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Downslope Velocity Increase

ASCE has approved a potentially important modification to the calculation of the flow velocity at the site when the site is located on a downslope; that is, where the land slopes down from the shore side of the site to the inland side of the site over a 200 ft expanse centered on the  site (±100 ft). Based on numerical studies, it was determined that the flow velocity should be increased in this situation, with a cap on the increase of 6 ft/s (1.83 m/s). This will be in section 6.6.2 of ASCE 7-22. This increase has been implemented in the EGL software. When applicable, an alert is issued announcing the calculated increase. The user has the choice of accepting the increase or staying with the smaller flow velocity as calculated per ASCE 7-16. Note that the velocity profile and the reported Froude number are not changed.

The Standard is unclear on what to do if the site is within 100 ft of shore or the runup location. As a design decision, the EGL software does not apply any increase in these cases; otherwise some very strange scenarios can be easily imagined that wouldn't make a lot of sense.