Dynamic Tidal Analysis
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Transcript of Dynamic Tidal Analysis
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Dynamic Tidal Analysis Generating Forces
Gravity & inertia
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The Tide Wave
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The Tide Wave Free wave
~200 m/sec Forced wave at the equator
Balance between friction & gravity
Less in higher latitudes
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Progressive Wave Tides Tide wave that
moves, or progresses, in a nearly constant direction
Western North Pacific
Eastern South Pacific
South Atlantic Ocean
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Progressive Wave Tides Cotidal lines
Marks location of crest at certain time intervals
1 hour Shallow water
wave
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Standing Wave Tides The reflection of the tide wave can create
a rotary standing wave
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The bulge on the western edge of the basin creates a pressure gradient (to the east) as the earth continues to rotate
At some point the water will flow down the pressure gradient and be deflected to the right in the Northern Hemisphere.
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Due to the Coriolis effect the water forms a mound in the South
This bulge creates another pressure gradient (to the north)
When the water flows it is deflected once again to the right and piles up in the eastern margin
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Once this balance is reached the tidal bulge that forms is called a rotary wave This wave is similar to the wave that can be
produced by swirling a cup A rotary wave creates both high (crests)
and low (troughs) tides each day
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The node is seen half-way along the basin, where the color is always greenish-yellow regardless of the phase of the wave.
Rotary Wave Movement
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Tide crest rotates counterclockwise around the basin
Tidal current rotates clockwise because the current is deflected to the right in the Northern Hemisphere
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Amphidromic Point Node for a
rotary wave
Tidal range is zero
Tidal range increases away from node
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Corange Lines Lines of equal tidal
range
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Rose Diagram Shows direction of
tidal current at a specific hour
Speed of current correlated to length of arrow
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Progressive-Vector Diagram Diurnal
One complete circle
Semidiurnal Two circles
Mixed Two unequal circles
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Tides in Small & Narrow Basins Tides can be quite different due to the
shallowness, smallness and shapes of many bays and estuaries
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In the nearby Bay of Fundy it is much narrower and more elongated (restrictive basin) the tidal wave cannot rotate as it does in the open ocean Instead the tide moves in and out of the
estuary and does not rotate around a node
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The Bay of Fundy Two reasons:
Gradual tapering & shallowing that constricts tidal flow into the bay
Dimension of the bay Tidal resonance This creates a seiche causing the water to slosh back
and forth like a standing wave
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Tidal Bores High tide crest that
advances rapidly up an estuary or river as a breaking wave
3 conditions contribute to tidal bores Large tidal range,
greater than 17 feet A tapering basin
geometry Water depths that
systematically decrease upriver
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Tidal Bores Qiantang River
9m 40 km/hr (25 miles/hr)
Amazon River Pororoca
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Tide Predictions