Canal outlet and module performance criteria

A canal outlet (module) is a small structure that diverts water from a distributary or minor to a water course and fixes the discharge supplied to the command area of the chak.

Criteria for judging the performance of a module

1. Flexibility $F = \dfrac{dq/q}{dQ/Q}$: shows how the outlet discharge responds to changes in the distributary discharge. $F = 1$ is proportional, $F > 1$ hyper-proportional and $F < 1$ sub-proportional.
2. Proportionality: the outlet should draw its share in proportion to the supply (equitable distribution).
3. Sensitivity $S = \dfrac{dq/q}{dG/D}$ (with $G$ the distributary gauge reading and $D$ its depth): the outlet should be insensitive to small level changes; a low sensitivity gives a stable discharge. It is related to flexibility by $S = nF$.
4. Setting: the ratio of the depth of the outlet's sill below FSL to the distributary depth; it controls the flexibility and the silt drawn.
5. Minimum modular head: the least head loss needed for the outlet to work as designed. It should be small so that command is not lost.
6. Silt-drawing capacity: the outlet should draw silt in proportion to the water, so that the distributary does not silt up.
7. Tamper-resistance and cost: simple, cheap and not easily altered by farmers.