An approximate solution to the flow field on vegetated intertidal platforms: Applicability and limitations

Abstract

Tidal wetland evolution is governed by interactions between topography, vegetation, and the flow field. Aiming to provide an appropriate hydrodynamic tool within a long‐term geomorphic model of vegetated wetlands, we describe an approximate procedure to model the depth‐averaged flow field on vegetated intertidal platforms. The procedure is tested by a qualitative comparison with laboratory experiments and quantitatively comparing with a numerical model, focusing on the influence of spatial variations in friction on the flow field. Overall, satisfactory comparisons are obtained. Nevertheless, some limitations of the approach are apparent. These are discussed in the light of the model assumptions. We analyze the impact of the observed limitations on the ability of the approximate solution to describe the morphodynamic evolution of the bed elevation. This is performed by evaluating the changes in the bed elevation after one tidal cycle on the intertidal platform based on flow velocities obtained with a numerical model and those of the simplified procedure. It is found that the bed evolution on the platform is reasonably described with the approximate solution, even though the accumulation of sediment is underestimated near the watershed divide by the approximate model. Taking into account the computationally economic character of the approximate procedure, the analysis indicates that the model provides a suitable tool to investigate the long‐term morphodynamic evolution of tidal wetlands.

The shaping role of self-organization: linking vegetation patterning, plant traits and ecosystem functioning

“…In contrast to this positive effect at the small scale, the formation of turbulence around vegetation patches can reinforce wave impact, largely preventing plant colonization at a larger spatial scale (such scale depends on the neighbouring vegetation patches). This long-range negative effect has been confirmed by previous studies based on models and field observations on hydrodynamic conditions next to vegetation patches in intertidal salt marshes [31,59]. Taken together, the short-range facilitation and long-range inhibition are coupled and self-reinforced by the colonization and growth of plants, thus exhibiting a clear SDF.…”

“…These contrasting plant performances can be explained by scale-dependent feedbacks. Physical stress caused by wave impact is usually the limiting factor for colonization and growth of plants in tidal front areas [59]. It has been repeatedly observed that the protection from neighbouring established plants can effectively ameliorate such an impact [31], making local plant-plant facilitation the prime mechanism underlying the enhanced performance of S. mariqueter within the vegetation patches.…”

Observations of tidal and storm surge attenuation in a large tidal marsh

“…). This can be expected as the flow field on the marsh platform is frictionally dominated due to the high friction exerted by the vegetation present (e.g., Van Oyen et al , ). Taken together, our field measurements demonstrate the importance of marsh channel geometry for tidal and storm surge propagation in marshes.…”

Distributary Channel Networks as Moving Boundaries: Causes and Morphodynamic Effects

“…In tidal studies where this assumption is commonly made, the external forcing is that of a periodic tidal wave, and Λ∼ UC f . Several studies have shown that this linearization performs well relative to fully nonlinear flow across simple and complex domains (Marani et al, ; Van Oyen et al, , ), although significant errors do arise from spatially variable friction and very shallow flows. An important property of this linear model is that it conforms to Poisson's equation, ∇ 2 h w =Λ/( gH 2 ) ∂H / ∂t (Rinaldo et al, ; note that ∂H / ∂t signifies the changing spatially averaged tidal water depth).…”