Historical/Current: To assess the project location’s exposure to storm surge in the Historical/Current time-frame, a conservative screen of 10 meters is applied. That is, if the project elevation is 10 meters above the present maximum high tide level, then the project will not likely be exposed to storm surge.
The 10 meter elevation threshold indicated above is roughly the elevation of the greatest historical storm surge and wave run-up heights.
The highest storm surge in the past century occurred during the Great Bhola Cyclone of 1970 in the Bay of Bengal, when a storm surge of 10.6 meters occurred during one of the highest high tides of the year.10 The highest storm surge on record in the United States was from Hurricane Katrina in 2005, measured at 8.4 meters above the normal astronomical tide level.11
There are far more sophisticated techniques for estimating maximum storm surge involving numerical modeling. However, the threshold approach in this tool is adequate for the coarse, rapid screening purposes of this tool. (However, it is important to note that increases in sea level are not equivalent to increases in storm surge height.)
Future: To assess whether the project will be exposed to future storm surge, the tool helps the user to identify whether the project elevation is within 11 meters’ elevation of the present maximum high tide level. Storm surge height is likely to be increased by sea level rise. The 11 meter threshold is based on a combination of the maximum present day surge values (10 meters) and the upper end of sea level rise projections for 2050 (0.6 meters).(See “Storm Surge: Historical/Current” section above and “Sea Level Rise” section on preceding page).
Both thresholds suggested under this (storm surge) hazard are intended to be conservative screens to determine whether the project location could experience storm surge. They do not reflect whether the project location is likely to experience tropical cyclones or the distance inland that a storm surge may travel. (For assessments of exposure to cyclones and other wind hazards, see “Strong Winds” section, next page.)
More precise estimates of changes in the magnitude of future storm surge are difficult to make and are relatively uncertain. There is high confidence that storm surge extremes will increase with sea level rise, yet there is low confidence in region-specific projections in storminess and storm surges.12As noted above, numerical modeling techniques can be used to simulate storm surge if more precise information on storm surge is needed to refine the estimates of risk to the project.