A culvert is a closed conduit under a roadway or embankment used to maintain flow from a natural channel or drainage ditch. A culvert shall convey flow without causing damaging backwater, excessive flow constriction, or excessive outlet velocities.
In addition to determining the design flows and corresponding hydraulic performance of a particular culvert, other factors can affect the ultimate design of a culvert and shall be taken into consideration. These factors can include the economy of alternative pipe materials and sizes, horizontal (H) and vertical (V) alignment, environmental concerns, and necessary culvert end treatments.
In some situations, the hydraulic capacity may not be the only consideration for determining the size of a culvert opening. Fish passage requirements often dictate a different type of crossing from what would normally be used for hydraulic capacity. Wetland preservation may require upsizing a culvert or replacing a culvert with a bridge. Excessive debris potential may also require an increase in culvert size. Bridges and fish passage culverts are covered in more detail in Chapter 7 but require a PEO approved by the State Hydraulics Office to complete the design.
The design policy in this chapter applies only to culverts with non-fish-bearing channels. For culverts associated with fish-bearing channels, refer to Chapter 7.
Section 3-2 discusses the data acquisition and documentation required when designing culverts. Culvert design considerations are discussed in detail in Section 3-3, and various end treatments are discussed in Section 3-4. Section 3-5 covers other miscellaneous design considerations that have not been previously discussed.
