What alignment is recommended for a hill irrigation canal?

Contour or side-slope alignment with a gentle bed slope, avoiding landslide-prone and saturated ground

A straight line across ridges and gullies to shorten length

Along the bottom of gullies where water collects

Through fractured, saturated slopes to minimise excavation

Why are drops, chutes and energy dissipators needed in hill canals?

Steeper slopes give high velocity, so excess fall must be taken up to prevent erosion

Hill canals carry too little water to flow

They increase seepage into the hillside

They are needed to raise silt factor

How are hillside runoff and stream crossings handled?

Aqueducts, culverts, siphons or flumes at streams and catch drains above the canal

By letting streams flow into the canal and removing them at the tail

By making the canal wider to take storm flow

By building no escapes so water is conserved

Which combination suits unstable hill slopes and local operation?

Retaining/breast walls with bioengineering, and simple cheap structures the WUA can maintain

Large complex gated structures run by a central agency

Unlined earthen sections with no slope protection

Deep cuts with no retaining walls to save cost

2064 Kartik (old course) · 4 marks

Short note: Design of 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.

Write a short note on specific design considerations for hilly irrigation canals.

Irrigation canals in the hills of Nepal face steep, unstable and rocky terrain, high rainfall and small command areas, so they need special design.

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.
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.
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.
Cross-drainage works: many streams are crossed, so aqueducts, culverts, siphons or flumes are needed; provide catch drains above the canal for runoff.
Spillways and escapes: frequent escape structures to release excess flow in storms and protect the canal.
Sediment control: intake with a sediment trap/settling basin and flushing arrangements.
Retaining and breast walls on the hillside; bioengineering (grasses, shrubs) to stabilise the slope.
Small structures: simple, cheap, locally constructed, easy for WUA to operate and maintain.
Access for repair, and farmer participation; allow for lower efficiency and seasonal damage.
Safety: guard rails and covers at crossings.

✓ Answer checked by Claude Opus 5.5 (high effort)

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Short note: Design of hilly irrigation canals

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