This section lists the methodologies used to compute the flood elevations and the various components used in the calculations. The most common methodology used to calculate flood elevations for a stream is a step-backwater computer program, such as HEC-2 or HEC-RAS. For more complex flooding situations, a computer program that models two-dimensional flow may be used.

HEC indicates the model was developed by the US Army Corps of Engineers Hydrologic Engineering Center (HEC). RAS is an acronym for their “River Analysis System”.