Scientists will learn from Duluth flooding

It was just after midnight on Wednesday when a water flow and quality gauging station on Amity Creek sent its final transmission, according to Richard Axler, a researcher with the University of Minnesota Duluth's Natural Resources Research Institute, who oversees a network of such stations. Duluth had experienced an epic rainstorm in the hours before. The rains, as most know by now, continued and sent torrents of water down the city's hills toward Lake Superior, tearing up streets and overburdening creeks and rivers.

It seems the water also took out the gauge on Amity Creek, along with four others on other trout streams. "I think we probably lost all of our gauging stations in all of the streams," said Axler. "The water went over the tops of many bridges. We don't know exactly what's even there yet because the flows have still been too high."

[image]

U of M Duluth researcher Richard Axler/Photo by Jennifer Vogel

Since 2005, Axler and partners like Jesse Schomberg and Valerie Brady from the Minnesota Sea Grant program, have been studying Amity Creek, which flows into the Lester River and eventually Lake Superior, as a demonstration project to develop techniques that could help other North Shore watersheds. In 2009, with help from the city of Duluth, the South St. Louis Soil and Water Conservation District and others, they completed two major bank restoration projects designed to reduce erosion and the flow of mud, both of which appear to have been damaged by the storm.

People in and around Duluth, in fact, have embarked upon a number of initiatives designed to slow, clean and cool the water that runs downhill during storms, as I wrote about last fall. The approaches--neighborhood rain gardens and barrels, pervious parking lots, a new and progressive city development code and the bank stabilization projects--have been remarkably collaborative, including partners like Axler, Schomberg, Brady, Duluth project coordinator Chris Kleist and a long list of others.

[image]

Blake Mosel, left, and Trevor Samsa inch close to the edge of a rock on Amity Creek Wednesday afternoon in Duluth, Minn. (Derek Montgomery for MPR)

Yet the efforts couldn't keep up with the recent storm. The city recently installed a series of enormous sanitary overflow tanks, designed to keep sewage out of Lake Superior during rains. In an email on Wednesday, Kleist wrote, "...we have had some overflows. Short answer is yes, they did prevent tens of millions of gallons of sewage escaping to the environment, but there is also a limit to their capacity and a record storm like this is just impossible to build for. "

"I feel sorry for the folks at city stormwater, like Chris," said Axler. "They've done a lot of really good work, particularly over the past 10 years or so, and so have MnDOT, St. Louis County, the soil and water conservation districts and others. They've done all kinds of projects for erosion control and bank stabilization. There are success stories out there."

"I'm sure on individual sites, a lot of these things helped," Axler said. "In terms of individual homes and flooding and washing out driveways and lawns and basement flooding, absolutely. We'll all be scrambling to assess whatever information is available and make it available as widely as possible."

"But when you're talking the overall footprint of the city, when you build a city on top of the land and replace vegetation and soil with asphalt and concrete and roofs, there is an awful lot of water that no longer soaks into the soil before entering the streams. Streams flood naturally, even without cities, but pump all that water off the roads at once and you get these isolated bottlenecks where the infrastructure implodes. It's a physics problem."

Axler said it didn't help that the ground, loaded with clay, was already saturated due to previous big rains, such as a storm in late May. Trees were uprooted and washed downstream, causing additional damage by blocking culverts. The city's parks, many of which are along water bodies, took a beating, he said. "Clay poses particular problems. You get that much rain and things let go."

It's not clear yet exactly how Axler and others will move forward. But the team should be able to repair the Amity bank stabilization sites, along with some other damaged areas, thanks to a grant from the EPA's Great Lakes Restoration Initiative. "The [project] was a nice model for these types of unstable banks along the north shore. We took the best engineering approach possible. Lessons were learned no matter what on how to deal with the weather events we just had. The strategy will change a bit. We are at the assessment stage."

"I think everybody who has been working on it is a little bit in shock," said Axler. "You can feel sorry for yourself because it's been a lot of work by a lot of people, but it's nothing compared to the personal tragedies that have occurred."

Yet, the scientist said, "You always learn from things like this. The long-term view is that it's a lot cheaper to protect things than to try to fix them after they are damaged. You need to do source water protection and watershed protection and get builders and landscapers and planners and individual residents to understand that. Investment in that are orders of magnitude cheaper than the cost of repairing the damage from this."

He hopes upcoming efforts to rebuild the city's stormwater infrastructure will create more capacity. "The general consensus is that much of the older infrastructure is undersized based on current weather trands, even without getting into the seemingly endless and in my opinion unscientific debate about who caused climate change and does it exist. The weather is clearly different in last 15 years or more. According to analyses of existing data, there is an increased frequency of big, intense storms."

"Certainly all the engineering folks are aware of the need to learn from this experience," he said. "It's a data point. It's data that didn't exist before. That's how engineering works."

• Annandale watches special session for broadband help
• DNR pushes ahead with its groundwater planning
• Broadband providers seek $44 million from state fund
• Shifting rain could be lowering groundwater