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<br />coefficient. Fig. 14 shows the results of the tests. With the sill located <br /> <br />on the downstream end of the normal broad crested weir, the flow over the <br /> <br />crest of the structure was subcritical. It would be easier therefore, to <br /> <br />obtain current meter measurements on the structure. Note that there was a <br /> <br />significant difference in the discharge coefficient between the rounded sill <br /> <br />and the square sill. <br /> <br />Weir F <br /> <br />A modification of Weirs D and E was made in Weir F. By providing <br /> <br />an adversely sloping crest, sediment deposition on a substantial portion <br /> <br />of the crest was prevented. The sloping crest, however, created non-uniform <br /> <br />flow and considerable difficulty would be experienced in obtaining current <br /> <br />meter measurements of discharge. Stage measurements to a sloping water sur- <br /> <br />face would not be particularly objectionable as long as the rating remained <br /> <br />constant. The variation in coefficient of discharge is shown in Fig. 15. <br /> <br />Weir G <br /> <br />Weir G is a modest variation of Weir E with the only change being <br /> <br />the point at which the downstream slope of the structure begins. By start- <br /> <br />ing the downstream slope at the top of the sill, necessity for aerating the <br /> <br />undernap of the over fall was eliminated. Most of the studies conducted on <br /> <br />Weir G were Inade in the clear-water 2-ft flume. <br /> <br />Water Surface Profiles - Water surface profiles over the weir at <br /> <br />various unit discharges are shown in Fig. 16. The dimensions are given in <br /> <br />terms of the prototYlle. For unit di scharges up to about 25 cfs per ft there <br /> <br />is a level water surface over approximately the middle one~third of the <br /> <br />-22 <br /> <br />'~\ ~ ,.. i'""! <br />li '--I ~ '_. , <br />