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<br />if the presence of the bridge piers were ignored. . However, for a super- <br />critical reach the "starting point" is a. previously determined depth a.t <br />Section 1 rether than Section.3. If the momentum flux in the constriction <br />determined from Figure 2a. on the basis of the depth a.t Section 1 is grea.ter <br />than MCRIT, flow as in Figure 3d will occur. If the two momentum fluxes <br />are equal; flow as in Figure 3e will occur. If McaIT is the grea.ter of <br />the two momentum fluxes, a. hydraulic jump will occur upstreBlll from the <br />bridge piers as shown in Figure 3f. <br />Subroutine BLFLO in !lEe programs 22-J2-L2l2 and 22-J2-L232 determines <br />low-flow profileS using the a.bove procedures (see :flow chart, Figure 4) <br />a.ccording to the following steps: <br />(1) The momentum flux for the constriction is determined ou the <br />basis of a. previously ce.1.cula.ted upstream or downstreBlll depth "(Equations <br />on Figures 2a. and 2c); <br />(2) The critice.1. momentum flux (minimum possible), McaIT, is <br />determined for the constriction; <br />(3) The type of flow (i.e" one of the types shown in Figure 3) is <br />determined by comparing the momentum fluxes determined in steps (1) and (2); <br />(4) Unknown flow depths a.re determined for the particular flow type <br />by using the appropria.te portions of equation (6), with the exception tha.t <br />if the :flow type is tha.t shown in Figure 3&, Yarnell's equation, which is <br />given below, is used. <br />Da.ta collected and aneJ.yzed by the los Angeles District, Corps of <br />Engineers (reference 8) indicate tha.t a.pplica.tion of the semi-empirice.1. <br /> <br />. <br /> <br />8 <br />