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<br />001303 <br /> <br />40 <br /> <br />Grigg (41) suggested the following relationship for the cost of <br />installed pipe (plus manholes and laterals) as a function of pipe <br />diameter: <br /> <br />x <br />C = aD <br />p <br /> <br />0) <br /> <br />where <br /> <br />C = installed pipe cost per foot of pipe, <br />p <br />D = diameter of pipe, in feet, and <br /> <br />a,X= regression parameters. <br /> <br />Using a basin in the Denver, Colorado area and 1975 prices, he found the <br />regression power parameter (x) to be 1.663. <br />If we assume full pipe flow (not under pressure) we can use <br />Mannings' equation to rewrite equation 1 in terms of the discharge (Q). <br />That is: <br /> <br />Q = 1.49 ~R2/3S1/2 <br />n <br /> <br />(2) <br /> <br />where <br /> <br />Q = peak discharge (cfs), <br /> <br />n = Manning's friction factor, <br />A = cross-sectional area of flow (ft2), <br />R = hydraulic radius (ft), <br />S = friction slope (ft/ft), <br />= pipe invert slope at full pipe flow but not pressure flow. <br />For full circular pipe flow (not under pressure): <br /> <br />2 <br />A = nD 14 <br /> <br />R = 0/4 <br /> <br />. <br /> <br />n,S = constants. <br /> <br />So, equation 2 becomes: <br /> <br />or <br /> <br />Q = al08/3 <br />D - Q3/8 <br />- aZ <br /> <br />~) <br />