## Full Flow |

The velocity within a full flowing culvert is calculated as:

Where:

*V
*= Average velocity in the culvert barrel [ft/s or m/s]

*Q*
= Flow rate through culvert [ft^{3}/s
or m^{3}/2]

*A*
= Full cross sectional area of the flow [ft^{2 }or m^{2}]

When flowing full, the friction loss within the culvert
barrel, *H _{f}*,
over a given length of culvert, L,
is calculated based on the friction slope,

To calculate the friction slope, __Manning’s
equation__ is rearranged into the following form:

Where:

n = Manning’s roughness coefficient

j = Constant of 1.00 for metric and 1.49 for English units

*R *= Hydraulic radius
[ft or m]

When full flow conditions exist, FishXing uses the
friction slope and culvert slope, *S _{o}*,
to calculate the height of the hydraulic grade line (

If the hydraulic grade line intersects the top of the culvert, FishXing switches between full flow and open channel flow calculations.