Improving stormwater management in Vermont, New York, and New Hampshire

By Elissa Schuett, Rebecca Tharp, and Grant Taylor, Lake Champlain Sea Grant

The Green Infrastructure Collaborative, a partnership between the Lake Champlain Sea Grant and the Vermont Department of Environmental Conservation, sponsored a trip to the University of New Hampshire (UNH) Stormwater Research Center. Engineers, landscape designers, researchers and state agency employees from Vermont, New Hampshire, and New York attended the tour to learn about green stormwater infrastructure design, implementation, and maintenance practices. 

The UNH Stormwater Center is nationally recognized for their research on Green Stormwater Infrastructure (GSI). Technologies used by the research center and discussed during the tour included bioretention, subsurface gravel wetlands, hydrodynamic separators, and tree pits.

Some of the key takeaways from the tour are:

• Subsurface gravel wetland vegetation must be completely harvested every three years to avoid Phosphorus loading from decomposing plant material. This should be a standard component of any maintenance plan for these systems, particularly if nutrient removal is the primary goal.

• Undersized gravel wetland installations perform better in the field than models suggest. At year two, performance of a retrofitted quarter sized system far exceeds expectations with the close to full-size phosphorus reduction. In space-constrained urban areas, installing designs that are below optimal size can have significant impact on reducing pollutant loading.

• Manufactured hydrodynamic separators – flow-through structures that mechanically remove particles from stormwater – exhibited no better (and in some cases worse) nutrient and total suspended solids (TSS) removal than basic catch basins. (See detailed data in table below)

• Successful bioretention and/or gravel wetland installations can serve as important seed sources for new installations. The UNH team gather perennial seeds from existing installations to spread on new sites for the best germination rates. Further, the group takes water samples from past projects to seed new sites with the active organisms needed for optimal system performance.

• Planting plans should carefully consider location and aesthetic goals. In some cases, mowed grass can have comparable removal rates of pollutants, to that of native ornamental plants, and may have preferable maintenance regimes. 

Following the tour Becky Tharp, Program Manager for the Green Infrastructure Collaborative, has continued to work with local organizations and state employees to facilitate the connection between researchers and government agencies. The knowledge gained from the research center has provided valuable information to Lake Champlain Sea Grant partners, including being used in rewriting the State of Vermont stormwater manual.

Connections and partnerships are an important part of Lake Champlain Sea Grant, providing users with up to date information and research for best practices that community organizations wouldn’t get elsewhere.