Analytical models for bar patterns and braiding threshold

Analytical models for bar patterns and braiding threshold

Type

Hydromorphological models

Basic principles

Linearized fundamental equations for conservation of water mass and water flow momentum, time-averaged over all turbulent fluctuations, spatially averaged over water depth (2DH) or nor spatially averaged (3D). Linearized parameterized relation for effect of helical flow on bed shear stress direction. Linearized equilibrium sediment transport predictor or advection-relaxation equation for sediment transport. Linearized empirical relation for effect of sloping beds on sediment transport magnitude and direction. Linearized Exner equation for conservation of sediment mass.

Outputs

Number of bars per cross-section, bar length, bar stability.

Rivertypes

• Segment
•    Segment
• Reach
•    Reach

Related Pressures

• Surface water abstraction
• Groundwater abstractions
• Alteration of instream habitat
• Sand and gravel extraction
• Sedimentation and sediment input
• Embankments, levees or dikes
• Loss of vertical connectivity
• Impoundment
• Alteration of riparian vegetation
• Channelisation / cross section alteration

Related Measures

• Improve/Create water storage
• Reduce water consumption
• Increase minimum flows
• Recycle used water
• Improve water retention
• Reduce surface water abstraction with return
• Water diversion and transfer
• Reduce surface water abstraction without return
• Reduce groundwater extraction
• Create low flow channels in over-sized channels
• Narrow water courses
• Widen water courses
• Allow/increase lateral channel migration or river mobility
• Remeander water courses
• Shallow water courses

Useful references

Selected software systems

REGMEANDER

Theoretical background

Blondeaux P. and Seminara G. (1983): Bed topography and instabilities in sinuous channels. In: River Meandering, Proc. Conf. Rivers 1983, New Orleans, Ed. C.M. Elliott, ASCE, 1984, pp.747-758.

Colombini M., Seminara G., Tubino M. (1987): Finite-amplitude alternate bars. J. Fluid Mech., vol.181, pp.213-232.

Crosato A. and Mosselman E. (2009): Simple physics-based predictor for the number of river bars and the transition between meandering and braiding, Water Resources Res., AGU, 45, W03424, doi:10.1029/2008WR007242.

Struiksma N., Olesen K.W., Flokstra C., de Vriend H.J. (1985): Bed deformation in curved alluvial channels. J. Hydr. Res., IAHR, Vol.23, No.1, pp.57-79.