This section describes how the starting water surface elevations (WSELs) were determined in a study.

Starting WSELs are the flood elevations used at the first downstream cross section in the step-backwater computations for riverine studies.

For Starting WSELs, absent established downstream elevations or a control cross section, FEMA generally uses normal depths, which are computed using the channel slopes and cross-sectional areas (also known as slope-area method).