DESIGN OF STABLE CHANNEL

Abstract

Channels in alluvium are constructed for conveyance of water from storage and diversion structures for irrigation and hydropower generation. Over a period of time, various methods of their design have been evolved In India and abroad. To name some of them are those due to Kennedy, Lacey, Lindley, Inglis, Blench, Chitale, Engelund and Hansen, and Kondap. While some of them considered sediment transport rate implicitly, others included it in their design equations explicitly with other parameters. The alluvium and the sediment entering into the channels are inveriably graded and nonuniform. Somehow none of the investigators in the past considered the nonuniformity of the sediment. Most of them adopted the median size d50 to represent sediment In their equations. In the case of nonunlfoim material, it Is not only the transport rate of sediment, but also its size distribution for which the channel needs to be designed. In other words, the quality and quantity of sediment being transported by the channels should be the same as the quality and quantity of the sediment entering into it through channel head regualator. These being same, the bed material constitution of the canal will reach an equilibrium, different from that of the former. In this thesis, Lacey's equations have been used as the basis. The design variables viz. discharge Q, median sediment size d . and Kramer's co-efficient have been selected in their practical ranges. For each set of these variables, the channel was designed using different representative sizes di of the nonuniform sediment. For each design, the transport. rate was computed using fractionwise estimation method of Samaga. The median size dT and Kramer's coefficient MT of the transported sediment. Design relationships between di/dt.; and the dimensionless r parameters Q~ I = gl/2Qd5/2 ,' QT` = Bps ~s_ ~r ga3 MT l T 3 ASS di and particle Reynolds number RT [= 2 1 have been developed pfv J using the results of the computations described above. A method of design of stable channel for specified transport rate of nonuniform sediment have been proposed