Neumeier U. & Amos C.L. (2006) The influence of vegetation on turbulence and flow velocities in European salt-marshes. Sedimentology, 53/2, 259-277.
Flow hindrance by salt-marsh vegetation is manifested in the structure of the
tidal current; it has a significant impact on sediment transport and it has been
related to increased sediment accretion. The flow characteristics in three
different vegetation types (Spartina maritima, Sp. anglica and Salicornia sp./
Suaeda maritima) were measured on three salt-marshes in Portugal and
England. These in situ measurements differ from laboratory flume experiments
with ‘clean’ vegetation by the complexity of natural canopies. Skimming flow
develops above the Spartina canopy when the vegetation is fully submerged.
In this situation, a low turbulence zone with nearly constant velocity in the
denser canopy is separated from the skimming flow above by an interface
characterized by high Reynolds stresses. In the low turbulence zone, a positive
relationship exists between turbulence intensity and shoot density, which is
due to wake turbulence generated locally in the canopy. The rate of particle
settling should be increased in that zone. The lower limit of skimming flow is
best predicted by the height within the canopy that includes 85% of the
biomass. For emergent Spartina canopies and the short Salicornia/Suaeda
marsh, the maximal velocity-gradient is shifted upwards compared to a
standard boundary layer over bare sediment and the turbulence is attenuated
near the bed, but to a lesser extent than for fully submerged Spartina canopies.
A turbulence reduction near the bed was observed in all measured profiles;
that should enhance sediment deposition and protects the bed against
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