June 4, 2016
IT IS late afternoon on May 10, 2016. The wind is blowing hard and cold in my ears. The sky is dull and heavy. Large breakers roll into Kitty Miller Bay and drive across the steel-grey water in thick white lines.
I am standing at the bottom of the stairs at the western end of the full-moon shaped bay. The tide is so high I am being splashed by waves as they smash against the back of the beach.
Each wave explodes on the shore and surges forward in a mass of white water that swallows the whole beach. The water churns like a machine into the grassy berm that rims the base of the dune then turns from white to brown as it fills with sand and drains back down in horizontal waterfalls.
Some waves hurl themselves over the top of the berm flinging up bits of cuttlefish, seaweed, mangled dune plants and tiny pieces of plastic. The water withdraws leaving tangles of sea rocket trailing across the smooth wet sand. Seagulls swoop and feed among seaweed as each wave recedes.
Cracks form along the edge of the berm where the next slice of sand will fall. Already a tall vertical wall of sand has been gouged around the back of the beach.
This is no ordinary stormy day. Today the tide was predicted to reach 1.85 metres by 2.46 pm. That’s about as high as a spring tide can get on a coast with a two metre tide range.
No matter how many times I’ve seen it before, I am always shocked when I see a beach freshly eroded by a storm. I know I shouldn’t be alarmed on a beach like this where waves arrive parallel to the shore. It is part of the natural process of cut and fill, the cycle of destruction in stormy weather and construction over a period of calm.
During fine weather, low waves spill gently onto the shore. Frothy white swash fans out, delivering little loads of sand to the beach. Over time the sand builds into a broad flat ridge, a berm extending from the base of the dunes.
In stormy weather, large steep waves plunge violently onto the shore. As each wave retreats, a backwash scours sand from the beach. When storms come with spring tides (king tides) the sea cuts deeper and further into the backshore zone.
But the sand is not lost. It settles in the shallows of the nearshore zone. Some collects into flat beds where seagrass grows, feeding places for fish when the tide is in and for shorebirds when the tide is out.
Some years ago, a stairway was constructed down the side of the high dune at Kitty Miller Bay. At the end of the stairs is a three metre ramp that leads onto the beach. Sometimes the ramp is covered with sand, sometimes it is suspended in the air like a bridge. The ramp is a constant measure of how the sand comes and goes.
In May last year, after a spring tide of 1.8 metres and a week of stormy weather, the beach at Kitty Miller Bay had been depleted. The berm was cut back to the rear of the stairs and the ramp’s footings were exposed.
A mild winter followed and by mid-August sand had filled the space beneath the ramp. Spring rains failed and summer was very dry.
By March this year, after the prolonged period of fine weather, a broad sandy berm had returned to the back of the bay and the ramp was smothered with sand. Sea rocket, grasses and several coast saltbush shrubs had colonised the berm.
On April 11, a storm arrived with a 1.75 metre tide. Waves cut sharply into the berm carving a clean slice around the back of the beach. The ramp was left resting at the edge of a 400-millimetre cliff of sand and only two of the coast saltbushes remained clinging to the berm.
One month later, after the May 10 spring tide, sand had disappeared from beneath the ramp leaving it jutting over the beach. In places the sandy cliff stood 700 millimetres high and the coast saltbush shrubs had been swept away.
The stormy days and big tides continued through May. By the end of the month, the berm had been cut back to the base of the stairs and the legs of the ramp were exposed. The beach had returned to the same shape as it was at the same time last year.
The cycle of cut and fill should be no cause for concern, but the 1.85 metre tide of May 10, 2016 shows how destructive the sea can be when it bites into the land. Sea level is predicted to rise by 0.74 metres by the end of the century due to global warming. Spring tides are a warning of the urgency of cutting greenhouse gas emissions.