Question

PROBLEM #2 The drawing shown below on this page (Figure 16) is a cross section through the entrance of a concrete-lined irrigation canal at a low di. version dan. The reservoir water surface is maintained at 6.0 feet above the canal invert. REQUIRED: (a) If the canal invert slope is 0.0003 ft/ft, what is the maximum discharge through the canal? (b) As the canal invert slope is increased, at what slope will no further increase in the discharge occur? (e) What is the maximum discharge for the condition des cribed in (b)? (d) that would be the effect if backwater existed at the outlet for the canal invert slope as described in (a), and in (b)? A 6.0' † LOA 10.0' SECTION a Section 4.4

Answer 1

Answer:

From the given data,

a) Depth of flow= 6 ft

Width of channel= 10ft

Channel is concrete lined, so Manning’s roughness coefficient is n= 0.015

So discharge of the channel, Q= 1/n*A*R^2/3S^1/2

A= depth x width=6*10= 60 sft

Wetted perimeter, P= 6*2+10=22 m

R= A/P= 60/22=2.727 m

S= bed slope=0.0008 ft/ft

Q= 1/0.015*60*2.727^2/3*0.008^1/2

Q = 698.33 cft.

b) Discharge is maximum at critical state of flow. So when the slope reach at critical slope, further increase in slope , discharge will not increase.

c) Discharge is maximum at critical stage. So maximum discharge

Qmax= sqrt(A³g/T)= sqrt( 60³*32.17/10)= 833.6 cft

d)In both a and b  discharge is maximum at critical state of flow. So when the slope reach at critical slope, further increase in slope , discharge will not increase.