Once familiar with culvert design theory as presented in this chapter, the PEO shall use one of several commercially available culvert design software programs. FHWA has developed a culvert design program named HY-8 that uses the same general theory presented in this chapter. HY-8 is a user-friendly, Windows-based software, and the output from the program can be printed and incorporated directly into the hydraulic report. HY-8 is free software distribution. It is available by contacting either the RHE or the State Hydraulics Office at the following link.
In addition to being user-friendly, HY-8 is advantageous in that the headwater elevations and outlet velocities calculated by the program tend to be more accurate than the values calculated using the methods presented in this chapter. HY-8 computes an actual water surface profile through a culvert using standard step-backwater calculations. The methods in this chapter approximate this approach but make several assumptions to simplify the design. HY-8 also analyzes an entire range of flows input by the user. For example, the program will simultaneously evaluate the headwater created by the Q25 and Q100 flow events, displaying all the results on one screen. This results in a significantly simplified design procedure for multiple flow applications. The HY-8 program contains a help guide accessed internally to aid in the system’s operations. Additional guidance will be provided in future revisions to the Hydraulics Manual.
