Canal Regulation and Canal Regulation Work

 

 Canal Regulation

The water which enters into the main canal from the river has to be divided into different branches and distributaries, in accordance with the relative urgency of demand on different channels. This process of distribution is called 'Regulation'.

• To distribute water effectively, the discharge has to be adjusted to any required value. This can be achieved by means of regulators.

Canal Regulation Work

The work which are constructed in order to control and regulate discharges, depths, velocities etc. in canals, are known as canal regulation works.

• These structures ensure the efficient functioning of a canal irrigation system, by giving full control upon the canals.The important of these structures are-

1.  Canal fall
2. Canal Regulators [ Head regulator and cross regulator ]
3.  Metering flumes
4.  Canal outlet and Modules.

1- Canal Fall

Whenever the available natural ground slope is steeper than the designed bed slope of the channel, the difference is adjusted by constructing vertical fall or drops in the canal bed at suitable intervals as shown in fig.

Canal fall

• Such a drop in natural canal bed will not be stable and, therefore, in order to retain this drop, a masonry structure is constructed.Such a pucca structure is called a canal fall or canal drop.
• The location of fall in a canal depends upon the topography of the country through which the canal is passing.

Types of canal fall

1.  Ogee falls
2. Trapezoidal Notch fall
3. Well type fall or cylinder fall or syphon well drop
4. Simple vertical drop type and Sarda type fall
5. Straight Glacis falls
6. Montague types falls
7. Inglish falls or Baffle falls

2- Canal Regulators

Alignment of the off-taking channel

When a branch channel takes off from the main channel [ called parent channel ], the off-take alignment must be designed very carefully.

The best ideal alignment is : when the off-taking channel makes zero angle with the parent channel initially and then separates out in a transition, as shown in fig.

Alignment of the off-taking channel

The transition will have to be designed properly, so as to avoid accumulation of silt. As an alternative to transitions, both the channels should make an angle with the parent channel upstream of the off-take as shown in fig.

Alignment of the off-taking channel

• When the parent channel has to be carried straight, the edge of the canal rather than center line should be considered in deciding the angle of off-take as shown in fig.

Distributary Head Regulator and Cross Regulator

A distributary head regulator controls the supply of the off-taking channel ; while a cross regulator controls the supply of the parent channel.

A head regulator provide at the head of the off-taking channel, controls the flow of water entering this new channel. While a cross regulator may be required in the main parent channel down-stream of the off-taking channel,and is operated when necessary so as to head up water on its upstream side, thus to ensure the required supply in the off-taking channel even during the period of low flow in the main channel.

• The main function of a head regulator are:

1. To regulate or control the supplies entering the off-take channel.
2. To control silt entry into the off-take channel.
3. To provide as a meter for measuring discharge.

• The main function of a cross-regulator are:

1. To effectively control the entire canal irrigation system.
2. When water level in the main channel is low, it helps in heading up water on the u/s side and to feed the off-take channels to their full demand in rotation.
3. They help in absorbing fluctuations in various sections of the canal system, and in preventing the possibilities of breaches in the tail reaches.
4. Cross regulators in often combined with a road bridge, so as to carry the road which may cross the irrigation channel near the site of the cross regulator. It is also usually  combined with fall [ if required at the site of cross regulator]; when it is called a fall regulator.

• A regulator essentially consist of piers placed across the canal at regular intervals with grooves, in which either planks or gates can be used to control the supplies. Planks called Karries can be used for small channels only, as the maximum height of the planks which can be handled manually is about 2 meters. for large channels, either hand operated or mechanically operated gates are used.
• The hand operated gates can have spans of 6 to 8 m, while mechanically operated gates can be as wide as 20 meters or so. A light bridge platform has to be laid on the piers for operation of planks or gate.

• It is often economical to combine a regulator with the bridge and also to flume the channel at the side of the regulator, so as to reduce its floor width for affecting economy.

Canal Escape

• An escape is a side channel constructed to remove surplus water from an irrigation channel  [ main canal, branch canal, or distributary, etc.] into a natural drain. The water in the irrigation channel may become surplus due to some mistake; or difficulty in regulation at the head; or due to excessive rainfall in upper reaches. Sometimes, the cultivation may find that the demand of water is over and may close their outlets suddenly. In such circumstances, the canal supplies shall become surplus, and this excess may overflow the banks unless escaped.

• No doubt, in all such circumstances, the supplies shall be reduced or stopped from the head work, but the effect of this reduction is felt only after a certain time. Therefore, In order to avoid damage, some immediate action is required, and this is achieved by means of Escape, generally called a surplus water escape.

• The importance of such escape is realised more, in case of a breach occurs in a channel. If a breach occurs, immediate information is sent to the head, so as to close down the channel supplies. But the water already contained in the channel from the head to the breach site will cause wide spread damage if allows to pass through the breach is opened and most of the water is allowed to escape.