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Super King Tide in the Cove

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janinerFri, 05/01/2018 - 12:44pm
Flooding by King Tide
King Tide in January 2018

The Cove had some minor flooding this week. It coincided with the summer king tide, which this year was higher than normal.

Spring tides occur every fortnight and roughly coincide with the new and full moons. There are two king tides a year, one in summer and one in winter. This is all caused by the orbit of the moon around the earth and to a lesser extent the orbit of the earth around the sun.

The first full moon this year was a “super moon” when the moon was closest to the earth- a full 50,000km closer than its furthest extent. This causes extra gravitational pull. This event also coincided with the earth being 5 million km closer to the sun than in July.

This all comes together in an 18 to 19 year astronomical tidal cycle which means that you reach the absolute highest astronomical tide about once every 18 years. We are at that peak now and it gives a tidal range of about 2 metres as exceptionally high tides always go hand in hand with exceptionally low tides.

Then there is the impact of weather. Strong low pressure systems raise the water levels slightly and are especially damaging as they usually coincide with strong winds and waves. The natural phenomena of El Nino and La Nina weather systems can also affect ocean levels by up to 20cm.

And what about climate change? The annual rate of increase in sea level at Fort Denison is thought to have been 1.68mm since 1986. That’s 3.3cm over the last 20 years. Sea level is forecast to rise by 40 to 50cm in the next 50 years.

Our forecast king tide this January was on Wednesday 3rd January with a 2.07 tide midmorning at Fort Denison. Our tides in the Cove are very close to one hour later than at Fort Denison. We had minor flooding along the shore line and there was one house where the water level was just below the floor boards- a good thing that the wind was from the south and the low lying houses were reasonably protected from the waves.

The birds had a great time as all the bugs and spiders in the grass started to swim on the surface. Our dog also had a great time chasing all the insects.

I was here when we were at the top of the astronomical tidal cycle 18 years ago. I remember it well because my son had a visiting mate who became sick and I had to call the parents to travel up from Sydney and get him. The parents arrived to find us inundated with water and I think the level in January 2000 was higher in the Cove than it was this time.

Even if we can’t really see any difference yet in water level in the Cove, water levels similar to a king tide will become a normal event in future years. We need to think about what actions we would like local council to take so that erosion of our foreshore is minimised. Should we be allowed to raise our sea walls and fill in the low lying water front land? Should the building line be moved further back from the water? Do we need better drainage? Or should we just wait and see? We are on the boundary of two local council areas and we the community needs to make its voice heard by both councils.

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