Test and Evaluation of Surf Forecasting Model

A model forecasting wave height and longshore current distribution inside the surf zone is applied to an extensive set of laboratory and field data for testing and modification. The models are tested on planar beaches as well as barred beaches for a variety of wave conditions. The wave transformation model is based on solving the energy flux equation using a bore dissipation mechanism and describing the random wave heights with the Rayleigh distribution. The two model parameters, B and gamma, where B describes the amount of foam of a breaking wave and gamma is the proportionality constant which relates the rms wave height to the water depth, are combined into a single parameter BG. BG is shown to be a function of deep water surf similarity parameter. Applied to the present data sets, the rms error of the measured wave height and the model predicted wave height was usually less than 9% and ranged from 1.5% to 15.7% with a mean of 5.3% and a standard deviation of 3.1% for the whole 74 data sets. The wave transformation model is highly robust in describing the wave height distribution in the surf zone. The longshore current model is based on solving the steady state, alongshore momentum balance for straight and parallel contours using the radiation stress concept. The model requires specifying the bed shear stress and turbulent mixing coefficients. Applied to the present data sets the rms error between the measured and modeled longshore current values ranged from 4.5% to 55.5% with a mean of 24.6%. Turbulent mixing is not required for planar beaches, but is required for barred beaches to describe the longshore currents inside the surf zone. Theses.