Waves I & II

A wave is a progression of energy from one point to another

The wave does not move forward only the energy in it progresses

Wave is almost friction free

Properties of waves
Wavelength: Distance from one crest to the next
Period: Time taken  for one wave to pass a fixed point
Frequency: Number of waves per second that pass a fixed point
Velocity: Speed with which the waves are moving past a fixed point

Orbital motion

Classification of waves: according to the way they are formed or destroyed

Major formation forces:

Restoring forces: Try to flatten out the waves Deep and shallow water waves Wave velocity
  1. Deep water waves
  2. Shallow water waves
When a deep water wave moves into shallow water it slows down

Trade wind wave (8 second) 28 mph in deep water in 1 metre deep water speed is 3.1 m/sec=7 mph

Wind wave formation

  1. Wind attempts to "stretch" surface skin of ocean
  2. Surface tension: capillary wave
  3. Wind deflected upwards, adds energy to wave pushes it forward
  4. Low pressure behind wave contributes to forward motion
  5. Continued wind, wave period and height grow together
  6. Waves are peaked in areas of formation, rounded swell away from formation regions
Wave progression Maximum development of wind waves is the result of 3 factors:
  1. Wind strength
  2. Wind duration
  3. Uninterrupted ength of ocean that wind blows over (Fetch

  4. The stronger the wind the longer the duration and fetch needed to fully develop the sea
    Rarely get fully developed seas for strongest winds
    Highest waves found around Antarctica, constant wind, uninterrupted ocean

Wave steepness and dispersal from a storm Surf prediction

See Pat Caldwell's predictions

Example: Fall 95 storm ~ 1,000 miles from Oahu

  1. Get meteorological and oceanic data from weather buoys in region
  2. Storm pressure 964 mbar, winds 50 knots, fetch 1200-1500 miles, duration only 24 hrs, not enough for a fully developed sea
  3. Swell 30 ft, period 12 seconds
  4. Wave velocity = 40 mph, group velocity = 20 mph
  5. Travel time to Oahu ~ 2days
  6. Wave height attenuation 30%/day
  7. After 1 day wave height 2/3 x 30 = 20ft
  8. After 2 days wave height 2/3 x 20 = 12ft
  9. Shoaling effect
Waves approaching the shore
  1. As wave train approaches shore "feels" bottom at depth = 1/2 wavelength
  2. Wave energy packed into shallower depth, becomes peaked
  3. Wave slows, period is constant, wavelength decreases
  4. Bottom of wave slows even more as gets shallower, wave crest moves ahead of base of wave
  5. Wave breaks when wave height to water depth ~ 3:4
Types of wave breaks Wave refraction
  1. Wave approaching coast at an angle
  2. End of wave entering shallow water slows down, rest of wave continues at full speed
  3. Wave bends towards shore (towards the slowest end)
Wave diffraction Internal waves