Windy Point Erosion Protection Works

Throughout the first half of 2015, a number of concerns were raised with the Board regarding accelerated erosion at the end of the sand filled bag wall at Windy Point, which resulted in slumping of some of the bags. Sand replacement is a temporary fix, limited by the size of our trucks and the area is at risk of erosion underneath the road with a series of storms in close succession. 

Following the Board meeting in May 2015, consulting engineers Haskoning (authors of the Coastal Hazard Study) were engaged to undertake detailed design of a rock wall to protect the most critical section of the beach scarp located just north of the sand filled bag wall. The decision to use rock was based on:

  • the superior performance of rock in seawalls
  • the more natural result of rock
  • the ability to import from the mainland using empty barges to be brought back to the Island to remove the plant and equipment used in the runway project

The project involves the removal of the existing 25m long sand filled bag wall adjoining the concrete Seabee sea wall and construction of a rock revetment wall up to 64m long, commencing at the end of the Seabee wall. Rock will be stockpiled on the beach in front of the new rock wall and in the vacant grassed area at May Shick’s lease. Sand and other materials may be needed as backfill behind the new wall and will be sourced from several locations, possibly including Lagoon Beach in front of The Pines. If all stockpile areas are filled, there may be a need to close one lane of Lagoon Road (closest to the Lagoon) from the site south towards the runway to stockpile materials close to the site.

As with any hard structure in a sand environment, erosion at the northern end of the wall is expected. The impact of this has been considered through the curving of the wall back into the sand dune to provide better end protection, and also through maximising the distance between the end of the new wall and the Pinetrees Boatshed.

The recovered sand filled bags will be stockpiled on the beach north of the Boatshed for later use:

  • as protection between the end of the new wall and the Pinetrees Boatshed, or
  • as protection in front of the Boatshed, or
  • as a groyne to capture sand north of the Boatshed.

Delivery of the first barge of rock was expected on 1 September but has been delayed until 14 September due to bad weather and not having a 1.7m high tide in daylight hours.  Construction is expected to be completed in mid-November.

A Review of Environmental Factors (REF) prepared for the project highlighted the most significant impacts are related to the removal of habitat for the Wedge-tailed Shearwater, the LHI Skink and LHI Gecko. This has been justified on the basis that without these works, the habitat will be lost to erosion anyway. However, to mitigate potential impacts, the following activities will be undertaken:

  • Regular inspections of areas will be carried out for the Skink and Gecko
  • Areas of clearing and no-go zones will be clearly fenced
  • Vegetation will be stripped and stockpiled off-site so that Shearwater activity can be easily observed
  • Shearwaters will be relocated to new burrows constructed elsewhere in the area
  • Works will be completed before 23 November to avoid Shearwater egg laying
  • Dogs to be on leash in the beach and foreshore areas south of Pinetrees Boatshed until early 2016

Work on the site over the last few days has involved a specialist seabird researcher, Dean Portelli, and Board staff. Using hand tools, the area has been cleared of vegetation to expose burrows. The burrows have been checked for birds and any found birds have been relocated to newly constructed burrows nearby and out of the construction area. When the area is clear of all burrows, the topsoil and remaining vegetation is removed by machine so that birds are visible on the sand surface, and can be relocated to their new burrows. Dean is typically observing at dawn and dusk and relocating birds as necessary. Dean will remain on-site during the early phase of construction or until the birds are reliably returning to their new burrows.   

During unloading of the rock from the barges, there will be many trips required by a large Moxy truck-see picture below. The truck will drive from the Windy Point airport gate along Lagoon Road and drive onto Lagoon beach at the entry opposite the Oval. The truck will have an escort vehicle, but everyone needs to be aware of this vehicle and give it space, as it will have 30 tonnes of rock on it and will not stop quickly.

The other photo below shows an example of a rock wall construction on the NSW coast.

Moxy Truck

 

 

 

 

 

 

 

 

 

 

 

Rock Wall Construction NSW Coast

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

A cross section through the new rock wall is shown below.

Cross Section Rock Wall

As well as the additional traffic on portions of Lagoon Road, changes that community should be aware of are:

  • the area south of Pinetrees Boatshed will be fenced off as a construction site with no public access
  • during the rock delivery phase, Lagoon Beach from the Passion Pit south may have restricted access to prevent accidents with the Moxy truck
  • during and after construction Lagoon Beach and the foreshore area south of the Pinetrees Boatshed will be a dog on leash area, so that the Shearwaters are protected

There will be lots of activity around the Windy Point area during the 2 month construction period and not a lot of room for people to observe safely, so please avoid stopping near the area.

If you have any questions, please contact Andrew Logan on 6563 2066 or andrew.logan@lhib.nsw.gov.au

 

Penny Holloway

CHIEF EXECUTIVE OFFICER

Date: 2 September 2015