| David Walker supervises LCRA's River Operations Center, where forecasters monitor storms and manage the Highland Lakes to lessen the impact from floods. |
 USTIN - Each weekday morning, Bob Rose scans the computers in his office at the Lower Colorado River Authority in Austin to compile volumes of complex meteorological data and formulate a daily weather forecast. His prognostications help guide LCRA's operations from the Texas Hill Country to Matagorda Bay.
But, of late, Rose's focus has been split. In addition to weather patterns over a large portion of Texas, the LCRA meteorologist has been keeping a close watch on the tropical Atlantic Ocean. That's where warm water and moist, tropical air give life to massive, rotating storms often 300 miles or more in diameter -- hurricanes. Kickoff of season
June 1 was the kickoff of the Atlantic hurricane season. It did not take long for the storms to start churning. Long-term records indicate there have never been so many named storms so early. Tropical Storm Arlene, the first tropical storm of the season, formed on June 9. Later, it moved ashore near Pensacola, Fla. Its 50 mph winds caused little damage. That was also the case for tropical storms Bret (which moved into Mexico) and Cindy (which moved into Alabama). Then on July 10, Hurricane Dennis, roared into Florida and Alabama, near the same area hit in 2004 by Hurricane Ivan. Dennis then drenched much of the eastern half of the U.S. While Dennis was still acting up, Hurricane Emily emerged. On July 20, it smashed into the Mexican coast about 75 miles south of Brownsville. "Indications are that it's going to be a very busy season," Rose said. As an organization that manages the lower Colorado River, and the periodic floods that occur there, LCRA keeps a close watch on hurricanes -- and the often devastating rains they bring with them. Once formed, tropical storms and hurricanes churn, generally, north and northwest. Some smash into Florida or farther north on the Atlantic seaboard. Others rumble past Mexico's Yucatan Peninsula, across the Gulf of Mexico and inland over the Texas coast. The more hurricanes there are, the greater the likelihood a specific area -- like Texas -- will be struck. That's why predictions for an atypically busy season have caused concern. Forecasts based on several factors
Rose, who has worked at LCRA for 10 years, said the forecasts are based on several factors. Two of those are warmer than average surface sea temperatures in the tropical Atlantic and an absence of westerly winds sometimes launched by El Nino, a massive weather phenomenon in the Pacific Ocean. Meteorologists at the National Oceanic and Atmospheric Administration (NOAA) agree. They are predicting as many as 12 to 15 tropical storms in 2005 with seven to nine of those strengthening to hurricane force with sustained winds at 74 mph or greater. NOAA is predicting that of the storms that become hurricanes, three to five will be classified as major storms with winds exceeding 110 mph. In 2004, 15 named tropical storms spawned nine hurricanes. Four of those smacked into Florida in one horrific, 44-day period. The toll was staggering: 126 dead and at least $20 billion in damage. Texas was spared. Texas overdue for a major storm
Larry Eblen, a meteorologist with the National Weather Service office in New Braunfels, said statistics hold that a storm might hit Texas soon. In the 16-year period from 1989 till now, three hurricanes have come ashore in Texas. Before 1989, a hurricane hit the state, on average, once every four years. "If you believe in averages, we're due," Eblen said. The last two hurricanes to hit Texas were Bret in 1999 and Claudette in 2003. Claudette moved inland over Matagorda Bay and dumped heavy rain over Matagorda and Wharton counties. Bret came ashore north of Brownsville and had no impact on the Colorado River basin. But remnants of a tropical storm or hurricane that reach Central Texas and stall could have devastating effects. "We've learned looking over the data for the past 20 or 30 years that the number one cause of death related to a tropical system is inland flooding," Eblen said. "And we are in the number one flood-prone area in Texas." That's driven largely by the geography of the Colorado River basin northwest of Austin. The basin is wider north of Austin and narrows as the river heads south. The Hill Country's steep slopes mix with thin soils over a hard, rock shell. Heavy rain triggered by a hurricane, tropical storm or other weather system adds to the threat of flash flooding, Eblen said. That's why the region is known as Flash Flood Alley. A hurricane or tropical storm can fuel such an event. In August 2001, two months after Tropical Storm Allison dumped 37 inches of rain on the Houston area, LCRA ran a computer model to find out the impact that that magnitude of rain over the Hill Country would have on the river, the Highland Lakes northwest of Austin and the people who live around them. The results were striking: -- Runoff would raise Lake Travis 26 feet above the spillway at Mansfield Dam, which forms Lake Travis. LCRA would have to open all Mansfield Dam's 24 floodgates. -- Even with all nine floodgates opened at Tom Miller Dam, water in Lake Austin would crest about 20 feet above the spillway at Tom Miller Dam. -- Downstream, the water would create record or near-record floods, with the water going as high as 34 feet over flood stage in some places. LCRA has upgraded its resources
David Walker, supervisor of LCRA's River Operations Center, said the study served as a reminder that careful operation of the Highland Lakes and other precautions taken by LCRA can lessen the impacts of floodwaters, but they cannot contain a massive flood. The study "was used as a point of reference for the design work that was already going on in the dam safety project," Walker said. That $52 million project was completed ahead of schedule (and more than $6 million below budget) earlier this year. It strengthened four of LCRA's six Highland Lakes dams to withstand what is known as the probable maximum flood. The four dams are Tom Miller Dam (which forms Lake Austin); Wirtz Dam (which forms Lake LBJ); Inks Dam (which forms Inks Lake); and Buchanan Dam (which forms Lake Buchanan). Mansfield Dam, which forms Lake Travis, and Starcke Dam, which forms Lake Marble Falls, did not need upgrades. LCRA continues to expand its Hydromet system, which consists of more than 200 monitoring gauges deployed at key locations throughout the basin. The system provides real-time monitoring of rainfall and streamflow and lake levels. "We have a better handle of the amount of rain on the ground that will be draining into the river system," Rose said. "The more information we have about the amount of water on the ground the better our forecasts for how high the lakes and streams will rise. These better forecasts will give us longer lead times to pass along information to emergency management officials and the public." The risk this year is even more acute because LCRA's water supply lakes -- Lake Buchanan and Lake Travis -- were filled by the heavy rains of 2004, the third wettest year on record for the region. Even with drier conditions this spring, Lake Travis -- the only reservoir of the Highland Lakes system designed to store floodwaters -- continued to be well above its average elevation for this time of year. As of mid July, Lake Travis was more than four feet above its average elevation for July. Fortunately, Lake Travis has a flood storage pool that could handle more than 240 billion of gallons of water, if needed. Unfortunately, a growing number of people have chosen to build in that flood pool. "The flood pool is our ace in the hole to protect Austin and downstream communities when the floodwaters come from the Hill Country," Walker said. "It has helped save lives and property downstream before, and no doubt will do so again." Jerry White is a writer employed by the Lower Colorado River Authority. To comment on this story, contact him at jerry.white@lcra.org. |
