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STORMWATER MANAGEMENT MANUAL <br />TYPICAL ROUGHNESS COEFFICIENTS FOR OPEN CHANNELS <br />TYPE OF CHANNEL AND DESCRIPTION MINIMUM NORMAL MAXIMUM <br />LINED OR BUILT -UP CHANNELS <br />a. CONCRETE <br />1. <br />TROWEL FINISH <br />0.011 <br />0.013 <br />0.015 <br />2. <br />FLOAT FINISH <br />0.013 <br />0.015 <br />0.016 <br />3. <br />GUNITE, GOOD SECTION <br />0.016 <br />0.019 <br />0.023 <br />4. <br />GUNITE, WAVY SECTION <br />0.018 <br />0.022 <br />0.023 <br />b. CONCRETE <br />BOTTOM FLOAT FINISHED WITH <br />SIDE OF <br />1. <br />DRESSED STONE IN MORTAR <br />0.015 <br />0.017 <br />0.020 <br />2. <br />RANSOM STONE IN MORTAR <br />0.017 <br />0.020 <br />0.024 <br />3. <br />DRY RUBBLE OR RIPRAP <br />0.020 <br />0.030 <br />0.035 <br />C. GRAVEL <br />BOTTOM WITH SIDES OF <br />1. <br />FORMED CONCRETE <br />0.017 <br />0.020 <br />0.025 <br />2. <br />RANDOM STONE IN MORTAR <br />0.020 <br />0.023 <br />0.026 <br />3. <br />DRY RUBBLE OR RIPRAP <br />0.023 <br />0.033 <br />0.036 <br />d. ASPHALT <br />i <br />1. SMOOTH 0.013 0.013 -- <br />2. ROUGH 0.016 0.016 -- <br />i <br />e. GRASSED -a. 20.030 0.040 0.0503, <br />0 <br />REFERENCE: <br />U/�C 909;Ff4 K CHOW, V.T., OPEN CHANNEL HYDRAULICS TABLE 8020 <br />McGRAW HILL BOOK COMPANY 1'959 <br />