7. Causes and Impacts of Coastal Inundation

According to NOAA’s Office of Coastal Management, inundation events are the dominant causes of natural-hazard-related deaths in the U.S. and are also the most frequent and costly of the natural hazards affecting the nation. The effects of inundation in other nations such as Bangladesh, Indonesia, Thailand and India are often devastating. While the long-term rises in mean sea level as discussed in Part 1, Chap. 3 are instrumental in allowing inundation to reach farther inland and to ever higher elevations, it is the short-lived episodic, non-tidal, events that cause the most damage. Included among these inundation causes are tsunamis, storm surges, coastal flooding caused by onshore winds and wave-induced set up, river and inland flooding and extreme rainfall events. The deepest flooding occurs when two or more of these phenomena reinforce each other and coincide with perigean spring high tides (aka. “king tides”). For example, it is common for tropical cyclones to bring storm surges along with heavy rainfall and wave induced set up of mean water level. Structures such as levees that are designed to protect can also impede the return of floodwaters once overtopped. Navigation channels can also provide funneling pathways for surges.