Laserfiche WebLink
<br />The computed upstream water surface elevation is simply the downstream <br />water surface elevation plus H3. With the upstream water surface ele- <br />vation known, the program computes the corresponding velocity head and <br />energy elevation for the upstream section. <br />Class B low flow can exist for either a subcritical or supercritical <br />profile. For either profile, class B low flow occurs when the profile <br />passes through critical depth in the bridge constriction. For a sub- <br />critical profile, critical depth is determined in the bridge, a new <br />downstream depth (below critical) and the upstream depth (above critical) <br />are calculated by finding the depths whose corresponding momentum fluxes <br />equal the momentum flux in the bridge for critical depth. With this so- <br />lution, Statement 5227 DOWNSTREAM ELEV IS X, NOT Y, HYDRAULIC JUMP OCCURS <br />DOWNSTREAM is printed with the elevation! as the supercritical ele- <br />vation. The program does not provide the location of the hydraulic <br />jump. A supercritical profile could be computed starting at the down- <br />stream section with a water surface elevation X. For a supercritical <br />profile, the bridge is acting as a control and is causing the upstream <br />water surface elevation to be above critical depth. Momentum equations <br />are again used to recompute an upstream water surface elevation (above <br />critical) and a downstream elevation below critical depth. For this <br />situation, the Statement 5920 UPSTREAM ELEVATION IS X NOT Y, NEW BACK- <br />WATER REQUIRED is printed indicating a subcritical profile should be <br />calculated upstream from the bridge starting at elevation !. <br />Class C low flow is computed for a supercritical profile where <br />the water surface profile stays supercritical through the bridge con- <br /> <br />8 <br />