Ground & Roof Rainwater

Rainwater design flow from regional intensity formulas, and non-full pipe velocity & capacity verification.

Rainwater design flow

Region (city)

Surface

Return period P (yr)

Rainfall duration t (min)

Catchment area (ha / per 100 m²)

Runoff coefficient ψ

Design rainwater flow

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L/s

Non-full pipe velocity & capacity check

Partially-full circular pipe by Manning's equation with a submergence correction factor.

Pipe diameter D (m)

Slope S

Roughness n

Submersion ratio h/D

Design flow to satisfy (L/s)

Pipe velocity v

—

m/s

Pipe capacity Q

—

L/s

Self-cleaning (v ≥ 0.7 m/s)

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Capacity check (capacity ≥ design)

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Velocity ≥ 0.7 m/s is self-cleaning; otherwise the pipe cannot self-clean. Capacity must be no less than the design flow.