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~ ~ ~ ~ ~ ~ ~ <br />~ ~ ~ ~ ~ <br />v e <br />H <br />`~. <br />+~~ <br />,- SEDCAD+ Version 3 <br />Training Manual <br />Dr. Richard C. Warner <br />University of Kentucky <br />Agricultural Engineering Department <br />Cooperative Extension Service <br />Ms. Pamela J. Schwab <br />Civil Software Design <br />Civil Software Design <br />P.O. Boz 706 <br />Ames, IA 50010 <br />~ ~ ~ <br />~ ~ ~ ~ <br />APPENDIX C: Time of Concentration <br />Land Use 8 and 9 <br /> <br />Two additional equations have been developed and <br />added to the SCS Upland Curves (SCS,1972. National <br />Engineering Handbook, Section 4. Hydrobgy) to ap- <br />proximate the time of concentration for channel lbw <br />based on Manning's equation. <br />For largo gullies, diversions, end shallow flowing <br />streams, the following equation provides en acceptable <br />approximation of the time of concentration for most <br />nodal applications: <br />V=3~ <br />where V Is the velocRy In feet per second, end S Is the <br />slope In percent. This equallon Is based on the follow- <br />ing assumptions: <br />~^~ .. -Hydraulic Radius, R, Is equal to 0.61eet <br />_~j,, - Manning's n equals 0.035 <br />I ~ <br />i <br />Three different me)or scenarios were used es the basis <br />of this equation: <br />1. A 5 foot wide gutty flowing 1 foot deep and <br />having en approximate trapezoidal shape with 1:1 <br />side slopes. (R=0.77) <br />2. A 12 foot wide rock nprap diversion 8owing 1 loot <br />deep wXh 2:1 skle sopes. (R=0.85) <br />3. A 25 foot wide rectangular shallow stream <br />flowing 6 inches deep. (R=0.48) <br />Monolog's n is expected to be between 0.3 and 0.4 for <br />~ all cases. Applying R=0.8 and n=0.035 to Manning's <br />equation yields <br />V= 30.2 <br />V= 3~(S <br />(S=fUft); or <br />S=% <br />The potential error associated wNh using the above <br />equation approximation to determine time of concentra- <br />tion for these various channel conligurallons Is t 309'a <br />r <br />