--- title: "Canal outlet and module performance criteria" subject: "Irrigation and Drainage Engineering" chapter: 7 key: "semester_6/irrigation_and_drainage_engineering:canal-outlet-module-performance-criteria" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-outlet-module-performance-criteria site: BCT Engineering --- # Canal outlet and module performance criteria Irrigation and Drainage Engineering · Chapter 7: Regulating Structures - Asked in: 2065 Kartik (old course), 5 marks - Video: [FLEXIBILITY , SENSITIVITY, PROPORTIONALITY,SETTING OF OUTLETS](https://www.youtube.com/watch?v=_3T_nqc4LIY) — Civil Engineer FBH - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-outlet-module-performance-criteria - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-7 ## Question Define canal outlet. What are the criteria for judging the performance of modules? ## Short answer A canal outlet diverts water from a distributary to a water course. Performance is judged by flexibility (ratio of relative discharge change to relative distributary discharge change), proportionality, sensitivity, setting, minimum modular head, silt-drawing capacity, and tamper-resistance. ## Answer 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is a canal outlet? A. A structure that drops the canal bed level B. A structure that carries canal water over a drainage C. A small structure that diverts water from a distributary or minor to a water course D. A gate that closes the canal at the head Answer: C. An outlet (module) delivers water from the distributary to the water course of a chak and fixes its discharge. (Key point: Meaning of canal outlet) 2. An outlet with flexibility F greater than 1 is called what? A. Proportional B. Sub-proportional C. Modular D. Hyper-proportional Answer: D. F = 1 is proportional, F > 1 hyper-proportional, F < 1 sub-proportional. (Key point: Flexibility classification) 3. What should a good outlet have for sensitivity? A. Low sensitivity so discharge stays stable when levels change slightly B. High sensitivity C. Sensitivity equal to flexibility times 10 D. No requirement Answer: A. A low sensitivity gives a stable discharge against small level changes. (Key point: Sensitivity) 4. Why should the minimum modular head be small? A. To increase silt drawn B. So command is not lost, since the least head loss needed is taken from the available level C. To make the outlet hyper-proportional D. To reduce the setting Answer: B. Minimum modular head is the least head loss for the outlet to work as designed; a large value would reduce command. 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