Erosion of Cohesive Bottom Consisting of Sand and Clay by Wave Action on Beach

 

Presented by

Tingting Zhu

Ph.D. Student

Center for Applied Coastal Research

 

ABSTRACT

The erosion processes of consolidated cohesive sediment under irregular breaking waves are 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 are simplified and incorporated into an existing cross-shore numerical model.  The model is compared with flume experiment data with measured till erosion rates of the order of 0.05 cm/h.  The calibrated model is used to simulate the temporal change of the till erosion rate for the duration of 100 h.  The scale effect is examined in hypothetical prototype tests of the same till with a length ratio of 1/4.  The prototype 200-h simulations predict 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.

 

REFERENCE

Kobayashi, N. and Zhu, T. (2020), “Erosion by Wave Action of Consolidated Cohesive Bottom Containing Cohesionless Sediment.” Journal of Waterway, Port, Coastal and Ocean Engineering, ASCE, 146(2), 1-8

Zhu, T. and Kobayashi, N. (2019), “Erosion of Consolidated Cohesive Bottom Containing Cohesionless Sediment by Wave Action on Beach.” Research Report No. CACR-19-01, Center for Applied Coastal Research, University of Delaware, Newark, Delaware