Stable Slopes of Alluvial Channels

by Mohammad N. Cheema, Univ of California, Davis, United States,
Miguel A. Mariño, Univ of California, Davis, United States,

Abstract: An alluvial channel responds to the variation in the incoming sediment by changing its cross-section and especially the slope. Regime relations formulated by Lacey (1930) and many subsequent researchers are supposed to predict the so-called stable geometry and the slope of the channel for a known discharge. Some of the regime relations also use the sediment load as an input parameter (Chang 1985; Stevens 1990). Perhaps, the major factor responsible for changes in the cross-section and slope of the channel is the variation in its hydraulic roughness as the bedforms develop with the transport of the sediment. A procedure is presented which makes use of the simple formula of the grain roughness along with the law of conservation of the mass of sediment to compute changes in the hydraulic roughness of the channel as erosion or deposition takes place on the channel bed. The procedure is tested on data from Pakistan canals, all of which pertain to the lower flow regime as defined by Karim and Kennedy (1990). The computed roughness is compared with the roughness predicted by Simons (1976) and Karim and Kennedy (1990). The roughness predicted by the proposed procedure gives a better correlation with the observed data.

Subject Headings: Alluvial channels | Hydraulic roughness | Channel stabilization | Slopes | Sediment transport | Stable channels | Geometrics | Cross sections | Asia | Pakistan

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