GEOGRAPHIC EXTREMES SOCIETY

 

AUSTRALIAN RECORDS

Tides

 

Nowhere can you see the influence of the gravitational effects of the sun and the moon as when you watch the tidal stream flood and ebb over reef flats, through channels and up coastal estuaries. When perigee and full moons coincide, which happens in either March or April, extreme tidal variation takes place right around the world. Due to the cyclic phase of the moon’s rotation, the last extreme supermoon was met with much fanfare in January 2016, and we’ll need to wait until November 2034 for the next one.

While Australia has some of the greatest tidal variations in the world, it is the Bay of Fundy, and Ungava Bay, both in Canada the provide us with a most extreme tidal variation. These tidal variations can result in a staggering difference of up to 16.3 metres between high and low tides.

Largest Tides

Bay of Fundy – Largest tidal range in the world (equal) Image: NOAA

Regions where super-large tidal variations occur, all have a very similar funnel-like coastline and a long gently sloping shape of the seabed which magnifies the tidal influences. During the full and new moons, especially around the time of the equinoxes, massive tidal variations spew many cubic kilometres of water onto adjoining tidal flats, into estuaries and up rivers. During large tidal variations, incoming tides produce tidal bore waves that enter some estuaries in locations like the Styx River in central Queensland, the Daly and Victoria Rivers in Northern Territory, and the Fitzroy River in Western Australia. These tidal bore waves have the power to capsize fishing dinghies, with the stories of sharks following the bores more concerning for those who find themselves in the water.

With all the large tides we see, astonishingly, on average the open ocean yields a tidal range of a mere 0.60 metres.

It’s in north-west Australia that the continent’s largest tidal variation occurs. From Eighty Mile Beach to Wyndham in Western Australia, giant tides poor over extensive tidal flats twice daily, sweeping in nutrients from the sea.

The largest tidal range affecting the Australian coastline can be expected around the times of the March equinox, even more so if the equinox coincides with either a full or new moon.

Fastest Tidal Race

In north-west Western Australia, the Buccaneer Archipelago stretches east from Cape Leveque. The first group of islands are the Sunday Islands group and it is here that the world’s fastest tidal race occurs. The incoming tides have to move around the Dampier Peninsula and through the Sunday Island Strait to start to fill the enormous King Sound

Giant tides (4)

the Sunday Island Strait is the fastest tidal race in the world, capable of filling Sydney Harbour 166 times over with each tidal movement. The tidal stream, or race, is the speed of the current, as opposed to tidal variation, which is the rise and fall of the sea level.

Horizontal Falls. Fastest Tidal current in the World. Image:

However, I believe that the greatest tidal current in the world belongs to the Horizontal Falls at Tabot Bay. Huge tidal currents in Norway and the Pacific North-West are impressive, but when viewed alongside the tidal streams of the Buccaneer archipelago, they pale into insignificance.

Talbot Bay has two embayment’s to fill and the water levels must squeeze through narrow gaps in the ranges to empty into the sea or the bay. The larger opening is twenty metres wide while the smaller gap is only seven metres wide. With the bay being forty metres deep, there is a lot of water to mover through these openings. The speed of tidal current can be around thirty knots (approx fifty-five km/h).

 

 

Greatest tidal variation in Australia

Officially, the tidal gauges in Derby record Australia’s greatest tidal variation, at just over 12 metres. Official tidal predictions can vary depending on the presence of low-pressure systems, and on wind direction and strength. I was quite ready to accept the Bureau of Meteorology’s records of tidal variation, but a small interpretive sign at the Derby Wharf, made me stop and think. They contradicted the Bureau’s official records and declared that the nearby Yampi Sound in the Buccaneer Archipelago has the greatest tidal variation. My research showed that the location of the closest tidal gauge to Yampi Sound was at Koolan Island, and it tells a different story. The Koolan Island tidal variation is about half a metre less than that of Derby.

New research done by the Australian Navy has found the largest tidal variation for Australia to be at Raft Point, 70km east of Yampi Sound. During the survey voyage, named as HI 584, measurements were taken from February to May 2016 by the Australian Navy’s hydrological survey ships. The unpublished study of Survey HI 584 brought to light a gigantic tidal range of over 13 metres at Raft Point.

Raft Point. Largest tidal variation in Australia. Image: Diversity Charters

 

 

Smallest Tidal Variation

Nornalup Inlet near Walpole in the far south of Western Australia. Nornalup Inlet is renowned for having the least tidal variation of anywhere on the entire continental coast of Australia. We note some smaller tidal ranges on tidal gauges situated inside the highly modified inlets at Macquarie Harbour in Tasmania, and Illawarra Inlet in New South Wales. However, due to the extensive human modification of the harbour entrances, we are restricting tidal range records to unmodified, natural coastal locations.

On August 6, 2019, the tidal range at Nornalup Inlet was just six centimetres between successive high and low tides over a full 24-hour period. For many days on and around the neap tides, there’s minimal change in sea level. External factors such as freshwater run-off coming down the Frankland River, or strong winds or wave action at the mouth of the inlet influence the tides at Nornalup rather than the actual effects of gravitational forces.

Tide chart for Nornalup Inlet. Smallest tidal variation in Australia. Image: Willy Weather

 

Tide Records

GES Record: Largest tidal variation in the world –    Ungava Bay, Quebec Province. Canada 16.3m & Burntcoat Head. Bay Of Fundy. Nova Scotia 16.3m (Source: Peter White. Tides )

GES Record: Largest tidal variation in Australia – Raft Point. Kimberley. Western Australia. Over 13m (Source: RAN Survey HI584)

GES Record: Fastest tidal race (in the world?) – Horizontal Falls. Talbot Bay. 60km/h (Source: Bryne Tuckey. Horizontal Falls seaplanes)

 GES Record: Least tidal variation – Nornalup Inlet. Western Australia. 0.06m over a 24-hour period (Source: BoM)

The Geographic Extremes Society welcomes any input as to the veracity of these records and we encourage everyone to contribute to these extreme records by contacting us to initiate the discussion