Carnello, L

D'Alpaos, A

Lanzoni, S

Temmerman, Stijn

Van Oyen, Tomas

English

Ghent University Academic Bibliography

A simplified approach to describe the flow field on vegetated intertidal platformsT. Van Oyen1, S. Lanzoni2, A. D’Alpaos3, S. Temmerman4, P. Troch1 and L. Carniello21 Department of Civil Engineering, Ghent University, Belgium. tomas.vanoyen@ugent.be2 Dipartimento di Ingegneria Civile e Ambientale, University of Padua, Italy.lanzo@idra.unipd.it, carniello@idra.unipd.it3 Department of Geosciences, University of Padua, Italy. adalpaos@idra.unipd.it4 Ecosystem Management research group, University of Antwerpen, Belgium. stijn.temmerman@ua.ac.be1. IntroductionLagoonal and estuarine environments, typically, hoststriking intertidal features such as tidal salt marshes andmangroves. These geomorphological landscapes consistof periodically flooded vegetated platforms, dissected bya network of channels.Two-dimensional models have been developed (e.g.D’Alpaos et al., 2007) to describe the planimetric evo-lution of the intertidal platform. These studies, however,neglected the impact of vegetation variations on the flowfield, considering the hydrodynamic approach introducedby Rinaldo et al. (1999).Here, we describe and analyse a new simplified approachwhich is able to reasonable model the flow field on anintertidal platform taking into account also the impact ofspatial variations of vegetation (friction).2. Model and solutionThe flow field on the platform is described by the depth-averaged conservation equations of mass and momentum,which, in dimensionless form, readα(∂u∂ t+ r(u ·∇)u)=−ε∇ς − γλχ2Du, (1)dξdt+ ε∂ς∂ t+ r∇ · (Du) = 0. (2)In (1) - (2) four non-dimensional parameters appear(α,r,ε,γ) which, considering typical length- and velocityscales, are found to be α γ , ε < γ and r ∼O(1). Basedon these values, solutions to (1) - (2) are considered as anexpansion in the small parameters α and ε .At each order of approximation, by combining the mo-mentum and conservation equations, a linear diffusionequation is obtained, governing the variations in the freesurface elevation, while the flow velocity is related to thespatial gradients of ζ .3. ResultsTo investigate the capability of the simplified approach,the flow field obtained by the introduced approach iscompared with results found by using a numerical model(Carniello et al., 2011). In Figure 1, a comparison of theflow velocity on a flat intertidal platform with a cross-channel length of 400 m is provided for two instants dur-ing the flooding phase of the tidal wave. In the channels,a tidal wave with amplitude of 1 m and mean sea level of0.25 m is considered; H∗c = 0.25 + cos(ω∗t∗). In addi-tion, between 100 and 110 m the friction coefficient χ isdecreased to mimic the presence of a vegetation patch.A good comparison is obtained between the simple andnumerical approach even though the simple model under-estimates the flow field during the initial flooding of the   50   100   150   200   250   300   350   400 0.00 0.05 0.10y* − direction (m)u* (m/s)  Hc* = 0.5 mHc* = 0.75 mNumericalSimplifiedFigure 1: Comparison of the flow velocity u obtained bythe introduced approach and a numerical model(Carniello et al., 2011).tidal flat and the wake at the lee side of the patch is smallerfor the simplified approach.4. ConclusionsA simplified approach is described to model the flow fieldon friction dominated intertidal platforms. A comparisonwith a numerical model supports the adopted simplifiedmethod.AcknowledgmentsThis research was partly stimulated by the Scientific Re-search Network W0.027.p11N and by MIUR within theproject PRIN 2008.ReferencesCarniello, L., D’Alpaos, A., and Defina, A. (2011). Mod-eling wind waves and tidal flows in shallow micro-tidal basins. Estuarine, Coastal and Shelf Science, 92.doi:10.1016/j.ecss.2011.01.001.Costanza, R., d’Arge, R., de Groot, R., Farber, S., Grasso,M., Hannon, B., Limburg, K., Naeem, S., O’Neill,R. V., Paruelo, J., Raskin, R. G., Sutton, P., and van denBelt, M. (1997). The value of the world’s ecosystemservices and natural capital. Nature, 387:252–260.D’Alpaos, A., Lanzoni, S., Marani, M., and Rinaldo,A. (2007). Landscape evolution in tidal embayments:Modeling the interplay of erosion, sedimentation andvegetation dynamics. J. Geophys. Res., 112(F01008).doi:10.1029/2007JF000537.Mitsch, W. (2000). Wetlands. New York, Wiley.Rinaldo, A., Fagherazzi, S., Lanzoni, S., Marani, M., andDietrich, W. (1999). Tidal networks: 2. watershed de-lineation and comparative network morphology. WaterResources Research, 12:3905 – 3917.

A simplified approach to describe the flow field on vegetated intertidal platforms

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A simplified approach to describe the flow field on vegetated intertidal platforms

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