Aging stormwater systems weren't built for this volume of rain

Snowplowing, recycling and street repairs are all part of the job for Shoreview's public works employees. But the department's fastest-growing budget item these days isn't filling potholes.

It's stormwater.

"Stormwater management issues … have just absolutely consumed my staff," said Mark Maloney, the city's public works director. And homeowners' calls, he said, have a common theme: " 'Hey, why is everything wet?' "

---Across Minnesota, cities large and small are scrambling to upgrade storm sewers, culverts, roadways and drainage ponds as they find themselves deluged by ever-more intense storms and flash flooding. With global temperatures on the rise, this decade is likely to be the wettest in Minnesota history, according to retired state climatologist Mark Seeley.

All that water is overwhelming Minnesota's patchwork of stormwater systems, a huge, aging network of tunnels, pipes and culverts — some of it more than 100 years old — that carries water away to ditches, rivers and lakes. And all of it was designed to handle the climate of the past, said Ryan Anderson, stormwater program manager at the Minnesota Pollution Control Agency.

Rochester's public works department, for example, set up a special unit to tackle heavier stormwater loads. The city of Hutchinson plans to issue a 15-year bond to pay for a major stormwater upgrade that features a large new retention pond, complete with native plantings and a walking path, constructed on an old baseball field. Minneapolis is grappling with flooded basements and startling sinkholes near Lake Nokomis. And St. Cloud just added a new underground tank and tunnel system to hold and treat stormwater in an area prone to flooding.

By some estimates, the cost of these upgrades statewide could run into hundreds of millions of dollars in coming years, an expense that is likely to turn up in higher utility fees for homeowners and businesses. Nationally, the adaptation costs could reach $12 billion in coming decades, according to the U.S. Environmental Protection Agency.

Minnesotans see the evidence all around them: soggy lawns, crumbling curbs, flooded intersections, scoured stream banks. Even geysers erupting in the streets.

On the wettest days, stormwater can also wash into sanitary sewers — the pipes that carry sewage and other municipal wastewater to water treatment plants — resulting in emergency discharges of raw or partly treated sewage into Minnesota's lakes and rivers.

Such discharges now occur on average about 147 times a year, up from 120 times a year in the first half of the past decade, according to a Star Tribune review of state data.

To address these new climate realities, cities are upgrading their stormwater systems to handle a higher set of federal rainfall estimates, known as the Atlas 14 standards, that were recalculated by the National Oceanic and Atmospheric Administration for Minnesota in 2013. A 100-year storm that used to produce 6 inches of rain in the Twin Cities in 24 hours is now expected to produce 8 inches.

"That's a huge change," said Randy Neprash, a stormwater regulatory specialist with consultant Stantec.

On the worst days, in many communities, it is still triage: sandbags and pumps.

That's what Little Canada resorted to last spring when Twin Lake gushed over its shores. The small, deep lake, surrounded by older houses and towering trees, has had some flooding in recent years. But nothing like what happened in May and June, when melting snow and spring rains triggered a chain reaction. Put simply, Roseville's storm­water drains into the Shoreview area, and Shoreview's storm­water drains into West Vadnais Lake. When West Vadnais Lake filled up this spring, it spilled over and poured into little Twin Lake.

But Twin Lake is landlocked. With nowhere for the rising water to go, the lake began consuming yards. Residents and city crews responded with sandbags while the City Council took an emergency action to rent a large pump to lower the lake level.

It was a close call, said Val Eisele, who lives on the lake with his wife, Jessie Everts, and their two children. They felt powerless as the lake crept closer and closer to the back door of a house they "scraped and saved" to buy.

"To watch it approach the house is definitely terrifying," Eisele said. "Trees have fallen on people's docks."

Remarkably, no houses flooded. But months later, Stan Martin's backyard remains partly submerged.

"Look at this junk," Martin said one day in August, stepping through mud in the woods down a path on his property's edge. "Logs. Telephone poles ... everything came floating in. People used to come down here and get their wedding photos taken. Now it's just ... yuck."

The frustrated homeowner said he's not convinced climate change caused the flooding. He accused the Ramsey-Washington Metro Watershed District of mismanaging the lake's water flow. Either way, it was a mess.

"It stinks like a swamp," Martin said.

Tina Carstens, the watershed's administrator, said the flooding did result from increased rainfall and elevated groundwater due to climate change.

"Our infrastructure just wasn't built for this prolonged state of high water," Carstens said. "We haven't been here before. It's uncharted territory."

Little Canada's public works director, Bill Dircks, agreed. Standing by the pump near Martin's house in a bright orange vest, Dircks said he grew up in the area and has never seen Twin Lake flood as it did this spring.

"I've never seen the water get to that pipe before," Dircks said, pointing at an old concrete culvert.

To prevent a disaster, the pump has been sucking lake water through a 6-inch discharge pipe that snakes through the old culvert and across a field to a drainage pond dug out alongside Interstate 694. The water then flows under the freeway and eventually to Gervais Creek, which drains to Gervais Lake, which drains to Keller Lake and Lake Phalen, and eventually into a pipe that snakes to the Mississippi River.

The city finally turned the pump off last week, although it's keeping the equipment in place for now.

That episode alone cost the city about $70,000, money that will come from its general operating budget because Little Canada doesn't charge residents a stormwater utility fee. That may change.

Dircks said he's thankful the emergency fix worked. But it's not a solution. That could mean constructing a bypass to prevent overflow from going into Twin Lake.

"This is unprecedented stuff," Dircks said.

Facing a wetter future, Minnesota communities are embracing a changing stormwater design philosophy. Where they once focused on pipes to move runoff someplace else, engineers now aim to mimic nature and manage the water better where it falls. That means building more and larger retention ponds, installing underground filtration tanks, narrowing streets to reduce runoff from pavement and adding more features such as rain gardens, swales and tree trenches to soak up water. The state's Stormwater Manual offers plenty of guidance on dimensions and green infrastructure.

But there's no template, said Shoreview's Maloney.

"We almost have to wait for it to happen to understand the magnitude of it," he said. "I think a lot of Minnesota cities are finding themselves in this situation of dealing with something that was never even thought possible."