Definitions

"Tideline" is used to denote the recent historical average of the highest daily local tide level or, technically, the mean higher high water (MHHW) line. Within the United States, NOAA's VDatum tool is used for MHHW values; elsewhere, modeled tidal increments are added to recent historical average sea surface heights measured by satellite. Tideline projections add projected sea level rise.

"Annual flood level" is used to denote the water level at the shoreline that local coastal floods exceed on average once per year. In other words, ten floods are statistically expected to exceed this level over ten years, although some years might have two or more incidents, and other years none.

"Moderate flood level" is used to denote the water level at the shoreline that local coastal floods have a ten percent chance of exceeding each year.

"Major Flood Level" is used to denote that water level at the shoreline that local coastal floods have a one percent annual chance of exceeding each year. Commonly called the hundred-year-flood level. Option currently available only in the U.S. for data quality reasons.