Clustering of Storms

I read with interest the results of recent work by Ivan Haigh et al. on extreme sea level and storm surge events around the coast of the UK (Scientific Data, 2016, DOI:10.1038/sdata.2016.107). Robert Nichols from University of Southampton, in comments on this work, noted that clustering of storms as occurred in 2013-14, is an important issue with large socio-economic impacts and insurance losses; “ knowledge of typical lengths of time between storm events will help determine how much time emergency response teams have to repair a flood [or coastal] defence before the following storm arrives”.

Back in 1974, I wrote a paper on coastal erosion in east Australia in a now defunct journal ( Search, 5, May 1974). Note the date; the article appeared just weeks before the series of two big east coast lows of late May and June, 1974. The paper summarised the historical work on coast erosion picking up on studies by E.C. Andrews, Delft in SE Qld and Doug Foster amongst others. I listed erosion events from 1867 to 1971; this list has been greatly enhanced by Chapman et al., in various PWD reports and by Peter Helman. The point made in my early paper was the need to recognise that most of these major events involved more than one storm, in effect, a cluster. I went little further by saying although dramatic beach erosion can be associated with a single storm after a long quiet period, what had been observed in 1912, 1950 and 1967 was the impact of the “culminating storm” of a cluster. Of course, this is what we saw in 1974 with culminating effects seen as a result of the east coast low in June. Roger McLean and I had been documenting loss of beach sand at Moruya from erosion events in January and April of that year only to see the foredune cut back massively, first in May then June. Of interest, storms in 1975 and 1978 also cut the foredune as this was a period of poor post storm sand recovery; the beach has long since accreted back to former positions and it is becoming increasingly difficult to find the 1974-78 foredune scarp. Andrews had documented similar storm-wave scarping and post-storm recovery following events in 1889 and 1912 in his classic 1916 paper on Botany Bay.

In 2013, the Water Research Lab at UNSW produced a report for the Australian Government as part of a project assessing coastal sediment compartments and coastal erosion (Mariani et al., WRL Report 253). This is a must read report in my view for anyone trying to gain further insights into the nature of coastal dynamics in NSW. In one section they look at coastal responses to short-term processes and review storm demand predictions developed by Angus Gordon and others. One of their conclusions from two case studies in modelling Synthetic Design Storms was that the sequencing or clustering of two or more storms is necessary to produce estimates of storm demand that match historical measurements. They conclude by saying that “to provide realistic predictions of beach erosion during storm events, storm clustering needs to be taken into consideration as well as two-dimensional effects such as rip currents, sediment loss due to longshore currents and overwash”.

We are now in a much better position to link clustering to wave climate at decadal to inter-decadal time scales and even beyond following the work of Ian Goodwin and others. Nichols and the WRL report remind us of the importance in finding ways to use that information in coastal planning and management in eastern Australia.

Words by Prof Bruce Thom. Please respect Bruce Thom’s thoughts and reference where appropriately: (c) ACS, 2017, posted 15th March 2017, for correspondence about this blog post please email admin@australiancoastalsociety.org

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