![]() ![]() Suspended fine grain sediments are deposited offshore in deeper water where the bottom is stirred only slightly as depth approaches L/2 or not at all by waves (below L/2 depth). The dominant sense of motion is now forward and backwards resulting in the forward swash of water followed by the backwash.Ĭoastal Sedimentation: In the wave dominated shoreface and nearshore environment fine sediments (silt and clay) remain suspended and are winnowed away, leaving behind the coarse grain sediments (sand and gravel). Eventually the bottom of the wave slows drastically and the wave topples over as a breaker. There is a growing proportion of back and forth motion and less up and down motion as the wave moves through shallower and shallower water. Orbital motions of water molecules becomes increasingly elliptical, especially on the bottom. The waves get closer together and taller. Waves at the Shoreline: As a wave approaches the shore it slows down from drag on the bottom when water depth is less than half the wavelength (L/2). At a depth of one-half the wavelength the orbital waver motion is nearly zero (actually 4% of the surface orbital diameter). This orbital motion is greatest at the sea surface and decreases with depth below the surface. The result is that water molecules move in orbital paths as waves pass. After the crest the water molecules move down and backward. Open Ocean Waves: As a wave passes, water molecules rise up and move forward (in the direction of wave motion) until the crest passes. The period (T) is the time between passage of successive wave crests (or troughs). The wavelength (L) is the distance between two crests (or troughs). The wave height (amplitude) is the difference in height between the crest and the trough. Waves have crests (high spots) and troughs (low spots). The greater the fetch (area over which the wind is blowing - size of storm) the larger the waves. The greater the duration of the wind (or storm) the larger the waves. The greater the wind speed the larger the waves. Wave height in the open ocean is determined by three factors. The shoreline is affected by waves (produced by wind at sea) and tides (produced by the gravitational effect of the moon and sun).
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