A.8 Manning's N – Open Channels
| Channel Type | Manning n |
| Lined Channels | |
| - Asphalt | 0.013 - 0.017 |
| - Brick | 0.012 - 0.018 |
| - Concrete | 0.011 - 0.020 |
| - Rubble or riprap | 0.020 - 0.035 |
| - Vegetal | 0.030 - 0.40 |
| Excavated or dredged | |
| - Earth, straight and uniform | 0.020 - 0.030 |
| - Earth, winding, fairly uniform | 0.025 - 0.040 |
| - Rock | 0.030 - 0.045 |
| - Unmaintained | 0.050 - 0.140 |
| Natural channels (minor streams, top width at flood stage < 100 ft) | |
| - Fairly regular section | 0.030 - 0.070 |
| - Irregular section with pools | 0.040 - 0.100 |
Source: ASCE (1982). Gravity Sanitary Sewer Design and Construction, ASCE Manual of Practice No. 60, New York, NY.