Instream Flows for Recreation: A Handbook on Concepts and Research Methods

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Classifying River Channels Schumm (1977) has classified rivers as bedload channels, suspended -load channels, or mixed -load channels. Bedload channels transport greater than 11% of their total sediment load as bedload. They generally are straight -to- sinuous, have high width -to -depth ratios (>40) and fairly steep gradients. Conversely, suspended -load channels transport less than 3% of their total sediment load as bedload. They have high amounts of fine sediments (silts and clays) in their channel beds and banks, low width -to -depth ratios (<10), and typically have low gradients and high sinuosities. Mixed -load channels are intermediate between suspended load and bedload channels in their characteristics. Simons and Li, Associates (1987) further classify bedload channels as sand -bed or gravel -bed channels, because of the differing influences those bed types have on sediment transport. Schumm's classification permits an analysis of how a channel will respond to altered flows. Rosgen (1985) has also developed a stream classification system based on descriptors of hydraulic geometry, and existing channel characteristics. Rosgen uses the variables of watershed position, stream sinuosity, gradient, bed materials, cross - section width and depth, valley confinement, channel entrenchment, and depositional features to group streams into five major classes and more than 20 different sub classes. The major classes are derived primarily from landscape position, ranging from steep headwater streams to deltaic streams. The sub - classes are derived from sinuosity, width -to -depth relation, bed - and -bank material composition, and so forth. Rosgen's classification may help in generalizing the results of site - specific studies to other reaches or other rivers. Deshka River. Changes in flow have larger effects on these kinds of channels. 23