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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Rotary Wave Movement
The node is seen half-way along the basin, where
the color is always greenish-yellow regardless of
the phase of the wave.
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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