Standard Step Backwater Method
The Step Backwater Method, or Standard Step Method, uses the energy equation to “step” the stream water surface along a profile (usually in an upstream direction because most Texas streams exhibit subcritical flow). This method is typically more expensive to complete but more reliable than the Slope-Conveyance Method.
The manual calculation process for the Standard Step Method is cumbersome and tedious. With accessibility to computers and the availability of numerous algorithms, you can accomplish the usual channel analysis by Standard Step using suitable computer programs.
A stage-discharge relationship can be derived from the water surface profiles for each of several discharge rates.
Ensure that the particular application complies with the limitations of the program used.
Use the Standard Step Method for analysis in the following instances:
- results from the Slope-Conveyance Method may not be accurate enough
- the drainage facility’s level of importance deserves a more sophisticated channel analysis
- the channel is highly irregular with numerous or significant variations of geometry, roughness characteristics, or stream confluences
- a controlling structure affects backwater.
This procedure applies to most open channel flow, including streams having an irregular channel with the cross section consisting of a main channel and separate overbank areas with individual n-values. Use this method either for supercritical flow or for subcritical flow.