A two‐dimensional morphodynamic model of gravel‐bed river with floodplain vegetation

Artificially straight river channels tend to be unstable, and ultimately develop into river meanders through bank erosion and point-bar deposition. In this paper account is taken of the effects of riparian and floodplain vegetation on bank strength, floodplain flow resistance, shear stress partitioning, and bedload transport. This is incorporated into an existing 2D hydrodynamic-morphological model. By applying the new model to an initially straight and single-threaded channel, the way that its planform and cross-sectional geometry evolve for different hydraulic and floodplain vegetation conditions is demonstrated. The results show the formation and upstream migration of gravel bars, confluence scouring and the development of meandering and braiding channel patterns. In cases where the channel becomes unstable, the instability grows out of bar formation. The resulting braiding patterns are similar to analytical results. The formation of a transition configuration requires a strong influence from vegetation. Copyright © 2010 John Wiley & Sons, Ltd.

[1]  R. Millar.  Theoretical regime equations for mobile gravel-bed rivers with stable banks , 2005 .

[2]  Modelling gravel transport and morphology for the Fraser River Gravel Reach, British Columbia , 2008 .

[3]  P. Tassi,et al.  Estimates of flow resistance and eddy viscosity coefficients for 2D modelling on vegetated floodplains , 2004 .

[4]  M. Church,et al.  Sediment transport along lower Fraser River: 2. Estimates based on the long‐term gravel budget , 1999 .

[5]  R. Millar.  Influence of bank vegetation on alluvial channel patterns , 2000 .

[6]  G. Parker.  Surface-based bedload transport relation for gravel rivers , 1990 .

[7]  R. Millar,et al.  Simulating Bed-Load Transport in a Complex Gravel-Bed River , 2007 .

[8]  H. D. Vriend,et al.  Bed deformation in curved alluvial channels , 1985 .

[9]  J. Fredsøe.  Meandering and braiding of rivers , 1978, Journal of Fluid Mechanics.

[10]  R. Millar,et al.  Effect of Bank Stability on Geometry of Gravel Rivers , 1993 .

[11]  Vito Ferro,et al.  Flow Resistance Law in Channels with Flexible Submerged Vegetation , 2005 .

[12]  Nicholas Kouwen,et al.  FLEXIBLE ROUGHNESS IN OPEN CHANNELS , 1973 .

[13]  G. Nanson,et al.  Vegetation and channel variation; a case study of four small streams in southeastern Australia , 1997 .

[14]  M. A. Carson.  Characteristics of high-energy “meandering” rivers: The Canterbury Plains, New Zealand , 1986 .

[15]  D. Hicks,et al.  Cellular modelling of river catchments and reaches: Advantages, limitations and prospects , 2007 .

[16]  Kejun Yang,et al.  Flow Patterns in Compound Channels with Vegetated Floodplains , 2007 .

[17]  Peifang Wang,et al.  Hydraulic Resistance Characteristics of Riparian Reed Zone in River , 2007 .

[18]  G. Parker.  On the cause and characteristic scales of meandering and braiding in rivers , 1976, Journal of Fluid Mechanics.

[19]  Robert B. Jacobson,et al.  Woody vegetation and channel morphogenesis in low-gradient, gravel-bed streams in the Ozark Plateaus, Missouri and Arkansas , 1995 .

[20]  R. Callander.  Instability and river channels , 1969, Journal of Fluid Mechanics.

[21]  E. Andrews.  Bed-material entrainment and hydraulic geometry of gravel-bed rivers in Colorado , 1984 .

[22]  Stephen E. Darby,et al.  Effect of Riparian Vegetation on Flow Resistance and Flood Potential , 1999 .

[23]  Sean J. Bennett,et al.  A depth‐averaged two‐dimensional model for flow, sediment transport, and bed topography in curved channels with riparian vegetation , 2005 .

[24]  J. Pitlick,et al.  Morphologically based model of bed load transport capacity in a headwater stream , 2005 .

[25]  A. Crosato,et al.  Simple physics‐based predictor for the number of river bars and the transition between meandering and braiding , 2009 .

[26]  D. Rosgen.  A classification of natural rivers , 1994 .

[27]  J. Lewin.  Initiation of bed forms and meanders in coarse-grained sediment , 1976 .

[28]  Martin C. Miller,et al.  Threshold of sediment motion under unidirectional currents , 1977 .

[29]  C. Paola,et al.  Modelling the effect of vegetation on channel pattern in bedload rivers , 2003 .

[30]  G. Parker.  River meanders in a tray , 1998, Nature.

[31]  Yves Secretan,et al.  Integrated two-dimensional macrophytes-hydrodynamic modeling , 2000 .

[32]  J. Hewlett,et al.  Soil Water Absorption by Mountain and Piedmont Forests1 , 1965 .

[33]  L. B. Leopold,et al.  The hydraulic geometry of stream channels and some physiographic implications , 1953 .

[34]  R. Sellin,et al.  Factors Affecting Conveyance in Meandering Compound Flows , 1993 .

[35]  D. H. Gray,et al.  Root‐Soil Mechanics and Interactions , 2013 .

[36]  Julian C. Green.  Modelling flow resistance in vegetated streams: review and development of new theory , 2005 .

[37]  C. Paola,et al.  Dynamic single-thread channels maintained by the interaction of flow and vegetation , 2007 .

[38]  C. Paola,et al.  Riparian vegetation controls on braided stream dynamics , 2001 .

[39]  F Engelund,et al.  FLOW AND BED TOPOGRAPHY IN CHANNEL BENDS , 1974 .

[40]  V. R. Schneider,et al.  GUIDE FOR SELECTING MANNING'S ROUGHNESS COEFFICIENTS FOR NATURAL CHANNELS AND FLOOD PLAINS , 1989 .

[41]  Yasuyuki Shimizu,et al.  Vegetation effects on the morphological behavior of alluvial channels , 2007 .

[42]  C. Thorne,et al.  Stable Channels with Mobile Gravel Beds , 1986 .

[43]  J. Smagorinsky,et al.  GENERAL CIRCULATION EXPERIMENTS WITH THE PRIMITIVE EQUATIONS , 1963 .

[44]  B. Eaton,et al.  A conceptual model for meander initiation in bedload‐dominated streams , 2006 .

[45]  M. Jaeggi.  Formation and Effects of Alternate Bars , 1984 .