Storm Surge
From the October issue of 2508/2515 District News Magazine
It might already be a distant memory, but in the last week of August the Northern Illawarra coast experienced a fairly significant East Coast Low storm event that generated some of the highest wave run ups (how far up the beach the waves come) seen in decades. When the storm waves peaked in size around 9:30 pm that night I went to have a look at Coalcliff and could not believe how far the water was coming in – I’d never seen it come up so far. Waves were rushing all the way up the concrete ramp and were overtopping the sand bags (if you haven’t been to Coalcliff in a few years, it’s changed a bit). At Stanwell Park the water reached the lower car park below the surf club. I heard similar stories from people up and down the coast. They’d never seen the water levels so high. What was strange about this storm was that while the waves were big, we’ve had bigger waves from East Coast Lows in recent years (April 2015 and June 2016 come to mind) and the high tide wasn’t particularly high or unusual. So why did the waves come up so far this time? The answer is storm surge.
Storm surge is a term used to describe the super-elevation of the ocean water surface above normal tide levels and is usually associated with cyclones, typhoons and hurricanes, which are essentially the same things (intense low pressure systems), but with different names depending on where you live in the world. Over the ocean, these cyclones cause the water level to rise because there’s less pressure ‘pushing down’ on the ocean surface and the water basically rises up. At the same time, cyclones are associated with gale force winds that create large, messy waves and essentially push water towards the shore.
In this case, because the East Coast Low was pretty much centered just offshore of Wollongong we got a double whammy and an unusually high storm surge of about half a metre, which explains why the wave run up came so far up the beach and dunes. However, while our beaches definitely experienced erosion, it could have been worse and we were lucky that the storm didn’t coincide with a spring or king high tide and was relatively short-lived. It also helped that the wave direction was from the south. A bit more easterly and it could have been a lot worse. Or you could have been in the southern United States during Hurricane Ida a few days later and dealt with storm surges of more than 3 metres, which still doesn’t compare to the 14 m storm surge by Cyclone Mahina, the highest ever recorded, that hammered Cape York, Queensland in 1899.
Coalcliff ocean pool being overtopped after the storm