Why the water overwhelmed Duluthby Dan Kraker, Minnesota Public Radio
DULUTH, Minn. — It had just started raining when Duluth Police Sergeant Brad Wick started his 6 p.m. shift last Tuesday. By the time he got into his squad car at 9 p.m. to patrol the city's streets, water was gushing across the surface of the station's parking lot.
Police Chief Gordon Ramsay called to check in, but it was raining so hard Wick could hardly hear him. Calls started coming in quickly. Cars were stalling in puddles of standing water all around town.
But it wasn't until a little after midnight when Wick drove from west Duluth toward downtown on Interstate 35 that he realized this storm was monumental.
"I started meeting a bunch of cars coming the wrong way at me on the freeway," said Wick, who first suspected drunk drivers. "But when I looked and saw there's seven or eight coming at me, I thought there's something wrong with the road up ahead."
He flagged down a driver, then kept going until he saw cars in both directions submerged halfway up their windshields. Semi-trucks had stopped, unable to drive any farther. Freeway tunnels had become canals. In 26 years on the force he had never seen I-35 close due to flooding.
N.E. MINNESOTA FLOODS
• Flooded roads in ruin, repairs could take years
• In flooded Barnum, a community pulls together
• Q&A: Homeowners considering flood insurance
• Photos: Stunned Moose Lake comes together
• Photos: Duluth reeling from floods
• Photos: Gooseberry River in full roar
The next day, Duluth residents awoke to the worst flooding in recent memory. Water rushing down the hillside poured into homes and submerged cars. It overwhelmed a system designed to handle big storms — but not this big. In the first few hours of the flooding it became apparent that Duluth's aging sewers could not handle so much water.
As city workers clean the system, officials are weighing how to prepare for future storms of that magnitude. But after last week's record-setting deluge, they acknowledged that it may not be possible to prepare for such a storm.
GETTING THE WORD OUT
The National Weather Service had issued a flood warning about 6:30 p.m. Tuesday. By the time the I-35 flooded, meteorologists had upgraded that warning and their language.
"We started using terms like 'potentially life-threatening flash flood situation developing,' " said Dan Miller, science and operations officer for the National Weather Service in Duluth.
Miller, who worked the late shift that night, said forecasters worried that even the heightened language might not convey the urgency of the situation.
"We took a kind of extraordinary step...to personally call all the television meteorologists, tried to emphasize what we think is starting to evolve here," he said. "This isn't an ordinary flash flood warning."
Still, even then the National Weather Service was forecasting only 4 to 7 inches of rain. But some areas saw as much as 10. Miller said there was no way to predict something like that.
"Forecasting 10 inches of rain at a particular geographic location, and doing it with accuracy, is really outside the bounds of our science right now," he said.
The rain pummeled a huge area. It gushed along the surface of the steep hill that dives over 800 feet in some places, flooding homes and businesses, tearing up roads and completely defying the elaborate system devised to prevent such damage.
Starting in the late 1800s, the city had built a sprawling network of channels to control runoff and creeks. The system includes 430 miles of pipe, 100 miles of ditches, 3,000 culverts and 12,000 catch basins, all designed to funnel runoff and stream water under the city and into Lake Superior. But the storm quickly overwhelmed that system.
Last Wednesday, Brewery Creek expanded into a foaming brown torrent 10 feet wide and a couple of feet deep. Normally the river is out of sight in the center of town, diverted underground. But at the height of the storm the creek broke through not only its tunnel but also toppled a 20-foot retaining wall. The current rushed downhill and into several basement apartments, including that of University of Minnesota Duluth senior Nicole Kor.
Kor and her friend Hayley Moede, who came over to help her evacuate, were stunned by what they saw.
"We were driving on Fourth Street, and the manhole, it was just bubbling up to your waist," Moede said.
"It was gushing," Kor said. "It was crazy; that all came down to my house."
DRAIN SYSTEM AGING AND OVERWHELMED
Engineers planned the storm water system to handle a 100-year storm, a common practice for cities around the country. But last week's deluge was a 500-year storm, Duluth's chief engineer Eric Shaffer said.
"This was a huge storm," he said. "We would never be able to handle this storm, we would never design for such a huge magnitude of rain because it's not something that's going to happen often enough to justify the extra cost."
But Shaffer acknowledges Duluth's storm water system is old. Much of it dates back to the 1800s.
"The age hurts," he said. "When you get an old bluestone tunnel, there is potential, when water gets extra high, that it does take stones out that are maybe extra loose because they've been there for 100 years. But we do try to stay ahead of this as best we can."
The city regularly inspects and maintains pipes and culverts. But the flood caused problems that had nothing to do with that maintenance.
In a neighborhood on the west side of Duluth, city utility operations manager Steve Lipinski pointed out where the storm washed out an eight-foot-tall culvert that crossed underneath an alley. The pipe is tall enough for someone to stand with hands overhead. During the storm it was completely blocked with trees and rocks the size of small cars that were dragged downstream in the flood.
"Once they're blocked it starts overtopping, and you get this undermining, this erosion that takes out everything alongside the pipe," Lipinski said. There are now huge gullies on either side of the pipe, several feet across, where the water washed the alley away.
That happened throughout the city. As catch basins and culverts were dammed, the water backed up. It overflowed street curbs, and gouged beneath roads, causing them to collapse.
PICKING UP AND PLANNING AHEAD
Utility crews have identified 187 sites around the city that need repair, with a preliminary price tag of $14 million. Some will be repaired in a couple days, because the roads are the only way to area homes. Others will take longer, but Lipinski estimates 99 percent of the projects will be complete by the end of the year.
A more immediate priority is cleaning out the storm water system. At one spot, Duluth utility operator Jim Palmi recently flushed a catch basin with a high-powered jet of water to clear it of debris before another storm hits. "It was just like they dumped two full dump trucks full of sand in here," Palmi said.
As utility crews suck out what the massive rains left behind, the big question facing Duluth and other cities is whether this "500-year storm" may be the new "100-year storm."
"We've been expecting more large events like this for a number of years," said Jesse Shomberg, communities education director for Minnesota Sea Grant, an environmental research group. "Predictions of climate change for decades have told us we should expect more large events."
Shomberg said officials need to start planning for bigger storms that dump large amounts of water. But he acknowledges that the cost of adapting drainage systems may be prohibitive.
"We can't afford to take out every one of the culverts around the city and double it, make it twice as big," he said. "We can't afford to make our bridges twice again as long to avoid the flows."
But the massive storm does provide an opportunity to replace the storm sewer pipes and other public structures destroyed in the flooding with something better able to handle larger storms, Shomberg said.
That's already happening. In the reconstruction of a section of Skyline Parkway, the city has replaced a culvert that washed out with a bigger one, a small step toward preparing for the next 500-year storm, one that could arrive earlier.
EDITOR'S NOTE: An earlier version of this story incorrectly stated the width of Brewery Creek. The current version is correct.
- All Things Considered, 06/27/2012, 5:18 p.m.