Yesterday’s tide at Fort Mahon was a big one.  The tidal range – vertical height difference between Low Water and High Water – was 9.97 metres (32 ft).

To put this in perspective, imagine yourself standing in the garden of a two storey house, with a pitched roof, that someone has foolishly built exactly on the low tide mark.  At low tide the ground under your feet would be just damp.

Six hours later, at high tide, the house will have disappeared from view and you will be floating so high above it you won’t be able to touch its highest point with your feet.

Fortunately tides are easily predictable and the range rarely varies from forecast heights.  Fort Mahon takes advantage of these large ranges by making use of the vast expanse of fine sand that they expose for recreation.

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New Tide Clock now on Sand-Blog

I thought I would go out sailing or rowing on the River Authie tomorrow, so I went online to check the time of High Water and found a useful Tide Clock for Fort Mahon that I could incorporate into the blog pages.You’ll find it on this page down near the bottom of the right-hand column.

Tide ebbing at La Madelon - River Authie

I built this boat last year for sailing and rowing outings on the River Authie

The tidal range (the difference between high and low tide) can be 20 feet or so on this coast, which explains why there is so much dry sand on the beaches to fly kites, do sand-yachting or just play on at low tide.  The tide here takes almost 7 hours to ebb, but only 5 hours to come back in, so it comes back in at quite a speed.  As it passes over the sun-warmed sand the water is warmed up – making it nicely warm to paddle and play in.

When the tide clock hand is at the top, it’s high tide at Fort Mahon.  When it’s at the bottom, it’s low-water.  You can gauge the state of the tide, and whether it’s rising or falling by where the hand is when it’s between high and low-water.  (It’s on French time, of course, which is one hour ahead of British time)

For me it’s important, because the boat can be launched easily on the river only when it’s about 2 hours either side of high water. Also, it’s hard work to sail or row downstream when the tide is flooding – or upstream when it’s ebbing.

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