Bedload transport within a patchy submerged canopy with different patch density and spatial configuration

HYOUNGCHUL PARK ^* H Nepf

• Massachusetts Institute of Technology, Cambridge, United States

This study conducted laboratory experiments to investigate the bedload transport within a patchy submerged canopy across a range of patch area densities and spatial configurations. The patch area densities (ϕ_p), defined as the bed area fraction covered by patches, ranged from 0 to 0.56, and the spatial configurations varied from channel-spanning patches to laterally unconfined patches. At low area density (ϕ_p<0.3), as ϕ_p increased, more flow passed over the top of the canopy, decreasing the near-bed velocity. However, the formation of turbulent wakes around individual patches increased the near-bed turbulent kinetic energy (TKE). These opposing trends led to a mild decrease in bedload transport rate with increasing ϕ_p. In contrast, at high area density (ϕ_p>0.3), both near-bed velocity and TKE decreased with increasing ϕ_p, resulting in a sharp decrease of bedload transport rate. Further, at the same ϕ_p, channel-spanning patches were associated with lower bedload transport, compared to laterally-unconfined patches. A predictive model for bedload transport rate that incorporated both near-bed mean velocity and TKE provided a better prediction than models based only on time-averaged velocity (bed stress) or TKE.