During calculations, the culvert is divided into three zones:

• Inlet Zone - for culverts with a span or diameter of 9 feet or less the inlet zone is 2 feet for culverts larger than 9 feet the inlet zone is 3 feet  (Belhke, 1992). FishXing reports the inlet zone as the first two nodes down the culvert.

• Barrel - all the nodes between the first two nodes and last two nodes in the culvert

• Outlet Zone -  the distance from the outlet invert to a distance equal to 4yc (critical depth) and is reported as the last two nodes of the culvert.

When Velocity Reduction Factors are applied they will be multiplied to the average cross section velocity in the specified zones at the nodes defining the zone.

For this application the Barrel Velocity (VB) is the average cross-sectional flow in the barrel approximately one culvert diameter downstream from the inlet and represents the area immediately downstream of the inlet Contraction and Expansion zone.

See also: Inlet Head Loss Coefficient, Inlet Contraction Velocity, Outlet Hydraulics, Velocity Reduction Factors