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Fire and Rain: The One-Two Punch of Flooding After Blazes

The great balls of fire that leapt from treetop to treetop in the Jemez Mountains of northern New Mexico earlier this summer, threatening the town of Los Alamos and a federal nuclear research laboratory, were apocalyptic enough.  They left behind a scorched landscape of dead trees, charred woods and blackened earth.  From June 26 until...

The great balls of fire that leapt from treetop to treetop in the Jemez Mountains of northern New Mexico earlier this summer, threatening the town of Los Alamos and a federal nuclear research laboratory, were apocalyptic enough.  They left behind a scorched landscape of dead trees, charred woods and blackened earth.  From June 26 until early August the Las Conchas burned some 156,000 acres, more than any other single blaze in New Mexico’s history.

Now, however, the threat has turned from fire to floods as the summer “monsoons” deliver high-intensity rains to these burned-out watersheds. Soils laid bare cannot absorb the rainfall and are prone to massive erosion.  Recent downpours have produced peak floods through mountain canyons of 20,000 cubic feet per second– thirteen times the average discharge of the Rio Grande – and have carried tree trunks, boulders and tons of blackened soil down to the valley and villages below.

This past week, the utility that provides drinking water to Albuquerque cut its intake from the Rio Grande by half to avoid problems of clogged equipment and the extra cost of treating the sediment-laden river water.  To make up for the loss, it pumped more groundwater from shrinking underground reserves.

If, as climate scientists predict, more heat and drought is in store for much of the western United States, fire and related flood risks in this region will only increase.

This year could be a harbinger.  In addition to New Mexico’s big burn, drought-plagued Texas has battled its worst wildfire season on record – with more than 3 million acres scorched and seven of the ten largest wildfires in the state’s history.  The massive Wallow Fire in eastern Arizona’s White Mountains burned some 538,000 acres, the largest fire in that state’s historical record.

Besides the obvious threat they pose to people and wildlife, mountain forest fires often unleash a cascade of impacts that include flash flooding, mudslides, water pollution and sediment buildup in reservoirs– all of which can exact a big toll.

Last week I headed to Cochiti Pueblo and surrounding areas of northern New Mexico to see firsthand some of the impacts from the fire and flooding. The village of 800 tribal members sits just east of the Jemez Mountains, a location highly vulnerable to flash floods emerging from the mountain canyons.

Phoebe Suina, a Dartmouth-educated environmental engineer and member of Cochiti Pueblo, has been monitoring the floods and overseeing extra protection measures to safeguard the village over the post-fire monsoon season. The past week, Suina told me, had been extraordinary.

After a two-inch rain, a mudflow as wide as a football field roared out of Cochiti Canyon, pulling down power lines, ferrying a 150-foot tree, and producing 15-20 foot waves of black water.

The changes have been jaw dropping, Suina said.  “You wouldn’t know you’re in the same canyon.”

The well-known Dixon Apple orchard was a casualty of the fire and flooding. Photo credit: Sandra Postel

One of the casualties is family-owned and operated Dixon Apples, New Mexico’s most famous apple orchard.  The Las Conchas fire burned the family home and toasted the canyon where they tend their apple trees.  Then came the flash floods, which destroyed outbuildings and encased their tractors in mud.

To the south, flash floods out of Peralta Canyon had left a wide trail of boulders, black mud, and charred debris.  They had also deposited ten feet of sediment in the channel, which will raise the level of subsequent floods.

Water behind Cochiti Dam empties into the Rio Grande. Notice the debris and poor water quality. Photo credit: Sandra Postel

Whereas floods through Cochiti Canyon empty into Cochiti Lake –a large reservoir built in the mid-seventies by the U. S. Army Corps of Engineers – the floodwaters from Peralta Canyon flow directly into the Rio Grande.  The river then carries those blackened, debris-filled waters toward Kewa, San Felipe, Santa Ana, and Sandia Pueblos, Albuquerque, Isleta Pueblo and farms to the south.

Unfortunately, such fire-and-flood stories are becoming all too familiar.  As communities have expanded through the arid West, the risk of fire impacts on water supplies has risen markedly.  Although fires are natural and ecologically beneficial in a healthy watershed, simply letting natural fires burn often presents unacceptable risks to surrounding populations.  Without periodic natural burning, many forests accumulate an excess of “fuel” that makes destructive mega-fires, such as Las Conchas, more likely.

As is often the case, the question is one of balance: how to have an ecologically healthy watershed that also provides benefits important to people – such as secure, high quality drinking water.  One solution that’s emerging is for water utilities to invest in watershed maintenance and rehabilitation, including forest thinning to reduce the risk of destructive fires in areas critical to their water sources.

Denver, Colorado, and Santa Fe, New Mexico are two cities pioneering this approach.

Colorado’s Buffalo Creek fire of 1996 and the massive Hayman fire of 2002 burned 150,000 acres of forest, about the same area burned this summer by New Mexico’s Las Conchas fire.  Following heavy rains in the scorched watershed, 1 million cubic yards of sediment poured into Denver Water’s Strontia Springs reservoir – four times the volume of sediment that had accumulated over the previous two decades.  The extra costs of water treatment, removal of sediment and debris, and infrastructure repair ran upwards of $30 million.

Rather than risk repeating those expenditures fire after fire, Denver Water has entered into a partnership with the U.S. Forest Service, which manages the forestlands that supply Denver’s water.  Called the Forest to Faucet Partnership, Denver Water will invest $16.5 million to match the Forest Service’s investment in watershed work.  The combined $33 million will be devoted to forest thinning and other watershed projects over a five-year period in areas critical to Denver’s water supply.

Santa Fe, not far from Cochiti Pueblo in northern New Mexico, has embarked on a similar effort.  As with Denver’s program, inspiration came from the impacts of a large fire – in this case, the 2000 Cerro Grande, which cost the city of Las Alamos $9 million to filter sediment and ash out of its drinking water supply.

In partnership with The Nature Conservancy (TNC), which has designed similar programs in Latin America, and with the U.S. Forest Service, which foot the bill to start the watershed program, Santa Fe has established a water fund to help pay for restoration efforts in the 17,000 acres of forest that source its water. The fund operates on a $200,000 annual budget, paid largely by voluntary fees on water users’ monthly water bills.  According to Laura McCarthy of TNC’s New Mexico field office, the goal is to invest $4.3 million in thinning and watershed rehabilitation over the next twenty years.

Indeed, it was forest thinning done after the Cerro Grande fire that may have saved Los Alamos National Laboratory from the Las Conchas fire this summer.  After the 2000 mega-fire, the Laboratory thinned some 8,000 acres of surrounding forest.

Phoebe Suina, the environmental engineer from Cochiti, worked at the Lab at that time and oversaw the thinning project.  The fact that this summer’s fire didn’t spread through those thinned areas but burned rapidly through untreated forests is, to Suina, “a poster-child example of why we need thinning.”

As I headed out of Cochiti, dark clouds gathered menacingly over the Jemez Mountains.  Suina was on the phone with the Albuquerque office of the National Weather Service to hear the afternoon rainfall prediction.


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Meet the Author

Sandra Postel
Sandra Postel is director of the Global Water Policy Project and author of Replenish: The Virtuous Cycle of Water and Prosperity. From 2009-2015, she served as Freshwater Fellow of the National Geographic Society. Sandra is also co-creator of Change the Course, the national water stewardship initiative awarded the 2017 US Water Prize for restoring billions of gallons of water to depleted rivers and wetlands. The recipient of several honorary degrees, she works to bridge science, policy, and practice to promote innovative ways of securing water to meet both human and ecosystem needs.