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: � <br /> � Step 8. Outle4 Structure <br /> In almost all cases the ou:le2 structure reruired will be per the detail <br /> shown in Figure 3. The orifice shown in Figure 4 can be sized by the <br /> following equations: <br /> D = 6.12� shar�redged orifices (inches} <br /> D = 4.83 h � rounded orific:e (inches) <br /> Although the units are not compatible, the above equations yield the correct <br /> � value and save some calcul�.tion time. Normally, orifices should Ix no <br /> smaller than 2.0 inches. . <br /> I <br /> i <br /> The riser mu�t be sized to pass the design storm in the developed condition, <br /> assuming the orifice is plu��,ged, without causing the water surface tn <br /> rise higher than the top of the restrictor catch basin or in the case af <br /> ponds, to within 1 foot of the top of the berm. Figure 5 shows the capacity <br /> ( <br /> of various risers as a function of head. The time of concentration for <br /> sizing the riser is the sum of the time of concentration in the developed <br /> state and the time of fifling for the detention facility. <br /> The outiet pipe must also be sized to accommodate the design _torm in <br /> - the develoed state. This can be done by use of a nomograph such as that. <br /> shown in Figure 6, or by Manning's equation: Q = 1.n9(Dj 2/3 1/2 DZ <br /> �/ (s) rr 4 <br /> Where S is tslope of the pipe in feet per foot, D the diameter of the pipe, and <br /> n th� pipe roughness. For concrete pipe n is 0.012, CMP with annular <br /> � coc•rugations is .024, and CMP with helical corrugations is 0.02. <br /> � <br />