Define the location, FEMA NFIP status, orientation, shape, and material for the culvert to be designed. In many instances, consider more than a single shape and material.

With consideration of the site data, establish allowable outlet velocity (v

max

) and maximum allowable depth of barrel.

Based upon subject discharges (Q), associated tailwater levels (TW), and allowable headwater level (HW

max

), select an overall culvert configuration -- culvert hydraulic length (L), entrance conditions, and conduit shape and material to be analyzed.

Determine the flow type (supercritical or subcritical) to establish the proper approach for determination of headwater and outlet velocity.

Determine the headwater elevation and outlet velocity.

Adjust slope or shape for excessive outlet velocity if necessary. Check effect on headwater elevation.

Continue to adjust configuration until headwater elevation and outlet velocity are within allowable limits. It may be necessary to treat any excessive outlet velocity separately from headwater and control by other means such as velocity controls.