ABSTRACT Proposal Number: CTS-9734109 Principal Investigator: Cox This CAREER grant is for the study of breaking waves. Wave breaking is the dominant process in the surf zone, but our understanding of the effects of wave breaking on the cross-shore wave transformation, undertow, and bottom boundary layer processes is rudimentary. The design of coastal engineering structures, predictions of nearshore wave and current conditions for amphibious landing, beach renourishment projects, and predictions of the suspension and transport of sediments all require a clear understanding of these processes. The study will focus on time-dependent and time-averaged fluid motion in the bottom boundary layer under shoaling and breaking waves in order to develop a new turbulent boundary layer model in the nearshore zone. The methodology will employ a hybrid approach of numerical modeling and laboratory experiments. The numerical modeling will consist of a time-dependent boundary layer model to second order with a one-equation turbulence closure scheme and will include pressure gradient effects due to the wave setup. In parallel with the development of the numerical model, detailed laboratory measurements will be made of the flow in the bottom boundary layer under breaking waves for the realistic case of irregular waves breaking over a barred beach. The data will be used to guide the development of the model by assessing the relative importance of each of the five terms in the turbulent kinetic energy transport equation and for the empirical coefficients used in the numerical model. It is emphasized that this type of detailed data is non-existent for the surf zone and that many surf zone models employ empirical coefficients that were obtained for steady flow conditions without wave breaking. Nevertheless, it essential to include the effects of the wave generated turbulence introduced into the bottom boundary layer inside the surf zone. In addition to studying the processes on short time scale s (on the order of the wave motion), an existing time-averaged surf zone model will be improved significantly using the same data set so that this model can be incorporated with confidence into practical sediment transport models on longer time scales (on the order of several hundred to several thousand wave periods, representing a large storm event). .
