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Waves
Wave characteristics
Average level
1 cycle1 cycle
Cycle = one unit of a wave
1 cycle = one complete waveCrest
Trough
Wave characteristics
Amplitude and Height
Amplitude
1 cycle
Height
Significant Wave Height (Hs) = average height of the one-third highest waves
Wave characteristics
Wavelength
wavelengthwavelength
amplitude
Wave characteristics
Frequency = how often the wave repeats itself (cycles) in one second.
Frequency = cycles per second = Hertz (Hz)
e.g., 4 Hz = 4 cycles /second
1st
1 sec.
4th
Wave characteristics
Period = the time it takes for a wave to complete one cycle.
period
.01
Time (sec.)
e.g., Period = 10 sec
Frequency = 1 = .10 Hz 10
Formula: f = 1 pp = 1 f
High frequency = small period
Low frequency = large period
10 20
Intertidal Zone
Wave particle displacement - Longitudinal
Particle displacement – Wave orbitals
Particle displacement – Wave orbitals
Particle displacement – Wave orbitals
Stokes Drift
A wave moving onto the shore
20.5-Tarbuck & Lutgens, 2005
Wave refraction
Rip currents
Breaking Waves
• Spilling
• Plunging
• Surging
When do waves break?– Limited by ratio between wave height and wave
length (H/L)– Limiting steepness 1/7
How are they predicted?– wave forecasting (or hindcasting) depends on
wind velocity, duration, and fetch.– Linear wave theory
Breaking Waves
11.19a-Segar, 2007
10.18b-Garrison, 2005
Spilling breakers
11.19b-Segar, 2007
10.18a-Garrison, 2005
Plunging breakers
11.19c-Segar, 2007
11.19d-Segar, 2007
Wave erosion
Wave erosion
• Breaking waves exert a great force
• Wave erosion is caused by
• Wave impact and pressure• Abrasion by rock
fragments
Wave erosion
20.6, 20.7-Tarbuck & Lutgens, 2005
Wave refraction • Wave refraction
• Bending of a wave• Causes waves to arrive nearly parallel to the
shore• Consequences of wave refraction–Wave energy is concentrated against the sides
and ends of headlands–Wave energy is spread out in bays and wave
attack is weakened–Over time, wave erosion straightens an irregular
shoreline
• Wave energy focused on headland
• Wave energy dispersed over bay
9.19b-Thurman and Trujillo, 2004
Wave refraction
10.20b-Garrison, 2005
Wave refraction,Maili Point, Oahu
Wave heights
Wave periods
