Components Of Barrage

 

Ø  What Is Barrage?

A barrage consists of number of large gates, which can controlled the amount of water passing through the gates, by opened or closed them. This barrage helps to irrigation system or other to regulate and stabilize the river water elevation.

·         A barrage and weir are working same but difference is that barrage provides gates, so the flow of water can be maintained,

·         The weir does not have gates, so that flow of water cannot be maintained.

·         The construction cost of barrage is more than the construction cost of weir.

·         A barrage has connectivity at its top of slab from one end to another, weir has not.

·         A barrage has greater height, but weir has small height up to 2 m.

Ø  Function of Barrage

·         Pond level is maintained by barrage.

·         During low supplies, a barrage raises the water level.

·         During higher floods, shutters or gates are closed, so that the overflow can be prevented. 

 

                

Ø  Components  of Barrage

1.      Main barrage portion

2.      Divide wall

3.      The fish ladder

4.      Sheet piles

5.      Inverted apron

6.       Flexible apron

7.      Under sluices : scouring sluices

1.      Main barrage portion

ü  It is the main body of the barrage which is normally made up of RCC slab, which supports the steel gate. In the X- section consists of:

ü  Due to Upstream concrete floor, the path of seepage is increased. It projects the middle portion where pier, gates, and bridge are located.

ü  At the required height, a crest above the floor on which the gates rest in their closed position.

ü  Upstream glacis have suitable shape and slope, which joined the crest to the downstream floor level. The length of concrete work is reduced on downstream site by the hydraulic jump forms on the glacis because it is more stable than the horizontal floor.

ü  Due to hydraulic jump, downstream floor is constructed by concrete. It causes erosion so; there is needed of care due to turbulence. To increase the friction and to destroy residual kinetic energy, form due to hydraulic jump, suitable shape of blocks also provided at particular distance which is determined by hydraulic model experiment.

 

2.      Divide wall

ü  The divide wall is a wall which is constructed perpendicular or right angle to the weir and barrage. The wall divides the weir or barrage properly from the under sluice.

ü  Beyond the beginning of canal HR, the wall extends. At downstream it extends up to the end of loose protection of under sluices lunching apron.

ü  Because of these, hydraulic jump covered that resulting in turbulence.

ü  When full discharge of river passing through weir, the wall is subjected to maximum differential pressure.

ü  It is costly structure, which served as tarp for coarser bed material.

ü  It serves a side wall of the fish ladder.

ü  It separates canal head regulator from main weir.

 

3.      The fish ladder

ü  The artificial barrier in either direction of divide wall is constructed so that fish can be moved easily and comfortably.

ü  There are differences in the level of upstream and downstream sides on the weir, so the narrow trough opening is provided long the divide wall towards weird side which is provided with baffles. The baffles control the flow of sand, liquid, etc.

ü  Due to presence of baffle wall, velocity of flowing water from upstream to downstream is cut down to less than  3 m/s.

ü  The location of fish ladder is adjacent to divide wall is more preferred because at downstream of river, under sluiced always water present.

ü  The optimum velocity should be required 6-8 ft/s in the fish ladder.

4.      Sheet piles

ü  Sheet piles are the supporting members which made up of mild steel.

ü  Its width is ½ ‘ to 2’ in, and thickness is ½” , length is depend on the requirement for having groove to link with the other sheet pile.

ü  In barrage, From the functional point of view the sheet piles classified into three types as follows:

1)      Upstream sheet piles

2)      Intermediate sheet piles

3)      Downstream sheet piles

 

1)      Upstream sheet piles

ü  They are sheet piles which are situated at the end of the upstream concrete floor which is driven into the soil beyond the maximum possible score that may occur.

ü  The piles protect structure from scour.

ü  The uplift pressure face by the barrage, these pile helps to reduce it.

ü  When barrage floor is designed as a raft, the piles help to hold the compacted sand as well as dense the sand between two piles to increase bearing capacity.

2)      Intermediate sheet piles

ü  They are placed at the end of upstream and downstream glacis.

ü  In the event of the upstream and downstream sheet pile, they protect the main structure of barrage, when the upstream and downstream sheet piles are collapsing due to advancing scour or undermining.

ü  They help to reduce uplift pressure and lengthen the seepage path.

3)       Downstream sheet piles

ü  They are placed at the end of downstream glacis.

ü  Their main function is to check the exit gradient, so their depths are greater than the possible scour occurred.

5.      Inverted apron.

ü  It is provided between the downstream sheet piles and the flexible protection.

ü  It consists of 6” sand, 9” coarse, sand and 9”  gravel.

ü  According to the size of particles forming in river, filter material may vary.

ü  By placing concrete blocks of sufficient weight and size, inverted filter is protected.

ü  By escaping water through blocks, silts are left.

ü  Its main function is to check the escape of fine soil particles in the seepage water.

ü  The length of the inverted apron should be 2 times of downstream depth of sheet pile.

6.      Flexible apron

ü  Flexible apron is placed at the downstream of the filter.

ü  It consists of large boulders which are not enough to wash away by the highest water velocity.  But the protection is sufficient to cover the slope of scour depth.

7.      Under sluices : scouring sluices 

ü  It is an opening controlled by gates and it is placed at the low level in the part of barrage which is adjacent to the off takes.

ü  On the two sides of divide wall and canal head regulator, under sluice form the downstream end of the still ponds bounded.

ü  They help to control entry of silt into canal as well as to scour the silt depositions in the pocket periodically.

ü  They protect downstream floor from getting damaged by hydraulic jump.

ü  They help to lower the highest flood level as well as able to discharge 10 to 15% of high flood discharge.

ü  Without dropping the weir shutter, they are able to pass the dry weather flow and low flood.