Laserfiche WebLink
<br />DRAINAGE CRITERIA MANUAL <br /> <br />RUNOFF <br /> <br />. Step 2: Using "Paved Area (Sheet Flow) & Shallow Gutter Flow" curve on <br />Figure 3-2 find the average flow velocity for the remainder 900 feet <br />of the uppermost 1000 feet in the watershed having a 1.0 percent <br />slope. <br /> <br />v = 2.0 ft/sec <br /> <br />Step 3: Calculate the travel time tt using the velocity found in Step 2. <br /> <br />L <br />tt = 60V = ( 60 <br />tt = 7.5 minutes <br /> <br />900 ft <br />sec/min)(2.0 ft/sec) <br /> <br />Step 4: Calculate the time of concentration (tc) using Equations 3-2 and <br />3-4. Select the smaller t of the two as the one to be used at the <br />c <br />first inlet. <br /> <br />. <br /> <br />tc = ti + tt <br />tc = 11.0 + 7.5 + 18.5 minutes <br /> <br />(Equation 3-2) <br /> <br />or <br /> <br />L <br />tc = 180 + 10 <br />tc = i~~O + 10 = 15.6 minutes <br /> <br />(Equation 3-4) <br /> <br />Since the Equation 3-4 gives the shorter value of tc' it controls. <br />Thus, at first inlet use <br /> <br />tc = 15.6 minutes <br /> <br />Step 5: <br /> <br />Continue the t calculations in the downstream direction. The flow <br />c <br />calculated at each design point is then used to calculate the travel <br />time (tt) in the downstream pipe, gutter, swale or channel to the <br />next downstream design point. <br /> <br />. <br /> <br />5-1-84 <br />