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Types of canal outlets

Short answer

Outlets are classified as non-modular (discharge depends on both canal levels, e.g., open sluice), semi-modular (depends only on distributary level, e.g., pipe outlet, AOSM), and rigid modular (constant discharge, e.g., Gibb’s module). Semi-modular are common for equitable distribution.

Explain different types of outlets used in irrigation projects.

A canal outlet (module) is a small structure that delivers water from a distributary or minor to the field water course.

Classification

Outlets are classified by how their discharge responds to water levels in the distributary and in the water course.

1. Non-modular outlets Discharge depends on the water level in both the distributary and the water course.

  • Open sluice, drowned pipe outlet.
  • Simple, cheap, flexible, but discharge varies with water levels in both channels.

2. Semi-modular (flexible) outlets Discharge depends on the water level of the distributary only; it is independent of the water level of the water course provided the minimum working head is available.

  • Pipe outlet (free flow), Kennedy's gauge outlet, Crump's open flume, adjustable orifice semi-module (AOSM).
  • They are very common because they are cheap, and give equitable distribution.

3. Rigid modular outlets The discharge is practically constant, independent of the levels in both channels within working limits.

  • Gibb's rigid module, Khanna's rigid module, Foote module.
  • They give a fixed discharge, but are costly, complicated and need maintenance.
  Distributary                 Water course
 ~~~~~~ FSL ~~~~~~~       ~~~~~~ FSL ~~~~
        (A) Non-modular: q = f(H_d, H_w)
        (B) Semi-modular: q = f(H_d) only
        (C) Modular: q constant

Other types by construction

  • Pipe outlet: a pipe through the bank; simple and cheap.
  • Open flume outlet: Crump's flume, a smooth weir in a flume with a throat.
  • Adjustable orifice: a roof block that can be moved to vary the opening.

✓ Answer checked by Claude Opus 5.5 (high effort)

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