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Mannings N: table 2
4. with short grass, few weeds to 7. on good excavated rock
Manning's n roughness coefficients for open channels and closed conduits — used in hydraulic flow calculations
| section | description | n max (dimensionless) | n min (dimensionless) | n normal (dimensionless) | subcategory |
|---|---|---|---|---|---|
| table 2 | 4. with short grass, few weeds | 0.033 | 0.022 | 0.027 | a. Earth, straight, and uniform |
| table 2 | 5. dry rubble or riprap | 0.035 | 0.02 | 0.03 | d. Concrete bottom float finish with sides of: |
| table 2 | 5. gunite, good section | 0.023 | 0.016 | 0.019 | c. Concrete |
| table 2 | 5. lined with roofing paper | 0.017 | 0.01 | 0.014 | b. Wood |
| table 2 | 5. medium to dense brush, in summer | 0.16 | 0.07 | 0.1 | c. Brush |
| table 2 | 5. same as 4. with flood stage reaching branches | 0.16 | 0.1 | 0.12 | d. Trees |
| table 2 | 5. stony bottom and weedy banks | 0.04 | 0.025 | 0.035 | b. Earth winding and sluggish |
| table 2 | 6. cobble bottom and clean sides | 0.05 | 0.03 | 0.04 | b. Earth winding and sluggish |
| table 2 | 6. gunite, wavy section | 0.025 | 0.018 | 0.022 | c. Concrete |
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