Dynamic Tidal Analysis Generating Forces

Gravity & inertia

The Tide Wave

The Tide Wave Free wave

~200 m/sec Forced wave at the equator

Balance between friction & gravity

Less in higher latitudes

Progressive Wave Tides Tide wave that

moves, or progresses, in a nearly constant direction

Western North Pacific

Eastern South Pacific

South Atlantic Ocean

Progressive Wave Tides

Cotidal lines

Marks location of crest at certain time intervals

1 hour Shallow water

wave

Standing Wave Tides The reflection of the tide wave can create

a rotary standing wave

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.

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

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

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

Tide crest rotates counterclockwise around the basin

Tidal current rotates clockwise because the current is deflected to the right in the Northern Hemisphere

Amphidromic Point Node for a

rotary wave

Tidal range is zero

Tidal range increases away from node

Corange Lines

Lines of equal tidal range

Rose Diagram Shows direction of

tidal current at a specific hour

Speed of current correlated to length of arrow

Progressive-Vector Diagram Diurnal

One complete circle

Semidiurnal Two circles

Mixed Two unequal circles

Tides in Small & Narrow Basins Tides can be quite different due to the

shallowness, smallness and shapes of many bays and estuaries

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

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

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

Tidal Bores

Qiantang River 9m 40 km/hr (25 miles/hr)

Amazon River Pororoca

Tide Predictions