Evaluation of Rolled Erosion Control Products and Seed Mixes for Vegetation Establishment on Slopes

About the report:

Because transportation construction projects often result in steep slopes with disturbed, bare soils that are sensitive to runoff and erosion processes, vegetation establishment is a continual challenge for transportation departments. The Virginia Department of Transportation (VDOT) regularly uses rolled erosion control products (RECPs) to mitigate erosion and provide an environment for vegetation to establish. RECPs range from erosion control blankets made of degradable natural or polymer fibers to non-degradable mats for permanent erosion protection. RECPs that promote rapid and reliable vegetation establishment help expedite environmental compliance for VDOT, a key criterion for project closeout for VDOT projects.

The purpose of this study was to (1) assess and compare the performances of RECPs in promoting vegetation establishment, (2) evaluate the performance of VDOT’s basic seed mix design when supplemented with specialty seed mixes such as pollinator and strip mixes, and (3) examine the influence of air temperature, precipitation, soil temperature, and soil moisture on vegetation establishment. RECPs were installed at four VDOT project sites, and vegetation was monitored across the spring, summer, and fall seasons. Evaluations of four commonly applied RECPs and three seed mixes were conducted on geotechnically stable 2:1 slopes with varying soil types. Selected RECPS included two degradable EC-2 mats (straw-based or coconut-based soil stabilization blankets) and two EC-3 mats (non-degradable plastic matting). An image analysis program was used to determine the percentage of vegetative cover.

Results showed that degradable EC-2 mats reliably supported vegetation growth and met permanent stabilization thresholds on 2:1 slopes, with EC-2 Type 2 (jute netting and straw fiber) reaching the 75% final stabilization criterion earliest and sustaining the highest percent cover across study sites. Findings pointed to two primary reasons for the superior performance of EC-2 mats, particularly the EC-2 Type 2: (1) soil temperature results indicated that the consistently higher temperatures in EC-3 plots contributed to slower and less consistent vegetative cover relative to EC-2 plots and (2) RECP material characteristics appeared to influence vegetation establishment. EC-2 mats, and the EC-2 Type 2 mat in particular, were more flexible and conformed better to uneven or rocky slopes, whereas EC-3 mats were more rigid, prone to folding and bunching, inhibited plant emergence in some areas, and required more careful installation procedures. This report recommends that VDOT prioritize the use of EC-2 Type 2 RECPs on 2:1 slopes in place of EC-3 mats because this approach would promote faster and more reliable vegetation establishment. Because of the lower purchase cost of EC-2 Type 2 compared with EC-3 mats, VDOT would save an estimated $400,000 during a 10-year period. However, the more important benefit of using EC-2 Type 2 mats is the reduction in reseeding or permit delays. This report also recommends that VDOT continue using its updated framework for seed mix selection, which includes options for pollinator and strip specialty mixes, with selections based on specific project goals.

Supplemental materials can be found at https://library.vdot.virginia.gov/vtrc/supplements

_{Disclaimer Statement:The contents of this report reflect the views of the author(s), who is responsible for the facts and the accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Virginia Department of Transportation, the Commonwealth Transportation Board, or the Federal Highway Administration. This report does not constitute a standard, specification, or regulation. Any inclusion of manufacturer names, trade names, or trademarks is for identification purposes only and is not to be considered an endorsement.}

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