Tidal Notes
Recording tide gauges are located at:
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Spurn
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Brough
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Grimsby
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West Walker Dykes
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Sunk Dredged Pile
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Blacktoft
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Immingham
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Saltmarsh
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Hull - King George Dock
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Goole
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Hull - Albert Dock
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Burton Stather
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Humber Bridge
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Flixborough
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South Ferriby
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Keadby
Tides on the Humber are described as semidiurnal, that is to say that high waters usually occur twice a day.
A spring tide is one of a fairly large range (typically 6.9 metres at Hull) and occurs around the times of new and full moon.
A neap tide is one of fairly small range (typically 3.5 metres at Hull) and occurs around the times of the moons first and last quarters.
At Spurn, at the outer part of the estuary, the flood and ebb tides are very nearly of equal duration, their periods being approximately 6 1/4 hours. As we progress further up the estuary and into its tributaries, the Trent and Ouse, these periods are greatly modified, mainly due to shallow water effects. For example, at Brough, in the upper Humber, the duration of a Spring flood tide can be as short as 4 hours, with an ebb duration of around 8 1/2 hours. At Gainsborough, the limit of our navigational interest on the River Trent, these periods can be around 2 1/2 hours and 10 hours.
This illustrates the possible danger to small craft or larger vessels moored at commercial wharves, of the rapid rise of tide at 'first of flood', when, as low water occurs and the flood tide begins, water levels can rise by as much as 1 metre in the first 10 minutes.
On-line tidal monitoring and recording is carried out by a series of 16 tide gauges situated throughout the port area, from Spurn Point, at the Humber entrance, through to Goole, on the Ouse and Keadby, on the Trent. These gauges are all referred to Chart Datum, as are a number of visual tide boards, in the Upper Humber and the lower reaches of the Trent and Ouse, which allows the mariner to apply readings directly to charted depths in order to ascertain available water for navigation.
Data from the on-line gauges is transmitted continuously to Vessel Traffic Services at Spurn, for the benefit of river users. This is especially useful when a negative surge, which can easily be more than 1/2 metre below predicted tide level, occurs. These negative surges are mainly caused by atmospheric pressure and wind effects from depressions centred north west of Scotland, although tide levels can be altered within the estuary, usually by gale force winds blowing directly with, or against, the tide.
For anyone wishing to find general information about tides, water levels and currents, the American National Oceanic & Atmospheric Administration (NOAA) has a very useful site at
http://co-ops.nos.noaa.gov/about2.html