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Hl~' I i ~ > :.-::-' _I ! I: I I I , I I I I :1 I I I I I I I I I I 1.1 Table 1 1/ Values of Manning's Roughness Coefficient n - Type of channel and description Normal I. Excavated or Dredged a. Earth, straight and uniform 1. Clean, recently completed- 2. Clean, after weathering- - 3. Gravel, uniform section, clean - - - - - - - 4. With short grass, few weeds- - - - - - - - - - - b. Earth, winding and sluggish 1. No vegetation- - - - - - - - - - - - - - - - - - - - 2. Grass, some weeds- - - - - - - - - - - - 3. Dense weeds or aquatic plants in deep channels 4. Earth bottom and rubble sides- - - - - - 5. Stony bottom and weedy banks - - - - - - - 6. Cobble bottom and clean sides- - II. Natural Streams a. Streams on plain 1. Clean, straight, full stage, no rifts or deep pools- 2. Same as above, but more stones and weeds - - - - 3. Clean, winding, some pools and shoals- - - 4. Same as above, but some weeds.and stones - 5. Same as above, lower stages, more ineffective slopes and sections- - - - 6. Same as 4, but more stones - - - - - - - 7. Sluggish reaches, weedy, deep pools- - 8. Very weedy reaches, deep pools, or floodways with heavy stand of timber and underbrush- - - III. Flood Plains a. Pasture', no brush 1. Short grass- - - - - - - - - - - - - 2. High grass - - - - - - - - - - - - - b. Cultivated areas 1. No crop- - - - - - - - - - - - - - - - - - - 2. Mature row crops - - - - - - - - - - 3. Mature field crops - - - - - - - - - - - c. Brush 1. Scattered brush, heavy weeds - - - - 2. Light brush and trees, in winter - 3. Light brush and trees, in summer - - - - - - - - - - 4. Medium to dense brush, in winter - - - - - - - 5. Medium to dense brush, in summer - - - - - - 0.018 0.022 0.025 0.027 0.025 0.030 0.035 0.030 0.035 0.040 0.030 0.035 0.040 0.045 0.048 0.050 0.070 0.100 0.030 0.035 0.030 0.035 0.040 0.050 0.050 0.060 0.070 0.100 2 RE:~OURCE: CON~ULTI\NT~ INC