Collaroy seawall needed to save major road from crumbling, say coastal engineers

THE ocean could undermine Pittwater Rd within 60 years forcing it to crumble if immediate protective work is not done, according to plans lodged to build a Collaroy seawall.

An application for a protective seawall has been put to Northern Beaches Council. Picture: John Grainger

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PITTWATER Rd could be undermined by the ocean within 60 years if immediate protective work is not done, according to plans lodged to build a Collaroy seawall.

The dire warning that the major arterial road could crumble comes from coastal experts hired to design a wall to protect the 10 properties severely undermined in June last year.

The $1.7 million plans were lodged by residents between Stuart and Ramsay streets and prepared by Horton Coastal Engineering.

The engineers warn that unless a seawall is built at the foot of the houses to stop further erosion, the road — including communication and sewer lines underneath it — could be damaged beyond repair by 2074.

Pittwater Rd Collaroy could be undermined if no action is taken. Picture: John Grainger

At present there are seawalls either side of the proposed new wall. The gap acts as a funnel pushing water into the unprotected area.

The report says that three of the 10 homes were still empty and residents could not move back in until protective works are completed.

A spokesman for the resident group said they were hopeful of a quick result.

“Clearly all 10 occupiers are relieved to have reached this milestone in our efforts to protect our homes,” said Garry Silk.

The report also warned that the council and adjoining landowners could face legal action if more damage was caused to the 10 properties and a seawall rejected.

It said there was “potential liability ... for any effects (additional erosion) that may be found to have occurred at the subject properties as a result of adjacent protection works”, if the plan was not approved.

Garry Silk in front of his home a year after the historic storm. Picture: Adam Yip.

The council’s chief executive officer Mark Ferguson said the plan would be considered on its merits.

The council owns land at either end of the proposed wall.

Mr Ferguson said if the plan was approved the council would pay to extend the seawall onto its land.

“In terms of liability, that is their opinion we would have a different opinion and from our point of view it is not really a major consideration in assessing the application,” he said.

He said the possible risk to Pittwater Rd was of utmost importance — and part of the reason the council was chipping in 10 per cent of the costs for the seawall.

Erosion on the Collaroy-Narrabeen beachfront, just in front of Pittwater Rd.

The State Government is also expected to put in 10 per cent, he said.

“Pittwater Rd is something that was considered, that is one of the reasons why council and the government believe there would be a good reason to contribute to it,” he said.

“We need to plan for an effective long-term protection.

“There is communication lines, sewerage underneath the road, but most importantly it is a major transport link and in some places, the only effective link.”

The sloping rock revetment would have “two layers of primary armour, two layers of secondary armour and two layers of underlayer rock form and be built 1m from within the property boundaries.

Council chief executive officer Mark Ferguson surveys the damage. Picture: Hollie Adams.

The application also argues that if the proposed works are not carried out there could also be major sewerage problems.

It says there will be an “inability to maintain a Sydney Water sewer main on the seaward side of the properties, needing relocation or acceptance of ongoing damage”.

Mr Silk added: “What we are seeking is permission to construct a rock revetment designed to replicate the beach conditions prior to the storm.”

Drone shows severe coastal erosion

He said their strip of beach would return to a “similar beach profile to what has been there for many a decades”.

“Hopefully, by this time next year the revetment will be constructed and covered with dunes that will be vegetated with appropriate native plants as illustrated in the application.”

The application shows plans to revegetate sand dunes with spinifex, coastal pigface and beach fan flowers, which were there before the storm.

“ Beach goers won’t see the revetment because it will be covered in sand,” Mr Silk said. “Life and the beach will return to normal.”