Type of Channel and Description

Minimum

Normal

Maximum

Natural streams - minor streams (top width at floodstage < 100 ft)

1. Main Channels

  a. clean, straight, full stage, no rifts or deep pools

0.025

0.030

0.033

  b. same as above, but more stones and weeds

0.030

0.035

0.040

  c. clean, winding, some pools and shoals

0.033

0.040

0.045

  d. same as above, but some weeds and stones

0.035

0.045

0.050

  e. same as above, lower stages, more ineffective
  slopes and sections

0.040

0.048

0.055

  f. same as "d" with more stones

0.045

0.050

0.060

  g. sluggish reaches, weedy, deep pools

0.050

0.070

0.080

  h. very weedy reaches, deep pools, or floodways
  with heavy stand of timber and underbrush

0.075

0.100

0.150

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

  a. bottom: gravels, cobbles, and few boulders

0.030

0.040

0.050

  b. bottom: cobbles with large boulders

0.040

0.050

0.070

3. Floodplains

  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 4. with flood stage reaching  branches

0.100

0.120

0.160

4. Excavated or Dredged Channels

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 as above, highest stage of flow

0.045

0.070

0.110

  4. dense brush, high stage

0.080

0.100

0.140

5. Lined or Constructed Channels

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 excavated rock

0.022

0.027

d. Concrete bottom float finish 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 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/stone paving

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