STORM SURGE |
Among the most damaging features of a hurricane is its storm surge. In areas prone to large surge, wind surge is the main component. But, ocean level rise due to pressure drop, waves breaking at the shore, and strong currents also contribute to surge. By definition, "storm surge" is the vertical water elevation above normal levels. While, "flood elevation" (sometimes called "storm tide") is the vertical water elevation above some datum, for example above mean sea level. So, flood elevation includes both storm surge and normal tide level.
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Flooding near Galveston, TX during Hurricane Ike in 2008 (photo courtesy of C. Parrish, U.S. Airforce).
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What Impacts Surge Magnitude?
Hurricanes can be described in terms of their intensity, size, speed, and landfall location. Of these, intensity, size, and landfall location most influence surge magnitude along continuous coasts. Hurricane intensity is typically defined as the hurricane's maximum wind speed, or Category. But, hurricane central pressure better indicates surge potential [5]. The figure shows that:
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Definition of storm surge and flood elevation.
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Why IS SURGE Higher IN SOME REGIONS? AN EXAMPLE FROM TEXAS
In Texas, the continental shelf changes dramatically. To the south, the shelf is narrow. To the north, the shelf is much wider. Because wind surge is only generated in shallow waters, larger surge may be generated when the continental shelf is wider. As an illustration, in 2008 Hurricane Ike, a very large Category 2 storm, made landfall in Galveston, TX. Highest recorded surges were on the order of 5 m (16 ft). The figure below shows what the surge would have been if Ike had taken a different path. If Ike had hit along the lower Texas coast, the surge would have been half as high.
Estimated peak surge if Hurricane Ike made landfall instead at the location shown. Values are shown as percent of the peak historical surge. Actual landfall location for Hurricane Ike is shown as a black diamond. Dashed line is 30-m depth contour—a measure of continental shelf width. Surge values estimated using Irish and Resio [6].
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Acknowledgements & Credits: Click here for literature cited in this section, "Hurricane Impacts." This material is based upon work supported by the Texas Department of Public Safety's Division of Emergency Management. Background photo courtesy of Mark Moran (Creative Commons license CC BY 2.0)
© 2019 Jennifer L. Irish & Steven M. Quiring. All rights reserved.
© 2019 Jennifer L. Irish & Steven M. Quiring. All rights reserved.