--- title: "Functions of head and cross regulator" subject: "Irrigation and Drainage Engineering" chapter: 7 key: "semester_6/irrigation_and_drainage_engineering:head-cross-regulator-functions-sketch" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/head-cross-regulator-functions-sketch site: BCT Engineering --- # Functions of head and cross regulator Irrigation and Drainage Engineering · Chapter 7: Regulating Structures - Asked in: 2079 Asoj, 2+3 marks; 2073 Magh, 2+2 marks; 2070 Bhadra, 4 marks; 2069 Bhadra, 4 marks; 2078 Chaitra, 3 marks; 2081 Chaitra, 3 marks (asked 6 times) - Video: [DHS Module2 - Canal Regulators - Head regulator and Cross regulator](https://www.youtube.com/watch?v=Am1OUSbupss) — AM CIVIL ACADEMY - 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/head-cross-regulator-functions-sketch - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-7 ## Question What are the functions of head regulator and cross regulator? Sketch the section of the head regulator / cross regulator. ## Short answer Head regulator controls the discharge and silt entry into an off‑taking canal, measures flow, and can shut off supply. Cross regulator maintains upstream water level to ensure off‑take supply, regulates downstream flow, and allows closure for repairs and rotational running. ## Answer #### 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 ```text 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. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Where is a cross regulator built? A. At the head of the off-taking channel B. At the tail of the distributary C. Across the parent canal just downstream of an off-take D. In the water course Answer: C. A cross regulator is across the parent canal; the head regulator is at the off-take. (Key point: Cross regulator location) 2. What is the main hydraulic function of a cross regulator? A. Disposes of surplus water to a drain B. Measures discharge to each field C. Drops the bed level D. Holds up water level upstream so the off-take gets its full supply even at low parent discharge Answer: D. Raising the upstream level lets the off-take draw its share. (Key point: Cross regulator purpose) 3. Which is a function of a head regulator? A. Regulates discharge entering the off-take and controls silt entry B. Raising the water level in the parent canal C. Escaping surplus water to a river D. Reducing canal bed slope Answer: A. The head regulator controls entry of flow and silt and can shut off supply. 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