TURIMETTA: Narrabeen Lagoon entrance to Bungan Beach

The first of a series of five videos taken by a drone offshore from Long Reef to Barrenjoey. Taken in 2021, repeat flights will reveal the rapidity of coastal change.
The latest IPCC report confirms climate change. Sea level rise has always been an issue and severe storms frequently erode our beaches. But we hear little about the smaller beaches, and almost nothing about cliff stability. This drone view provides new insights to geological features and has important warnings about coastal change.
· Big beaches such as Narrabeen and Mona Vale are backed by dunes and the embayments occupy former valley floors with deep sand. As sea level rises these beaches will erode in severe storms but in time, some of the sand will return. Over decades there will be a slow retreat landwards. Beach protection may work to slow the process.
· Smaller beaches such as Turimetta, Basin, and Bungan sit on coastal shore platforms and are backed by vegetated cliffs. The sand in these is a very small wedge and even limited sea level rise will wipe these beaches out and the cliffs will be subject to wave attack.
· Half of the cliffs are vegetated and only have a few small rock falls. But the cliffs without vegetation, especially the headlands, have many rockfalls. In 2007 the former Pittwater Council commissioned a study of rockfall frequency and volume which concluded that falls ranged in volume from 1 to 400 cubic metres and that on average we could expect 10 cubic metres of rockfall per km per year. The drone gives a better record and initial figures for Turimetta Headland show that the largest recent falls are three times the volume previously described, and ten times the average annual volume per kilometre. With a rise in sea level and more wave attack at the cliff base we should be concerned.
Which set of numbers is right? They are probably both ‘right’ because the drone view shows that places like Turimetta Headland are subject to larger and more frequent falls than elsewhere. This headland lies on a zone of close spaced rock joints and minor faults that is an extension of the Luna Park fault zone. This major structural weakness has not been projected so far north before and we should undertake a structural survey of all the cliffs to identify the critical locations.
Particular scenes:
0.0 Narrabeen Headland with a view into Narrabeen Lagoon.
0.46 Two small, relatively old, rockfalls at the back of the platform.
1.05 Turimetta Beach is backed by cliffs and sits on a buried shore platform.
1.32 Sea cave in the shadow is part-filled with sub-rounded boulders on top of which is a small Aboriginal midden. Boulders probably placed at a slightly higher sea level, perhaps as recently as 1,000 years ago.
1.43 Boulders here come and go, sometimes there is beach on this platform. The lower cliff reveals a river channel in the sandstone.
2.46 Close spaced vertical joints parallel to the cliff are the edge of the Luna Park fault zone.
2.56 Big slabs rotated off the cliff in about 2015 and are still moving.
3.29 Two earlier falls from the same fault zone
4.24 The purple beds are part of the Bald Hill Claystone, above that is the Garie Formation then the lower Newport.
4.58 Concrete plinth and ramp is the Warriewood sewer outfall. Three huge boulders were not there in the late 1970s.
5.16 Very unstable headland with multiple recent rockfalls and lots of open cracks.
5.47 Note the overhang, not a place for a picnic!
6.40 Large fall, partly vegetated but still unstable.
7.29-10.02 Sea cave complex, Warriewood Blowhole.
11.10 Warriewood beach backed by vegetated cliffs.
12.11 Mona Vale Beach in front of former Black Swamp has a high volume of sand in the embayment but was eroded by 2016 and 2019 storms.
13.24 Sand spit ties the rocky islet to the main beach.
15.40 Disconformity between Garie Formation and blocky Newport Formation.
15.50 Bald Hill claystone on platform.
16.05 More frequent rock falls on the headland.
21.22 Bungan Headland, make your own call about property risk.
22.45 Little sign of recent rockfalls, base of the cliff is vegetated scree and boulders that don’t appear to have moved much, but note the deep crevice in centre of the frame.
Dr P.B. Mitchell OAM

[@waacyweng]

thanks for the HD videos! really helped me finding a fishing spot!!! please keep up

[@threedot141]

Just beautiful scenery and music.

[@musicloverforever8475]

Absolutely stunningly beautiful footage.
I guess to ride my bike from longreef to bilgola beach, I couldn't ride around the bends. So I wen through there on the way to Avalon nth.
Spent the day and rode back home.
This brings back wonderful scenic memories.
And thanks t you I can see everything from the oceans perspective.
Enjoyed immensely
The music was beautiful also
God Bless you

[@danielwutfisho]

epic

[@musicloverforever8475]

Many Thanks for sharing this footage
The first shot behind the pool is where I played as a child.
The surf cams haven't worked in years and I have been wanting to see my home beaches for years
It's awesome
God Bless you