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Dam Diversion

LOS ALAMOS – Los Alamos County had just gotten going on a massive plan, 10 years in the making, to reinforce its decades-old dam in Los Alamos Canyon when the Las Conchas Fire ignited and scorched thousands of nearby acres.

Now, that work is on hold and crews are digging a bypass around the stripped-down dam, which officials say will give out if hard rains come and send floods its way.

“We finally get to the point where we have a contractor up there getting to work, and there’s another fire,” said John Arrowsmith, utilities manager for the Department of Public Utilities in Los Alamos.

Arrowsmith had to laugh. The county took over ownership of the dam from the federal government in 2000, when it assumed control of all water production for Los Alamos. Then the Cerro Grande Fire hit, and the state said the dam had to be reinforced to withstand significant overflow in the canyon’s reservoir.

Once the dam is completed, water at the dam will be piped into town to irrigate the Los Alamos High School campus, Arrowsmith said. The project is also part of a larger plan to reopen Los Alamos Reservoir to recreational use – it hasn’t been accessible for fishing and outdoor activities since Cerro Grande.

The work to reinforce the dam – higher walls, more concrete – began in April, with an eye toward finishing in September.

Then came Las Conchas.

Now workers won’t get back to the job again until September.

When the most recent fire struck, the dam had been broken down far enough that any floodwaters hitting it would likely cause severe damage, Arrowsmith said.

The dirt on its east side is meant to be covered in concrete, but for now is exposed, so a bypass is being dug around it. The thinking goes that water will rush through that new trench, around the dam, and on down the canyon.

Las Conchas burned hot enough in some segments of Los Alamos Canyon to harden the soil and render it hydrophobic, unable to soak up rainwater.

A light rain was falling Thursday afternoon while crews continued digging the bypass, but county officials say they’re worried about rains falling hard and fast. A light, continuous rainfall is healthy and won’t pool into floodwaters the way water from a torrential downpour might, a county spokesperson said.

Canyons all around Los Alamos are just as susceptible, and water mitigation like sandbagging and Jersey (freeway-style) barriers have been erected at the visitors center at Bandelier National Monument, deep in Frijoles Canyon, and around structures on Santa Clara Pueblo, where Las Conchas burned tens of thousands of acres.

There was some flooding in Santa Clara Canyon on the reservation on July 14, strong enough to cause two mud slides, but no structures were threatened. Since then there have been no reports of flooding in any of the canyons touched by the Las Conchas Fire.

Farther down Los Alamos Canyon from the dam, and closer to Los Alamos city proper, is the Los Alamos County Ice Rink, which is surrounded by Jersey barriers, stacked three high. Arrowsmith said the barriers built around the rink are all that will keep it safe if there’s a flood.

That was the job of the dam, but now water will simply flow around it, and then on for miles.