Numerical Model of Longshore Current for Bar and Trough Beaches

This paper describes a numerical modeling system called NMLONG that was developed to calculate the wave height, wave direction, mean water level, and steady‐state time‐averaged longshore current velocity across a multiple bar and trough beach profile. The modeling system includes the longshore current and change in mean water surface elevation produced by waves and wind, lateral mixing, wave driving by monochromatic or random waves as options, linear or quadratic bottom friction law as options, and wave‐current interaction as an option. The principal requirement for use of the model is longshore uniformity in bathymetry and waves. Verification against laboratory and field measurements of the wave height, longshore current, and mean water surface elevation (laboratory only) indicates that default values of the model calibration parameters should be acceptable for most engineering applications. Techniques are employed to minimize computer execution time, including efficient time averaging of the nonlinear bottom friction stress and a skillful first approximation in the iterative solution of the longshore current using the nonlinear bottom friction law, allowing the model to run effectively on a desktop computer.