Concerns have been allayed that a popular headland reserve is about to fall into the ocean.

Two days before Christmas (Friday, 23 December 2022), a social media post on the Nextdoor website queried why orange barrier fencing had been erected at the popular Robert Dunn Reserve at Narrabeen Park Parade, Mona Vale.

The reserve runs from Mona Vale Hospital to the top of the headland and is favoured by dog owners as it is a friendly off-leash exercise area. An area of beach immediately below the fenced off area is proposed for an off-leash dog trial.

Barrier fencing at Robert Dunn Reserve, Mona Vale

The barrier fencing ran for approximately 100m, cutting off well-used seating areas and the newly built ‘Lost At Sea’ war memorial. Members of the public visiting the area were perplexed when they were met with reams of bright orange makeshift barrier fencing and metal warning signs saying the area was unstable, with a picture of a person falling from the cliff.

Barrier fencing at Robert Dunn Reserve, Mona Vale

This led some to believe the area had been fenced off for mental health related reasons. Northern Beaches Councillor Michael Gencher, sensing that speculation was heading in an unhelpful direction, publicly admitted he had not been told why the fencing was in place but would endeavour to find out.

On Christmas Day (Sunday, 25 December), Cr Gencher made a social media post revealing the reason for the fencing.

Michael Gencher

Michael Gencher

“On Friday [23 December], an NBC [Northern Beaches Council] mowing contractor observed shrinkage cracking about 5m inside the fence line. You could insert your hand in some sections. As council has no expertise in this area it was decided to fence off the area until it could be assessed by Geotech engineers including a buffer zone of approximately 5-10m.

“Unfortunately, this did take out some of the seats but the precautionary fencing was determined to be the correct decision until NBC had a better understanding of the situation. The estimate is that there is still around 95 percent of the reserve still available for public use. The hang-gliding area is not impacted,” said Cr Gencher.

Cracking in the soil at Robert Dunn Reserve

Cr Gencher further revealed in his message that a consulting geotechnical engineer inspected the site same day (Friday afternoon, 23 December) and submitted a report to Council, advising:

“The cracking is unusual because it extends for a long distance (about 80m to 90m) and mimics the shape of the headland. Tension cracks associated with landsliding are usually crescent shaped. Furthermore, the cracking appears to coincide with an informal walking track people use to walk along the headland adjacent to the fence.

“There is also bare soil exposed along the track / crack alignment. This suggests that the cracking may be related to shrinkage cracking due to the exposed soil drying out due to the recent dry weather. However, as a precaution we recommend leaving the temporary fencing in place until the new year.”

With the explanation given, Cr Gencher wished everyone a happy Christmas and went back to his Christmas Day family activities.

Yesterday afternoon (Monday, 16 January), Cr Gencher was again at Robert Dunn Reserve (main image) with two of his children and their dog to inspect the area and declare the fencing would be coming down today (Tuesday, 17 January).

“It [the crack] was picked up by one of the contractors who was mowing, you can see the line. A metre below the surface is solid rock. They have done a core sample to see if there are any cracks, which would be a problem. The samples have shown no cracking in the rock, so it is safe and the fences will come down Tuesday.

“Obviously, the surface soil has slipped. But even if that were to give way, it’s a metre of soil shifting down, the cliff is not going to collapse. That means the dog trial can go ahead, the beach will remain safe to use,” said Cr Gencher.

Paragliders at Robert Dunn Reserve, Mona Vale

Although the news will come as a relief to dog owners and the many paragliders who also use the reserve, Cr Gencher said that the entire episode should have been better communicated.

“Straightaway it went to community uproar and it wasn’t necessary. There are three councillors for this ward [Pittwater] and none of us knew the reason for the fencing when it happened. I had to go find out for people.

“Council should have let us know they were concerned the headland might collapse. It’s a perfectly legitimate concern, but please let us know, let the community know,” said Cr Gencher.

Images: Northern Beaches Advocate

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