Mending the Mississippi: River tour highlights plans for backwater restoration
If you talk to environmental experts in Minnesota, they will tell you that the health of the Mississippi River in and around Hastings is not what it should be. The problems have been easy to see, they say: murky water, little to no aquatic plant growth, eroding islands and fewer birds and fish.
Efforts farther south along the river have proven to be successful at restoring river health and habitat, and stakeholders are hopeful that similar projects will be done on a more local piece of the river, known as pool 3.
On June 18, representatives from the Minnesota DNR, Wisconsin DNR, Audubon Minnesota, the Army Corps of Engineers, U.S. Fish and Wildlife Service, Dakota County Soil and Water Conservation District, National Park Service and the public spent a morning on the river to get a first-hand look at existing conditions in North and Sturgeon lakes and to talk about about the plans to restore those areas.
Historically, the river meandered through the land uncontrolled, creating a diverse floodplain habitat. It was the effects of manmade controls that have brought the river to its current state. Settlements along the river increased sediment levels, wing dams and dredging changed how water flows and the locks and dams flooded many areas, which led to more wind damage and erosion. Today, the river habitat in pool 3 is greatly reduced, those experts have said.
A citizen advisory group has been working over the past several years on the Mississippi Makeover project, which identified what residents and river users think are indicators of restored habitat and what indicators should be targeted in restoration here. Water clarity was a major issue.
“They want to see their paddle in the water when they canoe,” said Laura Jester, coordinator for the Mississippi Makeover project.
A quick look in the water in North and Sturgeon lakes revealed the reality. Although North Lake is only a few feet deep in most places, the lake bottom was never visible. Even the hulls of the boats used on the tour were hidden below the waterline by the sediment suspended in the water. Suspended sediment levels are at 42 milligrams per liter there; in Lake Pepin suspended sediments measure at less than 20 milligrams per liter.
Other indicators were poor diversity of aquatic plants and birds.
“We don’t have the (bird) populations that we could support … because we don’t have the habitat,” Jester said.
A recent study stated that lower pool 2 and upper pool 3 are the most degraded pools on the Mississippi River, said Tim Schlagenhaft of Audubon Minnesota.
Another indicator specifically in North Lake is the disappearing island. Historical data show the island was once much bigger, but erosion has reduced it significantly.
Another issue is increased water flows through the lakes from the river through the six inlets that connect the bodies of water. In 1991, 26 percent of the river flow found its way into the lakes. By 2012, that had increased to 43 percent. With so much water coming into the lakes, the river has less ability to move sediment, which leads to an increased need for dredging in the main channel.
The project being planned for upper pool 3 includes island building and water level drawdowns, both techniques that have been used successfully in other parts of the river downstream.
Islands act as windbreaks on the water, keeping wind from stirring the surface and slowing the current. North Lake is four miles from one end to the other, giving wind ample space to agitate the surface. The islands also serve as habitat for birds and insects. The Prairie Island community has built some small islands around its marina to shelter the area.
Islands in pool 3 could be built with dredging material. Dredge material, which is mostly sand, is already being piled up on various spots in and near the river.
Islands used to be a common feature in the Mississippi River backwaters, said Brenda Kelly of the Wisconsin DNR. New islands would be installed strategically to get the most benefit.
Water level drawdowns reduce the water level throughout the pool, exposing shallow areas and allowing aquatic plants to take root. Prior to the construction of the locks and dams, the river basin had regular low water seasons. Low water was a cue to emergent aquatic plants – plants that stick up above the water – to germinate and become established in the ground. But because the U.S. Army Corps of Engineers manages the water levels throughout the river in order to maintain the shipping channel, low water seasons have been lost. Conducting a drawdown simulates the natural dry season.
On average, drawdowns produce a 17 percent increase in vegetation, said Mary Stefanski of the U.S. Fish and Wildlife Service. A typical drawdown lowers the water level six inches to two feet. At that level, shallows are affected without disrupting traffic in the main channel, if weather conditions cooperate. In pool 3, a drawdown would expose about 2,000 acres.
In other areas where drawdowns have been done, surveys of recreational users showed that most people weren’t even aware a drawdown was being done.
“We really didn’t have an impact on recreational users,” Stefanski said.
Ideally, drawdowns are done two years in a row to get the most benefit. Benefits usually last anywhere from five to 10 years, she said.
The actual project in pool 3 would start with island building, with construction potentially starting in 2015. A drawdown might be possible once the channel is dredged out for island building material, but the timing for that process isn’t fully known yet.
Other project features include modifying side channel inlets to reduce the flow from the river into the backwaters, backwater dredging and shoreline stabilization.
The project is expected to cost $8 million. Of that, $5.2 million would be paid for by the U.S. Army Corps of Engineers, and the remaining $2.8 million would have to come from local sponsors. The Corps is still working on finding a local sponsor.