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Definition: best hydraulic section

Short answer

A best hydraulic section is the channel cross-section that maximizes discharge for a given area, slope, and roughness by minimizing wetted perimeter and maximizing hydraulic radius. For rectangular channels, width equals twice depth (b=2y); for trapezoidal, half the top width equals the sloping side length; for triangular, side slopes are 1:1 (45°).

Define best hydraulic section.

A best hydraulic section (most efficient or most economical section) is the channel cross-section that carries the maximum discharge for a given area, bed slope and roughness. From Q=ACRSQ = AC\sqrt{RS}, this occurs when the wetted perimeter is minimum, i.e. the hydraulic radius R=A/PR = A/P is maximum. Such a section also needs the least lining and excavation cost.

Conditions for common shapes:

SectionCondition
Rectangularb=2yb = 2y, R=y/2R = y/2
TrapezoidalHalf top width = sloping side; R=y/2R = y/2
TriangularSide slope 1:1 (45° with vertical), R=y/(22)R = y/(2\sqrt{2})

Example: best rectangular section with y=2y = 2 m has b=4b = 4 m and R=1R = 1 m.

✓ Answer checked by Claude Opus 5.5 (high effort)

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