Last reviewed 16 Sept 2026 · 7 min read
Why canals are lined
A canal lining is an impervious (or less pervious) layer on the bed and sides of a canal.
Advantages
- Reduces seepage losses — more water is available for irrigation; the area irrigated increases.
- Prevents waterlogging and salinity in the command area by preventing the rise of the water table.
- Higher permissible velocity — a smaller cross-section and less land and earthwork for the same discharge; flatter slopes possible, so more area can be commanded.
- Less maintenance — no weed growth, no silting or scouring; stable section; fewer breaches.
- Reduced flood danger from bank breaches; control of rodent holes.
- Lower friction (smoother surface) and better hydraulic efficiency.
- Resists erosion in unstable or rocky soils.
Disadvantages
- High initial cost.
- Repairs are difficult while the canal runs; closure needed.
- Shifting outlets and changes to the section become difficult later.
- Cracks and uplift damage if not designed with drainage.
Economics
Lining is justified when the annual benefits (value of water saved, reduced maintenance, land saved, prevention of waterlogging) exceed the annual cost (interest and depreciation on the lining cost plus maintenance), i.e. B/C > 1.
( = capital cost; = life of lining; = interest rate.)
Types of lining
Hard surface linings
| Lining | Features |
|---|---|
| Cement concrete (in situ) | Most durable and widely used for major canals; low friction; resists erosion and weeds; laid in panels with construction and contraction joints filled with sealants; may be plain or reinforced |
| Precast concrete slabs | Factory-quality slabs laid on prepared sub-grade; quicker, can be laid while the canal is partly operational; more joints (seepage paths) |
| Shotcrete (gunite) | Cement mortar sprayed under pneumatic pressure on the prepared surface (with or without mesh); suited to irregular sections, repairs and small canals |
| Burnt clay tile / brick lining | Common in India for small and medium canals where good bricks and labour are available; tiles laid in two layers with cement mortar (sandwich) on a plaster base; cheaper; more joints and somewhat higher seepage and roughness |
| Stone masonry / boulder lining | Where stone is locally available; durable; rough |
| Asphaltic concrete | Flexible, withstands minor settlements; less durable; weed growth possible if thin |
| Soil–cement | Local soil mixed with cement and compacted; economical in sandy soils |
Earth-type and membrane linings
| Lining | Features |
|---|---|
| Compacted earth | Local soil compacted in layers; cheap but susceptible to erosion and weeds; lower velocities |
| Clay puddle | Mixture of clay and water puddled into the bed; economical where clay is available |
| Bentonite | Swelling clay mixed with soil or placed as a layer; seals pores |
| Buried membranes (LDPE/HDPE film) | Thin polyethylene film laid on the sub-grade and protected by a soil or brick/tile cover; very effective seepage barrier, low cost |
| Exposed membranes / geomembranes | Stronger synthetic sheets; vulnerable to damage and UV if not protected |
Requirements of a good lining
Impervious; smooth (low roughness); durable against weathering, erosion and chemicals; structurally stable; economical; easy to repair; resistant to weed growth and burrowing animals; able to withstand minor settlements and thermal movements.
Design of lined canals
Lined canals are non-erodible, so the section is designed for maximum hydraulic efficiency within practical limits, using Manning's formula ( for concrete lining typically about 0.013–0.018 depending on finish).
Typical Indian practice:
- Triangular section with rounded bottom for smaller discharges.
- Trapezoidal section with rounded corners for larger discharges.
The side slopes are commonly about 1.25 H : 1 V (or as dictated by soil stability).
Triangular section with circular bottom (depth , bottom arc radius ):
Trapezoidal section with rounded corners (bed width , corner radius ):
( in radians.)
Freeboard and bank height are provided above the full supply level as in unlined canals; the lining is usually carried up to a little above FSL.
Velocity limits — lined canals can carry higher velocities (up to about 2 m/s or more for good concrete) without erosion; a minimum velocity is maintained to avoid silting and weed growth.