Field Study on Flow Structures Within Aquatic Vegetation under Combined
Current and Wind-driven Wave Conditions
Field measurements were conducted to study the influence of aquatic
vegetation on flow structures in floodplains with the hydrodynamic
conditions dominated by combined current and wind-driven wave. Wave and
turbulent flow velocity components were decomposed from the time series
of instantaneous velocity and analyzed separately. With the ratio of
wave excursion to stem spacing less than 0.5, the interaction between
wave and vegetation was weak in present study, leading to the vertical
distributions of time-averaged velocity (Uhoriz) and turbulent kinetic
energy (TKE) with the presence of vegetation similar with the vegetated
flow structures under pure current conditions. For emergent vegetations,
Uhoriz and TKE distributed uniformly through the entire water column or
increased slightly from bed to water surface. Similar distributions were
present in the lower part of submerged vegetations. Within the upper
part of submerged vegetations, Uhoriz and TKE increased rapidly toward
water surface and TKE reached its maximum near the top of vegetation.
With small Ew/S the wave orbital velocity (Uw) within vegetation was not
attenuated when compared with the Uw above vegetation, and Uw through
the entire water column can be predicted by the linear wave theory.
However, wind-driven waves made the turbulence generated near the top of
canopy penetrate a deeper depth into vegetation than predictions under
pure current conditions.