MISCELLANEOUS CANAL STRUCTURES

Canal falls, head regulators, canal escapes, metering flumes, canal outlets and modules are canal

structures.

The best alignment of off-taking channel is when it makes zero angle with the parent channel

initially and then separates out in transition.

* The main function of a head regulator is

1. To control the supplies entering the off-take channel

2. To control silt entry into off-take channel

3. To serve as a meter for measuring discharge

* The main functions of a cross regulator are:

1. Control canal irrigation system.

2. When the water level in the main canal is low, it helps in heading up water.

3. It helps in absorbing fluctuations in various sections of the canal system.

4. It is often combined with a road bridge and a fall, if required.

Canal Escapes

* A canal escape is a side channel constructed to remove surplus water from an irrigation channel.

* The importance of such an escape is realised more, in case, a breach occurs in a channel.

* Weir type and sluice type (regulator type) canal escapes are in use.

Canal Outlet or Module

* It is a small structure built at the head of the water course so as to connect it with a minor or a

distributary channel.

* The control and maintenance of canal network upto the module is under the jurisdiction of the state

government and beyond the module it is the responsibility of cultivators.

* Types of outlets (modules)

1. Non-modular: Open sluice and drowned pipe outlets.

2. Semi-modules or flexible-modules: Pipe outlets venture flume and orifice semi-module

3. Rigid-module or modular outlets: Cribbs module.

* Performance of modules is judged from:

1. Flexibility: It is the ratio of the rate of change of discharge of the outlet to the rate of change of

discharge of the distributary channel.

2. Proportionality: The outlet is said to be proportional when the rate of change of outlet discharge

equals the rate of change of channel discharge. (F = 1).

If F > 1, hyper proportionality, If F < 1, sub-proportionality

3. Setting: The ratio of the depth of the sill level of the outlet below the FSL of the distributary, to

the full supply depth of the distributary, is known as setting.

4. Sensitivity: It is defined as the ratio of the rate of change of discharge through the outlet to the

rate of change of water level of the distributary, referred to the normal depth of the channel. For

rigid modules the sensitivity is zero, since discharge is fixed.

* Types of non-modular outlets are

1. Open sluice 2. Pipe outlet

* Types of semi-modules or flexible outlets are:

1. Pipe outlet discharging freely into the air.

2. Venturiflume or Kennedy gauge outlet.

3. Open flume outlet

4. Adjustable orifice semi-module.

Cattle crossings In remote village areas where no major movement is involved arrangements are

made so that cattle, bullock carts, etc., can cross the canal. Such crossings are called cattle

crossings.

1. If water depth is of the order of 0.75 m, ramps are provided for the entry and exist.

2. If water depth is greater than 1.2 m the cattle have to swim certain distance across the canal.

Bed bars Bed bars are masonry or concrete toe wall like structure constructed along unlined canal,

so as to serve as permanent reference marks, and thus to indicate the correct alignment and

theoretical bed levels of the canal.

Cross-Drainage Works

* A cross-drainage work is a structure, constructed at the crossing of a canal and a natural drain, so as

to dispose of drainage water without interrupting the continuous canal supplies.

* Types of cross-drainage works:

1. By passing canal over the drainage

– aqueduct

– syphon aqueduct

2. By passing the canal below the drainage

– super passage

– canal syphon

3. By passing the drain through the canal

– level crossing

– inlets and outlets.