Laserfiche WebLink
<br />VELOCITY HEAD COEFFICIENT <br /> <br />Equations 6, 7, and 9 require the computation of the velocity head <br /> <br />V2 <br />29' Streambed roughness, cross-section irregularities, channel varia- <br /> <br />tions, obstructions, vegetation, channel meandering, and other factors <br /> <br />cause the velocity in a channel to vary from point to point. Because of <br /> <br />this variation in velocity, the velocity head, or the kinetic energy per <br /> <br />V2 <br />pound of water, is greater than the value computed from Z-. The true <br />2 g <br /> <br />velocity head is expressed as ~~ ' where alpha is the velocity head <br /> <br />coefficient. The velocity head coefficient, or kinetic energy coefficient <br /> <br />(Chow, 1959, p. 28), is computed as: <br /> <br />CL = <br /> <br />Ev3t,A <br />V3A <br /> <br />(14) <br /> <br />it were computed by the multiple-point method. <br /> <br /> <br />where v is the measured velocity in an elementary area t.A and the other <br /> <br />variables are as previously defined. Alpha was computed from the <br /> <br />discharge measurements made using equation 14 and the values are shown <br /> <br />in table 1. These values are based on the average ve(ocity in the <br /> <br />vertical subarea rather than on the vertical-velocity distribution (from <br /> <br />multiple-point velocity measurements) in each subarea because these data <br /> <br />were not available. Hulsing and others (1966) showed that the values of <br /> <br />alpha computed from multiple-point velocity measurements were similar to <br /> <br />the one-point (0.6 depth) and two-point (0.2 and 0.8 depth) velocity <br /> <br />measurements. The two-point method of determining velocity was used for <br /> <br />the majori ty of the measurements in th i s study. It is not known how <br /> <br />much alpha would differ for the steep-gradient streams in this study if <br />