2B.4A: Waves and Beach Morphology

• Wave length

  Horizontal distance from crest to crest (or trough to trough)
• Wave frequency

  Number of waves passing a particular point over a given period of time
• ​Waves in open sea

  • Waves are simply energy moving through water
  • The water itself only moves up and down, not horizontally
  • There is some orbital water particle motion within the wave, but no net forward water particle motion
• Wave size depends upon:

  • the strength of the wind
  • the duration for which the wind blows
  • water depth
  • wave fetch
  • this is the uninterrupted distance across water over which the wind blows, and therefore the distance waves have to grow in size. 
• Nearshore

  • Long and shallow
  • Friction slows down the wave and releases energy
• Destructive (plunging) Waves

  • High energy waves
  • Large wave height (>1 m)
  • Short wavelength (about 20 m)
  • High wave frequency (13-15 per minute)
• Destructive (plunging) Waves

  1. Strong backwash erodes material from the top of the beach

  2. Carrying down the beach to the offshore zone

  3. Deposited as an offshore ridge or berm
• Constructive waves alter beach morphology


  1. Cause net movement of sediment up the beach

  2. Steep the beach profile

  3. Produce berms at the point where the swash reaches the high tide line
• Berm


  A ridge of material across the beach
• Swash


  Carries sediment of all sizes up the beach
• Backwash


  Can only transport smaller particles down the beach
• Q: What is a wave?

  A: A wave is the transfer of energy from one water particle to its neighbor, with individual particles moving in a circular orbit. The size of the wave particle orbit decreases with depth.
• What determines the height of a wave?

  Wave height is determined by the energy transferred from the wind and the water depth. It is the vertical distance from peak to trough.
• What factors influence wave size?

  Wave size depends on the strength of the wind, the duration for which the wind blows, water depth, and wave fetch (the uninterrupted distance over which the wind blows).
• How do waves break at the shore?

  Waves break when their depth is 1/2 of their wavelength. The friction with the sea bed distorts the wave, slows it down, and causes it to topple forward.
• What are constructive waves?

  Constructive waves are low-energy waves with a low, flat wave height, long wavelength, and low wave frequency. They have a stronger swash than backwash, pushing sediment up the beach and creating berms.
• How do constructive waves affect beach morphology?

  Constructive waves cause a net movement of sediment up the beach, steepening the beach profile, and creating berms made of sediment, with larger particles at the back and smaller ones near the sea.
• What are destructive waves?

  Destructive waves are high-energy waves with large wave height, short wavelength, and high wave frequency. They have a strong backwash that erodes material from the beach and transports it offshore.
• How do destructive waves affect beach morphology?

  Destructive waves produce a net movement of sediment down the beach, flattening the beach profile. They also create offshore ridges or berms and transport sediment towards the offshore zone.
• What is the difference between sea waves and swell waves?

  Sea waves are produced by local winds and vary in height and direction. Swell waves are created when wind energy dissipates, and they can travel long distances before losing energy. They can produce waves even when there is no wind at the coast.
• How do seasonal variations affect beach profiles?

  In winter, destructive waves dominate, spreading shingle over the beach and forming offshore ridges. In summer, constructive waves dominate, steepening the beach profile and sorting particles by size.
• How does tidal variation influence beach morphology?

  During spring tides, the high tide occurs twice a month, creating berms at higher points on the beach. Neap tides create lower high tides, which produce berms at lower points, and as the tide rises, previous berms are destroyed.
• What is wave fetch?

  Wave fetch is the uninterrupted distance over which the wind blows. A larger fetch allows more energy to be transferred to the water, leading to larger waves.