Design of inundation canals

DESIGN CONSIDERATION OF INUNDATION CANALS

  • The head regulator should be installed a few kilometers D/S of the off-take point.
  • This measure would eliminate the risk of the head regulator being washed away.
  • As escape should be located D/S of the head regulator and escape channel should be joined to the river D/S.
  • If more water enters the canal at the off-take point it can be taken out through the escape.
  • In order to reduce the chances of silting of the canal.
  • The flood regulator should be provided with vertical lift gates that could be lifted in stages.
  • The full supply level of the canal should be fixed at a level at which the river water is more or less steady for a period of 40—50 days.
  • which the canal can be run full to irrigate the lands.
  • This steady level of water in the river is called fair irrigation level.
  • The bed of the canal should be as low as possible.
  • The low bed level of the canal can draw some river water even when the river is in lower stage.
  • The section of the canal should be kept liberal to carry the entire required discharge as quickly as possible within the limited time factor.
  • The longitudinal slope should be such that scouring velocities are not developed longitudinal.
  • The slope of the canal may be 0.25 m per kilometre length.
  • The slope of the canal depends upon the general slope of the area also.
  • The floodwater is heavily charged with silt. So these canals are more likely to be silted.
  • Silt clearance must be done after every season.
  • The canals may be aligned with a number of bends so as to trap the silt at intervals.

Advantages of Inundation Canals Following are the advantages of foundation canals.

  1. It is cheap, as no head work and other works have to be constructed.
  2. Water being rich in silt has good manurial qualities.
  3. The area is less liable to be waterlogged.

Disadvantages of Inundation Canals Disadvantages of foundation canals are as following.

  1. As there is no headworks structure the head of the canal is liable to be washed away during floods.
  2. The duty of water is very low.
  3. Since the availability of water is dependent upon floods, the scarcity of water is always felt.
  4. Irrigation water may be badly required and the floodwater in the river may not be available.
  5. Due to a lack of assured supply, the farmers take little interest in their work.
  6. Canals will have to be frequently cleared from silt.
  7. The bigger size of the canal is generally adopted.
  8. This is done to get as much floodwater as possible within a limited time.
  9. The alignment of the canal is not very precise.
  10. It may be silting at some sections and scouring at other sections.

Maintenance of inundation canals.

  • Inundation canals always suffer from the difficulty of silting, scouring and scarcity.
  • In order to maintain these canals in fine shape, the following provisions should be necessarily made.
  • Besides the main off-take point, subsidiary off-take points should be constructed.
  • In case, main off-take point is closed somehow, water could be admitted in the canal from subsidiary off-take points.
  • A feeder canal should be constructed linking several foundation canals, taking-off from the same river.
  • This measure avoids the necessity of constructing several subsidiary heads.
  • By this method, a good head of water can be availed for a considerable length of time.
  •  Provision of a pucca head regulator, attached with an escape, a few km D/S of the off-take point, also enables the exercise of good control on the inundation canal.

 

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