Major projects in Marine on St. Croix meant to keep runoff out of the river

Workers are repairing a bluff and rerouting stormwater after decades of erosion and contamination.




9 minute read

Highway 95 in Marine on St. Croix (Greg Seitz, St. Croix 360)

A busy stretch of Minnesota Highway 95 that passes through the town of Marine on St. Croix has recently featured attention-grabbing orange signs and cones. On the side of the road, workers are removing trees, rebuilding a gully, and beginning other major renovations to improve how water moves through the historic village.

The work will benefit the Mill Stream, the spring-fed creek that powered the first mill in what became Minnesota, and the St. Croix River the creek flows into.

The multi-part projects are being led by the city of Marine on St. Croix and the Carnelian-Marine-St. Croix Watershed District. The work is the first part of a Village Center Revitalization Plan the city has been developing for years, focused on restoring streets and improving its quaint downtown.

“Working together gave us a lot more opportunities,” said Mike Isensee, director of the watershed district.

Numerous stormwater control features are being built in the village. They’ll slow down flows, remove pollutants, and provide natural habitat for wildlife.

It’s all funded by city and watershed district taxpayers, the Minnesota Department of Transportation, the Land & Water Legacy Amendment sales tax, and the Environmental Protection Agency. Labor is coming from construction companies, conservation district staff, and volunteers.

Fixing past mistakes

Placing pipe in the trench where a gully was once washing the bluff into the water below. (Greg Seitz, St. Croix 360)

One afternoon this week, a worker was maneuvering a 25-ton excavator around a tiny patch of dirt on a precipice overlooking the village and the scenic river valley. Previously, small trees and invasive brush had blocked the view. The Wisconsin side was visible for the first time in years, the bluff streaked with yellow and red.

The unhealthy forest also concealed a growing gully, which had been expanding for decades — since the state highway was reconstructed. Every time it rained, road runoff was quickly collected and a torrent plunged down the bluff.

“The drainage system for the highway was converted to curb and gutter with storm sewer in the early 1990s,” Isensee said. “All runoff within and tributary to the highway corridor were concentrated to this single discharge point.”

The gully was washing literally tons of sediment downhill, obliterating a natural spring seep and the creek it fed. Eventually, the washout could have reached the edge of the road, endangering the busy transportation route.

The excavator operator was part of a crew helping stop the erosion.

Scenes from the work site on the Mill Stream project in the village. (Greg Seitz, St. Croix 360)

Meanwhile, down in the village, an arborist high up in a cherry-picker chainsawed the limbs off a silver maple. Several trees and a lot of brush are being removed in the area between the Brookside Bar & Grill and the highway, primarily to make room for ponds and wetlands that will hold back runoff from the highway.

All the rain that previously fell on or near the highway, all the way up a big hill, is currently collected into a storm sewer that flowed down toward the village.

When it got there, it emptied directly into the Mill Stream.

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But that won’t happen starting next year. Water from the highway will flow under the road in its own culvert, and pass through basins that will let much of it evaporate or soak into the soil.

Due to funding and other limitations, some water might still flow directly into the Mill Stream. But that will only happen after the biggest rainfalls, and after the first couple inches of precipitation washes most of the contaminants into the ponds.

By reconstructing the paths water takes from the bluff to the river, the gully repair and runoff reroute will help protect beloved waterways.

Keeping the creek clean

Mill Stream Day 2016 (Greg Seitz, St. Croix 360)

Every May, Marine hosts Mill Stream Day to celebrate the historic and beautiful little creek. Kids dance around a maypole on the banks in Burris Park. Traditional Morris dancers perform and fresh brook trout is served. The singing stream is a beloved part of the community.

In recent years, numerous rain gardens and other improvements have been made by the watershed district, city, and citizens in the upper part of the village. Those projects slowed down a lot of water that otherwise rushed down city streets toward the creek and river.

But stormwater that still flows off the highway asphalt and into the lower Mill Stream carries nutrients, soil, road salt, chemicals, and cigarette butts. Perhaps worst of all, it’s usually quite warm. The coldwater Mill Stream, fed primarily by groundwater and home to fish and other species that are sensitive to temperature, was degraded.

The creek can carry pollutants all the way to the river. The St. Croix already gets too much runoff from many such sources, and it adds up to the fact the lower river is impaired with nutrients and the algae it feeds.

From where the runoff enters the Mill Stream at the highway, the creek plunges through a culvert, twists through Burris Park, flows behind the fire station, and rushes through the basement of the Brookside. When the restaurant patio is quiet, the creek provides background music.

Following the lower Mill Stream through Marine on St. Croix. (Greg Seitz, St. Croix 360)

From there, it goes under Judd Street and gushes out of a culvert, down a cascading waterfall, and leaps down the last leg to where it joins the St. Croix River.

The section of the river where the Mill Stream enters was just added to the state’s list of polluted waters last year, and projects like these are intended to keep reducing the harmful runoff that flows into the river.

Water carrying nutrients and other material provide food for algae that grow in the river, causing unnaturally large blooms. It hurts recreation and the delicate ecosystem.

Efforts to protect it have been underway since Environmental Protection Agency designated the lower river as “impaired” in 2008. That designation means that projects that improve the lower St. Croix are eligible for federal funding. (Last year’s designation added the stretch above Stillwater.)

That money was essential to making this fall’s work possible. The work in Marine is costing watershed taxpayers about $100,000 and the city about $100,000, and has received $300,000 in state and federal funding.

Ravine repair

The gully in 2018. (Greg Seitz, St. Croix 360)

One of the major causes of nutrient impairment in the St. Croix River is rapidly-eroding gullies. Minor changes on top of the bluffs — farming, development, highways — can upset the careful natural balance between water and earth.

“Over 100 years of poor land practices have resulted in a few continuous highly eroding ravines and gullies that when corrected, significantly reduce annual sediment and phosphorus loading hot spots to the river,” Isensee said.

The washout next to the highway was a challenge. It drops 82 feet in just over the length of a football field. The natural spring that emerged halfway down had already created its own minor gully, but when runoff from the highway hit it, it grew into a dangerous and unstable slope.

Below the bluff, a natural wetland was filling up with sand and soil.

Ravine repairs underway. (Greg Seitz, St. Croix 360)

With homes on both sides, the highway above and the swamp below, there was not much room to work. Several options were ruled out, before a final design was agreed on that used a pipe to carry runoff down the slope to a settling pond below.

It will get the water down the hillside under the soil, not through it.

A 50-foot buffer was cut on both sides of the ravine, where all the invasive buckthorn was removed. This non-native brush releases a chemical through its roots than kills other plants, and can shade out other vegetation. Removing it was an important first step to stabilize the slope.

Then, over the next couple years, workers from the Washington Conservation District and Minnesota Conservation Corps, along with volunteers, will plant native vegetation on the slope. There will be grasses and sedges, flowers and bushes, and some trees.

“We will plant 8,000 to 10,000 plants,” Isensee said. “We’re always shooting for part sun conditions. It allows us to create a hardy plant palette.”

Birds, bees, and other wildlife will find a priceless swath of natural habitat where there was little for them before, and where the bluff was previously threatening to wash away.

Clean water, healthy habitat

The Marine General Store was built in 1870, and is today the oldest such store in the state of Minnesota. Behind it, there’s a trail down to the St. Croix River, following the last leg of the Mill Stream.

The path passes through the Marine Mill Historic Site, managed by the Minnesota Historical Society. This is where the first mill in Minnesota was established in 1838. Its ruins are still visible on the other side of the stream.

Next to the trail is a ditch-like channel where spring water trickles downhill — except when it rains and runoff from the streets and parking lots uphill rushes through the channel and into the St. Croix.

In the future, a new stormwater basin will slow those flows. Water will come out of the pond through a culvert, and then down the channel, which will be rebuilt. Isensee climbed down into the channel and showed how it had been previously constructed with carefully placed stone.

Mike Isensee of the Carnelian-St. Croix-Marine Watershed District shows where a stream channel flowing to the St. Croix River will be rebuilt. (Greg Seitz, St. Croix 360)

The rock that will be used to strengthen the channel and improve water flows will come from bedrock excavated from settling ponds next to the highway.

“This is an entrance to historic site, so it’s important to use local materials,” he said.

The area around the channel will also be planted with native vegetation, providing more soil stabilization and habitat for animals. Isensee is working with the community to come up with a final design. He is concerned about the culvert opening, and how it can be designed so it isn’t all people see as they walk up the trail.

All told, the work being done this fall will keep about 50 lbs. of phosphorus, or more, out of the river each year. Similar efforts are underway throughout the region. It all adds up to big reductions.

In the summer, many people get ice cream at Nita Mae’s, a few steps from the trail, and walk down to enjoy it by the river. They might find a boat beached there, or kayakers launching or landing. A boardwalk leads back up to the waterfall below Judd Street.

Through it all, the Mill Stream pours over logs and rock ledges, twists between its banks, and finally spills into the St. Croix.


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Major projects in Marine on St. Croix meant to keep runoff out of the river