Hydraulic Structures: Fourth Edition

9.2.5 Canal outlets

The canal outlet is an intake structure for small canals, usually designed
for proportional distribution of irrigation water supplies from the parent
canal. These structures do not require any control works in the parent
canal and function automatically with no manual control. Except for
routine inspection they require very little maintenance (Mazumdar, 1983).
The flexibility of an outlet (F) is the ratio of the fractional change of
discharge of the outlet (dq/q) to the fractional change of discharge of the
parent (distribution) canal (dQ/Q). Thus,

F(dq/q)/(dQ/Q) (9.25)

whereqandQare the outlet and parent canal discharges respectively,
given by

qkHm, (9.26a)

QcDn, (9.26b)

His the head acting on the outlet and Dis the depth of water in the distri-
bution canal (Fig. 9.25).
Combining equations (9.25) and (9.26) gives

F(m/n)(D/H)dH/dD. (9.27a)

Since dHdD(change in Dresults in an equal change in H), equation
(9.27a) becomes

F(m/n)(D/H). (9.27b)

INTAKES 401

Fig. 9.25 A submerged pipe outlet (non-modular type)