Critical Flow Measurement

Peak storm runoff using the critical depth and flow value later used for slope area N value verification.

Critical Depth Sections:
Froude=1=V/(g*D)^0.5 gives:
Q=A*(g*D)^0.5 where D=mean depth as Area/TopWidth
and is much preferred to Slope Area measurements.
V=5.67*D^0.5

Free Culvert Outfall Section:
at lip Depth=0.7 Critical Depth
so Critical Depth is measured upstream 4 * lip depth.

Culvert Inlet Critical Section:
dc=0.66*H1 at width of box upstream.

Critical flow at channel bottom rise and fall or constriction.

USGS Measurement at culverts:
https://pubs.usgs.gov/twri/twri3-a3/pdf/TWRI_3-A3.pdf