2 According to Kennedy the critical velocity ratio Vc in a channel may be defined as the mean velocity of flow which will just keep the channel free from silting or scouring.His investigations pertain to Upper bari Doab canal in UP.m = Critical velocity ratio= 1.1 to 1.2 for coarse sand= 0.8 to 0.9 for fine sand
3 KENNEDY’S METHOD OF CHANNEL DESIGN PROCEDURE Q = A x V
4 Assume a depth of flow = d, m Compute the critical velocity from kennady’s formulaCompute are of c/s of flow = Q/VcAssuming a side slope of channel, say 0.5:1 compute the bed widthCompute the wetted perimeter for the assumed depth abd computed bed widthCalculate C from Kutter’s formula and then the velocity of flow by Chezy’s equationIf the Velocity computed now is same as found by kennady’s method the design depth is correctOtherwise repeat the above steps by assuming different depth of flow
5 CWPC PRACTICE FOR “n” Type of soil Canal discharge (cumecs) Value of n 1. Soil other than rockUp to 0.0140.14 to 1.41.4 to 14Above 140.030.0250.02250.0202. Rocky cuts1. When rock portion at least 15 cm above the excavated bed level is left out in working out cross sectional area.0.035 to 0.052. When no portion above bed level is left out0.05 to 0.080
6 Channel of conditionValue of n1. Very good0.02252. Good0.0253. Indifferent0.02754. Poor0.03
7 He also defined critical velocity as non-silting –non-scouring velocity and gave a relation between critical velocities to the depth of flowing water.
8 The relation is,V0 = 0.55 D0.64(OR V0 = 0.84 D in F.P.S UnitsIn generalV0 = CDnV0 = Critical velocity, in (m/s)D = Depth of water over bed portions of a channel in mn = any index number
9 The equation has been derived on the basis of observations on one canal only, it is applicable to only those channels, which are flowing, in sandy silt of the same quality or grade as that of Upper Bari Doab system.
10 Kennedy later realized the importance of silt grade on critical velocity and introduced a factor ‘m’ known as critical velocity ratio (C.V.R) in his equation. The equation is then written asV0 = 0.55 m D0.64Where, m = C.V.R = V/ V0
11 Sand coarser than the standard was assigned value of m from 1. 1 to 1 Sand coarser than the standard was assigned value of m from 1.1 to 1.2 and those finer than the standard from 0.9 to 0.8. Generally, in a system of canal, higher C.V.R. is assumed in head reaches and lower value of C.V.R is assumed towards its tail end.
12 The value of constant C in equation for various grades of material may be assumed as follows: Types of materialValue of CLight sandy silt0.53Coarser light soil0.59Sandy loam0.65Coarse silt0.70
13 Value of m Type of silt Value of m Light sandy silt in the rivers of northern India1.00Somewhat coarser light sandy silt1.1Sandy loamy silt1.2Rather coarser silt or debris of hard soil1.3Silt of river Indus in sindhu0.7
14 Drawbacks in Kennedy’s theory Kennedy did not notice importance of B/D ratio.He aimed to find out only the average regime conditions for the design of a channel.No account was taken of silt concentration and bed load, and the complex silt-carrying phenomenon was incorporated in a single factor m.Silt grade and silt charge were not defined.Kennedy did not give any slope equation.Kennedy use kutter’s equation for the determination of mean velocity and therefore the limitations kutter’s equation got incorporated in Kennedy’s theory of channel design