Delft, The Netherlands, 21 Jun 2016

Sydney storms and coastal risk

On 18 June 2016, The Sydney Morning Herald (Australia) published an article entitled “Counting the costs of major storm events before they hit Sydney's beaches.” For this article, Prof. Rosh Ranasinghe, Professor of Climate Change Impacts and Coastal Risk at UNESCO-IHE was interviewed on predicting and quantifying Coastal Risk.

The storm that battered the East coast of Australia on 4-5 June, resulting in 4 deaths and over $ 50 million of damage, is widely believed to be the biggest storm that has occurred in over 40 years. The storm came with massive waves that were up to 13m high. One Sydney beach, Narrabeen- Collaroy, took a particularly severe beating from the waves, losing nearly 50m of beach within a day with several houses suffering serious damage.

The severe risk of erosion that the damaged houses (1134-1146 Pittwater road) and neighboring houses along Narrabeen-Collaroy beach were facing was clearly shown in a UNESCO-IHE led study which was published earlier this year in the Journal Ocean and Coastal Management (R. Jongejan, R. Ranasinghe, D. Wainwright, D. Callaghan and J. Reyns. 2016. Drawing the line on coastline recession risk. Ocean and Coastal Management, Vol. 122, 87-94.

Australian Rosh Ranasinghe, UNESCO-IHE’s Professor of Climate Change Impacts and Coastal Risk, who has been studying Narrabeen-Collaroy and other New South Wales beaches for over 15 years, says, “In this study we derived a detailed risk map for the Narrabeen-Collaroy beach where the risk faced by beach front properties, both now and at the turn of the 21st century, were quantified in terms of dollars per square meter for every meter along the beach.

Furthermore we determined the economically optimal coastal setback line, the idea being that the risk of damage faced by any property located seaward of this line is too great to justify the economic gain the property might potentially provide (i.e. return on investment). The blue asterisk in the figure shows the location of the most severely damaged houses along this beach, together with the contemporary risk map and economically optimal setback line published in the aforementioned article. Clearly, the damaged houses were in the ‘unsafe’ zone. If a similar storm arrived from a slightly different direction, adjacent houses that are located seaward of the setback line shown in the figure are also very likely to face severe damage. This unfortunate incident highlights the increasingly urgent need for relevant authorities to make risk informed coastal zone management decisions.”

UNESCO-IHE works with many governments, national and local, using state-of-the-art modelling techniques to quantify coastal hazards and risk, enabling risk informed on-the-ground planning and management decisions. 

Read the full article of the Sydney Morning Herald here.