Irrigation Engineering

“Weir & Barrage”

GANDHINAGAR INSTITUTE OF TECHNOLOGY

What is WEIR ?

• Weir is a solid obstruction put across the river to raise water level and divert the water into canal .

• If water is store for a small period of short supplies it is called storage weir.

• The main difference between a storage weir and a dam I only in height and duration for which the supply is stored.

• A dam stores the supply for comparatively longer duration.

• It is a one type of structure, constructed across the river to raise water level in river and divert the required quantity to the canal.

What is diversion head work ?

• A weir is a structure constructed across a river to raise its

water level and divert the water into the canal....and it is a

part of diversion head work

Cont...

Weir

Masonry weir with vertical

drop

Rock fill weir with sloping aprons

Concrete weirs with a downstream

glacis

Typesf

weirs

• This type of weir is suitable for any

type of foundation.

• This type of weir is very old so it is

design on the base on Bligh’s

theory.

• Example : Bhimgoda weir across

Ganga near Haridwar

Masonry weir with vertical drop

Rock fill weir with sloping aprons

• This type of construction is very

simple and its stability is not

amenable to extract theoretical

treatment.

• But it requires large quantity of

stone.

• Example ; Okhala weir, across

Yamuna River Delhi

It is relatively new of its kind.

It has slope at both the u/s and

d/s sides.

Sheet piles are at u/s as well as

d/s of weir, up to maximum

scour depth.

This type of weirs may be

constructed on pervious

foundation.

Concrete weirs with a sloping glacis

Causes of failure of weirs

Due to subsurface

flow

By piping By uplift pressure

Due to Surface flow

By suction By scour effect

• Due to Piping or undermining

1. Providing sufficient length of impervious floor so that path of

percolation is increased and exit gradient is decreased.

2. Providing sheet piles at the d/s and u/s ends of impervious

floor.

Remedies for failure due to

• Due to uplift pressure

1. Providing sufficient thickness of the impervious floor.

2. Providing sufficient length of impervious floor

3. Providing pile at u/s end of impervious floor so as to reduce

uplift pressure at d/s.

Cont...

• Due to surface flow

1. Providing additional thickness of impervious floor to counter

balance the suction pressure due to standing wave.

2. Constructing floor as monolithic concrete mass instead of

different layers of masonry.

Cont...

• Due to scour

1. Providing deep piles at u/s &d/s end of imperious floor up to a

depth much below calculated scour depth.

2. Providing launching aprons of suitable length and thickness at

u/s & d/s end of impervious floor.

Cont...

• The function of barrage is similar to that of weir but the heading up

of water is effected by the gate alone.

• No solid obstruction is put across the river. The crest level in the

barrage is kept at low level.

• During the floods the gates are raised to clear off the high flood

level, enabling the high flood to pass downstream with minimum

afflux.

Barrage

Barrage

• When flood recedes the gates are lowered and flow is obstructed,

thus raising water level to upstream of barrage.

• Due to this less silting and better control over the levels.

• How ever barrage are more costlier then weir.

Cont...

Different parts of barrage

• An artificial barrier across a river to prevent flooding ,aid irrigation or

navigation or to generate electricity by tidal power.

• A barrage is a type of low head , diversion work which consist of

number of large gates that can be opened or closed to control the

amount of water passing through it, thus regulates elevation of water

in irrigation system.

• Barrage word is borrowed from French word meaning dam.

Cont...

• Key difference between barrage and dam is that a dam is built for

water storage in a reservoir, which raise the level of water

significantly.

• A barrage is built for diverting water and raise its level for few feet,

they are generally built on flat terrain across wide rivers.

Cont...

Thank you