In shallow water where depth is less than half the wavelength, which transition in particle motion occurs?

In shallow water where depth is less than half the wavelength, which transition in particle motion occurs?

• A. Shallow-Water Wave
• B. Swell
• C. Surf Beat
• D. Transitional Wave

Answer: (D)

The main concept is how the actual path of water particles changes as waves move into shallower water relative to their wavelength. In deep water, particle motion is nearly circular. When depth is less than half the wavelength, the bottom starts to constrain vertical movement, so the particle orbits become more flattened into ellipses and the vertical motion decreases, with motion becoming almost horizontal back-and-forth along the direction of travel as the depth gets very shallow. This change in the character of the particle motion is captured by calling it a transitional wave. So the best answer emphasizes this shift in motion form with depth, rather than just naming the regime or a different sea-state phenomenon. Swell and surf beat refer to other aspects of waves, and shallow-water wave describes the depth regime rather than the transitional motion itself.

The main concept is how the actual path of water particles changes as waves move into shallower water relative to their wavelength. In deep water, particle motion is nearly circular. When depth is less than half the wavelength, the bottom starts to constrain vertical movement, so the particle orbits become more flattened into ellipses and the vertical motion decreases, with motion becoming almost horizontal back-and-forth along the direction of travel as the depth gets very shallow. This change in the character of the particle motion is captured by calling it a transitional wave.

So the best answer emphasizes this shift in motion form with depth, rather than just naming the regime or a different sea-state phenomenon. Swell and surf beat refer to other aspects of waves, and shallow-water wave describes the depth regime rather than the transitional motion itself.