The impact of submersed aquatic vegetation on the development of river mouth bars

Abstract

This work is inspired by the sudden resurgence of the submersed aquatic vegetation (SAV) bed in the Chesapeake Bay (USA). Because the SAV bed occurs at the mouth of the Bay's main tributary (Susquehanna River), it plays a significant role in modulating sediment and nutrient inputs from the Susquehanna to the Bay. Previous model studies on the impact of submersed aquatic vegetation on the development of river mouth bars lacked a complete mechanistic understanding. This study takes advantage of new advances in 3D computational models that include explicit physical‐sedimentological feedbacks to obtain this understanding. Specifically, we used Delft3D, a state‐of‐the‐art hydrodynamic model that provides fine‐scale computations of three‐dimensional flow velocity and bed shear stress, which can be linked to sediment deposition and erosion. Vegetation is modeled using a parameterization of hydraulic roughness that depends on vegetation height, stem density, diameter, and drag coefficient. We evaluate the hydrodynamics, bed shear stresses, and sediment dynamics for different vegetation scenarios under conditions of low and high river discharge. Model runs vary the vegetation height, density, river discharge, and suspended‐sediment concentration. Numerical results from the idealized model show that dense SAV on river mouth bars substantially diverts river discharge into adjacent channels and promotes sediment deposition at ridge margins, as well as upstream bar migration. Increasing vegetation height and density forms sandier bars closer to the river mouth and alteration of the bar shape. Thus, this study highlights the important role of SAV in shaping estuarine geomorphology, which is especially relevant for coastal management. © 2019 John Wiley & Sons, Ltd.

The Impact of Submerged Breakwaters on Sediment Distribution along Marsh Boundaries

“…Breakwater effects on sediment supply to salt marsh were modelled under different scenarios of waves and tide conditions. This same numerical modelling approach has already been used to investigate the impact of waves on coastal morphology [28,29], estimate the effect of tides on the alternative deposition of mud and sand [30], examine the influence of vegetation on bars evolution [31], and simulate wave propagation in harbors [32].…”

Effect of offshore waves and vegetation on the sediment budget in the Virginia Coast Reserve (VA)

“…For rigid vegetation, such as that in salt marshes dominated by S. alterniflora, Delft3D uses the equations proposed by Baptist (2005). In the case of flexible Z. marina, Delft3D assumes a greater degree of roughness (Lera et al, 2019).…”

“…Vegetation produces multiscale interactions with flow and sediment transport (Fagherazzi et al, 2004(Fagherazzi et al, , 2013Moore, 2004;Larsen and Harvey, 2010;Nardin and Edmonds, 2014;Lera et al, 2019). Models have supplied quantitative approaches to vegetation-sediment feedback related to emergent marsh vegetation (Temmerman et al, 2005;Nardin et al, 2016) or seagrasses (Newell and Koch, 2004;Carr et al, 2010;Folmer et al, 2012).…”

Biogeomorphology, quo vadis? On processes, time, and space in biogeomorphology

“…Möller et al ., 2014; Spencer et al ., 2016; Lokhorst et al ., 2019; Yuan et al ., 2019), and numerical modelling (e.g. Fagherazzi et al ., 2012; D'Alpaos and Marani, 2016; Nardin et al ., 2018, 2020; Lera et al ., 2019).…”