Pittwater Online News

February 18 - 24, 2024: Issue 614

Narrabeen Lagoon Entrance Closed Again: Council's Update - february 2024

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

Narrabeen Lagoon entrance on Thursday February 15, 2024. Photo by Joe Mills

Thursday, 15 February 2024: By Council - ;

In August 2022 the elected Council, following extensive community consultation, approved a comprehensive entrance management strategy for Narrabeen Lagoon which included more frequent sand excavations to reduce the risk of flooding.

In keeping with this strategy, last year 25,000 cubic metres (around 45,000-50,000 tonnes) of sand was extracted from the lagoon entrance ahead of the busy summer swimming season.

Despite these significant works, the entrance closed in early February when a four-metre swell washed sand into the entrance, compounded by a high degree of clockwise beach rotation in the Collaroy Narrabeen embayment.

Beach rotation relates to the width of sand on the beach near the entrance, and North Narrabeen Beach is currently the widest it has been in decades due to large volumes of sand moving northwards up the beach. With sand moving northward, natural closure of the entrance is accelerated and difficult to prevent, especially when the wave and tidal conditions are right.

Although the entrance has closed, the flood risk to the low‐lying area surrounding Narrabeen Lagoon remains lower than usual as a result of the recent clearance works.

The works intentionally dredged a higher volume of sand from the west of the Ocean St bridge compared to past clearances in accordance with expert advice. While the area closer to the beach fills up with sand from the ocean, the deeper area to the west will allow for faster flow of water out of the lagoon should heavy rainfall raise the water level to allow an emergency opening at the entrance, thus reducing the risk of flooding.

Once reopened, the works will also significantly increase the chance of the lagoon remaining open for a longer period.

Council’s coast and flood engineers will continue to closely monitor weather forecasts, lagoon water levels and the state of the entrance and be ready to open it mechanically when lagoon water levels rise and weather, tide and swell conditions allow for a successful opening.

Narrabeen Lagoon entrance on Monday February 12, 2024. Photo by Joe Mills

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From Issue 613: Narrabeen Lagoon Entrance Blocked Again

Narrabeen lagoon entrance is blocked again, after recent storm swells, and Council spending $1.5. million on moving the sand south to Collaroy for weeks.

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 is to be deposited at Collaroy-Narrabeen Beach between Goodwin and Stuart Streets.

Works were expected to start in the coming weeks, although the above photo shows they were commenced immediately, and were completed in time for the Summer school holidays, which commenced on December 19 2023. This means the lagoon entrance was open for around 6.5 weeks prior to the big seas which moved so much sand over the past few days of weather conditions as the tail end of Cyclone Kirrily moved south.

After impacting Queensland, ex-Tropical Cyclone Kirrily crossed the border into western NSW on Monday afternoon, February 5, bringing heavy rainfall and flash flooding to inland communities, before reaching Sydney early the next day bringing 21mm of rain and localised flash flooding, along with strong winds.

This had preceded by swell set to peak at 4 to 4.5 metres in Sydney over the weekend of February 3-4.

However, at high tide about 6 inches of water still goes over the top of the entrance and into the lagoon. Joe Mills' (Turimetta Moods) sent in pictures this week (week ending Friday February 9 2024) of Pelicans standing in the shallow overflow at high tide - see below.

Joe said; ''They are waiting (with the Cormorants and Seagulls as well) for the small fish brought in by the waves.''

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