On Tuesday afternoon, February 20 2024, at 3:20 pm Council announced it was opening Narrabeen lagoon entrance prior to anticipated rainfall expected over the following days.
Residents had been sending in photos of the lagoon waters breaching their perimeters and flooding adjacent fields in the hours prior to this.
Narrabeen lagoon at 11:24 am Feb 20, 2024. photo supplied
Narrabeen Lagoon at 7.20pm, Feb 20, 2024. photo supplied
Council stated the works would take 1-2 hours.
These works were commenced immediately, although, as can be seen via the second image above, waters took some time to recede.
Narrabeen's Wakehurst Parkway, which had been closed at 1.00pm the same day due to flooding and remained closed for hours, and the creeks that fill the Narrabeen Catchment and Warriewood valley, were also adding to the volume of water running into a closed lagoon.
The volume of water can be seen in the below screenshot of just one of the creeks that flows into the lagoon.
screenshot from video by Michael Gleeson, posted at midday on Tuesday February 20, 2024, Mr. Gleeson stated; 'Our creek in Elanora going off and over a cliff into Deep Creek. Coming at you Narrabeen.'
On Friday February 16 more flooding on Wakehurst Parkway at Oxford Falls Road also limited residents access along this road.
The BOM rainfall table (5/02/2024 to 21/02/2024) - shows significant falls in the surrounding areas and those that have creeks that run into Narrabeen Lagoon.
Station name:
MONA VALE GOLF CLUB: 106.2mm
BELROSE (EVELYN PLACE): 130.0mm
TERREY HILLS AWS: 109.8mm
This Wakehurst Parkway alert, posted by Northern Beaches Police Area Command on Thursday Feb. 22, 2024, further underlines the amount of water that mpoved through the Narrabeen Lagoon catchment on February 20, 2024:
Council's works have opened a wide channel from the lagoon to the ocean, making for clean waters and a good flow from and to the lagoon.
Photos: Narrabeen Lagoon Open again - photos by Kevin Murray, taken on a sunny Thursday February 22, 2024:
More in Issue 614 report: Narrabeen Lagoon Entrance Closed Again: Council's Update - February 2024
Council's Update: Thursday, 15 February 2024
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.
_______________________________________________________