Geological parameters for canal alignment

A canal carries water over long distances, so geology decides its stability, seepage loss and cost.

Geological parameters

1. Soil and rock type: firm, compact, impervious soil (clay, silty clay) gives low seepage loss and stable banks. Avoid loose sand and gravel (high seepage), very soft clay (settlement), black cotton or swelling soil, and rock needing costly excavation.
2. Permeability and seepage: avoid cavernous limestone, fractured rock and coarse gravel unless lined. Canal loss reduces supply and raises the water table.
3. Slope stability: in the hills, use stable slopes; avoid landslide areas, steep cuts in weak rock, and talus. On a hillside, beds dipping out of the slope (toward the valley) cause slides.
4. Geological structure: avoid faults, shear zones, and highly jointed rocks along the line; cross faults at right angles.
5. Topography: a gentle gradient is needed; side-hill cut-and-fill canals need a stable ground.
6. Groundwater: high water table causes waterlogging and bank failure; salinity affects soil.
7. Drainage crossings: number and type of cross-drainage works; geology at their foundations; flood-prone areas.
8. Seismic and flood hazards.
9. Construction materials: earth for embankment, stone, gravel and sand nearby.
10. Excavation conditions: depth of cutting, rippability, rock excavation cost.

Investigation: geological mapping, test pits at intervals, borings at structures, permeability tests, and soil tests (compaction, shear strength, swelling).