This circular contains a series of hydraulic capacity charts which permit the direct selection of a culvert size for a particular site without making detailed computations.
The charts in this circular do not replace the nomographs of Hydraulic Engineering Circular No. 5 (HEC No. 5). The procedures given in the two circulars supplement each other by providing a solution for most designs likely to be encountered. Both circulars give identical answers in certain ranges of hydraulic operation, but the nomographs of HEC No. 5 must be used for the higher headwater depths and in cases of submerged outlets. This circular discusses the requirements and limitations for the use of the capacity charts and the instructions tell when HEC No. 5 must be used.
The designer, after becoming familiar with the capacity charts, will discover that these direct-reading charts have advantages over the trial and error procedure used in HEC No. 5. For instance, the capacity of the various types and sizes of culverts in common use can be compared rapidly and the charts provide a more accurate solution for low headwater depths which is the main limitation in the use of HEC No. 5. Sometimes the chart answer must be modified if a special culvert is used or an unusual site condition is encountered, but for the majority of culvert problems the capacity charts are adequate for the selection of a culvert size.
A list of the culvert capacity charts is provided for easy reference. All symbols, notations, and descriptive terms used are the same as in HEC No. 5 and the appendix contains a discussion of the hydraulic computation methods used in compiling the culvert capacity charts.
In addition to the capacity charts and instructions for their use, this circular includes a brief discussion of other design considerations to emphasize that culvert capacity is only one of the many problems confronting the engineer in the design of a culvert.
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