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Area of potential storm damage: Click on the image above to see how winds from a Katrina-strength storm might affect the Texas Colorado River basin. This is for illustrative purposes only.
For comparision: See image from the National Weather Service with wind speed predictions issued at the time of Katrina's landfall on Aug. 29. |
The last-minute northeasterly turn of Hurricane Rita spared the Colorado River basin recently, but left LCRA workers who study storm disaster models with an important question. If a major hurricane were to come ashore in Matagorda Bay at the mouth of the Texas Colorado River, what would happen in that basin?
The answer: Wind and rain would wreck the coast and many miles inland, according to LCRA weather and emergency experts.
“The impact in the coastal counties would be devastating, similar to that seen along the Mississippi and Alabama coast,” said Ed Schaefer, LCRA emergency management coordinator and president of the Emergency Management Association of Texas.
Farther upriver, there could be significant wind damage and flooding. The extent of flooding would depend on where and how much rain fell. This in turn would depend on where and how long the storm lingered. Flooding on the Colorado River would be moderated – but not prevented – by the Highland Lakes dams, especially Mansfield Dam, which forms Lake Travis, the only one of the Highland Lakes designed to store floodwaters. LCRA is responsible for managing those dams through extremes of floods and droughts.
In August, Hurricane Katrina entered the Gulf of Mexico, then spun north to Louisiana and Mississippi to wreak destruction on much of those two states. Then in late September, Rita churned, making a beeline for the mid-Texas coast, just two days before weakening and touching land at the Texas-Louisiana line. Rita flattened trees, homes and businesses and left flooding in her wake.
| While preparing for the possible landfall of Rita, LCRA officials planned for the worst.
That's because LCRA not only manages the waters of the lower Colorado River, it also is responsible for thousands of miles of electric transmission lines, about three dozen water and waswtewater systems, three irrigation systems with 1,100 miles of canals in Colorado, Wharton and Matagorda counties, and 40 parks and recreation areas.
- Emergency planning and parks: At Matagorda, a communications plan is in place among LCRA’s emergency management staff, the Matagorda County sheriff, the Texas Parks and Wildlife Department and County Emergency Management of Matagorda County. Among other things, when a warning is issued that the area is threatened, the parks are closed, customers at LCRA parks and employees evacuated in a coordinated manner, and, if necessary, construction equipment used to develop the park left behind.
- Power lines: Winds from the hurricane would damage both high-voltage transmission lines and the smaller distribution lines in its path, leaving larges numbers of homes and businesses without power for many weeks. For LCRA, this would mean damage to its transmission lines from the coast well into Central Texas. This is because most of the lines were built before 2002 when a new standard required lines to be built to withstand higher winds. "We could very well expect substantial, heavy and catastrophic damage from a Category 3, 4 or 5 hurricane to most of our transmission facilities," said David Turner, manager of LCRA's Transmission and Distribution Line Engineering.
As much or more damage is likely to be inflicted by wind and fallen trees and debris on the distribution lines that carry power directly to homes and businesses. Throughout much of Central Texas these lines are owned and maintained by cities and electric cooperatives that buy power wholesale from LCRA and sell it to the end-use customers. (Transmission lines are those that carry high-voltage bulk power from power plants to substations where voltage is reduced so that it can be used in homes and businesses. Distribution lines extend from the substations to those end-use customers.)
- Water utilities: Although LCRA’s wastewater systems are not immune to flooding, there are procedures in place to protect the equipment and facilities so that staff can restore operations soon after waters recede, said Tony Skeen, project manager for LCRA Water and Wastewater Utility Services.
One of the biggest threats to LCRA’s wastewater systems is managing the rapid and excessive inflow of water and the attendant loss of electrical power to keep plants and lift stations running, according to Skeen.
Water systems, too, rely electricity for the water to be pumped into tanks and maintain adequate pressure in the system. When the pressure becomes too low, which can happen when electricity fails, there’s the potential for contamination. If that happens, LCRA typically urges consumers to boil water before using it to drink or cook.
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The potential damage from a 'Katrina'
Katrina remains the worst hurricane of the season and the most costly and destructive ever to hit the United States. Had it landed at Matagorda and moved upward, communities along the river, including the Highland Lakes, likely would have sustained flooding from rain but not the devastation that New Orleans experienced, according to LCRA emergency managers.
Although a major, hurricane-related flood could occur along the river, topographical differences between the river basin and City of New Orleans are obvious. New Orleans was built below sea level and levees hold back the waters of Lake Ponchartrain. Upstream from the Colorado River, the elevation increases and the waters of the Highland Lakes are held back by sturdy dams, not levees. Several of those dams have been made even sturdier over the past 10 years by LCRA with a $52 million modernization designed to have them withstand the worst possible flood on the river.
"We have invested millions of dollars in our dam modernization program to make sure the dams remain safe and function at their best," said Mark Jordan, manager of LCRA River Operations. "We feel confident that we are ready for the next big flood when it occurs."
Many homes and businesses have been built within the 100 year-floodplain along the Colorado River. However, the number of structures that would be affected by flooding caused by a hurricane is a fraction of those affected when the New Orleans levees failed.
Despite the elevation differences, damage could still be severe in the Colorado basin, Schaefer said.
“If there’s a bad one thrown at us, businesses will be destroyed, structures will be destroyed, lives could be lost,” Schaefer said.
- If a hurricane the size and force of Hurricane Katrina made landfall at Matagorda, the storm surge would sweep away structures on Matagorda Bay and the winds would flatten structures in its path for many miles inland.
- Gale-force winds of up to 54 mph would reach as far north as the Oklahoma Panhandle.
- Hurricane-force winds of more than 75 mph would strike as far as Lake Travis and possibly, Lake Buchanan.
“These winds would result in major damage to large numbers of structures,” Schaefer said.
Every storm is different
Although hurricane winds weaken rapidly as they move inland, the remnants of the hurricane would bring tremendous rains. Every storm is different, so it is difficult to preduct how much rain would fall in the basin and how much flooding would result.
Hurricane Beulah of 1967 brought rain that resulted in heavy flooding in southern Texas. Rainfall reached nearly 30 inches in some areas and an estimated 15 people were killed, mostly from flooding. In 1961 Hurricane Carla produced widespread heavy rain, with more than 13 inches recorded in Wharton. The hurricane killed about 30 people in Texas.
By comparison, about 12 inches of rain fell on New Orleans as a result of Katrina.
In Texas, Rita produced nearly 10 inches of rain, most of which was in the Beaumont-Port Arthur area.
Less than 8 inches of rain can easily produce floods in Central Texas, as happened in November 2004 when 4 to 7 inches fell across a large part of the Hill Country.
Meteorologists expected a hurricane like Rita this year. Statistically, the Texas coast was due for a big one: Only three hurricanes have come ashore in Texas in the past 16 years; the long-term average is one every three years.
“Given the high activity we’ve had, the hurricane season will continue to stay active through October,” said Bob Rose, LCRA chief meteorologist. “We will need to be prepared in case the next one comes our way.”
Morales is an LCRA writer specializing in water issues. Contact her at info@lcra.org. |
