After decades of research on erosion control technologies, those that use natural principles and restore or maintain natural capital — as ecosystems have done for millennia — may be the best option.
Bio-based products reduce the carbon footprint of site development, and are less subject to price fluctuations than petroleum-based products. Some use locally available natural materials that are indigenous to the bioregion, adapted to native plants, and biodegrade easily. Interest in sustainable infrastructure and buildings has created an economic incentive to choose organic and natural materials to control erosion. In addition to these benefits, research shows they also offer the best performance.
Reducing sediment and nutrients in site stormwater runoff is essential to establishing, protecting, and maintaining healthy plant ecosystems on land and aquatic ecosystems in surface waters. A University of Georgia research project evaluating compost blankets in conjunction with hydromulch on field plots concluded that they reduced soil loss by 80%, nitrate-nitrogen runoff by 98%, total nitrogen by 58%, and phosphorus by 83%.
In a follow-up study, the university reported that, after 4 inches of rainfall, compost blankets absorbed nearly 80% of the total rainfall, which reduced runoff leaving the field plots by 60%. By contrast, straw mulch reduced runoff by only 27%. The blankets also reduced runoff peak flow rates by 43%, while straw mulch's rate was 21%.
These are important parameters for site planners and designers working under low-impact development (LID), green infrastructure, hydrologic, or ecosystem restoration guidelines. Water quality results showed that compost blankets, as compared to straw, reduced soil erosion by 80% and both total suspended solids (TSS) and turbidity in the runoff by 90%. Owners and developers trying to comply with new U.S. EPA Effluent Limit Guidelines for Construction Site Storm Water Discharges will be particularly interested in these results.
The research also revealed that straw mulch increased nitrogen and phosphorus loads in site stormwater by 20 and 30 times, respectively, compared to the amount contributed by compost blankets. This is due both to increased runoff and the need to use mineral fertilizers to establish vegetation with straw mulch. Consider these results when choosing the best management practice for sites near water bodies, wetlands, sensitive watersheds, and total maximum daily load-designated waterway segments.
In California, San Diego State University evaluated the performance of the 20 most commonly used erosion control products, including single-net and double-net straw blankets, coconut fiber blankets, excelsior fiber blankets, compost blankets, tackifiers, polyacrylamide (PAM), and various combinations of these products. Each product was exposed to 2 inch/hour, 4 inch/ hour, and 6 inch/hour rainfall intensities on 2:1 (H:V) slopes.
Researchers concluded that compost blankets, either alone or combined with netting, reduced erosion and runoff more than any other product tested for each of the rainfall intensities evaluated.
In addition to their effectiveness, compost erosion control blankets (CECB) can contribute to credits in the U.S. Green Building Council's recently updated — from Version 2.2 to 3.0 — LEED building rating and certification program (see table). If the product is used in a new way or is critically important to the region's environment, the project can be awarded additional credits through the “Innovation and Design” and “Regional Priority” sections (new for V 3.0).
— Faucette (firstname.lastname@example.org) is research and design services director for Filtrexx Land Improvement Systems in Grafton, Ohio.
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