A rain-packed tropical depression collided with the Texas-Mexico border region on Thursday, posing a new threat to cities already struggling with floods along the Rio Grande and its tributaries.
Police in Laredo were evacuating people in low-lying areas as the rain-swollen Rio Grande rose to more than 30 feet above flood stage and forced closure of two bridges linking Mexico and the U.S. Early reports indicated only minor flooding in homes near the Rio Grande, but the water was still rising near downtown, where the river was to crest Thursday evening.
National Guard troops arrived Thursday to help with evacuations.
Tens of thousands of people already had been forced from their homes in Mexican towns as officials dumped torrents of water into flood-swollen rivers to avoid the risk of dams overflowing out of control due to last week's Hurricane Alex and its aftermath.
Humberto Moreira, the governor of the border state of Coahuila, said that more than 20,000 homes had been flooded in his state alone, and about 80,000 people had "lost all of their furniture."
Gov. Eugenio Hernandez of the border state of Tamaulipas reported the first fatality there; telling an emergency evaluation meeting attended by President Felipe Calderon in the border city of Matamoros that the victim tried to cross a flooded road.
Hernandez said "now comes the part that has us worried, which is the rise in the level of river."
The tropical depression made landfall at South Padre Island late Thursday morning and is expected to dump four to eight inches of rain across the area, with as much as 10 inches in some parts, said the National Weather Service. That rain comes on top of the five to seven inches that Hurricane Alex deposited last week.
The rain, saturated ground, swollen rivers and releases from dams upstream have experts watching the Rio Grande closely.
In Laredo, where roughly half of all U.S.-Mexico trade crosses, authorities closed two bridges and severely limited traffic on a third. City Manager Carlos Villarreal said officials are monitoring the water and are hopeful the World Trade International Bridge can stay open despite the rapidly rising water. But much depends on the incoming tropical depression-driven rains.
The bridge carries roughly 8,000 18-wheelers a day, and closing it would cripple the nation's busiest inland port.
"We'll assess it on an hour-by-hour basis," Villarreal said. For the time being, authorities restricted traffic on the World Trade bridge to keep the weight load on the bridge to a minimum.
Another problem that could affect the bridges is a half dozen tractor trailers that were bobbing downriver in the fast-moving current after being left too close to the rising water, he said.
"It can cause a big, big problem for us," he said, noting the trailers could damage bridge structures. "It's like a missile headed for a target."
Farther south, part of the flooded Rio Grande was being diverted into miles of wide channels that will eventually send some of the flow to the Gulf of Mexico. The muddy water poured into the wide floodway Thursday, encroaching on a riverside park in Mission.
The International Boundary and Water Commission says the last similar diversion happened after 1988's Hurricane Gilbert. Farther downstream, more Rio Grande water was being diverted into a floodway in Mexico.
The goal was to maintain a flow on the lower river around Brownsville that would avoid flooding the potable water system in Matamoros, Mexico, said Sally Spener, IBWC spokeswoman.
Carlos Cascos, the top elected official in Cameron County, said that even with the IBWC saying that the levees are prepared to handle the volume, he's concerned there may not be enough time between storms to allow the water to evaporate and seep into the ground.
"I'm just not sure about them (the levees)," Cascos said. They have been improved in recent years but not tested, he said.
A tropical storm warning was in effect for the Texas coast south of Baffin Bay and for Mexico north of the San Fernando River.
Alfredo Vega, a meteorologist at the National Weather Service focusing on hydrology, said the main flooding concern for the lower Rio Grande Valley was Rio Grande City. The river was already at 49 feet and expected to rise to 52 feet by Saturday, which would take it very close to the level where it causes area flooding by backing up streams that normally feed it.
Hurricane Alex, unusually water-heavy, devastated the major Mexican city of Monterrey, and more than 100,000 people were still without water service this week. At least 12 people died in the flooding, according to Nuevo Leon state officials.
The hurricane's remnants caused rivers to rise across the area, forcing evacuations in Del Rio, Texas, some 110 miles (180 kilometers) upstream from Laredo, as well as in the Mexican state of Coahuila.
To the southeast, officials in the Mexican state of Nuevo Leon evacuated nearly 18,000 people from houses in Ciudad Anahuac for fear that water would overflow the Venustiano Carranza dam and threaten lives. Water was still rising in the town on Thursday.
An airplane on an inspection tour of the flood zone crashed Wednesday, killing the mayor of the border town of Piedras Negras, the state public works director, a municipal civil defense official, a government photographer and the pilot and co-pilot.
Water behind the binational Amistad Dam on the Rio Grande already was at its highest level since 1974, according to the International Boundary and Water Commission, forcing officials to release water from it at the fastest rate in a quarter century.
Water was also being released at Falcon Dam downstream Thursday.
Christopher Sherman reported from Mission, Texas. Associated Press writers Jorge Vargas in Nuevo Laredo, Mexico; and Oscar Villalba in Piedras Negras, Mexico; and Mark Stevenson in Mexico City, and Jeff Carlton in Dallas contributed to this report.
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