A vortex-based model of velocity and shear stress in a partially vegetated shallow channel

This paper presents a method for predicting the distributions of velocity and shear stress in shallow channels with a boundary of emergent vegetation. Experiments in a laboratory channel with model vegetation show that the velocity profile exhibits a distinct two-layer structure, consisting of a rapidly varying shear layer across the vegetation interface and a more gradual boundary layer in the main channel. In addition, coherent vortices are observed which span both layers, and are the dominant contributors to lateral momentum fluxes. From these observations, we propose a model for the vortex-induced exchange and find expressions for the width of momentum penetration into the vegetation, the velocity and shear stress at the vegetation edge, and the width of the boundary layer in the main channel. These variables, along with a momentum balance in the main channel, comprise a modeling framework which accurately reproduces the observed velocity and shear stress distributions. The predictions for the velocity and shear stress can provide a basis for modeling flood conveyance, overbank sediment transport, and scalar residence time in the vegetated layer

Flume experiments of sediment resuspension in wetland vegetation under wave-current conditions

Understanding suspended sediment transport over salt marshes is key to understanding their resilience to adverse conditions (e.g. sea level rise). Salt marshes are vegetated coastal wetlands in the intertidal zone , which contribute to coastal protection . Their vegetation modifies flow patterns, dampens wave action, and triggersturbulent eddies in its wake. The turbulence resuspends fine particles, which are then transported over the marsh. Our interest lies in identifying the threshold for sediment resuspension under wave current conditions using laboratory experiments , i.e. finding the minimum current and wave velocities under which resuspension occurs. The threshold has previously been studied in conditions with only currents (Liu et al., 2021 and or waves (Tinoco & Coco, but not yet in combination. Identifying this threshold helps to understand when sedimen

Patches in a side-by-side configuration: a description of the flow and deposition fields

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger

A comparison of two- and three-dimensional wave breaking

Journal of Physical Oceanography2871496-151

Flume experiments of vegetation-induced sediment resuspension under combined wave-current flows

Salt marshes and other vegetated foreshores are valuable ecosystems for coastal protection, but they may grow and retreat over time. Salt marshes are intertidal wetlands, whose vegetation attenuates waves, currents and stabilizes foreshores, thereby reducing the load on dikes (Vuik et al., 2016). They also sequester carbon and are an important habitat for marine flora and fauna. Fine sediments are the core of a salt marsh. These are brought in by tides and waves and are deposited on and around the marsh. Understanding the sediment transport dynamics is essential in order to predict the morphological evolution of the marshes and the future protection that salt marshes will provide.Vegetation modifies sediment transport dynamics compared to a bare bed. The vegetation modifies flow structure and produces turbulent eddies in its wake. It has been shown for pure currents (Liu et al., 2021; Tinoco & Coco, 2014) and pure waves (Tinoco & Coco, 2018) flows that these eddies reduce the velocity threshold for sediment resuspension, but it remains unclear how sediment resuspension responds to combined wave-current flows commonly found in estuaries. Our goal is to understand and quantify sediment resuspension under combined wave-current flows using flume experiments