Stream Bank Stabilization

Stream Bank Stabilization


What is "Stream Bank Erosion"?

Traditional bank stabilization measures include concrete lining, timber retaining walls, and shoreline reinforcements of broken concrete. The costs of these measures are great and far-reaching. The natural beauty of the stream is lost, water quality deteriorates as it flows through unnatural materials, and flows are accelerated in the absence of natural meanders and obstructions. Often these measures create additional problems downstream, including increased flooding and more erosion.

Bioengineering techniques, combining man-made structures with natural vegetation, are a logical alternative, protecting both the stream’s natural beauty and valuable properties alongside.

Two types of structures are installed at the toe of eroding banks: “lunkers” and “a-jacks.” They provide an aquatic habitat below water and stabilize the base of the bank. Imbedded among the structures are dormant willow posts, fast-rooting trees whose natural habitat is at the water’s edge. Their roots bind and strengthen the banks as they grow. Finally, banks are sloped, contoured, and planted with other water-loving vegetation.


How does bioengineering relate to stream bank erosion?

Bioengineering implies the use of engineering techniques along with biological expertise to control the erosion of stream banks. Engineering considerations include the hydraulics of the flow and the structural integrity of the banks. Biological considerations include the vegetation that keeps banks stable.

The techniques discussed here were designed specifically to reduce erosion of valuable property and maintain a more natural stream without increasing flow or velocity. Based on trials on rural streams in downstate Illinois, these techniques involve the introduction of stabilizing structures along with native vegetation.

What is the Willow-Post Method?

The willow-post method is a means of controlling stream bank erosion through installation of native willow cuttings to stabilize eroding stream banks.

How does is work?

The stabilization process is two-fold. First, the willow root network binds the soil together. Second, the willow foliage slows floodwaters near the eroding bank, which also helps reduce bank erosion downstream. With bank erosion under control, grasses and more valuable trees can grow.

What are its advantages?

Low cost, both in terms of materials and installation.
Willows are native to the region and easy to obtain. Installation is fast and permanent.

Environmentally sound.
The use of all native materials encourages natural habitats in and around streams and enhances their scenic beauty.

Ongoing maintenance costs are low and control is long-term
because the willow-post method creates a natural environment that is self-sustaining.

Tested and proven effective in Illinois
under flood conditions, even when heavy spring floods carry ice floes.

More valuable trees can grow
after the willows slow bank erosion.

How do costs compare to “traditional methods?”

The “traditional” methods for controlling stream bank erosion rely on the use of riprap or a variety of cement and steel retaining structures. These methods typically cost $50 to $200 per foot and require maintenance and repair through the years. The willow-post system can be installed for 7 to $15 per foot, with little or no maintenance. Landowners can ensure the establishment of valuable trees by planting tree seedlings.

Will the willows spread into adjacent fields?

No. When applied at severe erosion sites, the willows have remained at the water’s edge, which is their preferred environment. They have not spread upward into adjacent fields or clogged the channel.

Where can the willow-post method be used?

In Illinois the willow-post method has been used most successfully along streams in agricultural flood-plains without tree cover.

How can the technique be used most effectively?

The willow-post method for stream bank stabilization is most effective when incorporated into a “systems approach” to land and water management. The system should include an erosion control plan on the land upstream from the stabilized stream bank. On land sloping more than 2 percent, reduced-till and no-till farming should be practiced. Pasture and timber areas on steep slopes should be managed for adequate vegetative cover in order to slow water runoff. Floodwater should overflow onto the floodplain. The overflow slows erosion and allows rich soil deposition. Fields should be protected with a wider riparian border.

Why is stream bank erosion such a problem?

In most instances, stream bank erosion is an indication that significant changed in land use and management have occurred upstream. These changes are the result of agricultural trends that have produced a dramatic increase in the velocity and volume of farmland runoff into streams and waterways. They include:

  • Straightening and channelizing creeks and streams.
  • Clearing vegetation from stream banks.
  • Less land in soil-conserving crops of hay, pasture, and cereal grains.
  • More land in erosive row crops of corn and soybeans.
  • Larger farms and bigger equipment involving the removal of fence rows, hedgerows, and windbreaks.
  • Lack of proper land management on steep sloping pasture and timber areas.
  • Increased surface drainage to eliminate ‘wet holes’ in fields.

Woodbine Park Prairie Estates’ Stream bank Stabilization

Site Description

The stream bank erosion took place along a hairpin curve of Big Creek. During the early 1990s, high water levels began to scour the slope, reducing the width of the stream bank from 35 feet to 20 feet. The surface runoff and scouring from the base of the slope began to threaten an adjacent property.

Project Description

Stabilization of the toe of the slope to eliminate further scouring and reduction of the amount of additional slumping was needed. The toe of the escarpment was pulled out to the north edge of the existing stream bed. The north bank was then pulled back to maintain an average width of 35 feet. RR5 stone was used for 150 feet along the toe of the slope, reshaping the bank to a 1:1 slope. To divert the high water flow force past the hairpin curve and off the escarpment, a short cut-off channel was constructed. The channel was 35 feet wide at the base with 2:1 side slopes. The cutoff channel runs approximately 185 feet at an angle across the curve. The soil removed from the cutoff was placed on the escarpment above the longitudinal peaked stone. RR5 stone was placed in front of the debris dam and along the south edge of the cutoff channel. Two Bendway weirs were then constructed near the exit of the cutoff channel to direct the flow to the center of the channel.

The site was designated a wetland with a large wooded flood plain. An old gravel borrow pit located to the east had an opening to the creek in the northwest corner of the pit. Access to the site was limited for construction equipment and machinery, requiring construction of an access lane from the north end of the property.

Materials

  • 460 tons of RR5 stone in the toe protection and channel.
  • 60 tons of RR5 stone in the two weirs.
  • Two weirs measuring approx. 10 – 15 feet in length and 1 – 2 feet above average stream depth, sloping up toward the bank to a height of 4 feet above average stream depth.
  • Vegetation planted in open stream banks created by project.

​​                                                              4790 Janine Way  |  Mt. Zion, Illinois 62549