Mapping Nuisance Flooding Days – Simple Effective Information

The term “nuisance flooding” has been used to describe tidal flooding during conditions that extend to minor flooding levels. These sub-moderate events are familiar to most coastal residents as notable and disruptive but not overly dangerous; many can identify with the impacts/look of nuisance flooding. Recent work has highlighted the tipping point to nuisance flooding at around 30 days/year, however, this is a location/use specific value. When nuisance flooding coincides with moderate rain events the geographic extents and societal interruptions expand and can cause moderate to major issues locally. Development of the shallow coastal flooding threshold, changes in yearly frequency based on sea level rise (SLR), and mapping of the area by NOAA has been helpful to establish a common understanding of flooding frequencies and where they occur. The shallow coastal flooding zone is, however, static at present; it does not expand with SLR.

During a recent project Geoscience Consultants developed a high-resolution mapping product that builds on the nuisance/shallow flooding products from NOAA. It is a map of the calculated number of days per year a location will be inundated now (ca. 2025) and in the future based on SLR curves. This provides stakeholders with the ability to gauge future conditions of their specific area of interest by examining present (2025) locations that have a similar number of predicted future inundation events.

This nuisance flooding product is based on 20+ years of hourly high-water levels from a nearby tide station (in this case Charleston) that were corrected for SLR. Once the frequencies are developed, they can be applied to any level of SLR. The simple metric is easier to assimilate than calculating the difference in water levels from specific flooding events (e.g., 1-yr storm) at present and in the future.

If you are interested - here is a link to some work on Sullivan’s Island SC