Modelling transverse solute mixing across a vegetation generated shear layer

Hydraulic Efficiency of Green-Blue Flood Control Scenarios for Vegetated Rivers: 1D and 2D Unsteady Simulations

“…In addition, it is important to emphasize here that Manning's n coefficient values resulting from the 1D hydraulic simulations (0.10-0.40 m −1/3 s) well represent the actual vegetative flow resistance induced by patchy riverine vegetation, as reported by the previous ecohydraulic studies carried out by West et al [47] and Zhu et al [48]. Their works, respectively, modeled the impacts of real-scale riverine vegetation distribution on water level argumentation and hydrodynamic dispersion within vegetated open channels under different growth conditions of riverine plants in both flume laboratory and field-scale study cases.…”

Velocity and transverse mixing in open channel flow featuring interacting vegetated shear layers

“…The finite difference solution to solve eq. 3 proposed and validated by West et al (2021) was used to identify transverse mixing coefficients based on experimental data from single bank tests. To achieve this, the recorded channel was assumed as a rectangular grid with i × j nodes, with ℎ(𝑦), 𝑈(𝑦) and 𝐷 𝑦 (𝑦) specified at each node.…”

“…Vegetated banks may also affect local transverse mixing rates by increasing velocity gradients and turbulent diffusion across the vertical water/vegetation interface, creating a shear layer over the horizontal plane Nepf 2007, White andNepf 2008). The effects of vegetation inducing horizontal shear layers on mixing have recently been studied by West et al (2021), who produced a modelling framework to describe the evolution of solute concentrations across a shear layer in a partially vegetated channel. Transverse mixing coefficients under such layers are highly heterogeneous, being enhanced within the shear layer but potentially reduced within the vegetation itself relative to the main channel due to the reduction in turbulent length scales caused by the vegetation stems (Nepf 1999, De Serio et al 2018.…”

“…In many open channel flows, vegetation occurs in patches as well as on river banks, with relatively narrow sections of free flowing, unobstructed channel. However, to date studies on mixing processes within shear layers have focused on hydraulic conditions generated by a single bank of vegetation or around isolated patches (White and Nepf 2007, Meftah and Mossa 2016aand 2016b, West 2016, West et al, 2021. To the authors' knowledge, the interaction of shear layers caused by banks on either side of the channel width has not yet been extensively studied.…”

“…Where 𝐷 𝑦 is the transverse mixing coefficient, ℎ is the water depth, 𝑥 is the lengthwise coordinate, 𝑦 is the spanwise coordinate and 𝐶 is the solute concentration. West et al (2021) proposed both continuous (semi-Gaussian) and stepped distributions of transverse mixing coefficient over the shear layer region, and the parametrisation of the distribution properties was performed using the measured profiles of primary velocity by optimising the fit between measured and predicted concentration profiles using eq. 3.…”