design of a concrete chute. The critical section

where most failures have occurred is at the en-

trance where the structure passes through the berm.

As indicated earlier, a minimum freeboard equal to

one and one-half times the computed depth of flow

is recommended. A minimum depth of 3 inches is

suggested for the chute. Minor irregularities in the

finish of the chute frequently result in major flow

disturbances and may even cause overtopping of

Use Manning's equation (7-2) to determine depth

sidewalls and structural failure. Consequently,

of water:

special care must be given to securing a uniform

concrete finish and adequate structural design to

minimize cracking, settlement, heaving, or

creeping. A suitable means for energy dissipation or

erosion prevention must be provided at the end of

the chute.

Solving for d by trial and error, the depth of water

per second down a slope with a 25 percent grade.

is d=0.186 foot. For use in figure 7-4, the size of

The allowable head is 1 foot and Manning's n is

the angle of the chute is equal to 0.243 and q=Q/

0.014.

W=25/8=3.125. Thus, S/q1/5 equals 0.1935, which

corresponds to a design air concentration T = dair/

drop at the entrance, Q=3.1W(H)1/5, with Q=25

(dair+d)=0.471**. **Solving for dair gives 0.166 foot.

cubic feet per second and H = 1 foot.

Then, the total depth of flow is depth of water plus

depth of air, 0.352 foot. Wall height should be 1.5

25=3.1W(1)1/5 or W=8.06 feet

(eq 7-3)

times the total depth of flow or 0.528 foot. One

should use 0.5 foot. This design is shown in figure

Use W = 8 feet

7-5.

Now