Empire Wastewater Treatment Plant Restoration

[Map: Location of Empire Wastewater Treatment Plant.]

The Empire Wastewater Treatment plant is located along the Vermillion River, at the junction of two greenways that connect to the Mississippi River.

The Metropolitan Councils Empire Wastewater Treatment Plant sits on more than 400 acres of land on the Vermillion River in Farmington, Minnesota. After completing a natural resource management plan for the property in 2002, Friends of the Mississippi River has been conducting ongoing habitat restoration and natural resources management. The location of the property near two wildlife corridors, its size, and its location along the Vermillion River make it an important focus of restoration efforts.

In 2005, our ecological restoration work at the Empire Wastewater Treatment Plant was a finalist in the land use category for the Minnesota Environmental Initiative Awards. These awards are presented annually to projects that exemplify MEIs commitment to partnership and environmental outcomes. Their web site has more information about the Environmental Initiative Awards.

Management Planning

The property sits at the meeting point two wildlife corridors — one running along the Vermillion River, the other extending northeast through the University research station and Flint Hills Resources property link to the Mississippi River. Nearly half of the property is undeveloped and in a semi-natural state, while the treatment plant and some cropland occupy the rest. An area of about 50 acres that used to be a wet meadow was a prime candidate for wetland restoration — Drainage ditches installed in the mid-1900s enabled some cultivation of the soil in drier years, but parts of it were almost never plowable.

In 2002, the Met Council provided funding for FMR to develop a natural resource management plan for the entire property, in collaboration with the Minnesota Department of Natural Resources and Dakota Soil and Water Conservation District. The plan made four primary recommendations:

  1. stabilize the most vulnerable sections of the Vermillion River;
  2. restore a 50-acre agricultural field to wet meadow;
  3. remove buckthorn from the floodplain forest; and
  4. enhance species diversity in a 34-acre seeded grassland.

The Met Council subsequently provided most of the funding for these projects, which were started in 2002.

Implementing the Plan

Stabilizing the Streambanks to Reduce Erosion

The Vermillion River is a DNR-designated trout stream, and the two miles of river that pass through the Met Council property contain important spawning sites. Retaining the habitat for resident trophy fish requires stabilization of the banks.

[Photo: Erosion blanket covering riverbank.]

Before the bank soil is replaced on top of lunkers or root wads, coconut fiber blanket is laid down, then filled with soil and folded back to create a soil-filled pillow. Two layers were created at this site.

Streambank erosion is a naturally occurring process in streams and rivers. In many urban areas, however, this process has been dramatically accelerated by increased runoff from hard surfaces as natural landscapes give way to development. Increased erosion causes reduced water quality and loss of fish and other aquatic life due to siltation, sedimentation, decreased oxygen and increased water temperatures. High rates of erosion also cause loss of agricultural land and threaten homes and properties.

Careful studies of the river corridor by the DNR identified eleven banks at the plant property that were the highest priorities for restoration work. In Fall 2003, work began to stabilize a total of about 1,200 feet of these severely eroded streambanks.

[Photo: Boulder vane and J-hook in the river.]

Boulder vanes divert the current away from the banks. They are angled upstream and the j hook at the far end provides a resting place for fish.

Stabilization Techniques

Modern streambank stabilization methods rely on natural materials and vegetation, rather than artificial structures like concrete or rip-rap (coarse rock covering the riverbank to deflect erosive waves). Also referred to as bioengineering, the techniques used at Empire involve first regrading steep banks, then installing lunker structures, root wads, boulder vanes, erosion blanket, willow live-stakes and bareroot trees and shrubs.

[Photo: Lunker structure being placed in riverbank.]

Backhoe installs lunker structure so that the top of it will be just below the normal water level.

Lunker structures are large, heavy wooden frames that serve the dual purpose of anchoring the base of the bank and providing caves under the banks for fish habitat. Root wads consist of the root mass and several feet of trunk of an uprooted tree. They are anchored at, and perpendicular to, the bank edge to divert flows away from banks and provide fish cover. Boulder vanes also divert fast currents away from the bank. A vane consists of large (1.5-foot diameter), mostly submerged rocks placed in a line diagonal to the bank and directed upstream.

Coconut fiber erosion blankets are placed on the banks to hold the soil in place until planted vegetation develops adequate roots to anchor the soil. Willow and dogwood live-stakes are made by cutting 3-foot sections of about 1-inch diameter (or thicker) stems.

Putting these Techniques into Action

[Photo: Volunteer cutting willow stakes.]

volunteers cut sand-bar willow live stakes.

In November 2003, volunteers from Trout Unlimited and students from the University of Minnesota and Inver Hills Community College cut and installed about 1,200 dormant stems. Roughly 50 percent of the stems survived and grew in 2004. We discovered, however, that beavers found our willow stakes to be tasty winter treats! Fortunately, they did not eat all of our work.

In spring 2004, about 35 volunteers planted 750 bare root native trees and shrubs on the banks. About 65 percent of the installed plants survived the first year, in spite of high floods in early summer. Highbush cranberry was one of the most hardy shrubs. The combination of trees, shrubs, and grasses will provide good soil stability, filtration of runoff, and shade to keep the water cool.

[Photo: Volunteers planting trees on riverbank.]

In May 2004, volunteers installed 750 bare root, native trees and shrubs along the banks.

Major funding for the streambank restoration was provided by the Department of Natural Resources, Section of Fisheries, with additional funding from the Met Council. The Dakota Soil and Water Conservation District and the Minnesota Conservation Corps also assisted with portions of the installation and maintenance.

Monitoring the sites progress

[Photo: Good shrub growth on riverbank.]

Shrub species, such as the wild indigo seen here, were well-established at most of the banks after 3 growing seasons.

Over the next three growing seasons, we monitored the restored area and conducted some maintenance. Some results we observed include:

  • Spring and summer flooding alternating with summer and fall drought in 2005 and 2006 took a toll on shrub survival. Fortunately, the initial restoration plans anticipated significant shrub mortality, so far more plants were installed than needed for good coverage.
  • The willows and planted shrubs provided good stabilization, but they were not so abundant as to shade out ground cover grasses and forbs, which are very important for slowing runoff. The trees and shrubs provided a small amount of shade for the river by the end of the third growing season, but significant shade may still be a few years away.
  • Since the restoration work, all the streambanks have been well-vegetated and stable, with little or no active erosion. Reed canary grass, which was ubiquitous at the banks before restoration, was present at all the banks and dominant at several. Nevertheless, almost all of the native grasses and forbs (flowering plants) that were seeded had appeared at one or more of the banks, and were even dominant at a few. Even a few native plant species provide some food for native insects, birds, and other wildlife.

Restoring the former wet meadow

[Photo: Vegetation coverage in summer 2004.]

August of first growing season (2004), showing good vegetation coverage overall.

On the north side of the WWTP property is a 50-acre field that was historically a wet meadow wetland. Wet meadows generally have shallow standing water (up to 6 inches) for brief periods in the spring. They provide critical habitat for migratory shorebirds and a host of other species. Drainage ditches installed on the Empire property in the mid-1900s enabled cultivation of the site in drier years, but parts of it were rarely tillable. The management plan naturally concluded, therefore, to restore this site as a wet meadow.

Typical wetland restorations today are deep-water wetlands of cattails. Most of the wetlands impacted by development, however, are wet meadows. Since the number of wet meadows has drastically decreased, restoring these areas is essential for the wildlife and plant life that depend on them.

Wet meadow restorations can be tricky because the hydrology (properties, distribution and effects of water in the soil and underlying rocks) is difficult to predict. If the water supply is inadequate, wetland plants will not establish and a prairie will result. Though not undesirable, a prairie would not contribute the same value to the landscape as a wet meadow.

[Photo: Abundant native species in 2005.]

By fall of the second year (2005), native species are abundant.

Restoration work began in Fall 2003 by creating very shallow basins and diverting flow from a nearby drainage ditch. Native seed was broadcast in November 2003. A ten-acre existing wetland within the site was also treated several times for reed canary grass. It was re-seeded in 2005 with a native wet meadow mix, and in spring 2006, a hardy group of about 25 volunteers installed 1,400 potted wetland plants to re-vegetate areas where weeds had been eradicated.

[Photo: After 3rd growing season, natives abundant.]

Native species dominant over most of the site after three growing seasons (2006).

Monitoring and maintenance of the site has continued for several years while native vegetation gets established. The entire seeded area was burned for the first time in 2006, and crews have done intensive weed control for thistles, ragweed, sweet clover, purple loosestrife, reed canary grass and others.

Though still in its early stages, this restoration already shows indicators of providing habitat for migratory shorebirds and other species. In spring 2006, numerous sora were using the site, as were several duck species. Later in the summer the site was a hot-spot for dickcissels.

The design and installation was conducted by Applied Ecological Services, Inc.

Floodplain Forest Management — Buckthorn, Begone!

In Fall 2002, the Minnesota Conservation Corps and a DNR-hired contractor spent four days cutting and treating buckthorn along the river. Buckthorn is detrimental to wildlife and also creates dense shade that inhibits plant growth. Removing this exotic invasive shrub will allow for more beneficial native species to grow, such a nannyberry, highbush cranberry and dogwood, as well as groundcover grasses and flowers. Additional buckthorn removal took place in winter 2005 along all the ditches around the property.

Grassland Enhancement

In 1987, a 34-acre pasture between Highway 66 and the river was seeded to native prairie grasses — big bluestem, Indian grass and switch grass. Since then it has been managed for Canada thistle and other weeds by periodic prescribed burns and herbicide application. The prairie grasses have grown well, but few other native prairie wildflowers or grasses are present. The grassland also has a large patch of reed canary grass and smooth brome grass, two exotic and very invasive species.

Since a diverse plant community leads to a diversity of wildlife and a much healthier ecosystem than a plant community dominated by just a few species, FMR initiated a project in Fall 2004 to increase the prairie plant diversity. The invasive grasses, which cover an area of about four acres, were eradicated and the area was reseeded in 2005 with a diversity of mostly flowering plants. Within a few years, the flowers should add a splash of color to the grassland, develop more characteristics of a native mesic prairie, and provide better wildlife habitat.

Science in the field

A small experiment in this prairie restoration is also underway to observe the effects of carbon enrichment on reed canary grass establishment. Saw-dust added to the soil increases the carbon levels, resulting in decreased nitrogen. Research studies have shown that reed canary grass grows poorly in nitrogen-poor soils, and some native species may gain a competitive advantage in those conditions. If successful, this method may facilitate native plant community establishment in areas where reed canary grass is abundant.

[Photo: Tractor tilling sawdust into soil.]

3 inches of sawdust were tilled into 3 study plots to study the effects of low soil nitrogen levels on reed canary grass establishment.

[Photo: Study plot in year 1.]

At the end of the first growing season, vegetative growth in the study plots was much less than in the restoration area.