Erosion Control Toolbox: Preserve Existing Topsoil
Preserving existing topsoil is an effective method to establish vegetation because it typically contains ideal physical, chemical and biological properties to do so. The existing topsoil is obtained within the project limits and includes excavating, stockpiling and placing topsoil on areas disturbed by construction activities.
When to Use This Treatment
Typically applied on slopes 1.5:1 (H:V) and flatter. The following application rates are suggested:
- Slopes 1.5:1 (H:V) - 2" maximum thickness
- Slopes 2:1 (H:V) - 3" maximum thickness
- Slopes 3:1 (H:V) - 4" maximum thickness
- Slopes ≤ 4:1 (H:V) - 6" maximum thickness
Caltrans Highway Design Manual Topics 110.2(2) and 110.2(4) (PDF) recommend considering the use of existing topsoil to treat disturbed soil areas for improved stormwater runoff quality.
- Reduced stormwater runoff volume and velocity
- Improved infiltration rate
- Improved soil water holding capacity
- Improved soil structure, porosity and texture
- Improved soil chemical properties - providing proper pH, carbon, nitrogen, potassium and phosphorus levels
- Improved soil biology - activity by bacteria, mycorrhizal fungi, nematodes, protozoa, microarthropod and earthworms
- Improved soil nutrient levels and nutrient cycling
- Improved potential for vigorous long term vegetation coverage
- More costly and effective than surficial treatments such as Erosion Control (Hydroseed)
- Requires temporary storage space within the project limits to stockpile materials
- Requires site accessibility by earthwork equipment
- Read Standard Specifications Section 19-2.03D Selected Material, which defines Selected Material in Section 19-2.01B Definitions. Note that all the requirements in Section 19-2.03 Selected Material apply to Preserve Existing Topsoil.
- Because Preserve Existing Topsoil is specified as "Selected Material," it is paid for as Roadway Excavation (Topsoil). Include bid item Roadway Excavation (Topsoil) in the Bid Item List.
- Show the areas to be excavated, stockpile locations and areas for topsoil reapplication on the layout or grading plans.
- Include Standard Special Provision 19-2.03D(2) Topsoil in the SSPs for the project.
To provide protection for the soil surface, consider combining this treatment with:
- Preserve Existing Topsoil should be specified as Selected Material
- Per Caltrans Standard Specifications Section 19-2, Selected Material is paid for as Roadway Excavation. Use Bid Item 190123 Roadway Excavation (Topsoil)
- Caltrans Highway Design Manual Topic 110.2(2) and Topic 110.2(4)
- California Department of Transportation, Environmental Analysis, May 2005
Updated: February 25, 2019