What would happen if a 1,000 year flood ripped through Hood River?

Could we handle it? Emergency workers gather at a FERC-mandated exercise to test and implement an evacuation plan

January 21, 2006

Sometime before midnight on Jan. 11, water was rushing into Laurance Lake from the Clear Branch, Pinnacle Creek and every gulley in the mountainous ravine, filling the 130-acre reservoir to its brim.

The overflow — about 1,000 cubic feet per second of water (cfs) — spilled out of Laurance Lake, down the 350-foot-long slide and into the Middle Fork of the Hood River.

Miles downstream, this water combined with the East and West Forks to peak at 8,000 cfs at Tucker Bridge, two and a half feet above flood stage and substantially higher than it has been for a few years.

While high, the early January flood by no means exhausted the liquid burden for which Laurance Lake’s dam engineers had prepared it.

They equipped the two spillways at the north end of the lake to alleviate up to 10,000 cfs.

But no more.

If the water continued to rise, the reservoir and spillway would be incapable of harnessing the breaching water from collapsing into the sides and backside of the dam, eventually tearing at the dam itself.

Middle Fork Irrigation District manager Dave Compton says a breached dam scenario is likely only during a 1,000-year flood.

What if this were the 1,000th year? What if a cold, moist system dumped 10 feet of snow in the mountains just before a pineapple express transformed that delicate white powder into violent mobs of liquid chaos.

“We’re not so far away from that scenario,” Compton told a group of emergency workers gathered Wednesday morning at the Waucoma Building.

In no more than two hours and 30 minutes, Compton said, that first surge of floodwater would have marched its way to the city of Hood River. And it would have pillaged the valley from the river’s headwaters to the Columbia, leaving behind a path of destruction.

It would have consumed the bridge at Dee in 60 minutes. Tucker Park in 105 minutes.

The train trestle in 135 minutes.

That’s not a heck of a lot of time to formulate a plan.

That’s why every five years, the Federal Energy Regulatory Commission (FERC) mandates and observes a dam-breach disaster exercise.

The dam operators — in this case Middle Fork Irrigation District — directs the exercise.

Using “9-8-5-8” as “9-1-1,” members from the local fire departments, sheriff’s office, 9-1-1 dispatch, Farmers and the Middle Fork irrigation districts showed up Wednesday morning to simulate the actual disaster.

The purpose, said Compton, is to implement the procedures of the evacuation plan and expose the problem areas within it.

“For the most part it went well, said Adan Archuleta, the FERC engineer in charge of Middle Fork Irrigation District’s project. “Everybody was interacting how they should be. They knew who to call.”

The scenario —

“It is Wednesday the 18th of January,” the scenario summary reads. “Laurance Lake is full and has been spilling for a couple weeks. Approximately 6 feet of snow with a water content of 15 inches was measured in the Clear Branch and Pinnacle Creek watersheds earlier this week. The weather forecast is for more rain with warmer temperatures and more rain over the next few days … Middle Fork Irrigation is running the powerhouses at full capacity and life is routine. There are some folks snowshoeing at Laurance Lake and reports of some extreme kayakers testing their skills in the high water above Tucker Bridge …”

At this point in the exercise, the water levels are worrisome. But certainly no disaster.

Much more pressing at this point in the exercise are the random calls of vehicular accidents and fist fights which flood the 9-1-1 dispatch center.

“At what point do they go into dispatching mode?” Compton says. “What triggers that? We don’t want to cry wolf up here. But at the same time, we’d like to err on side of caution.”

At 9:30, Middle Fork Irrigation calls 9-1-1, notifying its dispatchers of the developing emergency.

And 9-1-1 promptly dispatches the emergency officials in the area, releasing them to serve evacuation orders to the surrounding communities.

For the Hood River Sportsman’s Club, the fish hatchery and three to four households along Red Hill, it’s already too late.

They all lie near the banks of the river and within 30 to 45 minutes of the first flood surge.

By the time authorities have notified the residents to abandon their homes, the floodwaters would have already invaded them.

“The main areas of concern are folks in the flood plain area,” Compton said. “How to identify them. How to get to them as quickly as possible.”

Identifying the flood plain residents was also one of FERC’s top concerns after the exercise.

“They need to be among the first people notified,” Archuleta said. “By the time they are notified by enforcement it could be 45 minutes to an hour.”

What the plan uncovered —

The exercise revealed other problems as well.

Do residents know in which direction to evacuate, for example. Or, as Archuleta suggests, might they evacaute toward the flood surge?

If the dam would break, where would that place be? Knowledge of that will help analysts figure out where the flood surge will go.

Does the county have a full inventory on new homes and buildings that were constructed in the flood plain?

And what about a sunny day breach, when no one is expecting a disaster?

“They’re easy things to overlook,” Archuleta said. “But they could be significant. Overall, however, they did well. What we really look for is interaction. And they interacted very well.”

History suggests no one participating at the exercise on Monday will be alive when that 1,000-year flood does rip through the Hood River Valley.

Even the 23,300 cfs that pillaged the Hood River Valley during the flood of 1996 didn’t overwhelm the spillways at Laurance Lake.

Just 1,300 cfs drained from Laurance Lake down the spillway, according to Craig DeHart, hydro-foreman at Middle Fork Irrigation District.

And neither, for that matter, did the flood of 1964, when 33,200 cfs marched through the Hood River toward the Columbia.

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