Accounting for vegetation turbulence in a morphodynamics model of a delta.

Abstract:

Vegetation plays a complex role in fluvial morphodynamics. As a source of flow resistance, it may reduce near-bed flow velocity and thereby lower the bed stress that contributes to sediment transport capacity. However, the presence of vegetation may also lead to increased sediment transport rates. Recent research identifies different mechanisms that either increase sediment entrainment or reduce deposition, including turbulence generated from flow around stems and leaves. These effects are not typically included in morphodynamic models, which typically only consider vegetation to reduce sediment transport. In this study, we simulate a field-scale delta in Delft3D with a modified sediment transport algorithm that incorporates estimates of turbulence that is generated by flow through vegetation. We find that this addition leads to altered morphodynamics relative to traditional implementations of vegetation based on bed-stress. The biggest differences are located at distributary channel margins. Our model results are placed in context relative to field measurements of flow and sediment transport in coastal Louisiana marshes.