Flow Structures Within Aquatic Vegetation under Combined Current and
Wind-driven Wave Conditions: Field Observations in Floodplains of Poyang
Lake, China
Abstract
Field measurements were conducted in floodplains of Poyang Lake (China)
to study the influence of aquatic vegetation on flow structures under
combined current and wave conditions. Wave and turbulent velocity
components were decomposed from the time series of instantaneous
velocity and analyzed separately. With weak wave-plant interaction,
indicated as the ratio of wave excursion to stem spacing Ew/S
< 0.5 in present study, the vertical distributions of
time-averaged velocity (Uhoriz) and turbulent kinetic energy (TKE) with
the presence of vegetation were similar to that under pure current
conditions. For emergent conditions, Uhoriz and TKE distributed
uniformly through the entire water column or increased slightly toward
the water surface. Similar distributions were present in the lower part
of submerged vegetation, above which the Uhoriz and TKE increased with
increasing distance to bed bottom and TKE reached its maximum near the
top of vegetation. With small Ew/S the wave orbital velocity (Uw) was
not attenuated within vegetation compared with that above the vegetation
or near the water surface, and Uw through the entire water column can be
predicted by the linear wave theory. However, the turbulence generated
near the top of canopy can penetrate a deeper depth into vegetation with
the presence of wind-driven waves than without.