Category:748 Hydraulics and Drainage

To produce the most practical and flexible design, each hydraulic design aspect and the associated flood frequency must be considered and established based upon the relative risks and costs. The flood frequency establishes a design storm and associated discharge and the criteria establishes the acceptable level of performance during that event. In lieu of a single “design flood frequency”, the flood frequency associated with each hydraulic design aspect will be shown on the plans, i.e., “backwater design frequency”, “roadway overtopping design frequency”, “freeboard design frequency”, etc.

The Design High Water Elevation (DHW) will be based on the return period of the freeboard design. Design exceptions for frequency or criteria are encouraged when they are practical.