When measuring low and high tides where do they take the measurement from?

Question

to be specific at filey nort yorkshire

Answer 1

whitby harbour i think

Answer 2

The tides in most parts of the world are diurnal. That means on average there are two high tides and two low tides in twenty-four hours. Of the two low tides, one will be lower than the other and it's called the "lower low" tide. If you record the heights of all the lower low tides occurring at a particular place (say, filey nort yorkshire) for an entire year and calculate the average, it's called the "mean lower low tide." All future tide heights are then measured with respect to that mean lower low. (MLL on navigational charts.)

That's how it's done everywhere in the world -- by international maritime law. Don't believe that "chart datum" stuff above. Chart datums are used in map-making, and are not used to directly measure tide. You use "chart datum" when using a GPS to find your altitude. From this you can indirectly measure (ie, calculate) the tide height.

Answer 3

Simple answer - Newlyn in Cornwall.

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If you're referring specifically to the UK then all measurements on land and water are taken in relation to what's known as Ordnance Datum Newlyn (ODN). It might sound complicated but it's not - it's simply a white line drawn on the harbour wall at Newlyn in Cornwall and it represents the average height of the tide. It's been there for 86 years, prior to being at Newlyn it was at Liverpool Docks.

Every altitude, depth and so on in the UK is measured relative to ODN and as far as the UK is concerned ODN is the same as sea level. The Ordnance Survey (OS) is the UK's map making agency and on large scale maps you'll see two lines along the shore - one marked MHWS and the other marked MLWS, these are the Mean High Water Springs and the Mean Low Water Springs - the average of the highest and lowest tides (in this context spring has nothing to do with seasons). ODN is midway between the two.

There is another 'sea level' which operates on a world wide scale and this is something that has been agreed upon by international treaty. OND is 3.5 metres above the international sea level.

MHWS in Filey is 6.1m, MLWS is 1.1m - the average level of the sea is therefore 3.6m above the international treaty or 0.1m above OND.

In a few days Filey will have some of the highest tides of the year and if there's a strong wind coming in off the north sea there could be some interesting results.

Answer 4

Something called chart datum. This is a level that the tide does not usually fall below, and is referred to as 0m. The depths reported on navigational charts are in reference to chart datum. To find how deep water is in your area, you need to consult one of these charts.

This does not mean that there will be no water at the beach, or wherever, just that that is the lowest the tide normally gets. A 0.5m low tide means that there will be 0.5 m deep of water above datum; a high tide of 2.5 m means that there is 2.5m of water above datum.

A really really low tide, such as those in summer during full moon may occasionally be lower that datum, and the tide is given as a negative, eg - 0.22m.

NOTE:
I'm guessing the whiz is american, talking about lower low water and such. British admiralty charts all refer to Lowest Astronomical Tide (LAT, commonly caused chart datum). Using different datum can lead to navigational accidents such as groundings. A bit off the point, but such (small) misunderstandings between measuring systems led to the Mars orbiter crashing in 1999!

Answer 5

Filey Tides

Answer 6

Chart Datum Lowest Astronomical Tide LAT, this is the level of the water at a given point where the tide is never expected to go below this datum point.

Answer 7

The high tide line.

Answer 8

high tide line