Waves
Wind Waves, Surf, and Tsunami

How does a wave form?
• Wind blowing across calm water - capillary waves
– Generating force = wind; restoring force = surface tension
• Roughened surface = more friction
– As wind speed increases - wave becomes larger
– Restoring force => changes from surface tension to gravity
– Chop
– swells

Parts of a Wave
• Wavelength
• height
• Crest
• trough
• amplitude
• Frequency - # of waves passing a fixed point in a given length of time
• Period - time for successive crests or troughs (1 wavelength) to pass a fixed point

Wave Motion
• wave energy, NOT the water particles move across the surface of the sea
• How do waves move
– circular orbit
– diameter of the orbit equaling wave height.
– wave base

Wave Speed
• The speed or celerity of the wave is equal to
– C (celerity) = L (wavelength) / T (wave period)
– longer wavelength and longer period waves create a larger C or speed
– Speed may change but period remains the same

Deep-Water Waves
• DWW’s - Water > 1/2 L
• Progressive wind waves
• Free waves - dispersion
• Swell

Wave Height
• Wind speed
• Wind duration
• Fetch (the distance over which the waves are generated)
• What is the maximum wave size?

Wave Energy and Steepness
• Wave energy is proportional to wave height
• Potential energy versus kinetic energy
• Wave Steepness => S(Steepness) = H(height)/L(length)
• > 1:7 = too steep and wave becomes unstable and breaks

Shallow-Water Waves
• SWW’s occur when D < L/20
• Wave speed depends entirely on depth: C = square root of gXD
• Orbits of water molecules become elliptical
Waves Approaching Shore
• Refraction
• Diffraction
• Reflection

Waves Approaching Shore - Surf
• As a wave goes from deep water to shallow water
– C and L decrease as depth decreases - waves bunch up
– H increases
– Wave becomes unstable and breaks

Waves Approaching Shore - Surf
• Spilling Breakers
• Plunging Breakers
• Surging Breakers

Energy Release and Storm Waves
• Storm waves release enormous amounts of energy on a coastline
• Storm Surge
• Storm wave base versus normal wave base
• Coastline morphologies and offshore features = the result of storm waves…

Tsunamis
• Seismic sea waves - displacement on the ocean floor during earthquake
• Waves produced with extremely long L’s (100 km +)= shallow water wave
• Bunch up with wave height increasing as they approach shore

Wave Energy - A potential resource?