• U.S.

How the West May Flood: Winter’s Long, Long Reach

4 minute read
Tim Newcomb

First came the Mississippi. Then the Missouri. Now the nation’s West waits as the mountain snowpack perches at 300% more than average and flood watches blanket the region.

With minor flooding already hampering life in Montana, Wyoming and Utah, a sudden spike of warm temperature will send even more melting snow rushing into already filling rivers throughout the Rockies, Cascades and Sierras. “It’s kind of like a temperature time bomb,” says Pat McGrane, hydrologist for the Bureau of Reclamation. “But so far, so good. We have lucked out.”

(Lightbox: Storm Wreckage in Joplin.)

In a typical year, warm weather starts in May, gradually melting the mountain snow. And as farmers irrigate with reservoir water, river levels stay manageable. But record rainfalls throughout the Northwest equate to historic snowpack levels, no need for irrigation to tap into the surplus and dwindling wiggle room to store any deluge of melting snow in the largest water event since 1997. A string of hot weather, McGrane says, means the entire region “could be in big trouble.”

The Army Corps of Engineers has already given out one million sandbags in one month in western Montana and minor floods continue to breach levies, including one that spilled over the Clark Fork River into Plains, Mont., says Patricia Graesser, the Corps’ Northwest spokesperson.

Operating in an “active flood fight for over a month,” the Corps has repaired levies throughout eastern Washington, Idaho and Montana, including Missoula proper. In northern Idaho, the Lake Pond Oreille region receives special attention as the lake and associated rivers run above flood stage. The Corps even raised up an existing dam on Hayden Lake. Christy Jones, who coordinates emergency response for the Corps, says western Wyoming has dealt with minor flooding and the National Guard helped sandbag along the North Platte River near Casper.

(See TIME’s photoessay “Flood Waters Rise Along the Mississippi River.”)

With the chances for sudden spikes in temperature greater farther to the east, the scare of “big runoffs that go outside the banks” increases too, says Scott Pattee, water supply specialist for the Natural Resource Conservation Service. That worry spreads south to Utah and the Central Valley of California. James Brotherton, meteorologist with the National Weather Service, says he expects another surge in temperatures — over 70 degrees above 8,000 feet in elevation and 100 degrees in the low-lying Central Valley — this week, “likely melting off the majority of remaining snowpack and possibly causing some renewed flooding.”

With rivers likely peaking this week, crews have a bit of space left in reservoirs, says John Johannis, chief of the water management section for the Corps in the Sacramento district. “It will be a balancing act and we will control filling to avoid any uncontrolled spills,” he says. “Right now we are cautiously optimistic.” Sacramento — rated the nation’s second most susceptible city for flooding behind New Orleans — remains safe for now, Johannis says, and his main concern lies in the San Joaquin area. “Even last week we showed increases in snow water content,” he says.

There are consequences, however, even to effective flood control. In eastern Washington, the Grand Coulee Dam — one of the world’s largest concrete structures at 500 feet tall and a mile wide — holds the key for Washington and Portland, Oregon, where rivers now surge at over half a million cubic feet per second. As the Snake River Basin fills up, crews have dealt with the excess flow into the Grand Coulee reservoir — currently with 40 feet of space left — by purposefully sending water through the spillways, not the power plant.

This may be great news for flooding fears, but it isn’t for the ecology. As the water mixes with air it fills with nitrogen gas bubbles, threatening native salmon heading for the Pacific Ocean, McGrane says. A commercial fish farm immediately downstream of the dam loses up to 100,000 steelhead and trout each day in net pens due to the gas, according to a court filing looking to curb the dam’s flow. Cooler weather is the only hope to dissipate flooding fears — and to save the fish. “As long as we can continue melting snow [at a slow pace],” Pattee says, “the flooding risks will eventually just kinda go away.”

See the Top 10 Historic U.S. Floods.

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