In the larger sense a littoral cell is a three component system characterized by a sediment source, transportation zone, and a sediment sink. However, within a littoral system there are smaller wave-powered circulation systems.

Similar to a littoral cell is a sediment compartment which is an isolated system typically, but not always, contained between two headlands. The beach is concave facing the shore and there is little net longshore transport in or out of the system. A sediment compartment by contain one or more littoral cells.

• Wave generated coastal currents
  • Coastal cells or circulation systems are a necessary product of the mass balance of water in the shore zone (energy inflow = energy outflow)
• Mass Transport
  • When ocillatory waves breaks (d = 1.2 Hb) there is a mass transport of water towards the shore producing shore normal on-shore currents. However whatever water moves shoreward must also return back to the ocean either as a rip current or under tow (mid depth return flow).
  • Mass transport is a function of wave power; the rate at which energy is supplied to the shore per unit wave crest

  P_N = ECn-P_L

  where E=wave energy, C=wave phase velocity,
  n=group phase velocity (n=.5 for deep water waves; =1 for shallow water)

  • Terms
  • Swash: the uprush of water on the shore
  • run-up: the elevation to which wave swash runs up the shore
  • function of : breaker type, angle of wave approach, beach slope, inshore wave interference
  • run-up is least for spilling waves
• Return Flow
  • Mid-depth return flow
  • rip currents
• Long shore current
  • The long shore current, responsible for long shore transport, is the component of mass transport that is deflected along the shore. The longshore current increases with wave power and the angle of wave approach (a)

P_L (long shore wave power) = ECn (sin a cos a)

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Lindley Hanson/email /Gls214

Department of Geological Sciences, Salem State College, Salem, MA
last updated 5/19/03