Question

Critical Velocity Ratio is defined as the: 
1. Ratio of actual mean velocity (V) to the critical velocity (V_o ) given by Kennedy formula
2. Ratio of critical velocity (V_o ) given by Kennedy formula to the actual mean velocity (V)
3.  Ratio of actual mean velocity (V) to the critical velocity (V_o ) given by Lacey formula
4. Ratio of critical velocity (V_o ) given by Lacey formula to the actual mean velocity (V)

Answer 1

Correct Answer - Option 1 : Ratio of actual mean velocity (V) to the critical velocity (V_o ) given by Kennedy formula

Explanation

Kennedy’s theory:

As per Kennedy’s theory, critical velocity (Vc) in a channel is the mean velocity which is sufficient to prevent the channel from scouring and silting. Any velocity greater than critical velocity causes scouring in the channel and any velocity less than critical velocity causes silting in the channel.

Vc = 0.55 m D0.64

Where m is the Critical Velocity ratio and D is the depth of flow

Further, the Critical Velocity ratio (CVR) is the ratio of actual velocity (Va) to critical velocity (Vc) in the channel.

Now If,

CVR > 1 Va > Vc Scouring will occur.

CVR < 1 Va < Vc Silting will occur

CVR = 1 Va = Vc There will be no silting and scouring