--- title: "Canal cross-section in cutting and filling" subject: "Irrigation and Drainage Engineering" chapter: 3 key: "semester_6/irrigation_and_drainage_engineering:canal-cross-section-cut-fill" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/canal-cross-section-cut-fill site: BCT Engineering --- # Canal cross-section in cutting and filling Irrigation and Drainage Engineering · Chapter 3: Canal Irrigation System - Asked in: 2071 Bhadra, 5 marks; 2068 Chaitra (old course), 4 marks; 2065 Shrawan (old course), 8 marks (asked 3 times) - Video: [Design of Canal: partially cutting and filling। canal drawing। Irrigation system](https://www.youtube.com/watch?v=8C1DETPqb6k) — abtak 360 - 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-cross-section-cut-fill - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-3 ## Question Draw a typical cross section of a canal in partial cutting and partial filling and label at least five different canal elements on it. ## Short answer A canal in partial cut and fill has a bed, side slopes (1.5:1 in cutting, 2:1 in filling), full supply level, free board (0.5–1 m), banks (top width 1.5–3 m, service bank 5 m), berm (0.5–1 m), and ground level. The hydraulic gradient line through the bank must be covered by at least 0.5 m of earth. ## Answer A canal in partial cutting and partial filling has its bed below ground level and its banks built up above ground, using the excavated soil. ```text b b |----| |----| Bank_______ _______Bank top / \ FSL ~~~~~~~~~~~ / \ outer / \ ___ free board / \ slope ----/--berm--\_______________/--berm--\---- G.L. outer \ full supply / slope \ depth / \___________/ bed bed width B ``` #### Labelled elements 1. **Bed (bed width B):** the bottom of the canal. 2. **Full supply level (FSL) and full supply depth (FSD):** the design water level and depth. 3. **Side slopes:** typically 1.5H:1V in cutting and 2H:1V in filling. 4. **Free board:** the vertical distance between the FSL and the top of the bank (0.5-1.0 m). 5. **Banks:** embankments on both sides. The top width is 1.5-3 m for ordinary banks; the service bank, which carries the inspection road, is 5 m or wider. 6. **Berm:** a horizontal strip between the inner toe of the bank and the top edge of the cutting. It gives stability and reduces seepage, and is usually about 0.5-1 m wide (wider in deep cutting). 7. **Ground level (GL)** and **borrow pits/spoil banks** beyond the berm. 8. **Hydraulic gradient (seepage) line:** drawn from the FSL through the bank at a slope of about 4H:1V to 6H:1V (flatter for larger canals). The bank must be wide enough to keep this line covered by at least 0.5 m of earth at the outer face. When the cutting equals the filling, the section is economical (balancing depth). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is free board? A. Vertical distance between full supply level and top of bank B. Depth of water in the canal C. Width of the berm D. Distance from bed to ground level Answer: A. It gives safety against waves and overtopping, typically 0.5-1.0 m. (Key point: Free board) 2. What does the berm do? A. It carries the road B. It is a horizontal strip between bank toe and canal edge giving stability and reducing seepage C. It is the canal bed D. It stores silt only Answer: B. The berm adds stability and reduces seepage through the bank. (Key point: Berm) 3. What typical side slopes are used? A. 2H:1V in cutting and 1.5H:1V in filling B. 1H:1V both C. 1.5H:1V in cutting and 2H:1V in filling D. 3H:1V in cutting Answer: C. Cut soil stands steeper than made-up banks, so fill slopes are flatter. (Key point: Side slopes) 4. When is the section economical? A. When banks are as high as possible B. When no free board is given C. When only borrow pits are used D. When excavation equals the earth needed for banks (balancing depth) Answer: D. With cut equal to fill no earth is borrowed or spoiled. 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