Hurricane Preparedness, Rio Grande Valley: Storm Surge

Of the four primary hurricane hazards (wind, inland flooding, storm surge, and tornadoes), storm surge and associated battering waves are the most destructive to infrastructure on and near the coast, and have the potential to not only wipe communities off the face of the earth, but kill hundreds of people in one fell swoop. In Texas, one only has to look back to Hurricane Ike in 2008 to understand the sheer power of the sea. A surge of greater than 17 feet, enhanced by wave set up demolished most buildings, vehicles, and other structures on the Bolivar Peninsula northeast of Galveston. Across the Nation, nobody will forget anytime soon the catastrophe that was Hurricane Katrina in Louisiana, Mississippi, and Alabama. While the partial destruction of New Orleans from overtopped and breached levees became the seared memory for many, the truly awesome damage might have been along the Mississippi coast, where a surge of more than 27 feet scoured the coastline clean, including many long standing, stately homes. 2012’s Hurricane Sandy forever changed the perception of the power of storm surge for tens of millions of residents from Maryland through Connecticut, no matter the Saffir–Simpson Hurricane Wind Scale, which was barely at Category 1.

Storm Surge Defined
A storm surge is a large dome of water, about 50 to 100 miles wide on average, which sweeps across the coastline along and to the right of the center of a tropical cyclone as it makes landfall. The combination of prolonged hurricane force winds and increasing area affected by such winds will always increase the height of the storm surge. Cyclones with "tight" eyewalls moving steadily across a lower fetch (Hurricane Charley, 2004) will have less storm surge than larger, lumbering cyclones encompassing a much greater fetch of open water (Katrina, 2005; Ike, 2008; Hugo, 1989). Similar to other coastal communities across the world, storm surge poses the greatest threat to life and property for the lower texas coastal communities including the Town of South Padre Island, Port Isabel, Laguna Vista...and the Port of Brownsville.

Storm surge combines with astronomical tides to create the storm tide, which can increase the mean water level 15 feet or more in a large cyclone with a wide girth of hurricane force winds. Most of the communities on the Lower Texas Coast are below 10 feet in elevation, making the threat from storm tides real and potentially catastrophic in a worst case scenario. Due to the shallow nature of the continental shelf east of the Texas Coast, a storm surge from a landfalling tropical storm or hurricane will be significantly higher compared with a surge striking the steeply sloped continental shelf along portions of the Atlantic coast.

Possible Outcomes on the Lower Texas Coast
Computer simulations of a large, lumbering hurricane (such as Carla in 1961) making landfall near or just south of the mouth of the Rio Grande River show a huge impact from the resulting storm surge on the coastal communities of the Lower Texas Coast. Locations, particularly the Town of South Padre Island, would be completely inundated, and many properties in Port Isabel and Laguna Vista would be washed away, demolished, or made uninhabitable. Results of the simulation can be found on page 4 of the Hurricane Dolly left a 3 to 4 foot peak surge from the Gulf side; Hurricane Ike had Gulf water breach the sea wall in a few spots, due to the combination of wave set up and storm surge which reached a little more than 6 feet. Hurricane Allen's storm tide in 1980 hit Port Mansfield with 12 feet of water, but spared the more populated Lower Texas Coast as winds quickly turned offshore. Hurricane Beulah (1967) reportedly drove an 8 to 14 foot surge across South Padre Island and into the Laguna Madre, with a value of 12 feet reported at Port Isabel. The other formidable storm surge event in the past 100 years was in early September, 1933, when a reported 13 foot storm surge reached into areas east of Brownsville.

What You Can Do
For residents who own or lease property near the coast where storm surge flooding can occur, the one thing you can do now is obtain flood insurance. Flood insurance, backed by the National Flood Insurance Program, offers full coverage for inundation flooding and is backed by the United States Government. Homeowners insurance policies do not cover inundation. A flood insurance policy will not take effect until 30 days after the first payment is made and papers or signed, so the sooner you sign up, the faster a policy becomes active. As for storm surge mitigation, there is little one can do to counter the power of a large, battering storm surge. A structure with breakaway ground floors or one that is elevated well above the sand can offer protection from minor to moderate surge events. For a surge comparable to Ike or Katrina, rare as they may be on the Lower Texas Coast, all bets are off. You can run, but you cannot hide, from storm surge flooding.

Additional Storm Surge definitions and information can be found here.