11. ANNEX
11.1. Roughness Coecients
Manning´s equation roughness coefficients for various channel materials
The Manning´s equation is an empirical formula for open channel flow.
Function of velocity, flow area, channel slope and roughness
Q = vA with V = k
St
Rh
2/3
Ic
½
Q: Discharge
v: Flow velocity
k
St
: Roughness coefficient (Strickler)
R
h
2/3
: Hydraulic radius (cross sectional A / wetted perimeter P)
I
c
½
: Channel downward slope
Empirical roughness coefficients are listed in sets of tables (see below). The following symbols are used:
k
St
= Strickler coefficient (more known in Europe)
n = Manning Coefficient
k
st
[m
1/3
/s] = 1/n
OTE: N Information in the following tables was taken from Isco Open Channel Flow Measurement Handbook &
*CeCalc.com - Civil Engineering Calculations [2]
11.1.1. Closed conduit, Partly Full Metal Pipes
Material
Manning Coeff.
Strickler
Coeff.
n min n Norm n max kst
1. Steel a. Lockbar and welded 0.010 0.012 0.014 83
b. Riveted and spiral 0.013 0.016 0.017 63
2. Cast Iron a. Coated 0.010 0.013 0.014 77
b. Uncoated 0.011 0.014 0.016 71
3. Wrought Iron a. Black 0.012 0.014 0.015 71
b. Galvanized — — — —
4. Corrugated a. Subdrain 0.017 0.019 0.021 53
b. Storm Drain 0.021 0.024 0.030 42
Table 2: Specific roughness coefficients (Manning & Strickler coefficients) for closed conduit, partly full metal pipesl
Annex
Page 109 March 2021 HYB-UM-03155-EN-03
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