Highway-Stream Crossing Analysis
The hydraulic analysis of a highway-stream crossing for a particular flood frequency involves the following:
- determination of the backwater associated with each alternative profile and waterway opening(s)
- determination of the effects on flow distribution and velocities
- estimation of scour potential.
The hydraulic design of a bridge over a waterway involves the following such that the risks associated with backwater and increased velocities are not excessive:
- establishing a location
- bridge length
- orientation
- roadway and bridge profiles.
A hydrologic and hydraulic analysis is required for designing all new bridges over waterways, bridge widening, bridge replacement, and roadway profile modifications that may adversely affect the floodplain even if no structural modifications are necessary. Typically, this should include the following:
- an estimate of peak discharge (sometimes complete runoff hydrographs)
- existing and proposed condition water surface profiles for design and check flood conditions
- consideration of the potential for stream stability problems and scour potential.
See the
in Chapter 3 for a complete list of requirements.