Pittwater Online News

December 3 - 9, 2023: Issue 608

Narrabeen Lagoon sand removal completed ahead of schedule: berm at entrance removed

Narrabeen Lagoon entrance being opened again. Photo: Thursday November 30, 2023 by Joe Mills

Council announced on Tuesday, 28 November 2023 that the sand removal project at Narrabeen Lagoon has concluded two weeks ahead of schedule and well in time for the Summer break.

"Precisely 4388 truckloads of sand, equating to approximately 25,000 cubic metres or around 50,000 tonnes, were extracted from both the east and west of the Ocean Street bridge and transported to Collaroy/Narrabeen Beach, a fortnight ahead of schedule," says Mayor Heins.

“I’m pleased to say this work has been completed a fortnight ahead of schedule," says Mayor Heins.

Council contractors have packed down the site, and Council expected the Birdwood Park car park to be open for public use before the end of this week.

"Council teams are monitoring lagoon levels continuously and preparing to open the lagoon entrance this week should swell and forecasted rain improve the conditions for a successful lagoon opening.

“However as always, the timeline depends on the whims of Mother Nature.

“The love that locals and visitors have for Narrabeen Lagoon is not lost on us and we want everyone to be able to enjoy the beauty and recreational benefits of the lagoon this summer,” she said.

“In the event the conditions are not ideal to open the lagoon this week, Council plans to open it at an alternate time ahead of the NSW school holidays.

The school holidays commence for private schools on December 7 or 14 and December 19 for NSW Public schools.

Highlighting the broader significance of managing the lagoon entrance, Mayor Heins affirmed that, "This strategic initiative plays a crucial role in reducing flood risk to the local community, nearby properties, and essential infrastructure.

For those seeking an in-depth understanding of how Council manages Narrabeen Lagoon are encouraged to watch the video explainer available on Council’s website.

This project was partially funded under the NSW Government Floodplain Management Program.

Council announced on Tuesday, 12 September 2023 work to clear Narrabeen Lagoon entrance to reduce the risk of flooding to local homes and businesses.

''Council contractors will excavate more than 20,000 cubic metres (40,000 tonnes) of sand – equivalent to the weight of 100 jumbo jets – to the east and west of Ocean Street Bridge.'' it was stated

The sand was to be deposited at Collaroy-Narrabeen Beach between Goodwin and Stuart Streets.

The works have become more frequent in recent years, occurring on average every second year rather than the anticipated need to undertake sand clearing works every 3 to 4 years once projected by Council.

Council announced on Friday October 9 2021 they were getting works done to open the entrance of Narrabeen to let the water flow as ''there is rain forecast for every day this coming week''.

''Every 3-4 years we do a major excavation of sand from the entrance of the lagoon to help reduce flood risk and increase tidal flow. The excavator is moving in to start this work today.'' Council's statement said

Repairs to the abutments of Ocean Street Bridge were also to be done simultaneously to minimise disruption to the community.

The works were to take about 12 weeks to complete (weather dependent) with the entrance reopened in time for the Summer holidays. These works are generally timed to avoid the disruption from the Winter storm season but to reopen in time for the peak swimming season.

''These major sand clearances are conducted periodically as swell and tides gradually push more and more sand into the lagoon. Council completed the last Narrabeen Lagoon entrance clearance in 2018 and has had to undertake more frequent mechanical openings in recent months as the sand has built up.

''Works will be conducted using amphibious excavators to pump the excess sand through flexible pipes to a central stockpile location next to Birdwood carpark. From there it will be trucked down to Mactier Street where a bulldozer will spread it along Collaroy-Narrabeen beach.

Once the major excavation is complete, the lagoon is expected to remain open for a number of years, although as always, we are at the mercy of mother nature as to how long.'' Council stated

In July 2016 clearing the entrance of Narrabeen Lagoon was undertaken again. Almost 50,000 cubic metres of sand was shifted and used, once again, to replenish Collaroy–Narrabeen Beach which suffered devastating erosion in the June East Coast low.

In July 2016, weeks after the councils had been forcibly amalgamated and in response to the June 2016 storm, the NSW Coalition government installed administrator Dick Persson outlined a Draft Coastal Erosion Policy for Collaroy that resulted in the December 2016 Coastal Zone Management Plan for Collaroy-Narrabeen Beach and Fishermans Beach being formalised under the same administration.

That Administrators Minute stated:

I am advised that the initial estimates for 1.1km of works from The Marquesas to 1096 Pittwater Road has been estimated at approximately $22 million. While Council will work with the State Government to meet the cost of directly protecting public assets in this area (approximately $5.5 million), I will also ask the State Government to join Council in providing up to 10% each towards the cost of private protection as a contribution subject to a positive cost benefit analysis for these public assets. Early estimates suggest this contribution could be approximately. This contribution has been estimated at approximately $3.3 million ($1.65 million from State and $1.65 million from Council) and is in recognition of the public asset protection that is provided by these private properties.
....
A recent report by the Sydney Coastal Council’s Group identified that to combat the impact of sea level rise in the Collaroy-Narrabeen embayment significant volumes of sand will be required as these impacts are felt. For example, it is predicted that some 1.3 million cubic metres of sand (approximately 4 times the amount removed during the June storms) will be required for the first 10 year nourishment effort, and around 420,000 cubic metres for each following 10 year campaign.

In 2009 dollars this will cost around $30 million for the first 10 year nourishment, and around $12 million for each following 10 year campaign.
These costs are based on the assumption that sand nourishment will be undertaken across large areas of the NSW coast and the costs shared accordingly.
....
Works on this scale are simply unaffordable for Northern Beaches Council on its own, and the responsibility for delivery of offshore sands must be shared with benefitting Councils and also with State and Federal Government. The State Government is obviously best placed to co-ordinate and manage such an undertaking, and I will write to the Premier to request that the State provides a long-term sand replenishment strategy for NSW that addresses the many issues I have raised, and amends the Offshore Minerals Act (1999) to enable effective medium and long term beach amenity to be preserved.

At the time there was an outcry in Pittwater that residents here would be footing the bill for Warringah Council's plans for the Collaroy beachfront and ongoing sand nourishment, some even stating this was one of the primary reasons for the forced amalgamation.

The above costings from 2016 estimate the 'sand nourishment' is $1.2 million every year, if only one per year is undertaken, equates to around $45.50 per person in the LGA per year, or $273 per year for a family with four children. The Northern Beaches Council area Estimated Resident Population for 2022 was 263,298, with a population density of 1,035 persons per square km.

In May 2022 Council sought feedback on the draft Narrabeen Lagoon Entrance Management Strategy - Council's comprehensive investigation of all aspects of entrance management, including sand transport, flood benefits and entrance efficiency and dynamics.

It includes an assessment of potential entrance management options looking at technical feasibility and economic, social and environmental impacts and risks. The assessment was informed by a literature review of best practice, modelling, and a detailed cost benefit analysis by a quantity surveyor, and was peer-reviewed during its preparation.

Following the extensive assessment and analysis the draft Strategy recommends that Council:

continue periodic large scale sand clearance operations
trial more frequent sand clearances but with smaller volumes, in targeted areas
continue intermittent mechanical breakouts if the lagoon entrance closes between major clearances and in response to forecast high rain and swells
revegetate and maintain Birdwood Park dune to assist sand stabilisation
review mobile sand pumping (as an alternative to trucking) if lower cost pricing becomes available.

Then Mayor Michael Regan said the main objective of the draft strategy is to reduce the risk of flooding on the Narrabeen Lagoon floodplain.

“Residents on the floodplain know too well the stress that comes every time there is forecast high rainfall, large swells or flood warnings,” Mayor Regan said.

“The development of this draft strategy is about making sure we’ve canvassed all feasible options to reduce that stress, to reduce the risk and to make sure our lagoon management continues to follow best practice.

“Council has been actively managing the entrance to Narrabeen Lagoon to reduce the risk of flooding in the catchment while working on the longer-term management strategy.

“Fortunately, Council was able to complete the major sand clearance operation before Christmas ahead of the huge amount of rain that we’ve had in the first few months of this year.”

At the meeting on Tuesday 27 September 2022, Council adopted its Narrabeen Lagoon Entrance Management Strategy.

'The final adopted strategy includes a range of priority actions', the Council stated, 'which we will now begin to implement including:

trialling more frequent but smaller sand clearance operations (every two-three years rather than four-five years)
developing a more flexible set of the conditions which trigger Council intervention to open the lagoon if required
adjusting the alignment for the pilot channel
reshaping and revegetating the denuded part of Birdwood Park dune to assist with sand stabilisation
investigating the financial viability of mobile sand pumping as a longer term alternative to trucking.

Residents who have lived in the area and with the risk of flooding have suggested the dune built at Birdwood Park in the past is part of the problem and should be removed. They recall the flow of sand and tides through seasons along the whole of the Narrabeen to Collaroy beachfront worked better prior to this.

Historical photographs and one painting from the early 1800s show a steep bank in the Birdwood park area and a closed lagoon entrance, while one image from 1928 shows a steep bank present at Birdwood park.

There are also numerous reports in older newspapers of lagoon entrance clearance works being undertaken.