## Friction and Roughness of Culverts |

Water flows through culverts in two basic states
known as **subcritical** and **supercritical** flow, These states are
controlled by the constructed slope of the channel and geometry of the
culvert and fall into the category of Inlet
Control and Outlet Control.

Under outlet control conditions, the roughness of
the culvert will have a significant effect on the flow through the culvert.
The energy loss due to the hydraulic resistance or roughness of a culvert
is part of the "hydraulic price" of flow through a pipe. Two
commonly used equations to describe the flow as a function roughness in
a culvert are the Darcy
equation and the Manning
equation**.**

**See also: **Manning's n,
Darcy Friction
Factor