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<br />e <br /> <br />. <br /> <br />,. <br />. <br /> <br />e <br /> <br />. <br /> <br />-; <br /> <br />e <br /> <br />The general benefits of good culvert design procedures include <br />reduction of upstream flooding and highway damage due to underdesign <br />and lower culvert construction costs by avoiding gross overdesign. <br />If site conditions permit the use of an improved inlet, construction <br />costs may. be reduced still further. At times, improved inlets may <br />also be installed on existing culverts with inadequate flow capacity, <br />thus avoiding replacement of the entire structure or the addition of <br />a new parallel structure. <br /> <br />A field survey (14) of highway culverts with improved inlets <br />constructed in the United States before 1971 produced detailed <br />information on 66 installations which were estimated to have saved <br />a total of over two million dollars in capital outlay. Many <br />variations of the improved inlet designs discussed in this Circular <br />have been built but were not included in the survey. If a full <br />accounting of all improved inlets had been possible, the savings <br />would likely have been many times the amount reported. <br /> <br />Savings were reported ranging from $500 (12.5 percent), <br />resulting from reducing the diameter of a 200 ft. long reinforced <br />concrete pipe from 54 inches to 48 inches, to $482,000 (38.7 percent) <br />by reducing a 2,700 ft. box culvert from a triple 13 ft. by 14 ft. <br />to a double 12 ft. by 12 ft. The latter case illustrates that the <br />greatest savings usually result from the use of improved inlets <br />o~ culverts with long barrels. Short barrels should also be checked, <br />h6wever, especially when an improved inlet might increase the <br />capacity sufficiently to avoid replacement of an existing structure. <br />For instance, a $9,900 (72.2 percent) benefit was realized by <br />installing a variation of an improved inlet on an existing 60 inch <br />corrugated metal culvert 140 ft. long rather than replacing the <br />entire culvert with an 84 inch diameter culvert. <br /> <br />In the following sections, a short review of conventional <br />culvert hydraulics, a discussion of the types of improved inlets <br />suggested with definitions of the terms used, and design procedures <br />for box and pipe culverts with improved entrances will be presented. <br /> <br />13-3 <br />