Standing up for the Collaroy Seawall

I am writing in response to January’s article (“Seawall puts our beach in peril”) as well as to, what I believe, are sensationalised and misleading public comments by Surfrider Foundation Northern Beaches. 

Despite Surfriders’ campaign, targeting homeowners and the wall, many locals fully support our actions. We are a group of families who live on and love the beach, taking the steps necessary to protect our homes, and are acutely aware of the responsibility associated with building in such a sensitive environment. 

The Collaroy seawall will not only protect our homes but also Pittwater Road, and the many communication and public services installed under it, from inevitable future storm events. It’s important to also recognise, the wall is entirely on private land. Construction costs are 80% homeowner funded. Council and State Government contribute 10% each. 

As part of the Development Application process, experts – including Manly Hydraulics Laboratory, UNSW Water Research Laboratory and Royal HaskoningDHV – all supported the design. Manly Hydraulics concluded, “The proposed coastal protection works are expected to provide improved public access and vastly improved serviceability and public safety.” Further, “No discernible adverse impacts have been identified on existing coastal processes or amenity values compared to the existing situation.” On this basis, and the opinion of several local coastal engineers, the DA was approved.

Surfrider Northern Beaches argue a rock revetment wall should have been built. There are compelling reasons why this is incorrect. The vertical wall, which also has a rock boulder toe to assist with dissipating wave energy, has the following advantages:

•Smaller footprint, allowing the wall to be built further landward, entirely on private property, and ensure an additional 1,000sq metres of sandy beach against the face of the wall. If a rock revetment wall was built, this area would be bare rocks following storms, as a rock revetment would protrude much further outwardly towards the ocean. 

•A 10m wide east-west stretch of rocks that have been in place since 1967 will be removed from the Wetherill St beach area, giving greater access along the foreshore at what was a pinch point during high tides.

•Historical sand profiles show on average there will be 2.5m of vertical wall showing above the sand. Opponents claiming there will be a “7m high wall” factor in the foundations and toe rocks, which are buried well below sand the majority of the time.

Claims a vertical wall will cause greater sand loss and slower recovery from storms are not supported by the credible, peer-reviewed literature. The most significant literature on seawall impacts on beaches is a 1996 paper by Kraus and McDougal in the Journal of Coastal Research (see link in QR code below). They concluded, “During storms, the beach profile in front of a wall retains about the same amount of sand as a beach without a wall, because wave reflection does not appear to greatly influence profile shape”. This is supported from local experience where vertical or stepped vertical walls in active coastal zones at Palm Beach, Bilgola, Newport, Curl Curl, Dee Why and Manly, and a vertical wall since 1967 at one of the properties in our Stuart-Wetherill section, have not caused the beach to disappear or accelerated erosion beachward of them.

We are convinced that once the proposed walls have been completed along the Collaroy-Narrabeen strip, time will prove the correct decisions have been made for the benefit of owners, the general public and beach users.