Modeling surfzone to inner‐shelf tracer exchange

Abstract

AbstractA near‐shoreline, continuous dye release at an approximately alongshore‐uniform beach (IB09 experiment) is simulated with the wave‐resolving Boussinesq model funwaveC. The model generates surfzone eddies and transient rip currents but does not resolve inner‐shelf vertical variation or stratification. The funwaveC model reproduces well the observed surfzone and inner‐shelf dye observations over roughly 350 m cross‐shore and 2 km alongshore. Dye is advected alongshore by wave‐ and wind‐driven currents similarly in the observations and model. Near‐shoreline mean dye concentration decays downstream as a power law with similar observed (−0.33) and modeled (−0.38) exponents. Observed and modeled cross‐shore mean dye profiles are similar, though modeled inner‐shelf dye is somewhat elevated. Observed and modeled alongshore dye transports agree, though with compensating surfzone and inner‐shelf errors later in the release. For times <3.5 h (before observed and modeled dye advects beyond the model alongshore domain), observed and modeled dye budgets are similar to each other and close to within 10%, and half the observed and modeled dye is exported to the inner‐shelf. Later in the release, surfzone and inner‐shelf dye masses are under and overpredicted, respectively. Model‐data differences may be due to the model's lack of vertical variation, stratification, or tide. The good overall model‐data agreement indicates that nearshore tracer transport and dispersion are realistically simulated over 5 h and 2 km alongshore, and that the model transient rip currents accurately induce cross‐shore exchange between the surfzone and inner‐shelf.