All around this water-encircled continent, wherever there are pebbly or sandy shores, rocks and boulders by the sea, beach erosion is a fact of environmental life. Australian coastal geologists and environmentalists have singled out three areas for particular concern in the light of climate change and rising seas – the Gold Coast of Southern Queensland, Adelaide’s western seaside suburbs (in particular the stretch of coastline from Outer Harbour down to Marino), and Sydney’s Northern Beaches centred on the narrow sandy strip from Collaroy to Narrabeen.
Beach erosion from storm action is the expected end-product of a process when we get waves of higher height (measured from trough to crest) and of shorter periods (ie, the time interval in seconds between succeeding waves passing a specific point) repeatedly crashing onto shore. Storms of greater energy and intensity result in more sand being moved offshore and a storm bar builds up on the nearshore zone. For significant amounts of sand to return to the visible beach, ie, less erosion occurring (the process of accretion), Ocean and sea conditions need to be calmer. Unfortunately for the environment, and for coastal-clinging human habitation, all the trends are in the opposition direction! Concerned coastal watchers are increasingly preoccupied with the sense of a stark future, apprehensively eyeing the very real prospect of untrammelled beach attrition [‘Beach erosion: Coastal processes on the Gold Coast’, (Gold Coast City Council – Discovering Our Past), www.goldcoast.qld.gov.au]
Gold Coast: Human encroachment on a coastal cyclone zone
The Gold Coast at latitude 28° S is in a tropical cyclone prone zone, its history of cyclone events goes back to the 1920s, including crunch years such as 1967 when eleven cyclones hit the Coast in rapid succession. Like Sydney’s Northern Beaches (see separate blog post) the Gold Coast/Surfers Paradise area is especially susceptible to property damage due to the same development pattern of building too close to the beach (multi-millionaires’ coastal mansion syndrome?). A 2009 study by the Queensland Department of Climate Change (DCC) estimated that there are 2,300 residential buildings located within 50 metres of sandy coast and 4,750 within 110 metres” [Tony Moore, ‘Gold Coast beach erosion plan: Is the plan on the right track?’ Brisbane Times, 05-Jul-2015, www.brisbanetimes.com.au].
Queensland’s volatile summer storm seasons will undoubtedly continue to be exacerbated by climate change and rising sea levels. In recent years an intensification of the cyclonic onslaught on the South Queensland coast has seen the buildup of towering sand ridges on beaches like Narrowneck and Broadbeach, as a result of massive quantities of sand being gouged from the beach❖.
Gold Coast strategies to counter erosion
In direct response to the devastating 1967 cyclones the City of Gold Coast commissioned the Dutch Delft Report and established a Shoreline Management Plan to follow up its recommendations. New seawalls were constructed to bolster the beaches and an artificial reef created at Narrowneck Beach (the Delft Report called for Gold Coast beaches to be widened to withstand severe weather conditions and restorative work was intended to re-profile the vulnerable beaches). The Shoreline Management Plan strategy incorporates a scheme to shift sand from south of the Tweed River (from NSW) through a system of bypass pumping to replenish the beaches on the Gold Coast [‘Gold Coast Shoreline Management Plan’, Wikipedia, http://en.m.wikipedia.org. Transporting sand has proved a costly exercise for the Gold Coast Council ($20,000 a day during severe storm activity periods to shift 20,000 cubic matures of replacement sand) [‘Battling erosion on the Gold Coast’, (Splash ABC Queensland), www.splash.abc.net.au]
Adelaide hot spots
Adelaide’s north-western beaches’ susceptibility to the climatic forces of erosion mirrors that of the Gold Coast…and similarly it has been plagued by the same degree of imprudent decision-making by planners and developers resulting in property lines being positioned too close to the shoreline. A conspicuous case in point being Tennyson Beach 14km from Adelaide CBD. Tennyson locals recall that a stretch of its celebrated coastal dunes was washed away by massive storms in the 1960s…after it was restored to its previous height, amazingly houses were built on the same vulnerable dunes! Erosion at nearby West Beach has become so problematic that the West Beach Surf Life Saving Club has given consideration to moving the location of its clubhouse [‘Adelaide beachfront housing “facing erosion risks” like those at Collaroy, Sydney’, ABC Radio Adelaide, ABC News, 08-Jun-2016, www.abc.news.net.au
As elsewhere the fear for Adelaide coastal watchers is the inexorable rise of sea levels – scientists have predicted that its low-lying coastal land will be inundated with the bulk of the city’s beaches under water by 2050! Geologists and coastal experts such as Dr Ian Dyson have predicted that the great majority of Adelaide’s sandy beaches are at risk of being reduced to the same denuded state as Hallett Cove – once a glistening sandy beach, now a rocky foreshore bereft of sand¤. Dyson forecasts that the only beaches likely to survive, albeit as “pockets of beaches” on the metropolitan coast beyond 2026 will be at Glenelg, Henley Beach and Semaphore [Thomas Conlin, ‘Expert says key Adelaide beaches could disappear within a decade because of rising sea levels and erosion’, Sunday Mail (SA), 24-Jun-2016, www.adelaidenow.com.au
Notwithstanding the pessimism of scientific experts, the state government’s Coastal Protection Board maintains its sand-replenishment programs are effective in meeting the challenges which are undeniably formidable. Dr Dyson however has been critical of the authorities’ over-reliance on rock wall defences, contending that “retaining beaches (were) a losing battle without angled breakwaters or groynes at the southern end of erosion hot spots to slow sand movement [Conlin, ibid.]
Endnote: A dynamic problem – the natural drag of sand by the elements
An important factor contributing to beach erosion is the natural tendency of the ocean to drag coastal sand in a northward movement. This affects both Adelaide and the Gold Coast. On the GC’s southern beaches where sand is plentiful, the drift north to replenish the northern GC beaches is impeded by the presence of rock walls and groynes which interrupts the free flow of sand northwards [Tanya Westthorpe, ‘Sand erosion threat to prime Gold Coast tourist beaches’, Gold Coast Bulletin, 02-Aug-2012]. the top of the Gulf St Vincent. Sand replenishment and maintenance thus is a major challenge for the more southern lying beaches like Kingston Park and Seacliff which are in continually peril of being sand ‘starved’. Aside from the logistics of managing this, sourcing sand from quarries is proving an increasingly expensive exercise for the authorities [‘Sand carting plea to save Adelaide’s vulnerable beaches, including Seacliff and Kingston Park’, (E Boisvent), 12-Oct-2016, www.news.com.au]
* The title is of course a symbolic nod to King Canute (Cnut the Great) 11th century Anglo-Saxon ruler of the North Sea Empire, and the apocryphal anecdote of his futile but persistent efforts to turn back the tide on the seashore
❖ prompting sections of the media to jocularly re-label Broadbeach as “Steep Beach”
¤ Dyson blames ill-considered development and the construction of a beach marina for the degradation of Hallett Cove