The key requirement for this technique is a through culvert flow, without interruption or turbulence (in culvert and at the culvert outfall). In-culvert (or Corrugated Metal Pipe - CMP) obstacles and an outflow into a significant standing body of water, at the same level as the outfall, may compromise float through culvert measurements.

A float can be a ducky, or a similar buoyancy device, catching this at the outfall may require a sieve, and/or a sharp eye! Alternatively thin wood disks or simple cedar wood chips can be used, though for repeatability (and consistency) these need to be of similar dimensions.

This flow measurement technique needs two volunteers and may be safer and more reliable at high-flow conditions.

For a float through culvert flow measurement, a representative (“good first pass”) cross-section can be expressed by an arc inside a circle. Assuming a creek CMP is appropriate for flow measurement, the measurements needed are relatively straight foward... However, depending on the culvert length, it may take two folks to do the recording of the flow velocity, ie the through culvert float distance travelled and time through culvert.

The following parameters are needed for the float through culvert measurement technique

• Through culvert float distance (and float times over this distance)

• Wetted width (in culvert)

• Culvert diameter (this is fixed...)

• Maximum water depth

The above data above can be entered under "quantitative flow", "Flotation through culvert" in our V3 SSIFWC Field App.