West Hills Innovative Stormwater Demonstration

Final Report, Chapter 5: Implementing Recommended Practices
Restored Soils

What is it? The practice of amending compacted soils by mixing compost and other helpful materials into them to restore their ability to manage rainfall instead of generate runoff.

Read important note on lawn modification at the beginning of Chapter 5.

See fact sheet on landscape types that you might like after compost amending including lawn, meadow, or a perennial garden with shrubs and/or trees. Each has a different capacity to reduce runoff so the "Restored Soils" practice description always includes a description of the final proposed landscape, such as "Restored Soils (from Lawn to Perennial Garden).

How does this reduce runoff and protect water quality? Restored soil areas temporarily aerate the soil and restore the soil biology that permanently aerate the soil, protecting watersheds with the long-term ability to infiltrate rain. Even if a lawn area is returned to lawn after amendment and receives foot traffic like mowing and playing, studies have shown that the larger soil animals (beetles, worms, etc) keep aerating the soil.

Figure 5-3 Regardless of whether the area will be lawn, meadow, or perrenial garden, following the guidance in the fact sheet will result in a similar, high functioning soil profile.
Figure 5-4 Areas recommended for restored soils back to lawn are intended to look the same after the stormwater retrofit is in place, as before. In other words, in project 23 above, the before and after pictures look the same.

Where can it be done?

  • Disturbed or compacted soils: Any soil that has been disturbed or compacted will benefit from compost amending, however existing landscape will be damaged and need to be replaced.
  • Avoid areas around existing landscaping: If existing landscaping is to be preserved, areas under tree canopies and around other plants should not be tilled as this will damage roots.

What’s the maintenance?

  • Reduce or eliminate irrigation, fertilizers, herbicides, & pesticides: Maintenance practices of compost amended soils are the same as any landscape area, however improved soil health should allow reduction or elimination of irrigation, fertilizer, herbicide, and pesticide use.
  • Yearly mulch application: Keep soil in landscaped garden areas covered with 2-4" of compost by mulching once a year. Aerate turf areas and top-dress with fine mulch.
  • Irrigation: Using natives, irrigate during the 2-3 year establishment period. See the supplemental fact sheet including information on establishment irrigation.

What are some cost considerations? This practice varies with the type of landscape you choose to plant on top (lawn, meadow, shrubs, and/or trees). Long-term irrigation demand can be cut by 50% with a payback period of 3-7 years. For more info on unit costs, see Appendix B

More info: Please see the “Restore Disturbed Soils”, which is very detailed fact sheet created for this project for more information on what it is and how to implement it. Also see the Challenging Sites Supplemental fact sheet for information on the final landscape choices (lawn, meadow, perennial gardens, and trees), establishment period irrigation, and reducing water demand.

Final Design: A landscape architect, landscape designer, and/or an arborist to choose native flowers, groundcover, shrubs, and/or trees as desired (more info here) and create a planting plan would be required to finalize the design of these projects. While these projects are unlikely to exacerbate existing landslide issues, if the FHHOA has any concern whatsoever, engage a geotechnical engineer to provide feedback on practices.

After amending the soils, the final landscape will be either lawn, meadow, or perennial garden. Since these landscapes have different runoff and sediment export properties, even though all the sites proposed for soil restoration are lawns now, what they will become matters in the model; therefore, the restored soils practice is actually broken up into three different practices as follows:

  • Restored Soils (from Lawn to Lawn)
  • Restored Soils (from Lawn to Meadow)
  • Restored Soils (from Lawn to Perennial Garden)

indicating that the final condition of the project will be either lawn, meadow, or perennial garden.

Figure 5-5 At project 51, bare soil can be seen to be streaking across the low point of this roadway and into the catch basin across the street. Compacted lawn and bare soils are on either side of a nicely landscaped area and are contributing this dirt.
Fig 5-6 Restoring the soils and changing the lawn to perennial garden (not pictured, but just on the other side of the existing trees) and planting unplanted areas (shown) are be surprisingly effective at reducing runoff, which will reduce the amount of sediment carried to Mill Pond.
Green Web Hosting! This site hosted by DreamHost. This web site is hosted by DreamHost, a friendly, greeny-type company.
created by: Green Girl Land Development Solutions LLC
Maria Cahill 2124 SE Woodward St Portland OR 97202-2155 (503) 334-8634
Updated 3 Sep 2014
DISCLAIMER: Green Girl Land Development Solutions LLC provides information for educational and outreach purposes only, to enhance the sustainability of sites. Unless adopted by the appropriate registered professional, information provided is not for construction.