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<br /> <br />e <br /> <br />e <br /> <br />e <br /> <br />MEASUREMENT OF PEAK DISCHARGE AT CULVERTS BY INDIRECT METHODS 35 <br /> <br />'\. <br /> 1\\ <br /> "\ <br /> 1\ <br /> \ <br /> \~ ~ <br />~ ',- ~ <br /> " --- <br /> "- <br /> ',- SUPPorted jet <br /> -- -- I <br /> - u-rpporr..l!'t <br /> <br />On recent experiments with proto- <br />type size pipes, may be obtained by <br />use of figure 18. <br />The routing method can be applied to both <br />standard and nonstandard conditions, Deter- <br />mine type of flow and discharge coefficients from <br />the curves and tables in this manual. Consider <br />the velocity heads at starting and ending points. <br />Compute friction losses separately between <br />points where the bottom slope changes or wbere <br />contraction occurs. Between llny two points 1 <br />and 2, t,be friction loss is equal to LQ'jK,K,. <br />Compute entrance loss as (ljC'-I)V,'j2y <br />where C is the discharge coefficien t as deter- <br />mined in this chapter and V,'f2g is the velocity <br />head at the control or terminal section. Actually <br />the entrance loss occurs through the contractin~ <br />and expanding portion of the live stream, but it <br />is related to the velocity head at tbe control or <br />terminal section because of the methods used in <br />determining the discharge coefficients listed III <br />this chapter. <br /> <br />0,9 <br /> <br />0,8 <br /> <br />~I <br />-"10 <br /> <br />0,7 <br /> <br />0,6 <br /> <br />0,5 <br />2 <br /> <br />3 <br /> <br />4 <br /> <br />5 <br /> <br />6 <br /> <br />The routing- method is perfol'med Uf- follows: <br />1. Elevation uf wnter snrfncc nt. till' l'mHrol <br />section. <br />2. Plus velocity hend llt control secti,m, <br />3. Plus friction loss betw('t"1I control ~l'l.tion llud <br />entrance. <br />4. Plu.. entrance loss. <br />5, Plus friction loss between entrance "nd <br />approacb section. <br />6. Minus velocity head at approacb section. <br />7, Equal... computed headwater elevation. <br />Compare this computed beadwater elevatiun <br />with tbe known water-surface elevation and, if <br />different, make successive trials until they re"ch <br />agreement within 0.02 foot. <br />For types 2 and 3 flow an intermediate <br />assumption of depth at tbe culvert entrance is <br />made, Test tbe assumption by routing to the <br />energy gradient, "t tbe entrance (steps 1-3 <br />above), tben deducting tbe velocity head at the <br />entrance. Always verify tbe type of flow, <br />Remember that it is impossible to route through <br />critical depth. <br /> <br />7 <br /> <br />8 <br /> <br />9 <br /> <br />10 <br /> <br />II <br /> <br />12 <br /> <br />13 <br /> <br />Q <br />of <br /> <br />Figure 18.-Relalion befween outlet pressure lines and discharge for fype 6 flow through culverts of ci,cula, <br />section. Taken from ,eport by j. l. F,ench, 1956. <br />