Snapper Rocks before and after the autumn 2009 storms
Conditions
As surfers have observed, the autumn 2009 storms had a major impact on the sand bank at Snapper Rocks.
Seabed mapping by the Tweed River Entrance Sand Bypassing Project has shown that the major storms which occurred from February to May 2009 scoured about 70,000 m3 of sand from the seabed off Snapper Rocks / Little Marley's. The broader Snapper Rocks area deepened by approximately 3 m within about 100 m of the shore, and a hole up to 8 m deep formed in the surfing take-off area at the head of the Snapper Rocks sand bank.
Such an eroded condition has not been seen at Snapper Rocks since the early 1990s, well before the project began.
Beach and offshore sand levels in the vicinity of Snapper Rocks
Condition pre-project
Condition pre-2009 storms
Condition post-2009 storms
Condition five months after 2009 storm
Five months after the project's post-storm seabed mapping was completed, and despite consistent pumping of sand to Snapper Rocks East and West outlets by the project, there has not been much natural recovery at Snapper Rocks. Pumping outlet locations can be viewed on the Current activities page.
About 10,000 m3 of sand has migrated back into the Snapper Rocks/Little Marley's area, but sand volumes are still down by about 60,000 m3 compared to pre-storm conditions.
About 11,000 m3 of sand was pumped directly into this area in late July/early August 2009 from the Snapper Rocks West outlet and while improving eroded upper beach conditions, the sand did not significantly improve the eroded sand bank.
In October 2009, the seabed profile remains very flat and the Snapper Rocks surfing bank, while straighter than it was in June 2009, does not have a steep enough seaward face for waves to peel nicely over it. The hole at the head of the bank has filled in slightly, but it is still too deep to reinstate this as the surfing take-off zone.
Sand Pumping
Snapper Rocks East is the primary outlet for the sand bypassing system and the project has been pumping sand to Snapper Rocks East each month since the autumn storms. In August 2009, pumping to the Snapper Rocks West outlet was also trialled. A total amount of 90,931 m3 of sand was delivered to Snapper Rocks over the period from the July/August 2009 seabed mapping to the recent October 2009 seabed mapping.
Sand was pumped to Snapper Rocks as follows:
- 5-31 August: 27,865 m3 (22,847 m3 to the Snapper Rocks East outlet / 5,018 m3 to the Snapper Rocks West outlet)
- 1-30 September: 40,140 m3 (all to the Snapper Rocks East outlet)
- 1-23 October: 22,926 (all to the Snapper Rocks East outlet)
The project is only able to pump the amount of sand that is delivered to the pumping jetty by waves. Average sand supply conditions over the September to December part of the year are about 28,000 m3 per month, and in August, September and October 2009 more than an average amount of sand was delivered to Snapper Rocks over the whole of each month.
The project will continue to focus on pumping sand to the Snapper Rocks East outlet over the next couple of months, with a small allocation of up to about 15,000 m3 of sand to be delivered to Duranbah to repair storm erosion to the dunes at the northern end of the beach and provide protection against future storms.
September to December are typically the calmest months of the year for sand supply due to persisent North Easterly waves, and it is likely that only up to about 20,000 to 30,000 m3 of sand will be available to pump to Snapper Rocks per month in November and December 2009.
Monthly pumping records can be viewed on the Sand delivery page.
