The right hook delivered by the nastiest corner of Hurricane Ike is likely to leave lasting changes to miles of beaches between Galveston, Texas, and the western coast of Louisiana, experts reviewing the damage say.However, the damage from Ike's waves to dunes and beaches around the rest of the Gulf of Mexico may, in many places, be reversed naturally within a matter of months.Although Ike's top sustained winds Friday and Saturday apparently never surpassed 110 miles an hour, it was one of the largest hurricanes recorded in the Gulf in modern times, spreading tropical-force winds over a circle nearly 600 miles across.Those winds drove surf at least several feet above normal tides from the Florida Panhandle in the east to Texas' Padre Island in the west, eroding the shoreline extensively."There was an amazing extent of surge flooding and overwash in the area to the right of the eye. I've never seen evidence of the surge extending landward for tens of kilometers," said Asbury "Abby" Sallenger, a researcher with the U.S. Geological Survey, after flying a survey mission along the coastline at 600 feet for much of Monday."Between the Bolivar Peninsula and Sabine Pass, where the maximum surge occurred, so much water had ponded behind the beach that it's still submerged. There's a little waterfall extending for miles as the water returns to the Gulf. It's hard to imagine those areas coming back on their own."Robert Dean, a research professor of coastal engineering at the University of Florida, Gainesville, said the Bolivar shore that took the brunt of Ike "is mostly mud, with a shallow cover of sand. That kind of material typically gets carried way offshore by storm surge and doesn't get returned by normal wave action."In general, barrier islands and beaches with mud foundations, like those skirting the Mississippi Delta, have only a thin veneer of sand. Without new sediment from the land, they're more likely to be whisked away, according to several experts.Barrier islands made of coarser sand, more typical along many parts of the Gulf and Atlantic coasts, tend to be more resilient, even when they're overwashed by storm surge.Dauphin Island, Ala., for instance, has been swamped repeatedly by hurricanes in the past decade, from Georges in 1998 to Katrina in 2005 to Gustav last month. But as manmade dunes erode on the ocean side, the sand washes to the back of the island, attempting the natural migration of barrier islands toward the mainland."Most of the time, the islands endure, but the lots on the beach don't, and that's when you get into discussions about the cost and worth of rebuilding repeatedly," Sallenger said.Elsewhere around the Gulf, "if there's a dune system high enough to keep a barrier island from being overwashed, it's likely that the waves we saw in Florida and beyond the eye zone in Texas will leave most of the sand near the shore," said Todd Walton, director of the Beaches and Shores Resource Center at Florida State University in Tallahassee."People think just because the sand is beneath the water, it's gone, but most of the time it's in storage just offshore and if the wave action is right, we see the beaches start to rebuild in a week or two."On the other hand, conditions may worsen or sand pile up in select spots where natural or manmade structures, such as jetties or sea walls, have left sections of beach more prone to erosion, said coastal engineer Dean."There are negative and positive impacts from hurricanes. But, usually, if you've been losing beach steadily, even if a storm brings a little extra wave of sand ashore, you're not going to reverse the long-term trends."On the Net: http://coastal.er.usgs.gov/hurricanes/(Lee Bowman can be reached at bowmanl(at)shns.com.)
Post new comment