Hydraulic Structures: Fourth Edition

control systems and Lewin (2001) illustrates the application of such
systems to automatic methods of gate control. The requirements for
remote controlare that two independent means of communication are
available to transmit key information determining the operation of spill-
way gates and for monitoring the condition of essential equipment.
Thereliabilityrequirement of gates must be consistent with their
safety role and the overall dam safety. Various aspects of design flood
selection, freeboard and flood routing dealt with in Chapter 4 and dam
safety instrumentation and surveillance dealt with in Chapter 7 are here of
relevance. Some of the general reliability principles for the gates are that
the equipment must be able to perform its duty throughout its operational
life, no single random failure of operating equipment should prevent the
gate operation and without adding to the system complexity failure of any
kind is revealed to the site staff. Redundancy of equipment should be
incorporated into the flood discharge systems to achieve a defence in
depth against potential equipment failure.

Worked Example 6.1

A vertical lift gate discharges into a canal; the upstream depth is 3.0 m and
the downstream depth is (i) 0.5 m and (ii) 2.10 m. Estimate the discharge
and the force acting on the gate in case (i) and the force in case (ii) assum-
ing the discharge remains constant (as in case (i)).

(i) As y 3 /y 1 $0.5 free flow conditions will apply; assuming the coefficient of
contractionCc0.605 the gate opening is a0.5/0.6050.826 (see Fig. 6.9).

Cd 0.56 (see equation (6.4)

(neglecting the upstream velocity head, i.e. Hy 1 )

qCda(2gy 1 )1/20.560.826 (19.63)1/23.547 m^2 s^1.

From the momentum equation (assuming the Boussinesq coefficient 1)

g

1

2

y^21 

1

2

y^23  P q(V 3 V 1 )

9.8 103 (3^2 /2 0.5^2 /2) P3.547(3.547/0.5 3.547/3) 103 (20.97

 103 )

P(42.92 20.97)10^3 21.95 kN m^1.

0.605



^1 0.605

0.8

3

26



1/2

Cc



^1 CcH

a



1/2

WORKED EXAMPLES 285