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Monday, March 22, 2010
Flood Threat
By John Fleck
Copyright © 2010 Albuquerque Journal
Journal Staff Writer
Questions about the ability of the Albuquerque metro area's aging river levees to hold back a worst-case Rio Grande flood could mean insurance premium increases ranging from $500 and $2,000 annually for thousands of property owners.
Whether the potential flood risk for residents living behind 27 miles of 1950s-era levees is real, or just a risk on paper, is the subject of debate.
The U.S. Army Corps of Engineers has rated the condition of those 1950s-era levees as "poor," saying they have outlived their useful life. Still, the Corps has concluded they nevertheless are "likely capable" of withstanding a serious flood.
But the Federal Emergency Management Agency, cautious after the disastrous New Orleans levee failures following Hurricane Katrina in 2005, is considering removing the levees' certification, which could force many property owners who live behind them in Albuquerque's North and South valleys to spend more on flood insurance.
"It is very likely that in 2011 or 2012, all of the Albuquerque levees will be decertified," said Danny Hernandez, a board member of the Albuquerque Metropolitan Arroyo Flood Control Authority.
Officials say that would trigger a requirement that mortgage holders buy additional flood insurance.
"Anybody that has a mortgage has to buy flood insurance" when FEMA maps add them to the flood zone, said John Sapien, a Democratic state senator from Corrales whose constituents have already been hit by the first wave of levee decertification.
The levees do have problems that increase risk they would fail in a flood, Corps engineers found. Trees have grown on many of the levee banks, which can weaken them, and pipes intended to drain water to keep it from eroding levees in many cases no longer work, according to the Corps report.
The federal reviews were triggered by the Katrina failures, which also led to tougher standards for levee design, construction and maintenance.
"The levees are 50 years old and do not meet the Corps' new standard after Katrina," said Subhas Shah, chief engineer of the Middle Rio Grande Conservancy District, the local agency that owns and maintains most of the area's levee system.
For flood-mapping purposes, a decertified levee is treated as if there was no levee at all, said FEMA spokeswoman Susie Webb. "On our maps, it's like the levee doesn't exist," Webb said in a telephone interview.
That makes the problem more a bureaucratic and regulatory issue than a genuine danger, Hernandez said. "It's mostly a paper flood risk."
Two relatively small areas of the metro area, one in Albuquerque's South Valley and another in Bernalillo, have already been caught up in the review. After two short levee stretches were decertified, FEMA designated them flood zones in 2008. That drove up insurance costs for residents in the newly designated flood plain.
Now, a new mapping effort is under way that will consider whether the rest of the metro area's levees can be certified to FEMA standards. Up for review are 27 miles of levees protecting much of the metro area's North and South valleys.
Nearly 13,000 buildings and property worth $1.4 billion are within the area under study for possible inclusion in the flood plain, according to a Levee Task Force report.
One area especially at risk of being placed in the flood plain, officials say, includes the neighborhoods on the west side of the Rio Grande around Montaño NW, including Bosque School, an area where levees are substandard to nonexistent.
Rebuilding those levees would cost an estimated $120 million. The Corps of Engineers also estimates another $170 million in costs for levees in the Mountain View Neighborhood and Isleta and Belen areas that have never had adequate protection from Rio Grande floods and have long paid extra for flood insurance as a result.
The problem is rooted in the nature of the Rio Grande itself.
Before there were dams and levees, it wandered the entire Albuquerque valley, shifting its bed from one mesa to the other over a course of years. Flood control efforts begun in the 1930s confined the river to a narrow channel, with levees on either side to protect valley bottomlands so they could be turned into farms and eventually a city.
Under high flows, the river can push up against the levees, trying to find its way out across the flood plain.
The first levees were modest affairs, explained Deborah Foley, the engineer who oversees the Corps' levee work. "Those are just piles of dirt," she said.
Beginning in the 1950s, more substantial, carefully engineered levees were built with solid foundations. While they were state-of-the-art in their day, their design and construction does not meet today's standards, Foley said in an interview.
The problem is eased by Cochiti Dam to the north, which since the 1970s has provided protection from large spring runoffs, once the most serious flood threat. Today, the main danger in the Albuquerque metro area comes from summer thunderstorms, according to Foley.
The worst-case storm the Corps plans for has a 1 percent chance of happening each year — what used to be called a "hundred-year flood." Such a flood could put enough water into the Rio Grande to fill the main river channel and spread out, reaching the aging levees for six to 12 hours, according to Foley. The last time the Rio Grande had that much flood water in the Albuquerque area was in the 1940s, according to U.S. Geological Survey data.
Another problem: bosque trees. Corps standards call for a vegetation-free zone extending 15 feet from the base of a levee on both the river and land side, to allow maintenance access and prevent tree roots from weakening the levees. Most of Albuquerque's levees don't meet those standards, with cottonwoods in many cases growing from their base.
The 11-mile Corrales levee completed by the Corps of Engineers in 1997, for example, already doesn't meet the 15-foot vegetation clearance standard.
The Conservancy District, which owns the Corrales levee and is responsible for its maintenance, could apply for a waiver. If approved, the Corrales levee could meet FEMA standards and protect nearby residents from being placed in the flood plain for insurance purposes.
Also, FEMA is about to review the status of neighborhoods behind a newly built three-mile stretch of levee in the South Valley, which could be removed from the flood plain as a result of the construction.
But for the rest of the valley, bringing older levees into compliance with federal regulations would require complete reconstruction, Foley said.
"You can't just rehab them," she said. "To get them to today's standard, you'd have to rebuild them."
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