Culvert Modeling

A culvert is a simple structure, often a pipe, projecting through an embankment to allow runoff to move from an upstream to a downstream area. A culvert consists of an entrance, an exit, and a barrel connecting the two. Although a culvert is a simple structure, the hydraulics of a culvert can be quite complex. The culvert may or may not flow full, the exit may or may not be submerged, the flow regime can be subcritical or supercritical, and the culvert's capacity can be controlled by either the upstream or downstream flow conditions. The same culvert may switch from one condition to another as the discharge through the culvert changes. Because of all these conditions, correct modeling of culverts and the interpretation of the output can be a challenge. This chapter addresses basic culvert hydraulics and modeling procedures, along with using HEC-RAS to perform culvert modeling.