---
title: "Stepwise design of head regulator"
subject: "Irrigation and Drainage Engineering"
chapter: 7
key: "semester_6/irrigation_and_drainage_engineering:head-regulator-design-steps"
source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/head-regulator-design-steps
site: BCT Engineering
---

# Stepwise design of head regulator

Irrigation and Drainage Engineering · Chapter 7: Regulating Structures

- Asked in: 2078 Baisakh, 4 marks
- 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-regulator-design-steps
- Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-7

## Question

Write down step by step design procedure of head regulator.

## Short answer

Collect Q, levels, silt factor f. Fix crest 0.6-1.2 m above bed. Find waterway from broad-crested weir formula. Compute Lacey's scour R=1.35(q^2/f)^{1/3}, provide u/s and d/s cut-offs. Determine impervious floor length by Khosla's exit gradient, thickness from residual uplift. Add inverted filter and launching apron.

## Answer

The design of a canal head regulator proceeds in these steps.

1. **Collect data:** canal discharge $Q$, river HFL, pond level, canal FSL and bed level, silt factor $f$, safe exit gradient.
2. **Crest level:** fix the crest 0.6 to 1.2 m above the river bed or under-sluice crest, so that bed load is excluded.
3. **Waterway:** head over the crest $H = $ pond level $-$ crest; $L = \dfrac{Q}{C\,H^{3/2}}$ with $C = 1.7$ (broad crest). Provide bays and piers.
4. **Height of gates:** pond level $+$ free-board; top of piers above HFL.
5. **Scour depth and cut-offs:** $R = 1.35(q^2/f)^{1/3}$; d/s cut-off to $1.5R$ below the d/s water level, u/s cut-off to $1.0R$ or less.
6. **Impervious floor length:** from Khosla's exit gradient, $G_E = \dfrac{H_s}{d}\dfrac{1}{\pi\sqrt{\lambda}}$, with $H_s$ the maximum static head; $\alpha = b/d$ from $\lambda$; $b = \alpha d$.
7. **Floor thickness:** from the uplift pressure at key points by Khosla's method, $t = \dfrac{h}{G-1}$.
8. **Protection works:** d/s inverted filter and launching apron, u/s block protection, wing walls.
9. **Check** the stability of piers and the exit gradient; prepare drawings.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. How is the crest level fixed?
   A. At the bed level
   B. 3 m below the bed
   C. 0.6 to 1.2 m above the river bed or under-sluice crest
   D. At HFL
   Answer: C. This excludes bed load. (Key point: Crest level)

2. How is the waterway length found?
   A. L = Q H
   B. L = 4.75 sqrt(Q)
   C. L = Q/(1.7 H)
   D. L = Q/(C H^(3/2)), C = 1.7 for a broad crest
   Answer: D. A broad-crested weir formula. (Key point: Waterway)

3. How is the floor length found?
   A. From Khosla's exit gradient, G_E = (Hs/d)(1/(pi sqrt(lambda)))
   B. From Bligh's L = 0.06Q
   C. From Lacey's width
   D. From pitching thickness
   Answer: A. Hs is the maximum static head. (Key point: Floor length)

4. What depth are the d/s cut-offs?
   A. 0.5R
   B. 1.5R below the d/s water level
   C. R above bed
   D. Zero
   Answer: B. U/s cut-off is R or less. (Key point: Cut-offs)

## Related in Irrigation and Drainage Engineering

- [Design procedure: cross and distributary head regulator](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Across-distributary-regulator-design-procedure) — Irrigation and Drainage Engineering, chapter 7
- [Design cross and head regulator, Q 125](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Across-head-regulator-design-q125) — Irrigation and Drainage Engineering, chapter 7
- [Canal head regulator design, Q 200](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-head-regulator-design-q200) — Irrigation and Drainage Engineering, chapter 7
- [Canal head regulator design, Q 150](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Acanal-head-regulator-design-q150) — Irrigation and Drainage Engineering, chapter 7
- [Functions of head and cross regulator](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ahead-cross-regulator-functions-sketch) — Irrigation and Drainage Engineering, chapter 7, asked 6×
- [Head regulator; outlets and escapes](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Ahead-regulator-outlet-escape-importance) — Irrigation and Drainage Engineering, chapter 7, asked 2×

## Related in other subjects

- [Stepwise procedure of Mohr's circle](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Amohr-circle-procedure) — Strength of Materials, chapter 4, asked 2×
- [Superposition: stepwise procedure for bending moment](https://www.bctengineer.com/question.md?key=semester_3%2Fstrength_of_materials%3Asuperposition-stepwise-bending-moment) — Strength of Materials, chapter 1
- [Step-down chopper with 1 V drop: average and rms](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Astep-down-chopper-1v-drop-rms) — Power Electronics, chapter 4, asked 2×
- [Step-down chopper with 2 V drop: average and rms](https://www.bctengineer.com/question.md?key=semester_7%2Fpower_electronics%3Astep-down-chopper-2v-drop-rms) — Power Electronics, chapter 4, asked 2×