Model and laboratory study of dispersion in flows with submerged vegetation

[1] Vegetation is ubiquitous in rivers, estuaries, and wetlands, strongly influencing water conveyance and mass transport. The plant canopy affects mean and turbulent flow structure, and thus both advection and dispersion. Accurate prediction for the transport of nutrients, microbes, dissolved oxygen and other scalars depends on our ability to quantify the impact of vegetation. In this paper, we focus on longitudinal dispersion, which traditionally has been modeled in vegetated channels by drawing analogy to rough boundary layers. This approach is inappropriate in many cases, as the vegetation provides a significant dead zone, which may trap scalars and augment dispersion. The dead zone process is not captured in the rough boundary model. This paper describes a new model for longitudinal dispersion in channels with submerged vegetation, and it validates the model with experimental observations.

[1]  T. Atkinson,et al.  Longitudinal dispersion in natural channels: 2. The roles of shear flow dispersion and dead zones in the River Severn, U.K. , 2000 .

[2]  A. Roberts,et al.  Two‐Zone Model of Shear Dispersion in a Channel Using Centre Manifolds , 2004 .

[3]  H. Nepf,et al.  Observations of particle capture on a cylindrical collector: Implications for particle accumulation and removal in aquatic systems , 2004 .

[4]  Syunsuke Ikeda,et al.  Three-Dimensional Organized Vortices above Flexible Water Plants , 1996 .

[5]  Luca Ridolfi,et al.  The Effect of Vegetation Density on Canopy Sub-Layer Turbulence , 2004 .

[6]  Marco Ghisalberti,et al.  Mass Transport in Vegetated Shear Flows , 2005 .

[7]  Anne F. Lightbody,et al.  Prediction of velocity profiles and longitudinal dispersion in salt marsh vegetation , 2006 .

[8]  D. Gutknecht,et al.  Hydraulic resistance of submerged flexible vegetation , 2002 .

[9]  Octave Levenspiel,et al.  Notes on the diffusion-type model for the longitudinal mixing of fluids in flow , 1995 .

[10]  Carolyn Oldham,et al.  The effect of emergent vegetation on convective flushing in shallow wetlands: Scaling and experiments , 2001 .

[11]  H. Nepf.  Drag, turbulence, and diffusion in flow through emergent vegetation , 1999 .

[12]  The role of the submergent macrophyte Triglochin huegelii in domestic greywater treatment , 1999 .

[13]  S. C. Chikwendu,et al.  Calculation of longitudinal shear dispersivity using an N-zone model as N → ∞ , 1986, Journal of Fluid Mechanics.

[14]  Jonathan Sharples,et al.  Recipe for 1‐D Lagrangian particle tracking models in space‐varying diffusivity , 2004 .

[15]  Carl F. Nordin,et al.  Longitudinal dispersion in rivers: The persistence of skewness in observed data , 1980 .

[16]  D. Reed,et al.  Hydrodynamics and Sediment Transport Through Tidal Marsh Canopies , 2002 .

[17]  W. Thacker.  A Solvable Model of “Shear Dispersion” , 1976 .

[18]  R. Aris.  On the dispersion of a solute in a fluid flowing through a tube , 1956, Proceedings of the Royal Society of London. Series A. Mathematical and Physical Sciences.

[19]  Marco Ghisalberti,et al.  The Structure of the Shear Layer in Flows over Rigid and Flexible Canopies , 2006 .

[20]  Heidi Nepf,et al.  The Effects of Vegetation on Longitudinal Dispersion , 1997 .

[21]  E. Veling,et al.  Tracer experiments in the Rhine Basin: evaluation of the skewness of observed concentration distributions , 2005 .

[22]  K. Niklas.  THE SCALING OF PLANT AND ANIMAL BODY MASS, LENGTH, AND DIAMETER , 1994, Evolution; international journal of organic evolution.

[23]  Hugo B. Fischer,et al.  Longitudinal Dispersion and Turbulent Mixing in Open-Channel Flow , 1973 .

[24]  J. A. Sullivan,et al.  A model for diffusion within emergent vegetation , 1997 .

[25]  S. Chikwendu,et al.  Slow-zone model for longitudinal dispersion in two-dimensional shear flows , 1985, Journal of Fluid Mechanics.

[26]  H. V. Leland.  The influence of water depth and flow regime on phytoplankton biomass and community structure in a shallow, lowland river , 2003, Hydrobiologia.

[27]  Marco Ghisalberti,et al.  The limited growth of vegetated shear layers , 2004 .

[28]  T. Day,et al.  Longitudinal dispersion in natural channels , 1975 .

[29]  H. Nepf,et al.  Mixing layers and coherent structures in vegetated aquatic flows , 2002 .

[30]  H. Nepf,et al.  Shear layers in partially vegetated channels: analogy to shallow water shear layers , 2004 .

[31]  J. W. Elder.  The dispersion of marked fluid in turbulent shear flow , 1959, Journal of Fluid Mechanics.

[32]  Ian R. Wood,et al.  Longitudinal Dispersion with Dead Zones , 1977 .

[33]  Fabián López,et al.  Mean Flow and Turbulence Structure of Open-Channel Flow through Non-Emergent Vegetation , 2001 .

[34]  H. Hoteit,et al.  Three-Dimensional Modeling of Mass Transfer in Porous Media Using the Mixed Hybrid Finite Elements and the Random-Walk Methods , 2002 .

[35]  Marco Ghisalberti,et al.  Retention time and dispersion associated with submerged aquatic canopies , 2007 .

[36]  Fabián López,et al.  open‐channel flow through simulated vegetation: Suspended sediment transport modeling , 1998 .

[37]  R. H. Maryon,et al.  Treatment of Interfaces in Random Walk Dispersion Models , 1997 .

[38]  Ronald Smith.  A delay-diffusion description for contaminant dispersion , 1981, Journal of Fluid Mechanics.

[39]  Vito Ferro,et al.  Flow Velocity Measurements in Vegetated Channels , 2002 .

[40]  Heidi Nepf,et al.  Scalar transport in random cylinder arrays at moderate Reynolds number , 2003, Journal of Fluid Mechanics.

[41]  Nicholas Kouwen,et al.  Flow Retardance in Vegetated Channels , 1969 .

[42]  U. Netlogo Wilensky,et al.  Center for Connected Learning and Computer-Based Modeling , 1999 .

[43]  H. Nepf,et al.  Prediction of velocity profiles and longitudinal dispersion in emergent salt marsh vegetation , 2005 .

[44]  J. Finnigan,et al.  Coherent eddies and turbulence in vegetation canopies: The mixing-layer analogy , 1996 .

[45]  F. White.  Viscous Fluid Flow , 1974 .

[46]  Brian M. Stone,et al.  Hydraulic resistance of flow in channels with cylindrical roughness , 2002 .

[47]  M. Schulz,et al.  The influence of macrophytes on sedimentation and nutrient retention in the lower River Spree (Germany). , 2003, Water research.

[48]  Enrique R. Vivoni,et al.  Flow structure in depth-limited, vegetated flow , 2000 .

[49]  M. Luther,et al.  Flow hydrodynamics in tidal marsh canopies , 1995 .

[50]  H. Fischer.  Mixing in Inland and Coastal Waters , 1979 .

[51]  Akira Sase,et al.  Drag force due to vegetation in mangrove swamps , 1997 .