ocean waves lecture

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