MAY-JUNE STORMS 1974 – PART 2
As I write this blog fifty years ago to the day, the first of the two great 1974 storms had abated. Little did we know that another was coming a week later. We soon started stewing over the role of higher sea surface temperatures (SST) in storm genesis. On Monday 10th June a group of us at ANU expounded on the idea of a link between phases of coastal erosion with higher SST. We decided to have a chat with Ian Mason of the BoM based in Canberra. He was in charge of regional long-range forecasting. I met with Ian on 12th June and was shown lots of information on SST and other met data and several key references which I devoured that night. He was quite appreciative of the discussion of relationship between cyclonic activity (east coast lows), blocking highs, big seas and high SST. I also spoke to his contact David Wright in Melbourne who also was looking at these links. Years later I summarised this thinking as a climate/geomorphic model in a paper published in a book in honour of one of my mentors, Joe Jennings (“Coastal sand deposition in southeast Australia during the Holocene”, J. Davies and M. Williams eds., Landform Evolution in Australasia, ANU Press, 1978, p. 197-214).
What turned out to be an incredible coincidence was that in early May 1974, a paper appeared in the now defunct journal SEARCH on “Coastal erosion in Eastern Australia” (vol. 5, No. 5, p. 198-209). I was the author. It is wide ranging across time and place. Discussion in the section on contemporary erosion arose in part from meetings over several years with coastal engineers including Doug Foster, Neil Lawson, Angus Gordon; we called this the “Coastal Erosion Study Group”. Table 1 was a compilation of erosional events from 1857 to 1971 extracted from various sources. It was possible to use profile information from Gold Coast surveys pre and post 1967 storms to highlight trough and bar formation that accompanied the late June 1967 storm. This was followed by a period of post storm smoothing of the nearshore profile and beach recovery. It was an illuminating data set and excited us who were then doing regular surveys at Bengello (Moruya) Beach. But equally exciting was the work of E.C. Andrews, a NSW State Geologist who published an extraordinary paper in 1916 entitled “Shoreline studies at Botany Bay” (Journal and Proc. Royal Society of NSW, vol. 50, p. 165-176). He documented impacts of several east coast lows on Lady Robinsons Beach located well inside Botany Bay (1857, 1876, 1889, 1912). I cited some of his work in my SEARCH paper. Here are a few extracts from his encounter with the 1912 storm on 16th July 1912:
“Rollers broke on the beach and travelled alongshore from N to S with great velocity. Great waves commenced to break from 400 to 1000 yards off-shore. Heavy bay bar apparently formed off-shore… wide flattish beach formed and sand dunes cut back…No wind. Waves at maximum height…Large stones torn out of retaining walls tossed like corks along the beach from 6-10 feet above ordinary high-water mark”. He also noted that it were larger waves at 10–15-minute frequency “which accomplished the whole of the destructive work” . In looking forward to rebuilding of foredunes involving sand binding plants like Spinifex, he commented “It would take a period of 20 to 30 years to obliterate the trace of the storm unless indeed, in the meantime, an onshore storm still greater than that of 1912 should visit the beach”. Incidentally it was during the 1912 storm that the sandstone block known as the “Mermaid Rock” was thrown onto the platform below the cliffs at Ben Buckler, Bondi.
Andrews foreshadowed so much of what we have experienced in recent years. But it was what we witnessed in May-June 1974 that provided a more quantitative basis for understanding the scale of processes and responses that can occur during major storm events. Roger McLean and I were invited to present our survey results of the 1974 events at the Second Australian Conference on Coastal Engineering, held on the Gold Coast in 1975 (R. McLean and B. Thom, “Beach changes at Moruya, 1972-74”, p. 12-17). Our paper followed the most important paper to record the events of that year : “The storms of May-June 1974, Sydney, NSW” by Doug Foster, Angus Gordon and Neil Lawson (p.1-11). They documented the nature of both May and June storms outlining the meteorological and wave conditions for both ( e.g. synoptic charts for May 23-27th and June 8-15th ). Unfortunately, the wave rider buoy off Botany bay was out for maintenance, but they were able to use that off Port Kembla noting that because of the scale of the weather systems it could be seen as representative. There was also a buoy within Botany Bay that was used. The storms occurred during a phase of high astronomical tides and the paper discussed the tidal and surge components of the Fort Denison record: the maximum observed tide was 2.37m at c. 2300 hours on 25th May as compared to a predicted tide of 1.9m. Substantial wave set-up was observed which helped explain why many coastline structures on the open coast and inside the entrance to Sydney Harbour and Botany Bay were damaged (for instance Manly pool destroyed as was Paragon Restaurant at La Perouse). The paper summarises damage to various structures at 23 locations from Palm Beach to Cronulla. Of interest was there was no damage at Lady Robinsons compared to what had occurred in 1968 (and 1912). This was attributed to beach replenishment works and dredging in the Bay reducing wave heights along that beach.
Our paper was based on beach-foredune surveys that commenced in 1972 north of the Moruya airport. It highlighted the value of close interval surveys. This placed what happened in May-June in the context of changes over the previous two plus years. We had seen the beach accreting through to mid-1973 then in mid-June 1973 the beach was severely depleted by a storm cutting into the incipient foredune. This was the start of an erosional trend accompanying a series of smaller storms in February, March and April 1974 that pushed the foreshore landward. The beach was therefore “undernourished” and primed for the big event. As seen at many locations along the NSW coast the impact of May-June storms was dramatic attacking the established foredune leaving a vertical sand cliff. We recorded details of profile change both vertically and horizontally in the paper. One conclusion was that had storms of similar intensity occurred previously when the beach was in its full accreted condition, the response would have been less dramatic.
In the fifty years since the storms of 1974 much has been written about their significance. This is seen for instance in a neat note in 1975 by Ted Bryant and Rod Kidd on beach erosion along Central and South Coast NSW (SEARCH, vol. 6, 511-513). Like many others, including Ian Goodwin, Angus Gordon and my Moruya colleagues, Ted has attempted to frame such events in terms of atmospheric and oceanic climate conditions. We can still see vestiges of the impact of the 1974 storms along the NSW coast and their memory is enmeshed in the minds of those who experienced them. In my next blog I will offer a retrospective of their importance in NSW coastal management.
Bruce Thom
Words by Prof Bruce Thom. Please respect the author’s thoughts and reference appropriately: (c) ACS, 2024. For correspondence about this blog post please email admin@australiancoastalsociety.org.au
#260
May-June Storms 1974 Revisited