This is about coastal erosion.
It’s to challenge usual solutions involving “world’s best practice” ideas, from the biggest consultancies, so simple and obvious that they don’t work, despite/because of huge budget, huge concrete and/or rock walls.
It’s not quite as bad as the economic solutions which gave us the GFC but, per the question by the Queen about “Why could nobody could see [the] GFC coming?”, after 12 months’ deliberation, the answer was “complete failure of the collective imagination”.
Recently, it’s been reported that $29 million is needed to protect properties at East Cowes from storm surge inundation.
It’s said that sea level rise is the cause of the problem, either this or level of the beach is falling.
More recently, VicRoads (RRV), to enable road widening at San Remo, is asking for $20 million for more sea wall stabilisation.
One local person, with more than 50 years’ memory, advises that the beach west of the bridge was eroded and dumped east of the bridge, past the co-op, where you often see whitecaps over big shallow water, where beach used to be.
Are these related and how can they be explained?
The internet makes it easy, these days, to investigate all kinds of things.
It’s always sensible to analyse the problem before jumping to solutions.
The nature of waves approaching a beach might look like water is moving horizontally but it’s not.
A wave is like the single ripple which travels the length of a whip of a whip cracker.
Do kids still try to do this with a rope? The point is that the rope rises and falls but material of the rope never actually travels the length of the rope/whip. It’s exactly the same with a wave.
The slope of a beach depends on the size and rough/smoothness of sand grains. Grains drop out of suspension in water as the height of waves is reduced, until height of the beach is higher than the crest of the wave.
Problem arises when the slope runs out such that the wave rises against a vertical wall.
The volume of water in the wave, from trough to peak to trough, is then slammed into a skinny upwards vertical waterfall.
Whatever goes up must come down.
As it falls, the water needs to change direction, from vertical to horizontal.
There’s an old saying, “when an irresistible force meets an immovable object, something needs to give”.
The closer into the corner at the foot of the wall, the more the water wants to cut the corner.
This causes the sand to give, same kind of suction that makes house roofs fly off in heavy winds, except that water is 1000 times heavier than air, so the suction is extreme.
Amongst the specialists in the business of marine/civil engineering, the term for this suction is “toe scour”.
Toe scour rips sand grains, from the foot of a wall, even under footings/foundations, or even behind a wall.
Swirling of water keeps grains suspended until water is calm.
In the case of east Cowes, this means sand grains stay suspended while strong tidal currents transport them east.
Looking towards Mussel Rocks, water flows east to west, self-repairing the beach in December.
Obviously, damage is done in winter when flow is east to west. There’s a ridge between the Bay and this channel.
When waves are higher than the ridge, there’s nothing to stop them slamming into the vertical face, sucking sand out from roots of trees, destabilising further.
Further west, sand is sucked out from under the yacht club rock wall.
The point of all this is to ask if Bass Coast Shire or our State or Federal reps, are brave enough to find a few bob to chuck at a test before winter.
Using either a sand pump or big dozer (rather than previously using a small excavator), for this section, between the yacht club and Mussel Rocks, if sand can be shifted so that nature slope can be filled in, to the top of the vertical sand face, surely this can be a proving trial, to show that energy of waves will be dissipated, without damage, without toe scour, simply against just the slope of the beach.
Of course, it will help if geotextile can be spread at top edge, along with planting of suitable vegetation seedlings, for longer term stabilisation.
Bernie McComb, Cowes.