DIVERSION HEAD WORKS –ALL YOU NEED TO KNOW

It is a technique of diverting water to the canal, when a weir or barrage is constructed across a perennial river to raise the water level.Diversion headworks is a structure constructed across a river for the purpose of raising the water level in the river so that it can be diverted into the off taking canals. It is also known as canal headworks and performs the following functions.

It raises the water level on upstream side.
Other uses of this is to regulates the supply of water into canals.
It controls the entry of silt into canals.
It provides some pondage creating small pond.
It helps in controlling the vagaries of river.
To control the entry of silt into the canal and to control the deposition of silt at the head of the canal.
To control the fluctuation of water level in the river during different seasons.

LAYOUT OF A DIVERSION HEAD WORKS

Weir or Barrage

The Weir is an impervious barrier constructed across the river to raise water level on the upstream side, such that the water level rises upto the required height and the surplus water is allowed to flow over the weir. Weir is generally constructed across the inundation river.

The Barrage is an upgradation of Weir in which adjustable gates are installed over the weir to maintain the water surface at different levels at different times. The water level is adjusted by operating adjustable gates. These gates are operated by cables.

Divide wall

The divide wall is masonary or a concrete wall constructed at right angle to the axis of the weir and sepatares the weir proper from the under sluices. It extends from beyond the end of the head regulator on u/s side to loose protection of the under sluice on d/s side.

Functions of divide wall:-

To separate the under sluice portion from weir proper portion.
Increase the effectiveness of the under sluices portion.
To prevent cross current and flow parallel to the weir.
Divide wall incidentally acts as one of the side walls of the fish ladder.
To isolate pocket u/s of head regulator to facilitate scouring operation.

Scouring Sluices or Under Sluices

Scouring sluices are the openings provided at the base of the weir or barrage to allow the flow of slit deposited. These openings are provided with adjustable gates. When the gates are closed the silt gets deposited and after appreciable collection of silt, the gates are opened and the deposited silt flows towards the downstream through scouring sluices.

Fish Ladder

The survival of many fish species depends on migrations up and down rivers. Among anadromous fish such as salmon, shad, and sturgeon, downstream migration is a feature of early life stages, while upstream migration is a feature of adult life. Among catadromous, like the North American eel, the opposite is true. River obstructions such as dams, culverts, and waterfalls have the potential to slow or stop fish migration. Indeed, these impediments to fish migration are often implicated in the decline of certain fish stocks.

A fish ladder, also known as a fishway, provides a detour route for migrating fish past a particular obstruction on the river. Designs vary depending on the obstruction, river flow, and species of fish affected, but the general principle is the same for all fish ladders: the ladder contains a series of ascending pools that are reached by swimming against a stream of water. Fish leap through the cascade of rushing water, rest in a pool, and then repeat the process until they are out of the ladder.

Silt Excluder

It is found that, when the divide wall is constructed, the still water pocket is formed in front of canal head, where it is found that the lower layer of water contains heavy silt and the upper layer contains very fine silt. Since, the very fine silt is very fertile, it may enter the canal whereas the heavy silt causes sedimentation in pocket. To eliminate the suspended heavy silt, the silt excluder is provided. It consists of a series of tunnels starting from the side of the head regulator up to the divide wall.

The height of embankment depends on high flood level. To resist the erosion effect, wooden piles are driven along the river banks throughout the length of dyke.

Purposes :

Protects valuable agricultural land
Protects the town and villages from heavy flood
Retains the flood water or storage water within a specified section.

Barrage

If ponding of water is achieved by shutters or gates then it is called barrage. It has low crest wall with high gates.

Under sluices

The weir proper I constructed in the middle portion of diversion head works. At the ends under sluices are provided adjacent to the anal head regulators. A comparatively less turbulent pocket of water is created near the canal head regulator by constructing under sluice portion of the weir.The undersluices are the openings provided in the weir wall with their crest at low level. These openings are controlled by gates.

Functions of under sluices