Time of Concentration (Tc)

Ref: MSMA 2nd Edition (2012), Chapter 2, §2.2.2 & Table 2.1

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tc = to + td

Ref: MSMA 2nd Edition (2012), Chapter 2, §2.2.2 & Table 2.1

to = 107·n*·L^(1/3) / S^(1/5) (S in %)

Overland flow (MSMA Table 2.1, QUDM 2007)

td = L / (60·V)

Drain/channel flow

Overland Flow (to)

Horton's Roughness n* (overland)

MSMA Table 2.2: Paved 0.015, Bare soil 0.0275, Poor grass 0.035, Average grass 0.045, Dense grass 0.060

Overland Flow Path Length (m)

Max 50 m for steep (>10%), 100 m for moderate (<5%), 200 m for mild (<1%)

Overland Surface Slope (%)

In PERCENT per MSMA Table 2.1 (e.g. 2 for 2 %, not 0.02)

Drain Flow (td)

Drain/Channel Length (m)

Length of drain/channel to outlet

Flow Velocity in Drain (m/s)

Typical 0.6–2.0 m/s per MSMA Ch 14

Time of Concentration

—min

Engineering aid only — final design must be endorsed by a registered PE under BEM.

Disclaimer: This output is an engineering calculation aid only and does not constitute a final or endorsed design. All designs submitted to Malaysian authorities must be endorsed by a registered Professional Engineer (PE) under the Board of Engineers Malaysia (BEM) in accordance with the Registration of Engineers Act 1967.