Modeling the Impact of Riparian Vegetation on Flow Structure and Bed Sediment Distribution in Rivers

Abstract

The effect of instream vegetation growth has largely been ignored by hydrological and geomorphological research in river environments, which focused instead on the function of riparian vegetation as a regulator of bank stability or as a buffer for dissolved and particulate matter entering the channel from the hillside. However, in many lowland streams, instream vegetation can be very intensive, resulting in high biomass levels during the growing season. Instream plants have a significant influence on the dynamics of flow, sediment, and nutrients. Plant growth can cause increased frictional resistance to flow and can have a short-to medium-term effects on the geomorphology of the channel. Additionally, plant development influences the velocity of river flow, affects sedimentation dynamics and increases flood risk. To achieve a balance between flooding and ecological management of rivers in the presence of vegetation, a reliable method is required to predict the resistance of channels. In the current study, a two-dimensional hydrodynamic and morphodynamic model is developed and applied using a new scaling expression of shear stress based on vegetation characteristics. These first attempts at field simulations showed qualitatively acceptable results and demonstrated the effectiveness of the model in predicting hydraulic parameters in the presence of vegetation. This model is useful in predicting the effect of vegetation on stream flow and river morphology, as well as in managing flood hazards and stream ecology.