Table 5-4 Recommended range of values of Manning's n. ¹

1 2 3 4 Type of channel and description Minimum Normal Maximum

A Closed conduits flowing partly full

A-1 Metal

a. Brass, smooth 0.009 0.010 0.013

b. Steel

1. Lockbar and welded 0.010 0.012 0.014

2. Riveted and spiral 0.013 0.016 0.017

c. Cast iron

1. Coated 0.010 0.013 0.014

2. Uncoated 0.011 0.014 0.016

d. Wrought iron

1. Black 0.012 0.014 0.015

2. Galvanized 0.013 0.016 0.017

e. Corrugated metal

1. Subdrain 0.017 0.019 0.021

2. Storm drain 0.021 0.024 0.030

A-2 Nonmetal

a. Lucite 0.008 0.009 0.010

b. Glass 0.009 0.010 0.013

c. Cement

1. Neat, surface 0.010 0.011 0.013

2. Mortar 0.011 0.013 0.015

d. Concrete

1. Culvert, straight and free of debris 0.010 0.011 0.013

2. Culvert with bends, connections, and some debris 0.011 0.013 0.014

3. Finished 0.011 0.012 0.014

4. Sewer with manholes, inlet, etc., straight 0.013 0.015 0.017

5. Unfinished, steel form 0.012 0.013 0.014

6. Unfinished, smooth wood form 0.012 0.014 0.016

7. Unfinished, rough wood form 0.015 0.017 0.020

e. Wood

1. Stave 0.010 0.012 0.014

2. Laminated, treated 0.015 0.017 0.020
f. Clay

1. Common drainage tile 0.011 0.013 0.017

2. Vitrified sewer 0.011 0.014 0.017
3. Vitrified sewer with manholes, inlet, etc. 0.013 0.015 0.017

4. Vitrified subdrain with open joint 0.014 0.016 0.018
g. Brickwork

1. Glazed 0.011 0.013 0.015

2. Lined with cement mortar 0.012 0.015 0.017
h. Sanitary sewers coated with sewage slimes, with bends and connections 0.012 0.013 0.016

i. Paved invert, sewer, smooth bottom 0.016 0.019 0.020

j. Rubble masonry, cemented 0.018 0.025 0.030

B Lined or built-up channels

B-1 Metal

a. Smooth steel surface

1. Unpainted 0.011 0.012 0.014

2. Painted 0.012 0.013 0.017

b. Corrugated 0.021 0.025 0.030

B-2 Nonmetal

a. Cement

1. Neat, surface 0.010 0.011 0.013

2. Mortar 0.011 0.013 0.015

b. Wood

1. Planed, untreated 0.010 0.012 0.014

2. Planed, creosoted 0.011 0.012 0.015

3. Unplaned 0.011 0.013 0.015

4. Plank with battens 0.012 0.015 0.018

5. Lined with roofing paper 0.010 0.014 0.017

c. Concrete

1. Trowel finish 0.011 0.013 0.015

2. Float finish 0.013 0.015 0.016

3. Finished, with gravel on bottom 0.015 0.017 0.020

4. Unfinished 0.014 0.017 0.020

5. Gunite, good section 0.016 0.019 0.023

6. Gunite, wavy section 0.018 0.022 0.025

7. On good excavated rock 0.017 0.020

8. On irregular excaveted rock 0.022 0.027

d. Concrete bottom float finished with sides of

1. Dressed stone in mortar 0.015 0.017 0.020

2. Random stone in mortar 0.017 0.020 0.024

3. Cement rubble masonry, plastered 0.016 0.020 0.024

4. Cement rubble masonry 0.020 0.025 0.030

5. Dry rubble or riprap 0.020 0.030 0.035

e. Gravel bottom with sides of

1. Formed concrete 0.017 0.020 0.025

2. Random stone in mortar 0.020 0.023 0.026

3. Dry rubble or riprap 0.023 0.033 0.036

f. Brick

1. Glazed 0.011 0.013 0.015

2. In cement mortar 0.012 0.015 0.018

g. Masonry

1. Cemented rubble 0.017 0.025 0.030

2. Dry rubble 0.023 0.032 0.035

h. Dressed ashlar 0.013 0.015 0.017

i. Asphalt

1. Smooth 0.013 0.013

2. Rough 0.016 0.016

j. Vegetal lining 0.030 ..... 0.500

C Excavated or dredged

a. Earth, straight and uniform

1. Clean, recently completed 0.016 0.018 0.020

2. Clean, after weathering 0.018 0.022 0.025

3. Gravel, uniform section, clean 0.022 0.025 0.030

4. With short grass, few weeds 0.022 0.027 0.033

b. Earth, winding and sluggish

1. No vegetation 0.023 0.025 0.030

2. Grass, some weeds 0.025 0.030 0.033

3. Dense weeds or aquatic plants in deep channels 0.030 0.035 0.040

4. Earth bottom and rubble sides 0.028 0.030 0.035

5. Stony bottom and weedy banks 0.025 0.035 0.040

6. Cobble bottom and clean sides 0.030 0.040 0.050

c. Dragline-excavated or dredged

1. No vegetation 0.025 0.028 0.033

2. Light brush on banks 0.035 0.050 0.060

d. Rock cuts

1. Smooth and uniform 0.025 0.035 0.040

2. Jagged and irregular 0.035 0.040 0.050

e. Channels not maintained, weeds and brush uncut

1. Dense weeds, high as flow depth 0.050 0.080 0.120

2. Clean bottom, brush on sides 0.040 0.050 0.080

3. Same , highest stage of flow 0.045 0.070 0.110

4. Dense brush, high stage 0.080 0.100 0.140

D Natural streams

D-1 Minor streams (top width at flood stage <100 ft)

a. Streams on plain

1. Clean, straight, full stage, no rifts or deep pools 0.025 0.030 0.033

2. Same as above, but more stones and weeds 0.030 0.035 0.040

3. Clean, winding, some pools and shoals 0.033 0.040 0.045

4. Same as above, but some weeds and stones 0.035 0.045 0.050

5. Same as above, lower stages, more ineffective slopes and sections 0.040 0.048 0.055

6. Same as 4, but more stones 0.045 0.050 0.060

7. Sluggish reaches, weedy, deep pools 0.050 0.070 0.080

8. Very weedy reaches, deep pools, or floodways with heavy stand of timber and underbrush 0.075 0.100 0.150

b. Mountain streams, no vegetation in channel, banks usually steep, trees and brush along banks submerged at high stages

1. Bottom: gravels, cobbles, and few boulders 0.030 0.040 0.050

2. Bottom: cobbles with large boulders 0.040 0.050 0.070

D-2 Flood plains

a. Pasture, no brush

1. Short grass 0.025 0.030 0.035

2. High grass 0.030 0.035 0.050

b. Cultivated areas

1. No crop 0.020 0.030 0.040

2. Mature row crops 0.025 0.035 0.045

3. Mature field crops 0.030 0.040 0.050

c. Brush

1. Scattered brush, heavy weeds 0.035 0.050 0.070

2. Light brush and trees, in winter 0.035 0.050 0.060

3. Light brush and trees, in summer 0.040 0.060 0.080

4. Medium to dense brush, in winter 0.045 0.070 0.110

5. Medium to dense brush, in summer 0.070 0.100 0.160

d. Trees

1. Dense willows, summer, straight 0.110 0.150 0.200

2. Cleared land with tree stumps, no sprouts 0.030 0.040 0.050

3. Same as above, but with heavy growth of sprouts 0.050 0.060 0.080

4. Heavy stand of timber, a few down trees, little undergrowth, flood stage below branches 0.080 0.100 0.120

5. Same as above, but with flood stage reaching branches 0.100 0.120 0.160

D-3 Major streams (top width at flood stage >100 ft). The n value is less than that for minor streams of similar description, because banks offer less effective resistance.
a. Regular section with no boulders or brush 0.025 ..... 0.060

b. Irregular and rough section 0.035 ..... 0.100

¹ Chow, V. T. 1959. Open-channel hydraulics. McGraw-Hill, New York.