Collaroy Beach – New South Wales #1 coastal erosion hotspot

Adrian Turnbull, Greg Britton1

1Royal Haskoning DHV, New South Wales

Abstract:

BACKGROUND
Collaroy-Narrabeen Beach is characterised as having the most highly capitalised shoreline in Sydney’s Northern Beaches and is also classified as the most at risk from coastal processes in New South Wales, and the third most at risk in Australia. The main cause of the existing coastal hazards is that development has taken place well within the active coastal zone (within the primary foredune area). The challenge facing us today is how to manage the legacy of historic planning decisions in the face of current (and future) risks of living with a hazard on your doorstep…

SITUATION
Collaroy-Narrabeen Beach was settled (in the modern era) as a distant suburb of Sydney. The majority of early beachfront houses were lightweight “temporary” structures, generally single story timber framed dwellings, which have a history of suffering from the impacts of coastal erosion as early as the 1920’s.

As the city of Sydney expanded, and the northern beaches became more popular, significant increases in development occurred along the coastal area. Houses became more “permanent”, and large unit blocks were constructed that enjoyed absolute beachfront access. However, significant storms in 1967 and 1974 highlighted the risks of living in such a prominent location, and resulted in emergency actions to prevent further damage to property, including the construction of ad hoc “seawalls” along the 1.3km of “at risk” development.

Northern Beaches Council is fortunate to have some of Australia’s best coastal engineers and coastal scientists working and training within the local government area, including the State Government’s Manly Hydraulics Laboratory and the University of New South Wales’ Water Research Laboratory.

Collaroy-Narrabeen Beach is the site of one of just a handful of beaches worldwide where researchers have an unbroken and regular record of the changes that have occurred to this stretch of coast spanning several decades. Initiated in 1976 by Professor Andy Short of the Coastal Studies Unit at the University of Sydney, the beach has been surveyed every month using a variety of survey techniques, that has provided an amazing dataset which informs current and future decision making.

Some of Australia’s most respected coastal engineers have provided technical solutions as to how to provide appropriate “engineered” solutions to prevent further damage to properties along this coastline for over 50 years. However a combination of legal and social factors, including a public protest of over 3000 people forming a “line in the sand” in 2002, have prevented these solutions being implemented.

Following the internationally renowned June 2016 east coast low storm event (who doesn’t remember the “pool on the beach” photo?), the focus has shifted from theory to reality. Northern Beaches Council has worked closely with the New South Wales government, affected residents, and the wider community to put in place a plan to enable delivery of appropriately designed and constructed coastal protection works.

To do this, Council engaged Haskoning Australia (a company of Royal HaskoningDHV) to develop technical specifications for appropriate protection works, as well as a partnership between Manly Hydraulics Laboratory and the Water Research Laboratory to undertake an assessment of the proposed works to ensure that there would not be an adverse impact on coastal processes.

In a first for New South Wales (and even Australia), Council has adopted a policy position to actively support residents constructing coastal protection works, including providing a combination of Local and State Government funding contribution of up to 20% of the cost of the works.

Council is also actively protecting its own assets, and has constructed an engineered rock revetment in front of Collaroy carpark, which at 250 meters in length, is the largest of 11 public assets along Collaroy Beach.

The challenging situation of mixing public and private protection works has been an issue 100 years in the making, with the “answer” known for over 50 years, however collectively we are still in the early stages of delivering a solution to the problem.


Biography: