Divide wall

DIVIDE WALL

  • It is also called groyne, or groyne wall.
  • It is an embankment constructed in the river, U/S of the weir.
  • Its axis is kept at right angles to the axis of the weir.
  • The embankment is protected from all the sides with the help of stone or concrete blocks.
  • The divide wall separates weir from undersluices.
  • It extends a little U/ S of canal regulator and on D/S end upto loose protection of the under sluices.
  • It may be made of concrete or masonry, with top width of 1.5 m to 3 m.

This wall should be designed for following conditions.

(i) Silt pressure upto full tank level on the face opposite to the face lying towards the head regulator and minimum possible or no water on the face lying towards the head regulator.

(ii) During high floods the water level behind the weir should be assumed about 1 m to 2 m above the level of water behind the under sluices.

(iii) Top width is taken 1.5 m to 2 m, while the bottom width is found out on the basis that resultant of forces acting on divide wall life within the middle third of the base.

The main purposes of divide wall are as follows.

  • To separate the floor of channel formed behind under-sluices from the floor level behind the weir proper.
  • Level of channel is at lower level than that of weir proper.
  • The area enclosed between undersluices, divide wall and head regulator, is known as pocket.
  • The divide wall provides a relatively quite pocket in front of canal head regulator.
  • This phenomenon concentrates more silt in lower layers of water entering the pocket.
  • The lower silt laden layers are directly passed through the undersluices on D/S side and thus water entering the canal is relatively clear, having very little of silt.
  • Divide wall serves as one of the side walls of fish ladder.
  • Divide wall prevents formation of cross currents and thus avoids their erosive effect.
  • For this purpose sometimes more than one divide walls may have to be provided.
  • When undersluices are not worked, as in case during low water in winter, silt may get deposited behind the under sluices.
  • This silt is easily washed to D/S side by opening undersluice gates and thus approach channel is kept clear of silt.

 

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