Alluvial and non-alluvial canals

Alluvial canals

Canals excavated in alluvial soil (deposited by rivers, e.g. the Gangetic and Terai plains), which is fine, loose and easily eroded. The canal carries silt, so the bed and banks can be scoured or silted. The channel must be designed for a stable regime section, using Kennedy's or Lacey's regime theory; the slope and shape adjust themselves until the canal neither silts nor scours.

Non-alluvial canals

Canals constructed in hard soil, rocky terrain or non-erodible strata, e.g. hilly and peninsular areas, where the bed and banks are stable and the canal does not carry silt that changes its shape. They are designed with Manning's or Chezy's formula using permissible velocity and rugosity, so no regime theory is needed. They may be lined to reduce seepage.