seaweed arrive at the site each winter and rest against the existing groynes, resulting in release of gaseous odours and an unsightly mess. The groynes reach out into the bay and act as a natural trap for the weed.
The Department of Transport WA, on behalf of the Government of Western Australia and the Busselton Council undertook a $30m major structural change to the outer part of the Port Geographe Marina in Busselton, WA.
Majority of the site work was at the rock groyne and revetment works, which was undertaken by another contractor. During this rock realignment work CGC undertook dredging work and also engaged a sub-contractor to intercept weed and sand from the western end of the development and bypass the site by pumping it to the east of the development.
The purpose of the capital and maintenance dredging was primarily to maintain a navigable channel for users of the marina whilst groyne and channel realignment works were under way. A new channel formation was dredged while maintaining the old channel while it was open.
Significant accumulation of seagrass wrack also had the propensity to become a navigational hazard within the marina channel. Maintenance dredging of any of this material which is resting above design depths was required to maintain safe navigation for the marina users.
The capital dredging works involve dredging the new entrance channel alignment to the north-east whilst the groyne re-alignment was taking place.
The capital dredging project was scheduled between September 2013 and July 2014. The project involved the removal of ~100 000 m3 to form the re-aligned entrance channel to Port Geographe marina. The channel was dredged to a design depth of -2.8 m chart datum (CD).
The maintenance dredging project was completed between August 2014 and November 2014.