--- title: "Short note: Design of hilly irrigation canals" subject: "Irrigation and Drainage Engineering" chapter: 3 key: "semester_6/irrigation_and_drainage_engineering:hilly-canal-design-note" source: https://www.bctengineer.com/q/semester_6/irrigation_and_drainage_engineering/hilly-canal-design-note site: BCT Engineering --- # Short note: Design of hilly irrigation canals Irrigation and Drainage Engineering · Chapter 3: Canal Irrigation System - Asked in: 2064 Kartik (old course), 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/hilly-canal-design-note - Whole chapter: https://www.bctengineer.com/md/semester_6/irrigation_and_drainage_engineering/chapter-3 ## Question Write a short note on specific design considerations for hilly irrigation canals. ## Short answer Hilly canals use contour or side-slope alignment on stable ground, avoiding landslides. Sections are small, often lined with masonry or concrete, or use pipes in unstable areas. Steep bed slopes require drops and energy dissipators. Numerous cross-drainage works need catch drains. Spillways and sediment traps are essential. Retaining walls and bioengineering stabilize slopes. Structures are simple, locally built, with access for maintenance and safety features. ## Answer Irrigation canals in the hills of Nepal face steep, unstable and rocky terrain, high rainfall and small command areas, so they need special design. 1. **Alignment:** contour or side-slope alignment, following the ground with a gentle bed slope. Avoid landslide-prone, fractured and saturated areas; keep a safe distance from gullies; use short tunnels where needed. 2. **Section and lining:** small rectangular or trapezoidal, often masonry or concrete-lined, to avoid seepage and erosion. In unstable ground use pipes (HDPE/GI) or covered channels. 3. **Bed slope and velocity:** slopes are steeper (1 in 500 to 1 in 1000 or more), so velocity is high; check against erosion and use drops/chutes and energy dissipators to take up excess fall. 4. **Cross-drainage works:** many streams are crossed, so aqueducts, culverts, siphons or flumes are needed; provide catch drains above the canal for runoff. 5. **Spillways and escapes:** frequent escape structures to release excess flow in storms and protect the canal. 6. **Sediment control:** intake with a sediment trap/settling basin and flushing arrangements. 7. **Retaining and breast walls** on the hillside; bioengineering (grasses, shrubs) to stabilise the slope. 8. **Small structures:** simple, cheap, locally constructed, easy for WUA to operate and maintain. 9. **Access** for repair, and farmer participation; allow for lower efficiency and seasonal damage. 10. **Safety:** guard rails and covers at crossings. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What alignment is recommended for a hill irrigation canal? A. Contour or side-slope alignment with a gentle bed slope, avoiding landslide-prone and saturated ground B. A straight line across ridges and gullies to shorten length C. Along the bottom of gullies where water collects D. Through fractured, saturated slopes to minimise excavation Answer: A. The canal follows the ground on a contour with gentle slope and keeps away from unstable, fractured and saturated areas. (Key point: Alignment) 2. Why are drops, chutes and energy dissipators needed in hill canals? A. Hill canals carry too little water to flow B. Steeper slopes give high velocity, so excess fall must be taken up to prevent erosion C. They increase seepage into the hillside D. They are needed to raise silt factor Answer: B. High velocity on steep beds can erode the canal, so excess fall is dissipated. (Key point: Steep slope velocity) 3. How are hillside runoff and stream crossings handled? A. By letting streams flow into the canal and removing them at the tail B. By making the canal wider to take storm flow C. Aqueducts, culverts, siphons or flumes at streams and catch drains above the canal D. By building no escapes so water is conserved Answer: C. Many streams are crossed so cross-drainage works are provided, and catch drains stop runoff entering the canal. (Key point: Cross-drainage and catch drains) 4. Which combination suits unstable hill slopes and local operation? A. Large complex gated structures run by a central agency B. Unlined earthen sections with no slope protection C. Deep cuts with no retaining walls to save cost D. Retaining/breast walls with bioengineering, and simple cheap structures the WUA can maintain Answer: D. Hill canals use retaining walls and plants for slope stability and simple local structures easy for the WUA to operate. 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