Table 2.1. Manning's Roughness Coefficients for Various Boundaries.
Manning's n
Floodplains (continued)
Brush
1.
Scattered brush, heavy weeds
0.035-0.070
2.
Light brush and trees in winter
0.035-0.060
3.
Light brush and trees in summer
0.040-0.080
4.
Medium to dense brush in winter
0.045-0.110
5.
Medium to dense brush in summer
0.070-0.160
Trees
1.
Dense willows, summer, straight
0.110-0.200
2.
Cleared land with tree stumps, no sprouts
0.030-0.050
3.
Same as above, but with heavy growth of sprouts
0.050-0.080
4.
Heavy stand of timber, a few down trees, little undergrowth, flood stage
0.080-0.120
below branches
5. Same as above, but with flood stage reaching branches
0.100-0.160
Major Streams (Top width at flood stage > 30 m (100 ft)
The n value is less than that for minor streams of similar description,
because banks offer less effective resistance.
Regular section with no boulders or brush
0.025-0.060
Irregular and rough section
0.035-0.100
Alluvial Sandbed Channels (no vegetation)1
Tranquil flow, Fr < 1
1.
Plane bed
0.014 - 0.020
2.
Ripples
0.018 - 0.030
3.
Dunes
0.020 - 0.040
4.
Washed out dunes or transition
0.014 - 0.025
5.
Plane bed
0.010 - 0.013
Rapid Flow, Fr > 1
1. Standing waves
0.010 - 0.015
2. Antidunes
0.012 - 0.020
1
Data is limited to sand channels with D50 < 1.0 mm, details to be discussed in Chapter 3.
2.23
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