From: Sunshine Coast Daily
Maroochydore Beach is under threat from the highest tides of the year over the next five days. (Nicholas Falconer)
MACHINERY and men are on standby as Sunshine Coast beaches face a pounding from some of the highest tides of the year over the next five days.
The year's highest astronomical tide of 2.09 metres will occur on Friday morning, boosted a further 0.4 metres by a sea level rise caused by the La Nina pressure system.
NASA modelling shows the La Nina impact on sea level heights is at its greatest off the South-East Queensland coastline.
Beach accesses Maroochy M75A, M79A, M86B and M90D have been closed and are likely to remain so through the weekend.
The breakthrough area on Bribie Island, Golden Beach, the Alexandra Headland to Maroochydore strip and Dog Beach at Noosa Woods are all under threat.
Sunshine Coast council coastal zone manager Denis Shaw said close attention would also be shown to the restored beach at Mooloolaba.
While it had held up well in recent heavy seas, the area in front of Mooloolaba Surf Life Saving Club had taken a pounding.
Mr Shaw said the question that remained unanswered was whether sand pumped on to the beach in recent months would shift north to fill in the eroded area or go back out along the Mooloolah River training wall.
He said all hot spot areas would be carefully monitored, including Noosa Main Beach which had performed well after being topped up earlier in the year with pumped sand from the Noosa River.
Mr Shaw said plant hire operators had been put on standby so that any badly affected areas could be quickly protected.
Meanwhile, Jim Cash, a former Maroochy Shire councillor, marine biologist and teacher of marine studies including beach processes, has urged council to show caution before committing to a rock wall from Alexandra Headland to Maroochydore.
Mr Cash is fearful the proposal will do more harm than good.
He wants full consideration given to the Gold Coast model where rock walls buried in the sand well out of the wave zone have seen beaches stabilise in front of them.
He believes erosion problems along that stretch of beach may have started with the rock walling of the area in front of the Alexandra Headland Surf Life Saving Club and adjacent skate park.
“People are rightly concerned about the loss of sandy beach and potential loss of infrastructure,'' Mr Cash said.
“However, it is vital that the issue be fully investigated to ensure that any intervention maintains both the beach and the infrastructure behind it and does not make it worse.''
He said there was a strong possibility that a rock wall in the active wave zone would work against maintaining a sandy beach and could adversely affect Maroochydore Beach.
This was because rock walls built in the wave zone increased the reflective energy of waves.
The stronger backwash drags deposited sand out with it at a greater rate than a natural beach.
“Forever and a day you are left with the coffee rock exposed,'' Mr Cash said.
“This could also result in a stronger inshore current which could have negative erosive effects on Maroochydore Beach to the north.
“Research shows this to be true in other parts of the world.”