Under-Sluices or Scouring Sluices
The under-Sluices are the openings which are fully controlled by gates, provided in weir wall with their crest at a low level. They are located on the same side as the off-taking canal.
Under sluices are also called scouring sluices because they help in removing the silt near the head regulators.
Functions of Under-Sluices
i) Preserve a clear and defined river channel approaching the regulator.
ii) Control the silt entry into the canal.
iii) Pass the low floods without dropping the shutter of the main weir.
iv) Provide greater water-way for floods, thus lowering the flood level.
v) They scour the silt deposited on the river bed above the approach channel.
Design consideration of Under-Sluices
The silt of the under-sluice pocket is kept at or slightly above the deepest river bed and about 0.9 to 1.8 m below silt of the canal head regulator.