Functions of head and cross regulator

Head regulator

A head regulator is a gated structure at the head (off-take) of a canal, distributary or minor, built across the off-taking channel.

Functions

1. Regulates the discharge entering the off-taking channel.
2. Controls silt entry (a high crest and a silt excluder keep the bed load out).
3. Measures the discharge (gauge and rating at the gates).
4. Shuts off the supply during floods or repairs, or when no water is needed.

Cross regulator

A cross regulator is a gated structure built across the parent canal, just downstream of the off-take of a branch or distributary.

Functions

1. Raises (holds up) the water level on its upstream side so that the off-taking channel gets its full supply, even when the parent canal carries less than full discharge.
2. Regulates the discharge passing to the downstream reaches of the parent canal.
3. Helps to close the canal for repairs, and its deck serves as a bridge for cross-communication.
4. Allows the supply to be diverted to the off-take in rotation (rotational running).

Sketch of section

 Longitudinal section through a head/cross regulator
  FSL u/s ~~~~~~~~~~~~~|gate|~~~~ FSL d/s
                       | |
                  _____|_|______
  u/s bed _______|  crest wall  |_______ d/s bed
    |u/s cut-off|__ floor ______|d/s cut-off|
        u/s apron   (impervious)  d/s protection:
                                  stilling basin,
                                  inverted filter,
                                  launching apron

Section of the gates: piers carry a bridge deck and a gate hoist; gates (vertical lift steel) slide in grooves cut in the piers.