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Soil Bioengineering

Soil bioengineering (SB) uses live plant materials to provide erosion control, slope and stream bank stabilization, landscape restoration, and wildlife habitat. These techniques are used alone or in conjunction with conventional engineering techniques.

Soil bioengineering employs a partnership of the professions of soil science, landscape architecture, civil, hydrological, and geotechnical engineering, and horticulture.

Soil bioengineering is an excellent tool for stabilizing soil surface erosion. These methods should not, however, be viewed as the only solution to erosion problems.

Please see the topics below for more information.

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Before and after pictures of Soil Bioengineering techniques in Raymond, WA


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Slope treatment using a combination of brush layers, bare root plants, dead stakes and compost socks (SR 18 Maple Valley to Issaquah/Hobart Rd)


Benefits

  • Projects usually require less heavy equipment excavation. As a result, there is less cost and less impact. In addition, limiting crews to one entrance and exit route will cause less soil disturbance to the site and adjoining areas.
  • Erosion areas often begin small and eventually expand to a size requiring costly traditional engineering solutions. Installing soil bioengineered systems while the site problem is small will provide economic savings and minimize potential impacts to the road and adjoining resources.
  • Use of native plant materials and seed may provide additional savings. Costs are limited to labor for harvesting, handling, and transport to the project site. Indigenous plant species are usually readily available and well adapted to local climate and soil conditions.
  • Soil bioengineering projects may be installed during the dormant season of late fall, winter, and early spring. This is often when other construction work is slow.
  • Soil bioengineering is often useful on sensitive or steep sites where use of heavy machinery is not feasible.
  • Soil bioengineering systems are strong initially and grow stronger as vegetation becomes established. Even if plants die, roots and surface organic litter continues to play an important role during reestablishment of other plants.
  • Once plants are established, root systems reinforce the soil mantel and remove excess moisture from the soil profile. This is often the key to long-term soil stability.
  • Soil bioengineering provides improved landscape and habitat values.
     

Limitations

  • Soil bioengineering has unique requirements and is not appropriate for all sites and situations. On certain surface erosion areas, for example, distribution of grass and forb seed mixes, hydromulching, or spreading of a protective layer of weed-free straw may be satisfactory and less costly than more extensive bioengineering treatments.
  • On areas of potential or existing mass wasting, it may be best to use a geotechnically-engineered system alone or in combination with soil bioengineering.
  • Project areas require periodic monitoring. On highly erosive sites, maintenance will be needed until plants are established.
  • Established vegetation can be vulnerable to drought, soil nutrient and sunlight deficiencies, road maintenance sidecast debris, grazing, or trampling, and may require special management measures to ensure long-term project success.

Reference - A Soil Bioengineering Guide for Streambank and Lakeshore Stabilization FS-683 October 2002 by C. Ellen Eubanks and Dexter Meadows


Typical Costs
Cost information is in 2000-2001 dollars.

  • Typical cost estimates (pdf, 11kb) 
    Generic cost estimates for some typical soil bioengineering treatments.
  • Chelan Project (pdf, 29kb)
    Actual costs for terracing, biosolids treatment, and planting a 2,400 sq ft slope near Lake Chelan, WA.
  • Forks Project (pdf, 23kb)
    Actual costs for gully repair, terracing, and planting an 8,660 sq ft project near Forks, WA.
  • Raymond Project (pdf, 29kb)
    Actual costs for installing a cribwall, terracing, and planting a 28,075 sq ft project near Raymond, WA.
  • Eastern Region Project (pdf, 5kb)
    Estimated costs for gully repair, terracing, and planting a 2,000 sq ft project near Rosalia, WA.
  • North Central Region Project (pdf, 5kb)
    Estimated costs for gully repair, terracing, and planting a 4,500 sq ft project on SR 2.
  • Northwest Region Project (pdf, 5kb)
    Estimated costs for gully repair, terracing, and planting a 4,500 sq ft project on SR 2.
  • Olympic Region Project (pdf, 6kb)
    Estimated costs for gully repair, terracing, live staking, and planting a 600 sq ft project in Olympia, WA.
  • Southwest Region Project (pdf, 5kb)
    Estimated costs for gully repair, terracing, live staking, and planting a 600 sq ft project near Vancouver, WA.

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Tools and References
Soil Bioengineering References organized by author (pdf, 56kb)
Soil Bioengineering References organized by title (pdf, 57kb)
Soil bioengineering, biotechnical stabilization, native plant, erosion control, and other topics are covered in this list of 200+ scientific papers, journal articles, books, and other published materials.

Designer's Cheat Sheet (pdf, 8kb)
A simple guide for choosing among several soil bioengineering options, based on erosion conditions.

Biotechnical Stabilization of Steepened Slopes (pdf, 418kb)
By Donald H. Gray and Robbin B. Sotir, this scientific paper describes the basic principles of biotechnical stabilization. Guidelines are presented for analyzing the surficial, internal, and global stability of brushlayer reinforced fills. A case study is reviewed of live, brushlayer inclusions used to stablize steep slopes along a roadway.

Guidelines for Developing and Managing Ecological Restoration Projects (pdf, 108kb).
This document, from the Society for Ecological Restoration International, covers pre-planning, prelimiinary tasks, and post-installation tasks.

Soil Bioengineering An Alternative to Roadside Management (pdf, 1.42mb)
A practical guide by Lisa Lewis, US Forest Service. This guide covers basic soil bioengineering concepts. It includes a site evaluation and design, planning, and implementation checklist. It covers twelve different upland techniques.

WSDOT Roadside Manual Chapter 740 - Soil Bioengineering (pdf, 654kb)
This practical guide covers definitions, planning, design, implementation, site evaluation, and eleven upland soil bioengineering techniques. This guide is similar to the USFS guide, but gives WSDOT-specific information.

Soil Bioengineering for Upland Slope Stabilization - WSDOT Research Report (pdf, 2.16mb) 
This report covers three soil bioengineering projects near the City of Raymond, Lake Chelan, and the City of Forks.

Toward Quality Biosolids Management; A Trainer's Manual (pdf, 180kb)
By Dan M. Sullivan, Professor of Crop and Soil Science, Oregon State University. This is a resource for those who oversee and conduct biosolids training programs.

Engineering Field Handbook, Chapter 16 - Streambank and Shoreline Protection (pdf. 8.5mb)
This is a large file and may take several minutes to download.
By the USDA Natural Resources Conservation Service. This guide focuses on riparian protection and includes a planning and selecting measures section, separate streambank and shoreline sections, and useful appendices. (This download may be lengthy.)

Engineering Field Handbook, Chapter 18 - Soil Bioengineering for Upland Slope Protection and Erosion Reduction (pdf, 3.4mb)
This is a large file and may take several minutes to download. By the USDA Natural Resources Conservation Service. This guide focuses on upland work and includes sections on integrated planning and design, soil bioengineering combined with geotechnical engineering, and nine different soil bioengineering techniques. (This download may be lengthy.)

Willow Clump Plantings (pdf, 1.23mb)
This technical note, by J. Chris Hoag and Daniel G. Ogle, covers willow clump harvesting and planting methods. Case studies are included as well.

Vertical Bundles (pdf, 1.01mb)
Another technical note written by J. Chris Hoag. Describes how to build and install a vertical bundle (a streambank bioengineering treatment to establish willows and dogwoods on streambanks)

Plant Species with Rooting Ability from Live Hardwood Materials for Use in Soil Bioengineering Techniques (pdf, 57kb)
By the USDA Natural Resources Conservation Service. This technical note includes a list of species to assist with selecting plants for use in the application of soil bioengineering techniques. The list may also function as a tool to indicate the performance of a species in a specific soil bioengineering technique in a specific region of the country.

How to Plant Willows and Cottonwoods for Riparian Restoration (pdf, 1.72mb)
Written by J. Chris Hoag. This technical note focuses on willow and cottonwood riparian restoration and includes guidance with regard to site assessment, species selection, care and preparation of cuttings, planting methods and much more.

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Native Plant Suppliers
Supplies, materials and equipment for erosion control and soil bioengineering use can be very specialized, and therefore, difficult to find. The following are some sources of: native plant supplies, erosion control products and services, and WSDOT approved products (WSDOT Qualified Products List).

Many of these products and services have not been tested or approved in any way by WSDOT. WSDOT does not endorse any particular products or service providers over others, whether they are included or not. This is not an exhaustive list, please contact the organizations below to add your product.


Native Plant Nurseries
Native Plant Resources for the Pacific Northwest from Metro King County's Department of Natural Resources' Water and Land Resources Division


Products and Services
Pacific Northwest Nurseries List from Tardigrade.org... a native plant - centered web organization

WSDOT's Qualified Products List


Soil Amendments
Soil conditions are the key to a successful revegetation or restoration project. Many times, soil properties must be changed by adding soil amendments. Information on some of these is listed below.


Compost

WSDOT Standard Specifications
WSDOT's compost specification falls under Section 9-14.4 of the Standard Specifications.

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