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Longitudinal section of a head regulator

Short answer

A head regulator longitudinal section shows a raised crest with gates, upstream cut-off and floor, downstream stilling basin with energy dissipation, downstream cut-off, and protection works of inverted filter and stone apron. These elements lengthen seepage, reduce uplift, and prevent scour.

Draw a neat longitudinal section through a head regulator of an irrigation head works showing all components.

A canal head regulator is built at the off-take of a canal from the headworks pond (u/s of the weir). A longitudinal section along the axis of the canal shows the following components.

 Pond level ~~~~~~~~|  gate  |~~~~~~~ FSL canal ~~~~~~
                    |  hoist |
                 ___|  bridge|___
 crest level ___/ piers + gates \_____
 |u/s    |  u/s    |  crest     | d/s floor |  d/s
 |cut-off|  floor  |  (raised)  | (stilling)|  protection
 |  d1   |         |            |           | inv. filter
 |       |         |            |           | + apron
 |_______|_________|____________|___________|___ canal bed
                 <----- impervious floor ----->

Components

  1. Upstream cut-off (pile) and upstream floor: lengthen the seepage path and reduce the uplift and exit gradient.
  2. Crest wall: raised about 1.2 m above the under-sluice crest or river bed to exclude bed load.
  3. Gates and piers (vertical lift gates) with a bridge and hoist.
  4. Downstream floor (stilling basin): dissipates energy and withstands uplift.
  5. Downstream cut-off: keeps the exit gradient safe and protects the floor against scour.
  6. Protection works: inverted filter, loose stone apron, and wing walls splayed into the canal.

✓ Answer checked by Claude Opus 5.5 (high effort)

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