FLOW STRUCTURE IN AND ABOVE THE VARIOUS HEIGHTS OF A SALT-MARSH CANOPY - A LABORATORY FLUME STUDY

Flow velocity profiles were measured in and above varying height (80%, 60%,40% and 20%) of Spartina anglica canopies (350 stems m-l) in a flu me. Results demonstrate the flow complexity in and above the various h eights of the canopy. The shapes of the measured velocity profiles wer e generally controlled by the canopy height. Furthermore, in the lower part of the canopy there is a reversal of the flow velocity gradient partial derivative ($) over bar u/partial derivative z, resulting in a secondary dow velocity maximum in the Spartina anglica canopy. This s uggests that turbulent stress is transported downward from the upper p art of the plants within-canopy. Above the canopy, the velocity distri bution is semi-logarithmic. The physical implications, especially for the entrainment of cohesive sediment, are speculated.