Dam dangers

If you hear news of a dam breaking in the Sierra, grab the kids and get outta town

The sun shines in your window. You peek out at the bright blue sky and wonder why in the heck those sirens are shrieking along McCarran Boulevard. Must be quite a fire.

You turn on the TV. Some wannabe Tad Dunbar tells you to get the heck out of Reno, baby, because a 60-foot wall of water is headed your way.

At first, you’re doubtful. Floods are bad. But the last Reno flood wasn’t all that life-threatening. You and your buddies bought a case of Corona and took your lawn chairs downtown to watch the river revel down First Street. Yeah, the stream overflowed its banks and caused more than $500 million in damage, but you didn’t feel really threatened.

That’s because you don’t know what a real flood is. And you’ve probably never thought about how much water is waiting in huge buckets called reservoirs up in the Sierra. There’s enough water in reservoirs like Boca, Stampede and Prosser to get the Reno-Sparks area through a long season of drought.

But there’s also enough water to put the west end of Reno-Tahoe International Airport 43 feet under. Enough to turn the Truckee Meadows—at least everything below an elevation of 4,440 feet—into a good-sized lake.

Consider this a free public service announcement.

No, you don’t need to start packing the family photos. But if you hear a report of a dam failure and possible flooding, take it seriously. You won’t have long to get out of town, and, because the cities of Reno and Sparks have no written plan for evacution, it could get kind of messy.

Could the dams really fail and dump all that water on Reno? The federal government was concerned enough to order a study. Many of the dams that feed into the Truckee River are operated by the U.S. Bureau of Reclamation. In the 1990s, the government mandated a study and the creation of an emergency plan of action for all the high-hazard reservoirs that the BOR operates. The reservoirs in the Sierra above Reno are considered high-hazard, not because of any engineering flaws, but because of the huge number of lives and property that would be endangered in the event of a failure.

The study began even before the Flood of 1997. The BOR created full-color inundation maps that show Reno and Sparks as underwater worlds. The study looked at a variety of possible reservoir failures, including the failure of Lake Tahoe, Prosser, Stampede and Boca.

The study is scary.

It shows, for example, that if Stampede Reservoir springs a leak and fails, its 226,500 acre-feet of water head to Boca Reservoir. Boca, if already filled to its total capacity of 41,400 acre-feet, couldn’t take that much extra liquid. The combined 267,900 acre-feet of water would rush down the Truckee River, which would serve as a handy narrow pipe.

In only two hours and six minutes, the leading edge of what’s modeled to be a 67-foot water wall would hit the Chalk Bluffs Sewage Treatment facility on the west edge of Reno.

In three hours and 48 minutes, the leading edge would make its way through downtown and deluge the airport.

Before long, the entire Truckee Meadows would be a new lake, with water seeping slowly out the Vista reefs at the east end of town.

Don’t panic.

The possibility of such a flood, officials say, is pretty slim. The reservoirs are carefully monitored. To really mess one up would take a nasty earthquake, an act of terrorism, a mechanical failure of one of the gates that let water out of the dam, or extreme rain or snowmelt.

The reservoirs are safe, the dam experts say. The possibility of an extreme flood doesn’t keep Mike Larson, a BOR operations and maintenance engineer, awake at night.

“We have personnel out there 24 hours a day, seven days a week, 365 days a year,” Larson says. “You’d better believe it.”

The reservoirs and dam are inspected daily, weekly, monthly and annually. Inspectors watch for bleeding water, leaks, burrowing rodents or anything else that might compromise the integrity of the earthen dams.

And that level of concern is a really good thing, because you don’t want a leak at an earthen dam. And you don’t want water to go over the top of an earthen dam.

The BOR’s emergency response system relies on DEFCON-style warning codes so that teams from city and county governments can stay on top of the situation. A “heads up” serves as a general alert to possible trouble. “Get ready” signifies a potential threat at the dam. “Get set” means the threat has progressed to minor or moderate. “Go” is a major or catastrophic threat. “Gone” means the wall of water is headed down the Truckee tube.

“With earthen dams, you don’t even want to get to level two if you can help it,” Larson says of the system, which hasn’t had to be used.

If water starts going through or over an earthen dam, it’ll start to take some of the earth with it. (Water’s funny that way.) And as the water begins to erode the dam, the opening through which rogue rivulets are flowing gets wider, then the earth gives way altogether and collapses.

At five-mile-long Stampede Reservoir, water is held at bay by a dam built of rolled earth and rock fill. Boca Dam has a zoned, rolled earth-fill embankment and a rock-filled face. The Prosser Creek Dam, which rises about 139 feet above the streambed, is also an earth-filled embankment.

While Lake Tahoe holds more water than the above dams combined, it actually poses less of a threat in the event of a failure. That’s because there’s only about nine feet of water being held back from the lake’s natural rim, says National Weather Service hydrologist Gary Barbato.

“It’s not like you’d have this huge wall of water coming toward Reno,” Barbato says.

Washoe County and the city governments have worked with federal agencies like the BOR and the National Weather Service to issue warnings in the event of a dire emergency.

Barbato participated in an emergency response exercise two years ago that involved a hypothetical camper filled with dynamite in an inopportune place near one of the earthen dams. He seems awed by the thought of such a flood.

“We’re talking a million cfs [cubic feet of water per second] into Reno,” Barbato says. “It makes the 1997 flood look like nothing.”

The top flow of water during the 1997 flood was about 18,000 cfs. If Stampede broke and fed into Boca, the estimated flow of water would be 1,002,000 cfs as the water dumps into town, before the flow spreads out into the valley. By the time the wave reaches the airport, the flow would slow to a mere 859,000 cfs. But the distinction wouldn’t matter much at that point.

Also, if Boca failed by itself, there’d be only about 300,000 cfs flushing through Reno.

“But, hey, it’s kind of like the difference between a 100-mile-an-hour wind and a 150-mile-an-hour wind,” Barbato says. “They’re both going to blow you away.”

While the emergency response plan is great, if the worst-case scenario ever did transpire, it’d be nearly impossible to evacuate everyone, Barbato says.

“Once we hear about it, it’s almost too late,” Barbato says. “You’re not going to get the population of the Truckee Meadows [out of the valley] in time, in my opinion.”

This is the scary part. City governments have created no plan for the evacuation of Reno and Sparks during this kind of hazardous situation.

“There’s some bury-your-head-in-the-sand over this,” says Press Clewe, emergency service coordinator for Washoe County.

Though the Washoe County Sheriff’s Office has written instructions for evacuation in unincorporated areas, there’s no plan for the police departments in Reno and Sparks and no written guides to train emergency service personnel who might need to get hundreds of thousands of residents, business people and tourists out of the valley in two hours or less.

The city governments were told by the BOR during training sessions more than two years ago that they need to develop a plan.

“We know flooding will take place and can take place,” Clewe said. “They’re frightening, the inundation maps. They blew my mind when I first saw them.”

Being prepared for a dam disaster is especially imperative, because earthen dam failures do happen. On an early summer day in 1976, water began seeping from the newly built Teton Dam in Fremont County, Idaho. At 9:30 a.m. June 5, a leak had begun in the earthen dam. Bulldozers were sent in to plug the leak, but the wound continued to expand. At 10:30 a.m., law enforcement dispatchers were notified, along with TV and radio stations. By 11 a.m., the hole was 25 feet wide. Bulldozers were pulled into the whirlpool gushing through the gap, according to one report. Then, before noon that day, a third of the dam collapsed completely, and 80 billion gallons of water headed for the small town of Rexburg.

Eleven people were killed in the ensuing disaster. The fact that a flood could arrive with so little warning on a sunny summer day inspired a poem in the small town’s newspaper later that year:

I was working in the garden and the kids were in the yard to play.

The guy on the radio said, “Believe me if you can,

Because there’s 80 billion gallons headed for us from the Teton Dam!”

My hubby said, “We’ll probably get a little water in the basement, dear.

But just in case it’s worse than that, let’s take the kids and get on out of here.”

Thanks to geography, a dam failure would be much more damaging to the people of Reno and Sparks than the Teton Dam failure was to the folks in Idaho. The Truckee River is narrow and fast all the way from Boca to the west end of Reno. The water has no place to spread out and slow down as it rushes down the mountain. In fact, it’s kind of hard to put a name to the devastation that would be caused by such a fast, furious flush of water.

Barbato settles on “cataclysmic.”

"We’re ready to get the warning out," Barbato says. "Hopefully, we’ll never have to do it. Hopefully, it’s like that envelope we used to have in every office, sitting on the weather radio, that said: ‘Open only in case of nuclear attack.'"