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<br />The free flow discharge coefficients are shown in fig. 4.02 for <br />four basic weir shapes. Figure 4.03 shows the ~ffect of submergence <br />on these four shapes as well as the effect on an ogee-shaped weir and <br />a sharp-crested weir. Figure 4.04 shows the influence of shape and <br />flow on the point of incipient submergence (i.e., that point below <br />which changes in downstream water level have no influence on water <br />elevation upstream from the weir). <br />The weir equation is discussed in Section 5.04. The coefficients <br />in figures 4.02 and 4.03 were calculated from hydraulic model tests <br />in which the upstream and downstream gages were 1.5 feet (0.5 m) and <br />7 feet (2.1 m) respectively from the weir. The flume was 18 inches <br />(0.5 m) wide and could support a flow of 1.5 cfslft (140 literlsecl <br />meter). Weir crest lengths of 12, 18, and 24 inches (30.5,45.7, and <br />61 cm) were tested. The weir crest was 9 inches (22.9 cm) above the <br />approach channel and 7-3/4 inches (19.7 cm) above the exit channel. <br />These coefficients were not determined for the purpose of cal- <br />culating discharge from measured field data, but rather for calculat- <br />ing head loss for a range of discharges, weirs, and flow conditions. <br />As shown in fig. 4.02. weir shape is as important in submerged <br />flow as previous studies have shown it to be for free-flow conditions. <br />It is not wise to use the coefficient for one shape of weir in analyz- <br />ing head loss at a weir of another shape. <br /> <br />4.14 <br />