In his latest ‘Hello Fish’ column, Duncan Leadbitter looks at what this means for sea levels.
During February 2022 we had a series of big swell days that removed large amounts of sand from Stanwell Park beach. Previous erosion events have exposed a rock shelf hidden under the sand at the northern end of the beach but the 2022 event exposed more than I have ever seen.
Wandering among the exposed rocks I noticed what looked like coral in the crevices. Closer inspection revealed it to be a species of worm (Galeolaria caespitosa) that makes its own tube to live in. This tube is made of calcium carbonate and so it’s often called Sydney coral, as corals are made of a similar material. Galeolaria is normally found in the intertidal zone down to depths of 30m or so. It feeds when it is covered by seawater.
So, how did this worm come to be covered by 2.5m of sand? One conclusion is that it was once underwater, which implies that at some time there was no beach and that the rock shelf in which the Galeolaria was found was either covered by water all the time or, at the very least, covered by the tide.
The sea level along the NSW coast was once higher than it is now by about 1 to 1.5m. It reached its current height about 10,000 years ago but then continued to rise by 1.5m before dropping back to its current height about 4000 years ago.
So my Galeolaria could be about 4000 to 10,000 years old. I collected samples to give to a researcher and am hoping it may be Carbon-14 tested.
If the sea level was a metre higher than it is now, what would Stanwell Park look like? Well, the beach would be gone and the seawater would flood the parks, likely creating a small beach near the tennis court on Hargraves Creek and maybe a similar beach near the weir on Stanwell Creek.
The kiosk would be partly under water as would parts of Park Parade, Beach Road and Lower Coast Road. Stanwell Park would look like a small version of Wattamolla but with a double inlet. If a coastal geographer drilled some boreholes in the park we would get a feel for what the past could tell us, and what the future may hold as sea level rises and beaches either disappear or move inland.
