Application and validation of a three-dimensional hydrodynamic model of a macrotidal salt marsh

Abstract A three-dimensional hydrodynamic model is used to study the relative influence of salt marsh vegetation on flows in a macrotidal estuary using a system of three connected grids that resolve currents in tidal drainage channels incised in a marsh platform. The model incorporates the effects of vegetation on flow drag, parameterized by the stem height, diameter and plant density. Model predictions are compared to novel field observations of macrotidal water levels and tidal currents using pressure and acoustic current sensors over 6 tidal cycles at spring tide, collected in areas of different roughness corresponding to high marsh grass (Spartina patens), low marsh grass (Spartina alterniflora), and a muddy tidal channel bed. High resolution airborne Lidar and multibeam bathymetry data are used to define the bathymetry and spatially-variable vegetation maps in the multi-domain model. A detailed comparison between field observations and model results is presented, necessary for model validation in this macrotidal environment with large water level gradients and high sensitivity to model input parameter values. The model results indicate that the vegetation plays a major role in controlling flow speed and drainage patterns, especially over the macrotidal marsh platform. Differences in flow resistance between vegetated and un-vegetated areas result in faster flows over un-vegetated areas, with vegetated areas having flow directions locally perpendicular to channels as water levels exceed creek bank elevations and the marsh platform is flooded. Including the marsh grasses in the model causes stronger near-surface currents, significantly weaker near-bed currents, and concentrated flows in the channels resulting in strong vertical variation in the horizontal flow. The results indicate that including the effects of vegetation in a numerical model is crucial in simulating the hydrodynamic conditions over macrotidal salt marsh platforms and in channels.

[1]  Gert Klopman,et al.  NUMERICAL SIMULATION OF WAVE-CURRENT DRIVEN SEDIMENT TRANSPORT , 2001 .

[2]  N. Pope,et al.  Estimation of bed shear stress using the turbulent kinetic energy approach- : A comparison of annular flume and field data , 2006 .

[3]  C. O’Laughlin,et al.  Influence of varying tidal prism on hydrodynamics and sedimentary processes in a hypertidal salt marsh creek , 2013 .

[4]  R. Davidson‐Arnott,et al.  Hydrodynamics and sedimentation in salt marshes: examples from a macrotidal marsh, Bay of Fundy , 2002 .

[5]  Peter M. J. Herman,et al.  Impacts of salt marsh plants on tidal channel initiation and inheritance , 2013 .

[6]  T. Spencer,et al.  Tidal Flows in Salt Marsh Creeks , 1979 .

[7]  J. French,et al.  Hydrodynamics of salt marsh creek systems: Implications for marsh morphological development and material exchange , 1992 .

[8]  R. Mulligan,et al.  Variability in suspended sediment concentration in the Minas Basin, Bay of Fundy, and implications for changes due to tidal power extraction , 2016 .

[9]  Ian Townend,et al.  A review of salt marsh dynamics , 2011 .

[10]  Dirk Lauwaet,et al.  Flow paths of water and sediment in a tidal marsh: Relations with marsh developmental stage and tidal inundation height , 2005 .

[11]  Weiming Wu,et al.  Experimental Investigation of Wave Attenuation through Model and Live Vegetation , 2014 .

[12]  L. Leonard,et al.  The effect of standing biomass on flow velocity and turbulence in Spartina alterniflora canopies , 2006 .

[13]  Andrea Rinaldo,et al.  Tidal networks: 3. Landscape‐forming discharges and studies in empirical geomorphic relationships , 1999 .

[14]  D. Augustijn,et al.  Modeling the influence of a young mussel bed on fine sediment dynamics on an intertidal flat in the Wadden Sea , 2010 .

[15]  Gerben J. de Boer,et al.  Modeling large-scale cohesive sediment transport affected by small-scale biological activity , 2008 .

[16]  John Robert Lawrence Allen,et al.  Morphodynamics of Holocene salt marshes: a review sketch from the Atlantic and Southern North Sea coasts of Europe , 2000 .

[17]  Peter M. J. Herman,et al.  Spatial flow and sedimentation patterns within patches of epibenthic structures: Combining field, flume and modelling experiments , 2007 .

[18]  Matthias Kudella,et al.  Wave attenuation over coastal salt marshes under storm surge conditions , 2014 .

[19]  E. Poirier.  Seasonal influences on the ecomorphodynamics of a hypertidal salt marsh and tidal creek system , 2014 .

[20]  Inigo J. Losada,et al.  The role of coastal plant communities for climate change mitigation and adaptation , 2013 .

[21]  R. E. Uittenbogaard,et al.  Modeling the interaction between flow and highly flexible aquatic vegetation , 2010 .

[22]  P. Wiberg,et al.  Flow and Sediment Transport on a Tidal Salt Marsh Surface , 2000 .

[23]  T. Sun,et al.  A stochastic model for the formation of channel networks in tidal marshes , 2004, Geophysical Research Letters.

[24]  Giulio Mariotti,et al.  Wind waves on a mudflat: The influence of fetch and depth on bed shear stresses , 2013 .

[25]  F. Dupont,et al.  Modelling the sea level of the upper Bay of Fundy , 2005 .

[26]  J. Irish,et al.  Laboratory and numerical studies of wave damping by emergent and near-emergent wetland vegetation , 2009 .

[27]  R. Davidson‐Arnott,et al.  Seasonal and annual variations in the volumetric sediment balance of a macro-tidal salt marsh , 2006 .

[28]  L. Lynn,et al.  Marsh surface sediment deposition and the role of tidal creeks: implications for created and managed coastal marshes , 1999 .

[29]  Hongqing Wang,et al.  A numerical study of vegetation impact on reducing storm surge by wetlands in a semi-enclosed estuary , 2015 .

[30]  W. Mitsch,et al.  The value of wetlands: importance of scale and landscape setting. , 2000 .

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

[32]  S. Temmerman,et al.  Flow hydrodynamics on a mudflat and in salt marsh vegetation: identifying general relationships for habitat characterisations , 2005, Hydrobiologia.

[33]  S. Temmerman,et al.  Vegetation causes channel erosion in a tidal landscape , 2007 .

[34]  Kenneth Pye,et al.  Flow Structure in and above the Various Heights of a Saltmarsh Canopy: A Laboratory Flume Study , 1995 .

[35]  J. R. Allen.  A continuity-based sedimentological model for temperate-zone tidal salt marshes , 1994, Journal of the Geological Society.

[36]  M. Bertness.  Zonation of Spartina Patens and Spartina Alterniflora in New England Salt Marsh , 1991 .

[37]  G. Stelling,et al.  Development and validation of a three-dimensional morphological model , 2004 .

[38]  C. Garrett.  Tidal Resonance in the Bay of Fundy and Gulf of Maine , 1972, Nature.

[39]  W. L. Wood,et al.  An exploratory numerical model of sediment deposition over tidal salt marshes , 1995 .