Erosion by Wave Action of Consolidated Cohesive Bottom Containing Cohesionless Sediment

Abstract

The erosion processes of consolidated cohesive sediment under irregular breaking waves were formulated to predict the profile evolution of a cohesive sediment beach with a layer of sand. The cohesive sediment is eroded by turbulence generated by wave energy dissipation caused by wave breaking and bottom friction. Sand released from the eroded sediment is transported onshore or offshore by wave action. The cohesive sediment erosion rate is increased by a thin mobile layer of sand and decreased by a thick sand layer. The complicated interactions of waves, sand and cohesive bottom were simplified and incorporated into an existing cross-shore numerical model. The model was compared with flume experiment data with measured till erosion rates on the order of 0.05 cm/h. The calibrated model was used to simulate the temporal change of the till erosion rate for a duration of 100 h. The scale effect was examined in hypothetical prototype tests of the same till with a length ratio of 1/4. The prototype 200-h simulations predicted much larger till erosion near the shoreline and sand deposition in the surf zone. The model will need to be compared with actual field data.