COCHITI LAKE — Boosted by high snowfalls this winter in northern New Mexico and southern Colorado, the Rio Grande should flow full and strong for most of the summer — good news for chile farmers, river runners and the endangered silvery minnow.

But come July and August, residents of low-lying areas along the middle Rio Grande may be cursing the winter snows. The fear is that an already-high river would swell even further with the runoff from monsoon rains, driving the Rio Grande up against a 50-year-old network of levees that may no longer be strong enough to withstand the flood.

And such flooding may become more common in the future. At least some scientists suggest a new flooding threat is on the horizon: global warming.

 

History repeating itself?

 

A century ago, Albuquerque residents must have shuddered when spring arrived and the swollen Rio Grande roared through town. In those days, a winter of big snows farther north caused floods that wiped out crops, destroyed property and drove people from their homes.

 

“When the river flooded, people used to come in on boats,” Tomás Herrera told the authors of the book “Shining River, Precious Land: An Oral History of Albuquerque’s North Valley.” “The people on Griegos and Candelaria left for the hills. When the houses dried they came back.”

 
A decades-long effort ensued to rein in the tumultuous water, beginning with simple dikes and levees built by hand. Irrigation and drainage ditches came along in the 1920s.
 
But the crowning achievement of the river tamers was Cochiti Dam. A 5.3-mile-long pile of dirt, sand, gravel and rock built at the foot of the Jemez Mountains some 25 miles north of Bernalillo, it collects the runoff from nearly 15,000 square miles of northern New Mexico and southern Colorado and can hold about 180 billion gallons of water.



Looking out over the dark rock face of the dam on a recent sunny morning, Craig Lykins, the U.S. Army Corps of Engineers’ chief ranger at the dam put it simply: “This is Albuquerque’s protection. It’s here for those 100-year floods.”



The middle Rio Grande still floods, but it’s often intentional. With so much water expected to flow into Cochiti Lake this summer, river managers say they will open the floodgates — boosting the flow to around 7,500 cubic feet per second (cfs) — for several days to scour out the river channel, said April Sanders, the corps’ chief of reservoir control in Albuquerque.
 
 
That ’s likely to cause “over-banking” in shallow areas, especially south of Isleta Pueblo, where the river bed gets shallow. Managers also try to flood low-lying areas at certain times to benefit the endangered silvery minnow, Sanders said.
 
 
 
But Metro Albuquerque may be in for a challenge, primarily from a shift in weather. New Mexico residents can probably expect more flooding in the future, according to “When It Rains, It Pours,” a report issued in December by Environment New Mexico.
 
The authors reviewed decades of weather records around the United States and found that weather events in many parts of the country, including New Mexico, are getting more extreme. In addition, those extreme events are happening more frequently, they said.
 
 
In an ironic twist, that means the Southwest can probably expect less precipitation annually as a result of global climate change, the report says, but more rain or snow during individual weather events, “increasing the risk of flooding and other impacts.”



An example of those drastic swings is seen in recent precipitation records from the National Weather Service in Albuquerque. The period from November 2005 to May 2006, for example, was the driest seven-month stretch in Albuquerque in more than a century, while the summer that followed was the wettest ever, including the most rainfall in a single day. A record for the greatest snowfall on a single day occurred in December 2006.
 
 
If a combination of high water-flow coming out of Cochiti Dam and a big surge of runoff from summer monsoons could drive the Rio Grande over its banks, all that would stand between the river and residents of low-lying areas would be the levees.
 
 
And they may not provide as much protection as homeowners would like.
 
 
 
Old levees
 
 

Most of the levees were built in the 1950s, and they’re showing their age, according to a recent Corps of Engineers studies. “They’re old and they need to be replaced," said Sanders. But at an estimated cost of $120 million, that could take some time, particularly now that one of New Mexico’s best advocates for federal funding, long-time Republican U.S. Sen. Pete Domenici, is retiring.



As the Rio Grande flow hits its peak later this summer, managers will monitor water levels closely to see the river doesn’t reach the levees. Sanders said the levees can probably withstand a short burst of flooding, but not a sustained soaking. "If we were to get the 100-year flood, they’d have lots of problems," she said.
 
The best managers can hope is they don’t get big monsoon rains during the days when the Rio Grande is allowed to run at full bore, because it takes a day or two for the river level to drop after closing the valves at Cochiti.



Managing a river is a challenging task anywhere, but especially one in the desert with so many demands and limits placed upon it, said Beverly Noel, the Corps’ interim operations project manager at Cochiti. The Rio Grande and its tributaries support chile farmers, rafting companies, endangered species and urban water utilities, among others. And while the river has been substantially tamed, it’s still a formidable entity, she said.



“We always try to control where the water goes,” said Noel. “Sometimes it doesn’t allow us to have our way.”