A very wide rectangular channel is to be lined with tall sta

A very wide rectangular channel is to be lined with tall stand Bermuda grass to prevent erosion. If the channel slope is 0.01 ft/ft, determine the maximum allowable flow per unit of width and velocity for channel stability.

Solution

given in the question,

slope , S = 0.01 ft/ft

we will have to take a few assumptions for calculating , discharge

let\'s take manning\'s coefficient n = 0.08 ( for grassed channels depending upon the product of velocity and hydraulic radius i.e R , we decide value of n, generally it lies between 0.05 - 0.4 for a very high grass density)

Q = 1/n * A* R^2/3*S^1/2

= 1/.08 * B* d * ( A/ wetted perimeter)^2/3 * ( 0.01)^0.5

= 12.5 * B* d* (d/2) ^2/3*0.1

q (Q/B) = 1.25/1.33 *d^5/3

= 0.94 *d^5/3

V= 1/n *R^2/3* s^0.5

= 1/.08 * (d/2)^0.67*(0.01)^0.5

= 0.94*d^2/3