Laboratory Investigation of Vegetation-Generated Turbulence and Its Influence on Bedload Sediment Transport

Abstract:

Sediment transport in vegetated regions can be underestimated by orders of magnitude with classic bed-shear-stress models. Recent studies (Tinoco and Coco, 2016; Yang et al., 2018) have attributed this to turbulence generated by the vegetation and suggest that sediment transport in vegetated regions can be better described as a function of turbulent kinetic energy (TKE). Most previous studies of sediment transport in vegetated channels used model stems of a single diameter and did not consider the possible role of stem size. A larger stem diameter creates a larger turbulent eddy that interacts with bed particles for a longer duration of time, which may enhance particle dislodgement and channel-scale sediment transport. Laboratory experiments were conducted to study the turbulence generated by model rigid emergent vegetation and its influence on bedload sediment transport. Variation in stem diameter, solid volume fraction (SVF), flow velocity, and flow depth were considered. Results confirmed that larger stem diameters produce larger turbulent eddies, but at the same SVF, the magnitude of TKE was not strongly dependent on the stem diameter and the flow depth. Further, the channel-scale bedload transport rate had no clear dependence on stem size, but correlated strongly with TKE.