/ Hurricane Rita

12:43 AM EDT on Thursday, September 22, 2005

By DAVID McLEMORE / The Dallas Morning News

From a coastal plain flat as a skillet to the canyons and shallow rivers and creeks of the Hill Country, inland flooding is always a risk in Texas when tropical weather storms out of the Gulf of Mexico.

When it's a Category 5 hurricane like Rita, the potential hurt is hard to imagine.

While the waters pushed to land by the hurricane's winds – the storm surge – can be catastrophic, inland flooding from rainfall carried by huge tropical masses has caused more deaths in the past 30 years and can be a major threat to communities hundreds of miles from the coast.

How much of a risk depends on the hurricane – where it hits, how fast it moves and how much rain it hauls ashore.

As Hurricane Rita spins toward the coast, threatening landfall around Matagorda Bay, weather forecasters and hydrologists can't easily predict how bad the flooding will be.

But they say zones that are usually affected are likely to be hit again: the low-lying areas along the coast and the communities along the network of rivers and streams that flow into the Gulf of Mexico.

Forecasters say the storm could drench the region with 8 to 14 inches of rain.

"That carries significant potential for flash flooding on the flatter areas along the coast and on the creeks and streams along its projected track from the coast up toward Waco," said Mark Lenz of the National Weather Service.

Risk from slow storms

It doesn't have to be a Category 5 storm to pack a wallop. In June 2001, slow-moving Tropical Storm Allison inundated the region around Houston. There were catastrophic floods from Texas to Louisiana, with 41 people killed and $5 billion in damage.

One of the state's worst floods in recent memory occurred June 30, 2002, when a massive storm system stalled over South Texas for eight days. More than 35 inches of rain fell.

Runoff from the storms caused record flooding downstream on the Medina, San Antonio, Sabinal and Nueces rivers. For the first time since it filled in 1968, Canyon Lake near New Braunfels poured over its spillway, adding to the flooding in the Guadalupe River. Residents along the Guadalupe in Cuero and Victoria suffered extensive damage as the river rose out of its banks for several miles.

Twelve people died in the storm, and more than 48,000 homes were destroyed in 80 Texas counties. Total damage was estimated at more than $1 billion.

The destruction Rita will cause depends on where the storm lands and how it moves inland – whether it quickly dissipates or stalls over South Central Texas like the 2002 storm.

"Wherever Rita lands, the east side of the storm will get more rain and more risk of flooding," said Robert Blodgett, a geologist at Austin Community College.

"Fortunately, much of Central Texas is dry, and the ground can soak up a lot of excess moisture. If the storm dumps a lot of rain very quickly, however, it could produce flash flooding along stream beds and paved areas, such as urban streets and parking lots."

Authority's response

The Lower Colorado River Authority is ready for whatever problems the storm causes, said authority meteorologist Bob Rose.

"It does appear that it's heading to the middle or upper Texas coast and that it will have some effect on the Colorado River basin," Mr. Rose said. "If Rita strikes near Matagorda Bay, LCRA's irrigation districts will be heavily impacted by very high winds and heavy rains. If it strikes further south of the coast, it could have a greater effect for Austin and the Highland Lakes."

In 2001, two months after Allison dumped more than 37 inches of rain in the Houston region, LCRA ran a computer model to find out how that amount of rain on the Hill Country would affect the Colorado River and the Highland Lakes northwest of Austin.

The results were disturbing.

Runoff would raise Lake Travis 26 feet above the spillway at Mansfield Dam, which forms Lake Travis.

Even with all nine floodgates opened at Tom Miller Dam, water in Lake Austin would crest about 20 feet above the dam's spillway.

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.

Crews, monitors ready

If Rita makes its projected landfall, LCRA's River Operations Center would monitor rainfall levels, river flow and water levels around the clock through its system of rain and flow gauges.

The river authority has put transmission field crews on standby. Also, about 100 employees were told they might be needed to help handle calls to a flood hotline that would be established if necessary.

The authority operates more than 3,300 miles of electrical transmission lines statewide, providing service to a million people in 53 counties.

It also operates six dams on the Colorado River and manages water supplies to municipal customers, farmers and industry along the river's 600-mile run to the Gulf Coast.

E-mail dmclemore@dallasnews.com

Notable hurricanes that have affected Texas since 1900, with death and damage totals for Texas only:

July 15, 2003: Claudette, Matagorda Bay-Victoria; two inland deaths, $180 million in damage across central Texas coast from winds peaking near 100 mph.

Aug. 22, 1999: Bret, Kenedy County; four highway deaths in Laredo, scattered damage as storm with 140 mph winds moved into sparsely populated region.

Sept. 16-18, 1988: Gilbert, 125 miles south of Brownsville; one dead in San Antonio; tornado and wind damage of $5 million in Brownsville, Del Rio and San Antonio.

Aug. 18, 1983: Alicia, Galveston-Houston; 21 dead, more than $2 billion in damage; 22 tornadoes, winds at 130 mph.

Aug. 3, 1970: Celia, Corpus Christi; 11 dead, $50 million in damage; wind gusts to 160 mph.

Sept. 18-23, 1967: Beulah, Brownsville; 13 dead, $150 million in damage.

Sept. 14, 1919: South of Corpus Christi; 284 dead, $20.3 million in damage.

Sept. 8-10, 1900: Galveston; 6,000-12,000 dead; $30 million to $40 million in damage (around $800 million in today's dollars). Storm surge at 15-20 feet; winds estimated at 120 mph. Deadliest natural disaster in U.S. history.