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Last Updated: Thursday, January 5, 2012 1:08 PM

Soil Stabilization Projects

Sediment from the bank is washed into a drain inlet along freeway.

Eroded soil becomes sediment when transported by water or wind. Caltrans is conducting studies to determine better soil stabilization methods that will keep excess soil and sediment from getting into the highway storm drain systems – and ultimately our waterways.

When highway runoff laden with sediment is discharged into rivers and lakes, aquatic habitat can be affected. For example, sediment that settles to the bottom of streams and rivers can bury salmon spawning gravel and prevent reproduction. Suspended sediment can cloud water and block the sunlight needed by aquatic plants for photosynthesis. In addition, other pollutants, such as herbicides, can attach to eroded soil in runoff and get transported into our waterways.

These soil stabilization studies are providing Caltrans with important information about Stormwater pollution prevention, and will be used to further refine the overall Stormwater Program.

Vegetation Establishment and Maintenance Study

This study will aid in developing guidance for effective establishment and maintenance of erosion control vegetation for short-term first growth as well as long-term establishment. The vegetation examined in this study will include both native and non-native species. Caltrans will use the results of this study in an effort to decrease erosion and thereby improve water quality.

There is a need to address both vegetation establishment and regular maintenance needs, including time of year for planting, plant selection, soil stabilization, and vegetation needs throughout the lifecycle. Performance criteria include stabilization within 30 days and mature, stable vegetation in one to three years.

Tasks in this study include:

  • Developing vegetation establishment guidelines for plant species used for hydroseeding slopes for short-term stabilization and long-term cover to minimize soil erosion
  • Running rainfall simulation tests to access vegetation establishment using Caltrans District 5 parameters

Statewide Erosion Control Review

This recently completed study reviewed current erosion control practices used by the Department, assessed their effectiveness, and made recommendations for modifications to Department erosion control and soil stabilization practices. It includes a comprehensive database for statewide site evaluations including, but not limited to, soils, vegetation, slopes, and existing technologies.

Tasks in this study included:

  • Identifying current erosion control measures.
  • Evaluating the effectiveness of these technologies.
  • Optimizing erosion control performance of materials by determining technology limitations.

Roadside Vegetated Treatment Study

Eight sites with vegetated slopes located throughout the state along Caltrans right-of-way are being monitored in order to improve contaminant removal from stormwater. Test results from this study will detail pollution removal in biofiltration strips, which are vegetated slopes engineered specifically to increase contaminant removal from stormwater by filtration through grass, deposition in low velocity areas, and adsorption into the subsoil. Design criteria for biofiltration strips generally requires relatively flat slopes, long strip length, and high vegetation cover.

Stormwater runs off roadways as sheet flow, and the slope, vegetation type, soil, and hydraulic loading rates of the right-of-way determine the amounts of total suspended solids (TSS), such as soluble metals and nutrients, that are removed.

Erosion New Technology Report

This report provides a review of new technology and products for erosion control and soil stabilization practices and to identify potential erosion practices and technologies for possible field testing. This study included developing a document that outlines current erosion control technology and products.

Tasks in this study included:

  • Identifying technologies currently used by Caltrans for erosion control.
  • Researching various sources of information about new erosion control products and technologies. The sources of information include, but are not limited to, professional publications, conference proceedings, agency specifications, past Caltrans erosion control review studies and product literature.

To view reports on this subject CLICK HERE

Caltrans is partnering with California State University, Sacramento, and California Polytechnic State University on these pilot studies.

FOR MORE INFORMATION CONTACT

Division of Environmental Analysis, Stormwater Unit
California Department of Transportation
P.O. Box 942874, MS-27
Sacramento, CA 94274-0001
Email: Division of Environmental Analysis, Stormwater Unit