take this with a grain of salt:
http://www.chron.com/cs/CDA/ssistory.mpl/metropolitan/3046592
Very scary!
20-foot wall of water
More devastation would be caused by winds blowing over the Gulf of Mexico and pushing surface water inland -- creating up to a 20-foot storm surge. Such a wall of water would swamp most development near Galveston Bay, including Texas City, Kemah and Johnson Space Center. Varying levels of water would flood much of the area between Sam Houston Parkway and the bay.
On Galveston Island, the seawall could hold back much of the storm surge, but at some point the water would creep onto the island from the bay side. The island's highest point is just 22 feet above sea level.
Much like a river becomes deeper and more turbulent when it narrows, a storm surge also can increase in height and intensity when its source of water narrows. Dodson said this has profound implications for the Port of Houston. Some models ended with a 30-foot wall of water in the Ship Channel near the port's turning basin, he said. "It would be huge," he said. "It could overwhelm chemical storage facilities, water treatment plants and other sensitive areas."
The port's severe-weather plan calls for most cargo ships to exit the facility and weather the storm at sea in preparation for the possibility of flooded buildings.