Northern Beaches Council is poised to undertake the task of clearing the entrance of Narrabeen Lagoon. Almost 50,000 cubic metres of sand will be shifted and used to replenish Collaroy–Narrabeen Beach which suffered devastating erosion in the June East Coast low.

Narrabeen Lagoon is the largest and lowest of the Northern Beaches four coastal lagoons with a catchment area of approximately 55 square kilometres.

While the overall size of the Lagoon is large the entrance is only approximately 30metres wide and due to wave, current and wind processes, marine sand slowly closes this entrance approximately every three to five years.

“The sand that finds its way to Lagoon entrance is part of the same beach system that includes Collaroy–Narrabeen Beach and it is important that the sand is returned there to ensure ongoing replenishment of the area,” said Northern Beaches General Manager, Mark Ferguson.

As well as assisting with the replenishment of the beachfront, the removal of the sand from the Lagoon entrance increases tidal flushing, improving both biodiversity and water quality and helps reduce some low-lying flooding.

Council conducts these major clearances of the Lagoon entrance every three to five years. Full clearance of the entrance requires State Government approvals and licences and cannot commence until the entrance fully closes, which can take a number of years.

The Lagoon is also occasionally mechanically opened when required, in line with Council’s procedures and the State Government Licence, but this can only be done when water levels have risen high enough to maintain flow to the ocean.

These major entrance clearance works are undertaken in late winter to minimise storm and recreational impacts. Approximately 100 truckloads of sand per day will be removed from the eastern and western sides of the Ocean Street Bridge between July and October 2016.

“The Lagoon entrance was mechanically opened before the June East Coast Low however with more than twice the monthly average rainfall in the space of a day along with king tides and big surf, the flow of water from the Lagoon to the ocean was blocked. This would have still been the case if the major entrance clearance works had already been done,” Mr Ferguson said.

Northern Beaches Council manages the project, in collaboration with the NSW Office of Environment and Heritage (OEH).  OEH has funded two-thirds of the project under its Floodplain Management Program, and Northern Beaches Council has contributed one-third of the total project cost.

There have been nine major clearance works at the entrance since 1975, the most recent being in 2011.

Flood Plain studies for all catchments are reviewed periodically. The last Narrabeen Flood Study review was completed in 2013 and it will now form the basis of the Narrabeen Lagoon Flood Plan which will go on public exhibition later in 2016.