California Department of Transportation
 

Soil Rehabilitation

Soil Nutrients

Traditional approaches to erosion control and stormwater pollution prevention have often failed because the existing soil problems were not properly assessed and addressed. Compacted soils low in organic material and with low levels of nutrients will lead directly to impared plant health, limited plant growth, and non-sustainable vegetative cover, resulting in erosion and water quality problems.

The topics below identify key considerations to consider in the design of sustainable, long-term vegetative cover.

Problem Soils

Early identification of problem soils on a project site during the PID or PA&ED phase will alert the project development team of the need to budget for the appropriate stormwater quality and erosion control measures.  Typical problem soils found on Caltrans projects include decomposed granite, serpentine, sandstone, sand, silt, and clay.  It’s important to understand which problem soils are prevalent in your District, which of these soils have contributed to past slope failures and sediment run-off, and if there are any past erosion control treatments that have been successful in addressing the challenges presented by these soils.

The following video presented during the Advanced Sustainable Erosion Control course presents some of the key considerations when identifying and working with problem soils to design successful erosion and sediment control solutions.

 

 

Hydrologic Soil Groups

Hydrologic soil groups (HSGs) are classified as A, B, C and D and are defined by the minimum rate of water infiltration, primarily under saturated conditions.  When these soils groups are identified it provides the designer a better understanding of the infiltration and run-off characteristics of the project’s soils, which supports development of a sound strategy to achieve slope stability and revegetation.  Generally, Group C soils are the best soils to work with on construction sites.  These are made up of clay loams and sandy clay loams, and they tend to clump well which promotes slope stability.  Group C soils are considered some of the best soils for providing adequate infiltration with low run-off, and they are good at holding nutrients and water to promote vegetation.  Groups A, B, and D will require some level of amendments and in some cases geotechnical stabilization to ensure stability and revegetation.

The following video presented during the Advanced Sustainable Erosion Control course presents some of the key considerations when identifying and working with hydrologic soil groups to design successful erosion and sediment control solutions.

 

 

Soil Amendments

How to identify the proper quantities of soil amendments and fertilizer to add to help ensure long-term sustainable erosion control.

All sites have a minimum threshold level of nutrients that must be met for vegetation to establish and become self-sustaining. These nutrient levels can be restored by treating the project site with a variety of treatments, including topsoil, mulche, compost, as well as organic or commercial fertilizer. The process for developing a nutrient perscription typically follows the following event sequence:

  • Test Total Nitrogen Level - for reference and project site soils.
  • Identify Nitrogen deficiency in project site soils.
  • Determine nitrogen content and release rates of proposed amendments - Compost, Organic Fertilizer, and Commercial Fertilizer.
  • Calculate application rates of compost and organic fertilizer required to meet minimum threshold requirements.
  • Fill-out amendment application rates in project specifications.

Test Project Site Nutrient Levels

Soils should be tested by the erosion control designer as part of the project report and environmental documentation phase of work. Performing soils tests early allows the designer to include recommendations for the correct soil amendments to be included in the bid package for the Contractor.

The guidance below has been developed to identify methods of funding and executing the testing of soils for highway erosion control and planting projects.

Identifying Threshold Nutrient Levels

Identifying the threshold nutrient level (typically Nitrogen only) for a project site is a somewhat complicated, messy process. This process is well documented in the FHWA publication linked directly below, and it is suggested that designers follow this guidance to ensure sustainable vegetative cover that conserves water quality.

  • David Steinfield, Scott Riley, Kim Wilkinson, Thomas D. Landis, Lee Riley, et al. 2007. "Roadside Revegetation, An Integrated Approach to Establishing Native Plants" Accessed 2009-07-16

Calculating Nutrient Application Rates

Calculating nutrient application rates (typically Nitrogen only) for a project site is covered well in the publications linked directly below. Follow this guidance to ensure sustainable vegetative cover that conserves water quality.

  • David Steinfield, Scott Riley, Kim Wilkinson, Thomas D. Landis, Lee Riley, et al. 2007. Federal Highway Administration, US Department of Transportation, "Roadside Revegetation, An Integrated Approach to Establishing Native Plants"
  • Michael Hogan, 2009. "Sediment Source Control Handbook, An Adaptive Approach to Restoration of Disturbed Areas"

Prepare Project Specifications

Amendments can be added to a project site by using any one or combination of the erosion control treatments listed below:

External Links:

 

    Updated 04-14-2014