Channel Patterns Straight Occurs over short reaches not
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Channel Patterns • Straight: Occurs over short reaches; not very common; sinuosity < 1. 5 • Meandering: Most commonly observed pattern; Single channel system with a sinuosity > 1. 5 • Multichannel Systems – Braided: mobile bed, banks, and bars. – Anabranching (includes anastomosing channels); multiple channels separated by vegetated floodplain materials; generally consists of stable banks, and associated with avulsion.
Straight Channel Pool Riffle Bar Thalweg Channel Banks Bar Pool
Flow Patterns From Ritter et al. , 1995
Velocity Reversals From Ritter et al. , 1995
Meandering Channels T - thalweg B- bar R - riffle P - pool From Ritter et al. , 1995
Flow Patterns - Historic Model No Secondary Flow at Riffle Helical Flow From Ritter et al. , 1995
Flow Patterns - Current Model From Ritter et al. , 1995
Meander Geometry From Ritter et al. , 1995
Controls on Meander Geometry From Ritter et al. , 1995
Braided Channels (Central Bar Theory - Leopold and Wolman, 1957) From Ritter et al. , 1995
Braided Channels (Stalled Lingoid Dunes) From Ritter et al. , 1995
Parameters Influencing Braid-Bar Formation • Erodible Banks: Required for development of braided channel. • Sediment Transport and Abundant Load: Most carry large amounts of sediment; not overloaded; can be incising. • Rapid and Frequent Variations in Discharge: Not an absolute requirement, but may facilitate bar formation.
Pattern Classification After Schumm, 1981
Channel Pattern Thresholds From Schumm, 1977
Anabranching Channels (Associated with the Following) • Channel aggradation • stable, cohesive banks that limit channel widening • a flood-prone hydrologic regime
Types of Anabranching Systems From Nanson and Knighton, 1996
Flow Diagram of Controlling Factors From Ritter et al. , 1995
River Metamorphosis (After Schumm) • • From Ritter et al. , 1995 Qw - mean annual discharge or mean annual flood Qt - percentage of total load as bed material load w - channel width d - channel depth S - channel slope P - sinuosity F - width to depth ratio L - meander wavelength
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