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<br />A water surface profile can be calculated using the HEe program for such <br /> <br />a reach from a downstrelllll control to the downstream end of the bridge. <br /> <br />However, the depth thus calculated for Section 3 can only exist if the <br /> <br />momentum flux in the constriction calculated on the basis of the downstrelllll <br /> <br />depth exceeds the critical momentUlll flux in the constriction. Figure 2c <br /> <br />can be used to determine the momentum flux that would exist in the <br /> <br />constriction for a depth at Section 3 from water surface profile computa- <br /> <br />tions. The critical (minimum) momentUIII flux for the constriction is <br />represented by MCRIT iu Figure 2b. If the momentum flux in the constriction <br />calculated on the basis of the downstrelllll depth exceeds the critical <br /> <br />momentUlll flux, flow as in Figure 3a will occur. If the two momentum <br /> <br />fluxes are equal, flow as in Figure 3b will occur. If the critical <br /> <br />momentum flux is the greater of the two fluxes, a hydraulic jump will <br /> <br />be formed as shown in Figure 3c. For flow a.s in Figures 3b and c, the <br /> <br />momentum flux that exists in the constriction is the critical momentum <br /> <br />flUX, and unknown upstream and downstream depths can be determined l':rom <br /> <br />Figures 2a and 2c, respectively, using the critical momentum flux, MCRIT. <br />For flow as in Figure 3&, the momentum flux that exist.. in the constriction <br />can be determined from Figure 2c on the basis of a previously calculated <br /> <br />depth at Section: 3. The unknown depths upstream from and within the <br /> <br />. . <br />constriction can be determined for this momentum. flux from Figures 2a and <br /> <br />b, respectively, <br /> <br />Similar reasoning can be applied to ascertain the flow conditions <br />shown in Figures 3d, e and f for a reach where flow lIOuld be super-critical <br /> <br />.:.. . <br /> <br />7 <br />