Episodicity in Longshore Sediment Transport

Seven West Coast sites are selected having from one to three years of nearshore directional wave measurements several times a day during the period 1979–82. Time series of daily net longshore transport are estimated using the energy flux method, based upon measured Sxy. Investigations are made on frequency and cumulative distributions of transport, and from these, a number of statistics characterizing the degree of episodic transport are generated. The transport is found to be very episodic, with almost half of the gross transport occurring during only 10% of the time. The maximum transport occurring in a single day each year produced between ten times, and more than 600 times, the mean daily net transport. Inferences concerning the design requirements for sand bypass systems are drawn from the statistics of episodicity.