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<br />Ie <br /> <br />. <br /> <br />, <br /> <br />e <br /> <br />e <br /> <br />As shown by the inlet control nomograph on Chart 5, the capacity <br />of a thin edge projecting metal pipe can be increased by incorporating <br />the thin edge in a headwall. The capacity of the same thin edged pipe <br />can be further increased if the entrance is rounded, bevelled or tapered <br />by the addition of an attachment or the building of these shapes into a <br />headwall. Although research on improving culvert entrances is not com- <br />plete, sufficient data are available to permit the construction of <br />Chart 7, an inlet control nomograph for the performance of a bevelled <br />inlet on a circular culvert. A sketch on the nomograph shows the di- <br />mensions of two possible bevels. Al though nornographs have not been <br />prepared for other barrel shapes, the capacity of box culverts can be <br />increased at little cost by incorporating a bevel into the headwall. <br />In computing headwater depths for outlet control, when the above bevel <br />is used, ke equals 0.25 for corrugated metal barrels and D.2 for con- <br />crete barrels. <br /> <br />Figure 6 shows a photograph of a bevel constructed in the headwall <br />of a corrugated metal pipe. <br /> <br /> <br />Photo -- Courtesy of Dregon state Highway Department <br /> <br />Figure 6 <br /> <br />5-13 <br />