Flow Structure in and above the Various Heights of a Saltmarsh Canopy: A Laboratory Flume Study

Abstract

Flow velocity profiles were measured in and above varying height (80%, 60%, 40% and 20%) of Spartina anglica canopies (350 stems m^-2) in a flume. Results demonstrate the flow complexity in and above the various heights of the canopy. The shapes of the measured velocity profiles were generally controlled by the canopy height. Furthermore, in the lower part of the canopy there is a reversal of the flow velocity gradient ∂ū/∂z, resulting in a secondary flow velocity maximum in the Spartina anglica canopy. This suggests that turbulent stress is transported downward from the upper part of the plants within-canopy. Above the canopy, the velocity distribution is semi-logarithmic. The physical implications, especially for the entrainment of cohesive sediment, are speculated.