Laserfiche WebLink
Table 2-2 shows the values of C that may be used in formula 2-1 <br /> _ for certain composite areas in lieu of computing a composite <br /> value by the above method . <br /> 2 . 2 .2 Tributary Area, A <br /> The tributary area for each point of computation shall be based <br /> on actual field reconnaissance or use of appropriately scaled <br /> maps that clearly depict the drainage boundaries . <br /> All of the area that will contribute runoff to the drainage <br /> system shall be considered, regardless of the limits of the <br /> particular development under consideration. <br /> 2 .2 .3 Critical Flow Time <br /> The critical flow time is that time which results in the maximum <br /> flow rate for a given point in a drainage system. Maximum flow <br /> occurs when the product of the intensity and the contributing <br /> area corresponding to the flow time is a maximum. <br /> The time required for water to flow from the most hydraulicly <br /> 14 <br /> remote point in the watershed to the point in question is called <br /> the time of concentration. Using the intensity corresponding to <br /> this time and the entire drainage area in the Rational Formula <br /> usually results in the maximum flow rate for the point . <br /> The nomograph shown in Figure 2-2 shall be used to determine the <br /> time of concentration to the first inlet of the drainage system. <br /> If this time is less than the minimum inlet time shown in Table 2-2 , <br /> the values shown in the table shall be used . <br /> When any part of the storm waters are conveyed to the point in <br /> question by pipes or open channels , the flow time in these <br /> conveyances shall be added to the inlet time to compute the total <br /> 2-4 <br />