Laserfiche WebLink
<br />If ~ = 0.477 then b = o.fu = o,;Ti ~ 4,19 It, <br /> <br />This is the same procedure to be used with table 3, This table gives values of K' for use with equation (7) <br />to solve for the depth of flow y, <br /> <br />K' 2 I <br />f'\=- b' s' <br /><. n ' <br /> <br />(7) <br /> <br />Solving for K' in equation (7): <br /> <br />, Q.n <br />K - b"'S'12 <br />, <br /> <br />(8) <br /> <br />Attempting to verii)' the above example: <br /> <br />80. 0,028 <br />K' = 4,19"'0.0042'12 ='0,758 <br /> <br />Checking table 2 and interpolating, 0.758 corresponds with a ylb value of 0.478, resulting in a depth of <br />flow of 2.00 ft. This indicates the methods check against each Oth':L In the above design example, the <br />practical solution would be to specify the bottom width at 4,5 feet. <br /> <br />RULES OF THUMB AND SHORTCUTS <br /> <br />Figure 2 gives a table of discharge and required slopes of a common trapezoidal channel configuration. <br />This table is based on maintaining the flow velocity at 5 fps, which is generally the high end of the desir- <br />able range of velocities for a natural channel without requiring additional measures to stabilize against <br />erosion SIIch as concrete or riprap, <br /> <br />Asswnptions: <br /> <br />4;1 sideslopes, n = 0,030, V = 5 fps <br /> <br />Discharge (efs) and Channel Slopes at various bottom widths (ft) <br /> <br /> 2 4 ( <br />D 1 30 2.1% 40 1.8% 50 <br />E <br />P 2 99 .9010 118 .8% 140 <br />T <br />H 3 199 .5% 237 .5% 270 <br />F 4 365 .4% 398 .36% 437 <br />T <br /> 5 556 .3% 603 .28% 645 <br /> 6 724 .2% 837 .22%1 895 <br /> - <br /> <br /> 8 10 <br /> -- <br />1.63% 60 1.52% 70 1.45% <br />.76% 160 .71% 179 .67% <br />.48% 299 .45% 329 .43% <br />.34% 482 .33% 517 .31% <br />.26% 696 .25% 745 .24% <br />.21% 950 .20% 1028 .20% <br /> -.- <br /> <br />Figure 2 <br /> <br />Starting with this table will give a feel for initial sizing of th,: channel prior to final design. <br /> <br />Along with maintaiuing a natural channel velocity to less than 5 fps, it is also generally desirable from a <br />safety standpoint to keep the depth of flow in any channel to 5 feet or less, This is often difficult to achieve <br />in natural channel!. due to geometry restrictions, but should t.: considered in Ithe design stage. <br /> <br />PageS <br />fJreenhorne & O'Mara, Inc. <br />