Association of State Wetland Managers - Protecting the Nation's Wetlands.

The Compleat Wetlander: Will Post-Sandy Recovery Efforts Consider Wave Action in Future Storms?

When hurricanes arrive, the winds blow and the water rises higher and higher. Waves crash against the shore and then rush inland flooding coastal areas.  Afterwards the recovery begins: first with emergency services later followed by long-term recovery efforts including rebuilding communities.  At this point much of the discussion and public debate centers around where and how to rebuild—including what to do to protect people from future events.

It is essential to understand the terms used to describe a hurricane specifically storm surge versus wave action. Failure to do so can limit our collective understanding of the extent to which the recovery efforts protect against future events. In talking to floodplain professionals I find the distinction between the terms storm surge and wave action somewhat confusing.  I’ve been told that most of the water damage from hurricanes is caused by wave action. But all the reports focus on storm surge.  A quick perusal of websites that describe hurricanes and coastal storms confirm my perception that there is a lot of information about storm surge, but it is sometimes two thirds of the way through an article before wave action is mentioned.

The amount of damage done by hurricanes and major storms (including how far inland waves travel) is due to a combination of factors and the importance of each of these can vary from storm to storm.  The pamphlet “Introduction to Storm Surge” identifies many of these: http://www.nhc.noaa.gov/ssurge/surge_intro.pdf

Storm surge is the abnormal rise of water generated by a storm.  It can be visualized as a bulge in the base water level as the storm moves ashore.

The amount of storm surge is influenced by many factors: size and intensity of the storm, tide, wind, angle that the storm approaches to coast, shape of the coastline, width and slope of the ocean bottom, etc.

In addition there is wave run-up which is not part of storm surge. Also called wave action or defined as wave set-up + wave run-up, it describes the waves that pile on top of the storm surge and—depending on many of the factors that influence storm surge—it can be very significant.

The world record for storm surge is accredited to the Bathurst Bay Cyclone of 1899, a category 5 hurricane, with sustained winds in excess of 175 mph. One eye-witness camping on a 40 foot ridge ½ mile inland described being inundated by waist-high water.   Fish and dolphins were found on 49-foot cliffs.  However the storm surge was only 15 feet.  It was the wave run-up (the waves on top of the storm surge) that achieved the 50 foot height.  This means that if the storm surge was 15 feet, wave action added another 35 feet to the water column that inundated the coastline.  http://www.wunderground.com/hurricane/surge_world_records.asp?MR=1

There are various flood inundation maps, models and other sources of information available to understand storm surge and wave run-up.  Two products widely available are Hurricane Evacuation Study Inundation Mapping and National Flood Insurance Program-Flood Insurance Rate maps. They depict different areas of concern with respect to flooding, which are explained an article: http://www.iwr.usace.army.mil/nhp/docs/CoastalFloodMaps_Final.pdf In addition there are various models available to estimate combinations of storm surge and wave action.  What is important in the context of recovery efforts following Hurricane Sandy is that the public needs to understand whether post-hurricane efforts will protect them from only storm surge or storm surge and wave action.  The costs of rebuilding to address both will be much higher, but the public will be much safer.

Explanation of NOAA’s and WAVEWATCH models

Complexity of factors that shape height of surge and an explanation of why it is more difficult to calculate wave set up or run up.

32-Foot-Plus Waves from Hurricane Sandy Topple Records

Storm Surge and Coastal Floods

Tropical Cyclone Hazard Definitions

Climate Change and Coastal Hazards (New Zealand)

Powerful Hurricane Sandy slams into U.S. east coast

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