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<br />The travel time for flow in an open channel from the stOt'"i7l se~'er <br />outlet to the watershed outlet (or evaluation or design point) can be <br />determined by using Nanning' 5 equation to compute. average velocities. <br />Bank-full velocities should be used to compute teesE' averages. Channels <br />may be in either natural or improved condition. <br /> <br />An urbanized water shed is shown :,n Fig. 4.4.1./,-2. Three types of <br />flow conditions exist from the furthermost point of the watershed to the <br />outlet. Compute the travel time (Tt) and time of concentration (Tc) <br />based on the following data: <br /> <br />Reach <br /> <br />Description of flow <br /> <br />~;lo~ Length <br />(%) (ft. ) <br />7 500 <br />2 900 <br />1.5 2,000 <br /> <br />A to B <br />B to C <br />C to D <br /> <br />Overland (forest) <br /> <br />Overland (shallow gutter) <br /> <br />Storm drain with manho::.,e <br />covers, inlets, etc. <br />(n-0.015; diameter 3 fee~) <br /> <br />Open channel, gunite, trape- <br />zoidal (b-5; d-3; z-l.:; <br />!l-O,019) <br /> <br />0.5 <br /> <br />3,000 <br /> <br />D to E <br /> <br />A --........-._ <br />\ -~ <br />\So <br />,%. ) <br />"....,8 <br />~C ( <br />~~~, '-, <br /> <br />~ D ---___ <br /> <br />~. <br />,,~ E <br /> <br /> <br />-------. <br /> <br />~ <br /> <br />Fig. 4.4.1.4-2. Example of urbanized "atershed for determination <br />of Tc' <br /> <br />LCS-WM Manual <br /> <br />4.4---'15 <br /> <br />April 1979 <br />