How do the wavelength of a wave and the depth of the water influence a wave's behavior?

Answer 1

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Most characteristics of the ocean waves depend on their relationship between their wavelength and water depth. Wavelength determines the size of the orbits of water molecules within a wave, but water depth determines the shape of the orbits. The paths of water molecules in a wind wave are circular only when the wave is traveling in deep water. A wave cannot "feel" the seafloor when it moves through water deeper than half its wavelength because too little wave energy is contained in the small circles below that depth. Waves moving through water deeper than half their wavelength are known as deep-water waves. A wave has no way of knowing how deep the water is, only that is in water deeper than about half its wavelength.

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The situation is different for wind-generated waves close to shore. The orbits of water molecules in waves moving through shallow water are flattened by the proximity of the bottom. Water just above the seafloor cannot move in a circular path, only forward and backward. Waves in water shallower than 1/20th their original wavelength are known as shallow-water waves. A wave with a 20-meter wavelength will act as a shallow-water wave if the water is less than one meter depth.

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In general, the longer the wavelength, the faster the wave energy will move through the water. Once the wave moves into shallow water, though, depth becomes the principle variable in controlling wave speed.