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Unlined Canal Design: Kennedy’s vs. Lacey’s Regime Theories

 Designing stable alluvial canals requires preventing both silting (sediment deposition) and scouring (bed erosion). Two classical approaches govern unlined channel design:

​Kennedy’s Theory: Assumes silt-supporting eddies originate solely from the canal bed. The non-silting, non-scouring critical velocity is given by:

$$V_0 = 0.55 \cdot C \cdot y^{0.64}$$

Where y is depth of flow and C is the critical velocity ratio.

​Lacey’s Regime Theory: Recognizes that eddies are generated from both the bed and sides. Lacey established true regime relationships introducing the silt factor $(f = 1.76 \sqrt{d_{mm}})$:

Wetted Perimeter: $P = 4.75 \sqrt{Q}$

Velocity: $V = \sqrt{\frac{2}{5} \cdot f \cdot R}$

Unlined earthen canals in alluvial plains across India suffer from high seepage losses (often up to 30-40%) and heavy weed growth.

​Modern canal engineering in command areas like the Sardar Sarovar Project has shifted entirely toward composite geomembrane linings and mechanized slip-form concrete paving. Modern numerical design models optimize cross-sectional hydraulic efficiency while eliminating regime siltation problems entirely through controlled closed-conduit or lined distribution systems.

​Note: This technical content was curated and structured with AI assistance to support technical education.

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