Representing kelp forests in a tidal circulation model

The presence of kelp beds in the water column generates drag to flows and modifies hydrodynamic processes. In this paper we examine the modifications of tidal flows in the Hecate Strait by including an explicit representation of the kelp-induced drag in a three-dimensional numerical model. The model is evaluated against a theoretical solution and it agrees well with the theory. Model results show that kelp beds significantly change tidal circulation structures by damping tidal velocity by 40-80% in interiors of the beds, but enhancing tidal velocity by 15% along the edges. Comparing terms in momentum equations shows that the momentum flux caused by the kelp drag is able to become a dominant term with a magnitude comparable to that of the horizontal pressure gradient. Simulating the effects of kelp beds on particle trajectories shows that the drag due to kelp-beds decreases the dispersion rate of particles in the interiors of kelp forests, but increases the dispersion rate along the edges. Kelp beds form barriers along the edges and prevent particles from outside entering the interiors of kelp beds. The dispersion rate is in an inverse relationship to the kelp density in kelp-bed interiors, while in a positive relationship to the kelp density along edges.