Combined Wave and Current Bottom Boundary Layers: A Review
Abstract This Coastal and Hydraulics Engineering Special Report (SR) presents a general review of research in combined wave and current bottom boundary layers including laboratory, field and model studies. The purpose of this SR is to chronicle the state of the art in boundary layer research in order to identify research gaps and obtain guidance for developing and improving the next generation of combined wave and current bottom boundary layer models. One of the key research focus areas identified in this report is fine grained sediment transport processes in combined wave and current flows. Critical research gaps exist in the following areas: (1) the role of oblique waves and currents on bottom stress and flow kinematics, (2) the effect of wave asymmetry in combined flows and how this drives mass transport, (3) the process of wave transition in shallow water in the presence of strong alongshore currents, (4) the interaction between oblique waves and currents over a sediment bottom, and (5) the validity and performance limitations of existing bottom boundary layer models under the above conditions. Progress towards understanding these research questions hinges on experimental programs to measure sediment, waves, morphology, and currents under a range of forcing conditions.