Modelling algae transport in coastal areas with a shallow water equation model including wave effects

The transport of algae in the marine environment is becoming a major issue for integrated sustainable coastal management and can be nowadays investigated through numerical modelling. The Shallow Water Equations are a suitable tool for this purpose. In the framework of the present study, they are used to perform predictions of algae transport in the vicinity of a harbour, combined to a 3rd generation spectral wave model to take account of near-shore currents induced by wave breaking in the surf zone. The simulated paths of algae have been proved to be very sensitive to the effects of those wave-induced currents and exhibit a behaviour in acceptable agreement with on site observations. In particular, the effects of waves on currents is required to qualitatively predict the large recirculation pattern observed in the vicinity of one of the dykes of the harbour. This recirculation is suspected to be one of the major mechanisms of algae dynamics in this area of the coast. Stochastic (random-walk) diffusion was also tested to account for local dispersion of algae due to large turbulent eddies.