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June 16, 2022 <br />98 <br /> <br /> <br /> <br />b. Times of concentration shall be based on the following design parameters: <br />i. Overland Flow: The maximum length for each reach or overland flow before <br />concentrated ditch and/or sheet flow develops is three hundred (300) feet. <br />Figure 17. The Time of Concentration Nomograph shall be used for <br />determination of the times of concentration. <br />ii. Concentrated flows: At points where overland flows concentrate in field <br />depressions, ditches, gutters, curbs, or pipe collection systems, the time of <br />concentration between these design points shall be based upon Manning's <br />Equation and/or acceptable engineering design standards as determined by <br />the Planning Commission. <br />iii. The Rainfall Intensity-Duration-Frequency Chart shown in below and on the <br />following pages shall be used with the Rational Method to compute the <br />rainfall intensities. <br />c. Use of other criteria, assumptions, references, calculation methods and/or <br />computer modeling may be utilized, provided detailed design information and <br />programming with references are submitted and approved by the Planning <br />Commission. <br /> <br /> <br /> <br /> <br /> <br /> <br /> <br />