Characterizing natural riparian plant stands for modeling of flow and suspended sediment transport

Riparian vegetation imposes a critical control on transport and deposition of suspended sediment with important implications on water quality as well as channel maintenance. With a view on hydraulic and morphological modeling needs, the objective of this paper is to enhance the parameterization of foliated riparian vegetation and to determine how the properties of plant stands affect the erosion and deposition of suspended sediment on a naturally vegetated floodplain. We show that the drag forces of woody plants can be reliably predicted with a parameterization that takes into account their flexibility-induced reconfiguration and complex structure. Based on field investigations in a vegetated compound channel, a multiple regression model was constructed to explain the net deposition and erosion under vegetative conditions ranging from almost bare soil to sparse willows and dense grasses. Net deposition was positively correlated with the cross-sectional vegetative blockage factor and negatively correlated with the distance from the suspended sediment replenishment point, indicating that longitudinal advection was the most important mechanism supplying fine sediment to the floodplain plant stands under real field conditions. Deposition increased with decreasing flow velocity
within the natural stands. As an implication to hydraulic and morphological modeling, the proposed drag force parameterization can be easily implemented into model codes to improve the description of flexible, foliated vegetation. The paper concludes by providing guidance on how floodplain vegetation can be maintained to manage the erosion and deposition of suspended sediment.