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TIME OF CONCENTRATION <br />The "time of concentration" is defined as that time in minutes that it <br />takes a drop of water falling at the extreme upper limit of a drainage area <br />to flow to its exit from the drainage area. If the time of concentration is <br />less than the duration of the storm, this becomes the period at which the <br />maximum storm load is on the exit from the drainage area. <br />The time of concentration varies with the velocity of the flowing water <br />and the distance to be traveled. The velocity of a stream varies with the <br />characteristics of the drainage channel. As an example, water flowing across <br />a grassed area within this drainage basin can be expected to travel at 2.0 <br />feet per second during the storm; whereas the same storm water following the <br />same slope but on a paved street or curb and gutter section will flow at 6.0 <br />feet per second. <br />For the purposes of this study, all surface waters are assumed to be <br />flowing in a curb and gutter section except in the grassed cemeteries and <br />park areas. When the entire drainage basin has been fully developed, it is <br />anticipated that all storm waters within a given subdivision will be trans- <br />ported by curb and gutters to their point of concentration. <br />At the point of concentration for each drainage area the concentrated <br />storm waters must be disposed of in a channel or conduit that will protect <br />both the upstream and downstream properties from damage. This channel or <br />conduit will pick up drainage waters.from all concentration points and its <br />capacity must be increased accordingly as it traverses the drainage basin. <br />All concentration points do not discharge their maximum load into the conduit <br />at the same time so the actual maximum loading is not a summation of all con- <br />centration point maximums but is something less. than this total as determined <br />from engineering analysis. <br />- 13 - <br />