Laserfiche WebLink
<br />H . difference between the energy grade line elevation and the <br />roadway crest elevation <br />Q = total flow over the weir <br />The approach velocity is included by using the energy grade line eleva- <br />tion in lieu of the upstream water surface elevation for computing the <br />head, H. Values for the coefficient of discharge "C" are presented in <br />the section on Loss Coefficients. Where submergence by tailwater exists, <br />the coefficient "C" is reduced by the program according to the method <br />indicated in reference i. Submergence corrections are based on an <br /> <br />ogee spillway shape. As shown in Water Surface Profiles, I.H.D. Vol 6 <br />(reference l) the correction for submergence based on an ogee section <br />can lead to errors for high submergence on weirs with other shapes. <br />A total weir flow, Q, is computed by subdividing the weir crest into <br />segments, computing L, H, a submerg~nce correction and Q for each <br />segment, and summing the incremental discharges. <br />Combination Flow. Sometimes combinations of low flow or pressure <br />flow occur with weir flow. In these cases a trial and error procedure <br />is used, with the equations just described, to determine the amount of <br />each type of flow. The procedure consists of assuming energy elevations <br />and computing the total discharge until the computed discharge equals, <br />within one percent, the discharge desired. <br /> <br />Decision Logic. The general flow diagram for the special bridge <br />routine is shown in Figure 3. By following the decision logic associ- <br />ated with a bridge solution, the program user can determine what adjust- <br />ments he could make in the program input to alter the computed solution. <br /> <br />10 <br />