Numerical study of sediment transport on a tidal flat with a patch of vegetation

Abstract

To understand how vegetation canopies affect sediment transport on tidal flats, a numerical study of tidal flow and sediment transport on an idealized tidal flat with a patch of vegetation is conducted. The numerical model is firstly validated by laboratory measurements of flow and sediment deposition in a partially vegetated open channel. The idealized study shows that a finite patch of vegetation may produce circulation on the tidal flat with converging flow during flood and diverging flow during ebb. The vegetation patch can also generate a tidal phase lag between the vegetated and bare flats. Tidal currents in both zones are asymmetric, with stronger flood current in the vegetated zone and stronger ebb current on the bare flat. The duration of ebb is longer than that of flood. Computed sediment concentration on the bare flat is higher during ebb due to stronger ebb current and larger bottom shear stress. This is in contrast to the tidal flat without a vegetation canopy, where suspended sediment concentration is higher during flood. On the tidal flat without a vegetation canopy, landward net sediment transport occurs on the upper flat, while seaward net sediment transport occurs on the lower flat and subtidal region. On the partially vegetated tidal flat, however, net sediment transport on both the upper and lower flats are in seaward direction. It increases with increasing vegetation density. Alongshore net sediment flux converges inside the canopy and diverges on the bare flat. Sediment exchange rate between the vegetated and bare flats increases with decreasing vegetation density and sediment settling velocity.

Tidal flats of recent origin: distribution and sedimentological characterization in the estuarine Cruces River wetland, Chile

“…They are generally associated with extensive areas covered with Schoenoplectus californicus (totora) and Spartina densiflora (commonly known as espartina), which are assigned a major ecological value, because of their fundamental role as environmental engineers. These macrophyte species, model and stabilize the wetland shores against external hydraulic stress factors (Valdovinos et al, 2010), and capture suspended material in their canopy structures (Madsen et al, 2001;Bouma et al, 2005;Leonard & Croft, 2006;Anthony, 2008;Ma et al, 2014). Therefore, the occurrence and (Fig.…”

The World of Edges in Submerged Vegetated Marine Canopies: From Patch to Canopy Scale

“…As reported by Chung et al [11], the development of momentum in a vegetated patch is governed by the increased pressure at the canopy front, which occurs on a rapid timescale, while the development of turbulence requires the shear-induced structure above the canopy to grow in size until it reaches the water surface. The vegetation patch can also generate a tidal phase lag between the vegetated and adjacent bare flats with stronger flood currents in the vegetated zone and stronger ebb currents as on the adjacent bare flat [104].…”

Impact of a high rainfall event on the water level, current velocity, and total suspended solids in tidal flats environments of the estuarine Cruces River wetland, south-central Chile

“…emerging structures at site 2; that would result in higher current velocities than at site 1, where vestigial tree trunks probably slow down current velocities and thus, promoting lower resuspension of sediments and concentrations of TSS (e.g. Friedrichs et al 2000, Perillo 2003, Bouma et al 2007, Ma et al 2014.…”