Learn More
- Listen to the Diving Deeper: Tsunamis podcast to learn more about the causes of tsunamis and how to prepare for them.
- Visit the Glossary to view the definition of inundation terms commonly used throughout this website.
- Learn about the Coastal and Inland Flood Observation and Warning (CI-FLOW) project and how riverine flooding and coastal flooding events affect each other.
The first step is to understand what inundation is and why communities should be concerned.
Inundation and Coastal Communities
What Is Inundation? Water covering normally dry land is a condition known as inundation.
Impacts
Inundation events are among the more frequent, costly, and deadly coastal hazards that can impact coastal communities in the U.S. In fact, riverine and coastal inundation causes the highest number of natural-hazard-related deaths. With coastal states supporting 81% of the U.S. population and generating 83% of U.S. gross domestic product, the potential for catastrophic loss from inundation events is greater in these states than in other areas of the country.
In addition, future inundation risks may be exacerbated by local changes in climate and sea level. It is important to know current inundation risks to understand the potential effects of changing conditions.
Causes
Episodic Coastal Inundation Events
There are four primary causes of significant inundation: storm surge, tsunamis, inland flooding, and shallow coastal flooding.
Storm surge results from severe storms such as tropical cyclones (e.g., hurricanes, typhoons) and nor'easters, as strong winds combined with low pressure drive water onshore (NOAA, 2009). Hurricanes like Katrina (2005) and Hugo (1989), and the 1993 nor'easter (the "Storm of the Century"), caused extensive storm surge.
Tsunamis are large waves generated by an abrupt disturbance of the sea surface (e.g., from an earthquake or landslide). A tsunami caused by a local event arrives minutes after generation, while a tsunami caused by a distant event arrives hours later (NOAA, 2009). The 2004 Indian Ocean tsunami is the most recent example of the devastating effects of tsunamis.
Inland floods occur when moderate precipitation falls over several days, intense precipitation falls over a short period, or an ice or debris jam or a dam or levee failure causes a river to overflow (NOAA, 2009). Hurricane Floyd (1999), aided by Tropical Storm Dennis (1999), resulted in widespread severe flooding that caused the majority of the $3 to 6 billion in damage recorded after the storms.
Shallow coastal flooding is flooding that occurs when water is driven onto land from an adjacent body of water. This generally occurs when there are significant storms, such as tropical and extratropical cyclones (i.e., wind blowing landward from the ocean). Places like Savannah, Georgia, experience amplified impacts from shallow coastal flooding several times a year because of coastal development and low elevation.
Longer-Term Coastal Inundation
Sea level rise is an increase in the mean level of the ocean. NOAA has been measuring mean sea level for over 150 years, with tide stations operating on all U.S. coasts.
Global (or eustatic) sea level rise is caused by a change in the volume of the world's oceans due to expansion as the oceans warm and to the melting of land-based ice (i.e., glaciers, ice sheets).
Relative sea level rise refers to a local increase in the level of the ocean relative to the land due to ocean rise or land subsidence (e.g., from groundwater withdrawal, tectonic activity).
View works cited and additional resources for understanding inundation.
