Posted: Mon, 26 Jul 2010 10:25 AM - 9,955 Readers
By: Christopher Sherman
A local official said he felt helpless this month while the Rio Grande continued its rapid rise, flooding rural neighborhoods as a dam emptied the equivalent of two Olympic-size swimming pools every three seconds.
Judge Eloy Vera, Starr County's highest-ranking official, said a decision by water officials upstream to let more water flow from reservoirs made life difficult for downstream communities such as his.
The result was a Rio Grande that hopped its banks and spread to dimensions unrecognizable as a river, much less the lazy boundary between the U.S. and Mexico.
"It is kind of frustrating that we have no input into how much water is released," Vera said.
Vera, a civil engineer by trade, said he understands the technical reasons for the release. Still, it wasn't easy to explain that to owners of 130 homes — half in this tiny river community — whose property became a sopping mess despite a two-week stretch of sunny skies.
U.S. and Mexican officials insist the flooding earlier this month that inundated South Texas and northeastern Mexico was inevitable, even though much of it followed releases at Amistad Dam near Del Rio and Falcon Dam near Zapata. The waters have forced thousands from their homes and closed international crossings.
When hurricane season began June 1, Amistad was at its highest level for that day since 1992 but still below the so-called "conservation level," the maximum amount water managers are supposed to keep in a reservoir most of the time.
A month later, Hurricane Alex came ashore about 100 miles south of the Rio Grande, dumping heavy rain. That forced managers to begin increasing the flow from reservoirs, dumping water typically hoarded for agriculture and other uses.
Eight days after Alex, a tropical depression brought yet more rain to the river and its tributaries.
Several feet fell in some areas, and dam managers kept pumping water out of the reservoirs to avoid unplanned catastrophic failures as residents downstream evacuated.
Experts say there is some debate over whether the maximum reservoir levels should be lower during hurricane season.
"To take conservation level as the safe level is a little risky in my mind," said Gordon Wells, program manager at the Center for Space Research at the University of Texas at Austin, which assists the state in modeling storms' impact.
Storms can be big enough to overwhelm the reservoir space set aside for flooding, he said.
Alex and the tropical depression forced water managers to release large amounts of water after the storms flooded three of the Rio Grande system's four river basins simultaneously. Zone officials in the U.S. and Mexico used words such as "unique" and "extraordinary" to describe the impact.
Three weeks after the flooding began, the river and reservoirs remain well above flood stage.
Falcon Lake broke a high-level record set in 1958. A reservoir in northeastern Mexico that is Monterrey's primary water source absorbed a discharge comparable to the volume carried by the Mississippi at New Orleans.
And southwest of Laredo, floodwaters released from another swollen Mexican reservoir bottlenecked on the Rio Salado. The result was a new body of water that satellite images showed to be larger in surface area than the approximately 84,000-acre Falcon Lake toward which it was traveling.
"I cannot think of any possible storm that would have triggered high-magnitude floods in all three basins," said Wells, who used satellite images to spot the new lake in northern Mexico during a break in the clouds.
Infrequent flooding in the region tempts communities to creep into the flood zone until the river reclaims its territory in an event like this, said Jesus Luevano, spokesman for the Mexican side of the International Boundary and Water Commission (known as CILA by its Spanish initials).
"The damages have been very small considering the scale of this event," Luevano said.
Damage assessments remain in their early stages in both countries, but thousands of homes — most in Mexico — were flooded after the Alex rains and dam releases.
"In hindsight, if those lakes had been drained and made more room for water, we wouldn't have gotten the full impact of what we're getting right now," Vera said.
Water managers often face a delicate balancing act with their decisions. While the IBWC controls the reservoir releases during flooding, the Texas Commission on Environmental Quality is responsible for parsing out the water the rest of the time, and there are many demands for the water held there.
TCEQ Commissioner Carlos Rubinstein, also a former Rio Grande watermaster, said it would have been difficult to argue that the reservoirs should have been much lower at the start of summer. Large tropical storms usually don't hit until August and September, and if no storms had come, people with agricultural and municipal water rights might be asking where their water was by the end of summer, he said.
He says when the reservoirs are full, the impacts of unexpected weather patterns are "more marked and pronounced."
"You can never predict the weather," Rubinstein said.
The flood did point out some weaknesses in the system, though.
Wells said modeling the impact of the storms was complicated by large gaps in available information.
Alex dropped much of its rain in remote parts of northern Mexico with too few rain gauges, and in one spot, floodwaters washed out a water flow gauge.
IBWC Commissioner Edward Drusina said overall, the agency did well with the big storms.
"It was a huge storm, but we were managing," he said. "All in all, we're meeting the objective and that is to protect the community to the best of these facilities' ability."
