KENNDY'S THEORY AND ITS LIMITATIONS
R .G. Kennedy's an executive engineer in Panjab PWD .he studied exiting canals in UPPER BARI DOAB canal system"which did not show any problem of silting and scouring for previous 30-35 years . From his observations he concluded that the silt supporting power in channel cross-section is mainly depend upon the generation of the eddies from the channels bed due to the friction of the flowing water with the channel bed .
The vertical components of these eddies try to move the sediment upwards where as the weight of the sediment tries to bring it downward, keeping the sediment particle in suspension .Therefore the velocity is sufficient to generate the eddy's so as to keep the sediment just in suspension and there by silting is avoided .Based upon this Kennedy defined the critical velocity (v0) as the mean velocity in a channel which will just keep the channel free from silting and scoring .And express it as following:Vo = C Dn
Since his studies were based in a given canal system therefore to validate the expression of v throughtout India ,he introduced the critical velocity is now written as :-
Vo = 0.546 D0.64
If a given irrigation channel passing through Alluvial soil is designed for the above critical velocity then it will not show the problem of silting and scouring .
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| credit The Constructor |
Limitations of Kennedy's theory
1> According to Kennedy ,eddies are generated from the base of the channel ,however in real practice .Eddies are also generated from the sides of the channel.
2> Kennedy had not given his own formula for the calculation the actual mean velocity and instead had recommended to use Chezy's eqution or Manning eqution .
3> The value of critical velocity ratio had baan randomly related to the silt grade without giving any proper mathematical relationship .
4> He had not given his own eqution for the calculation of channel bottom slope.
5> He had not taken into consideration the effect of silt concentration and bed load
6> He had not given any importance to the width to depth ratio.
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