chapt11gh - Chapter 11 Tides A tidal bore is formed when a...

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Chapter 11 –Tides A tidal bore is formed when a tide arrives to an enclosed river mouth. This is a forced wave that breaks. Tidal range can be very large
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Tide - rhythmic oscillation of the ocean surface due to gravitational & centrifugal forces (‘inertia’) between the Earth, Moon and Sun. Tide Patterns - regular, cyclic patterns of low water-high water Tidal cycle – one low tide and one high tide consecutively diurnal tide - one low tide, one high tide a day; semidiurnal tide - high water-low water sequence twice a day; 2 high, 2 low, about the same level semidiurnal mixed tide - same as semidiurnal but 2 highs and 2 lows do not reach/drop to the same level; may be the result of a combination of tide types
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Tide Patterns - regular, cyclic patterns of low water-high water diurnal tide semidiurnal tide semidiurnal mixed tide
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Semidiurnal tides Diurnal tides Mixed tides d (ft) Mixed tide, Los Angeles Diurnal tide, Mobile, Alabama Semidiurnal tide, Cape Cod (m) 14 Higher high tide 4 10 Lower high tide 6 High tide 2 High tide 3 4 1 0 0 –4 Low tide –1 0 612 18 24 30 0 6 12 18 24 30 36 42 48 0 6 12 18 24 30 36 42 48 a Time (hr) b Time (hr) c Time (hr) Lower low tide Higher low tide Low tide 48 42 36 Most of the world’s ocean coasts have semidiurnal tides.
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Flood Tide: tide wave is propagating (onto shore) onshore – water level is rising High Tide: water level reaches highest point Ebb Tide: tide is moving out to sea – water level is dropping Low Tide: water level reaches lowest point Slack tide: period when tide wave is reversing – low current velocity Water currents are generated by the tides, the speed of the incoming tide is about the same but in the opposite direction of the outgoing tide. Moving waters have to slow down and reverse, from flood to ebb and vice versa ( slack tide) . This is a good time for navigation through narrow places, particularly those characterized by strong tides (East River, for example).
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Mean Tide Level = MTL - computed from measurements taken at a place over many years and averaging all water levels. Mean High-Water = MHW.
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chapt11gh - Chapter 11 Tides A tidal bore is formed when a...

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