资源环境科技发展态势分析平台

Previous studies have shown that sediment transport models based on bed shear stress (tau) are not accurate for regions with vegetation. The present study demonstrated that the inaccuracy arises from the influence of vegetation-generated turbulence. Bed-load transport rate, Q(s), and near-bed velocity were measured in a sediment-recirculating flume with model vegetation of different vegetation volume fractions (phi) and with bare sand beds. At the same tau, the measured Q(s) increased with increasing phi, suggesting that vegetation-generated turbulence, which also increased with increasing phi, was augmenting the bed-load transport. At the same near-bed turbulent kinetic energy, k(t), the Q(s) measured in both bare and vegetated channels agreed within uncertainty, suggesting that kt may be a more universal predictor of bed-load transport than bed shear stress. A tau-based bed-load transport model was reinterpreted as a k(t)-based model. The new k(t)-based model predicted the Q(s) measurements for both bare and vegetated channels.

Plain Language Summary Aquatic vegetated habitats, including wetlands and mangroves, are disappearing at an annual rate of 1% to 7%. These ecosystems provide habitat important to fisheries, enhance water quality by filtering nutrients from runoff, and also protect coastal regions from storm surge and waves. To mitigate the loss of these habitats, restoration projects import sediment to eroded areas. The success of the restoration depends on its ability to retain sediment, so that restoration design requires a good understanding of sediment transport within vegetated landscapes. However, this understanding is currently lacking, and many restoration projects fail due to unanticipated sediment loss from the restored regions. The goal of our study was to develop a predictive model for sediment transport in regions with vegetation. Using laboratory experiments with a model vegetation, we first showed that existing sediment transport models, based on studies without vegetation, underestimate by orders of magnitude the sediment transport in vegetated regions. Second, we demonstrated that the enhanced sediment transport was caused by vegetation-generated turbulence. Finally, we proposed and verified a new model for sediment transport that incorporates the role of vegetation-generated turbulence, which we believe will be an important guide for future coastal and riverine restoration projects.