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Channel Design Alluvial Channels
Alluvial Channels • Alluvial channel is defined as a channel in which the flow transports sediment having the same characteristics as that of the material in the channel bottom. Such a channel is said to be stable if the sediment inflow into a channel reach is equal to the sediment outflow • Channel cross section and the bottom slope do not change due to erosion or deposition
Approach • Two approaches have been used for the design of stable alluvial channels: • Tractive force method • Regime theory • Tractive force method is more rational • Regime theory method is purely empirical in nature and was developed based on observations • Regime theory is applicable when sediment concentration is less than 500 ppm by weight
Regime Theory • A regime channel is a channel carrying a constant discharge under uniform theory in an unlimited incoherent alluvium having the same characteristics as that transported without changing the bottom slope, shape, or size of the cross section over a period of time
Regime Theory • Lacey [1930] developed the following equations based on the analysis of a large amount of data collected in several irrigation canals in the India: • wetted perimeter, in m; • hydraulic radius, in m; • flow, in ; • diameter of sediment, in mm; • silt factor which takes into consideration the effect of sediment size on the channel dimensions (Choudhry, 2008)
Example • A channel has to be designed for drainage to carry flow from if the is , determine he channel size using the regime theory. The material size is .