Access the Open Channel Flow and Mannings Calculator here
| Natural Stream | Max | Normal | Min | ||
| Main Channel - [clean, straight, full stage, no rifts or deep pools |
0.025 | 0.030 | 0.033 | ||
| Main Channel - [same as above, but more stones and weeds] | 0.030 | 0.035 | 0.040 | ||
| Main Channel - [clean, winding, some pools and shoals] | 0.033 | 0.040 | 0.045 | ||
| Main Channel - [same as above, but some weeds and stones] |
0.035 | 0.045 | 0.050 | ||
| Main Channel - [same as above, lower stages, more ineffective slopes and sections] |
0.040 | 0.048 | 0.055 | ||
| same as "d" with more stones | 0.045 | 0.050 | 0.060 | ||
| sluggish reaches, weedy, deep pools | 0.050 | 0.070 | 0.080 | ||
| very weedy reaches, deep pools, or floodways with heavy stand of timber and underbrush | 0.075 | 0.100 | 0.150 | ||
| Mountain streams - no vegetation in channel, steep banks | Max | Normal | Min | ||
| Bottom - [gravels, cobbles, and few boulders] | 0.030 | 0.040 | 0.050 | ||
| Bottom - [cobbles with large boulders] | 0.040 | 0.050 | 0.070 | ||
| Floodplains | Max | Normal | Min | ||
| Pasture - [no brush, short grass] | 0.025 | 0.030 | 0.035 | ||
| Pasture - [high grass | 0.030 | 0.035 | 0.050 | ||
| Cultivated areas - [no crop] | 0.020 | 0.030 | 0.040 | ||
| Cultivated areas - [mature row crops] | 0.025 | 0.035 | 0.045 | ||
| Cultivated areas - [mature field crops] | 0.030 | 0.040 | 0.050 | ||
| Brush - [scattered brush, heavy weeds] | 0.035 | 0.050 | 0.070 | ||
| Brush - [light brush and trees, in winter] | 0.035 | 0.050 | 0.060 | ||
| Brush - [light brush and trees, in summer] | 0.040 | 0.060 | 0.080 | ||
| Brush - [medium to dense brush, in winter] | 0.045 | 0.070 | 0.110 | ||
| Brush - [medium to dense brush, in summer] | 0.070 | 0.100 | 0.160 | ||
| Trees - [dense willows, summer, straight] | 0.110 | 0.150 | 0.200 | ||
| Trees - [cleared land with tree stumps, no sprouts] | 0.030 | 0.040 | 0.050 | ||
| Trees - [same as above, but with heavy growth of sprouts] |
0.050 | 0.060 | 0.080 | ||
| Trees - [heavy timber, few down trees, little undergrowth, flood stage below branches] | 0.080 | 0.100 | 0.120 | ||
| Trees [same as 4. with flood stage reaching branches] | 0.100 | 0.120 | 0.160 | ||
| Excavated or Dredged Channels | Max | Normal | Min | ||
| Earth, straight, and uniform - [clean, recently completed] | 0.016 | 0.018 | 0.020 | ||
| Earth, straight, and uniform - [clean, after weathering] | 0.018 | 0.022 | 0.025 | ||
| Earth, straight, and uniform - [gravel, uniform section, clean] | 0.022 | 0.025 | 0.030 | ||
| Earth - [with short grass, few weeds] | 0.022 | 0.027 | 0.033 | ||
| Earth winding and sluggish - [ no vegetation | 0.023 | 0.025 | 0.030 | ||
| Earth winding and sluggish - [grass, some weeds] | 0.025 | 0.030 | 0.033 | ||
| Earth winding and sluggish [dense weeds, aquatic plants, in deep channels] | 0.030 | 0.035 | 0.040 | ||
| Earth winding and sluggish - [earth bottom and rubble sides] | 0.028 | 0.030 | 0.035 | ||
| Earth winding and sluggish - [stony bottom and weedy banks] | 0.025 | 0.035 | 0.040 | ||
| Earth winding and sluggish - [cobble bottom and clean sides] | 0.030 | 0.040 | 0.050 | ||
| Dragline-excavated or dredged - [no vegetation] | 0.025 | 0.028 | 0.033 | ||
| Dragline-excavated or dredged - [light brush on banks] | 0.035 | 0.050 | 0.060 | ||
| Rock cuts - [smooth and uniform] | 0.025 | 0.035 | 0.040 | ||
| Rock cuts - [jagged and irregular] | 0.035 | 0.040 | 0.050 | ||
| Channels not maintained - [dense weeds, high as flow depth] | 0.050 | 0.080 | 0.120 | ||
| Channels not maintained - [clean bottom, brush on sides] | 0.040 | 0.050 | 0.080 | ||
| Channels not maintained -[same as above, highest stage of flow] | 0.045 | 0.070 | 0.110 | ||
| Channels not maintained - [dense brush, high stage] | 0.080 | 0.100 | 0.140 | ||
| Lined or Constructed Channels | Max | Normal | Min | ||
| Cement - [neat surface] | 0.010 | 0.011 | 0.013 | ||
| Cement - [mortar] | 0.011 | 0.013 | 0.015 | ||
| Wood - [planed, untreated] | 0.010 | 0.012 | 0.014 | ||
| Wood - [planed, creosoted] | 0.011 | 0.012 | 0.015 | ||
| Wood - [unplaned] | 0.011 | 0.013 | 0.015 | ||
| Wood - [plank with battens] | 0.012 | 0.015 | 0.018 | ||
| Wood - [lined with roofing paper] | 0.010 | 0.014 | 0.017 | ||
| Concrete - [trowel finish] | 0.011 | 0.013 | 0.015 | ||
| Concrete - [float finish] | 0.013 | 0.015 | 0.016 | ||
| Concrete - [finished, with gravel on bottom] | 0.015 | 0.017 | 0.020 | ||
| Concrete - [unfinished] | 0.014 | 0.017 | 0.020 | ||
| Concrete - [gunite, good section] | 0.016 | 0.019 | 0.023 | ||
| Concrete - [gunite, wavy section] | 0.018 | 0.022 | 0.025 | ||
| Concrete - [on good excavated rock] | 0.017 | 0.020 | - | ||
| Concrete - [on irregular excavated rock] | 0.022 | 0.027 | - | ||
| Concrete bottom float finish with sides of: dressed stone in mortar | 0.015 | 0.017 | 0.020 | ||
| Concrete bottom float finish with sides of: random stone in mortar | 0.017 | 0.020 | 0.024 | ||
| Concrete bottom float finish with sides of: cement rubble masonry, plastered | 0.016 | 0.020 | 0.024 | ||
| Concrete bottom float finish with sides of: cement rubble masonry | 0.020 | 0.025 | 0.030 | ||
| Concrete bottom float finish with sides of: dry rubble or riprap | 0.020 | 0.030 | 0.035 | ||
| Gravel bottom with sides of: formed concrete | 0.017 | 0.020 | 0.025 | ||
| Gravel bottom with sides of: random stone mortar |
0.020 | 0.023 | 0.026 | ||
| Gravel bottom with sides of: dry rubble or riprap | 0.023 | 0.033 | 0.036 | ||
| Brick glazed | 0.011 | 0.013 | 0.015 | ||
| Brick in cement mortar | 0.012 | 0.015 | 0.018 | ||
| Masonry - [cemented rubble] | 0.017 | 0.025 | 0.030 | ||
| Masonry - [dry rubble | 0.023 | 0.032 | 0.035 | ||
| Dressed ashlar/stone paving | 0.013 | 0.015 | 0.017 | ||
| Asphalt - [smooth] | 0.013 | 0.013 | - | ||
| Asphalt - [rough] | 0.016 | 0.016 | - | ||
| Vegetal lining | 0.030 | - | 0.500 |
