Special Seminar: Young Investigator Lecture in Engineering and Applied Science

Vegetation is widely used in rivers and coastal areas to reduce erosion. However, some studies
show that under the same flow velocity, vegetation increases erosion. In this talk, I will discuss
the contradictory roles that vegetation plays regarding sediment transport (erosion). On the one
hand, vegetation slows down the flow and reduces mean bed shear stress. Because net sediment
transport rate has historically been parameterized as an increasing function of the mean bed
stress, vegetation was expected to reduce erosion. On the other hand, vegetation generates
turbulence, which correlates with the fluctuation of the instantaneous bed shear stress. Thus,
under conditions with the same velocity, channels with vegetation have higher instantaneous bed
stress than channels without vegetation, and as a result, have a higher net sediment transport rate.
I will present recent laboratory experiments on sediment transport in vegetated channels and a
turbulence-based model for sediment transport. The model can be integrated with large-scale
hydrodynamic models for predicting coastal and river channel evolution and for designing
erosion control plans.