• 1) Early wave-studies (Weber brothers, 1825) yielded 4 observations:

  • i) very little NET MOVEMENT of water; it is energy that moves
  • ii) water particles move in CIRCULAR ORBITS
  • iii) orbit diameter DECREASES with distance from surface
  • iv) waves reflect from vertical wall with NO ENERGY LOSS

• 2) First ripples form due to friction with air. Final wave height is determined by:

  • i) AVERAGE VELOCITY of wind
  • ii) LENGTH OF TIME wind blows, and
  • iii) FETCH (distance over which wind blows)

• 3) Wind waves generally fall in two categories:

  • i) SWELL (long-period 10-15s, regular, can occur WITHOUT WIND; largest confirmed swell height= 34m)
  • ii) LOCAL SEAS (='wind waves'; short-period less than 8s, irregular, ONLY occur if windy; offshore, they arise in a GENERATING AREA)

• 4) Swell can be described quite well mathematically

  • i) VARIABLES: wavelength (L, m), wave height (H, m), wave depth (D, m), period (T, sec), velocity (V, m/s), bottom depth (d, m), acceleration of gravity (g, m/s2)
  • ii) DEEP WATER WAVES (d greater than L/2) behave differently from SHALLOW WATER WAVES (d less than L/20)
  • iii) for DEEP WATER waves, velocity and length depend on PERIOD:
    V= L/T approx. 1.6T; L= VT aprox. 1.6T2; a stopwatch is all you need!
  • iv) for SHALLOW WATER waves, velocity depends only on water WATER DEPTH:
    V= sqrt(gd) = 3.1sqrt(d)

• 5) Shorelines cause waves to refract, waves break on shore when H/dapprox. 3/4 or H/L greater than 1/7 (depends on slope of bottom); whitecaps form (wave tops become unstable) when H/L is greater than 1/7

• 6) Most waves are a mix of swell and local seas. Fourier analysis can reveal the different wave components; ROGUE WAVES arise due to the unpredictable summation of several different wave trains

• 7) Giant waves: tsunamis (are NOT wind waves); the Lituya Bay wave is the largest wave ever recorded

• FURTHER READING (optional; these are great resources for helping to understand how organisms cope with life in currents & waves):

  • S. Vogel 1994. "Life in Moving Fluids: The Physical Biology of Flow". Princeton Univ. Press (2nd Ed.)

  • M.W. Denny 1988. "Biology and the Mechanics of the Wave Swept Enviroment", Princeton Univ. Press

  • M.W. Denny 1993. "Air and Water: Biology and Physics of Life's Media", Princeton Univ. Press

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