Last Saturday the evening high tide (two high tides daily) stood at 8 metres (that is 8 metres above mean sea level) whereas the previous low tide five and a quarter hours earlier stood at sea level (sometimes the low water level is a bit below mean sea level). This gave a tidal range across five and a quarter hours of eight metres or 26 feet (the average tidal range in the Severn Estuary is 50 feet, the largest in Britain). Apparently the time-span between that low tide and the previous high tide was seven hours so the amounts of time between each tidal extent vary although they usually total 24 and a quarter hours across each day. Tide times and heights are available on the Humber Tides website.
Eight metres is a spring (very high) tide. The waters could be seen lapping at the base of the flood bank in South Ferriby and ships sailing up-Estuary on the tide appeared higher-up than usual. As I understand it, tide times and levels for any point around the coast can be predicted years ahead as the ebb and flow is determined by the phases of the moon (lunar cycle). Saturday’s high tide followed the emergence of a ‘new moon’ two night’s before whereas a ‘full moon’ creates a much smaller tidal range (‘first quarter’ and ‘last quarter’ moons range between). A lunar cycle month previous to Saturday, Friday 11th March also saw an eight metre high tide. The lowest intervening tidal range was just over three metres (a neap tide).
Part Two t follow.