Shallow water waves are significantly influenced by the ocean bottom, while deep water waves are not affected by the bottom.
Understanding Ocean Waves
Ocean waves, often perceived simply as surface disturbances, are complex phenomena driven primarily by wind. As waves travel, the water particles beneath the surface move in orbital paths. The shape and extent of these orbits are crucial in determining whether a wave behaves as a shallow or deep water wave.
The Effect of Water Depth
The depth of the water relative to the wavelength (the distance between successive crests or troughs) dictates how the wave interacts with the seabed. This happens as the orbital motions of water that move the waves forward are affected by the change in water depth. When the water is deep enough, these orbital motions complete without touching the bottom. However, in shallower water, the orbital paths flatten out and are significantly impacted by the seabed.
Deep Water Waves
Waves in water deep enough so that the bottom has no effect on them are termed deep-water waves.
- Characteristics:
- Water depth is greater than half the wavelength (Depth > L/2).
- Water particles move in circular orbits that decrease in size with depth.
- Wave speed (celerity) depends on the wavelength (L) and gravity (g): C = sqrt(gL/2π).
- Wave period (T) remains constant.
- Typically found in open ocean environments.
Shallow Water Waves
...whereas waves most affected by the bottom are called shallow-water waves.
- Characteristics:
- Water depth is less than one-twentieth of the wavelength (Depth < L/20).
- Water particles move in elliptical orbits that flatten with depth, becoming nearly horizontal at the bottom.
- Wave speed depends on the water depth (h) and gravity (g): C = sqrt(gh).
- Wave height increases as they approach the shore due to energy conservation (shoaling).
- Wave crests tend to refract (bend) to become more parallel to the coastline.
- Examples include tsunamis and tides, which behave as shallow water waves even in deep oceans due to their extremely long wavelengths.
Comparing Wave Types
Here's a quick comparison based on the key factor: the influence of the seabed.
| Feature | Deep Water Waves | Shallow Water Waves |
|---|---|---|
| Bottom Effect | No effect on wave motion | Significant effect on wave motion |
| Depth vs. L | Depth > L/2 | Depth < L/20 |
| Particle Orbit | Circular, decreasing with depth | Elliptical, flattening with depth |
| Speed Depends On | Wavelength (L) | Water Depth (h) |
| Behavior | Generally maintain shape over deep distances | Shoal (height increases), refract, eventually break |
Understanding the distinction between deep and shallow water waves is fundamental in various fields, including coastal engineering, oceanography, and navigation, as their behavior and predictability differ significantly.
