Defensive Rock Walls on the Great Ocean Road

In 2017, the Great Ocean Road Coast Committee [GORCC] published a ‘Fact Sheet’ that sought to [1] inform and [2] garner public feedback for plans to upgrade the Torquay Front Beach Sea Wall. Although it is now four years old, it is still worth reading [1].

This document nicely sets out the options available to counter the clear and increasing encroachment of Bass Strait on the eroding ramparts of our treasured coastline. A précis of the key options include:

Option 1 – A natural rock sea wall. Rockwork is the cheapest solution. It proffers a gentler, sloping, rougher surface with inter-rock gaps that stabilise existing erosion, reduce wave energy, and mitigate the risks of sea-level rise and storm surges.

Option 2 – A bluestone sea wall. This is the most expensive option, does not dissipate wave energy or hold sand on the beach, and likely leads to further future erosion.

Option 3 – A concrete sea wall. Concrete is cheaper than bluestone but also does not reduce wave energy or hold sand on the beach, nor is it environmentally appealing.

Option 4 – A rock groyne (a sea wall off-shore) to ‘renourish the beach’ [whatever this means].  This solution would permanently alter the foreshore landscape.

Option 5 – Do nothing.

Admittedly this document only refers to Torquay – indeed, almost all documents relating to the Great Ocean Road (GOR) now seem to, whether they come from the Shire or the Coastal Authority [once GORCC, now GORCAPA].

As a brief aside, there is an affinity that ‘Johnny-come-lately Torquay’ now brazenly boasts with the GOR [NB: the GOR was deftly ‘hijacked in 1994 by Torquay when the Shire of Winchelsea was merged into the newly created Surf Coast Shire]. Until then, the GOR had always started at Eastern View and finished at Peterborough – and, in my view, still does. But bury my rancour! Think positive thoughts about sea walls and coastal protection!

The options for coastal and asset protection advanced in 2017 for the ‘rescue of the Torquay foreshore’ do seem highly pertinent for the greater task of ‘shoring up’ the GOR.

To start – and despite any ‘flat-earthers’ out there who choose to deny a rise in sea level – the sea level is rising. Rock shelves once permanently dry now fully submerge at high tide. Many beaches are narrowing – some are even disappearing: see graph [2].

True, all this has happened before. For example, parts of the Flinders Ranges once formed part of a giant coral reef complex when the east coast of Australia extended north from the Flinders Ranges [3]. Conversely, and as recently as 12,000 years ago, Tasmania and mainland Australia were joined by a land bridge [4].

Yet, it is hard to ignore that the coast is ‘on the move inland’ – perhaps as a natural continuation of the closure of that land bridge. It should be no real surprise that it is happening. It is just the rapidity of the change that has caught us off-guard. This is not the place to argue ‘climate change’ or the human contribution to it. Simply, we must acknowledge that momentous events do seem to be in progress. Wearing our ill-placed bravado against nature on our sleeves, we must either seek to be ‘the little Dutch boy with his finger in the dyke’ or – and better – conjure Darwinian adaptations for our survival.

From: https://en.wikipedia.org/wiki/Sea_level_rise

In 2019/20, the first short section of erosion and risk was ‘bandaged’ by GORCC and VicRoads – a low-lying stretch just before the old sawmill site at Kennett River. They chose [very wisely] to use Option 1 – to me, none of the other options appeals – and all praise to the engineers and workers who built it. While it is ‘unnatural’, it is unobtrusively so, and the wall exudes a certain beauty and resilience all its own. I have to say I love it.

A second section appeared just past the George during the Covid lockdowns of 2020, deftly blended with the natural rockfaces that stretch on either side and share its central section. Now, a more extensive section is nearly finished beneath the cliff face at Cathedral Rock [see photographs].  These, too, convincingly look as if they have ‘organically grown’ in-situ.

So… well done to GORCAPA [once known as GORCC] and your VicRoads teams. In my view, these walls rank with some of your finest work to date. While I have not always loved what Coastal Authorities do, this time you have kicked several serious, long-term, and meaningful goals. Let us all hope that, like the road they seek to protect, they will last long into the future.

But there is much more to do. Low running sections along Eastern View are badly eroding, while Apollo Bay is in dire straits. All it will take is one bumper Easterly during the king-tide season, and much of the shore-line bulwark could be lost with the viability of the road itself coming under threat. In all truth, it is a race against nature – and nature is an opponent that always has time.

Only one thing is sure – nature will always come for us sooner or later, and in one way or another. The issue is: should our defence be the same at all sites and in all situations, or should it be tailored and site-specific. Wisdom suggests the latter may work best.

Rock walls can protect property – and roads [like the GOR] – at least for a time but can ultimately be counter-productive as the turbulence created by wave action against their base erodes and scours the sand in front.  This turbulence ultimately erodes the footing and collapses the wall. Sloping ‘wash up’ rock slopes, not vertical ‘wash against’ sea walls, tend to offer a more sensible engineering solution [5]. There may be places where asset retreat, road realignment, or even abandonment may offer a better longer-term solution than an on-site Dutch boy patch approach, but I am no engineer, and far be it from me to offer any cogent advice.

Finally, to those almost intrepid rock-placers who drive their yellow cranes and dozers with such bravery and skill [Hey: Joe Public … one day stop and watch how deftly they place, turn, nudge, jiggle, and cajole each rock into just the right niche and angle] – you guys are artists!  I, for one, think you are doing an incredible job.

From a lay-person’s perspective of an engineers’ field, it’s been a good start, guys. So far, the aesthetics generated from your brave [though impossible] task of holding back the sea get an A+ rating from me.

Well done to all at GORCAPA and VicRoads. Keep it up – and make it fast!

References:

John Agar