Starting mid-June and finishing mid-August, 50,000 cubic meters of sand has been dredged from Port Hacking navigation channels and the spoil relocated to North Cronulla Beach.
Equivalent to 20 Olympic swimming pools, the sand is contaminant free, similar in colour and size to the nearby beach sand. The sand was transported by a trailing suction hopper dredge, with bottom opening capabilities and released in a special placement zone 200 to 500m offshore North Cronulla Beach, in waters -4m to -8m deep.
The resulting sand-only feature is a totally submerged and elongated mound of sand in the wave pre-conditioning zone, beyond the normal wave breaking zone. The seabed feature is acting as a temporary wave focusing sand slug, with an indirect influence on wave breaking patterns. At no extra cost to the campaign, the sand slug has indirectly provided the following benefits to the community;
1) Improved surfing opportunities inshore of the sand feature because of wave refraction and wave amplification, waves arrive as peaks and offer a long length of surfing ride. During and after the works, wave peel angle has varied between 30° and 60° with waist to head+ high waves, providing a longer length of surfing ride and a better quality surfing ride than normally experienced. At no time, have wave close-out conditions appeared. The life of the sand slug will be determined by future storm events, though double overhead waves in early August groomed and improved the feature.
2) Beach nourishment; a slightly wider beach has appeared in the lee of the sand feature, particularly after the double overhead waves of early August, as the sand slug was naturally dispersed in a shoreward direction, depositing more sand in front of the Prince Street seawall at North Cronulla. Unlike previous winters, this winter there was a beach in front of the seawall, pleasing to all in the community.
Sutherland Council is managing the project and McQuade Marine, owner of the Faucon dredge is undertaking the site work. The special placement zone template at North Cronulla was designed by Andrew Pitt. The Bate Bay Sand Placement Committee has been instrumental in the realisation of the wave focusing sand slug. The life cycle of the sand slug is still to be determined, though the impact should be evident for up to three months, depending on future storm frequency and intensity.
MORE INFO
[mappress]
Press Release, September 6, 2012