An in-demand speaker, Emily McCoy spoke at the NC Green Industry Council’s Water Symposium on Green Infrastructure and AmericanHort’s Cultivate ’15. She shared experiences with Andropogon’s Shoemaker Green project at the University of Pennsylvania in Philadelphia, a 2.75 acre SITES Pilot Project where she has partnered with the University to study site performance.
Based on actual performance, the rain garden cruised past expectations. The largest rain event, 3.16” (0.30”/hr) caused only 6” ponding, and there was no overflow. From its performance, the rain garden is capable of handing much more water than the 1”-storm that the City of Philadelphia’s stormwater model indicated it could handle, she said.
“The magic of green infrastructure is the capacity of plants and soils to do the work for us,” Emily said. Three years in, Emily and the team have a few of the early observations:
- Some plants are better at transpiring water than others—native floodplain species showed the highest relative transpiration rates (Nyssa sylvatica and Quercus biocolor have been standouts);
- Turf on un-compacted soil is also a transpiration workhorse;
- Holding more water in the root’s rhizosphere may allow more evaporation before anaerobic conditions develop in the rain garden;
- Rain garden soils show organic matter increases (perhaps due to use of compost tea);
- Salts are not a concern (they flush out in early spring) and alternative de-icing salts are working well;
- Performance during summer when plants are actively growing is greater than winter, indicating that stormwater system redundancy for winter months may be required;
- Overall, the site can handle three times more rain that its original design.
We need more research, she says. Which plants—trees, shrubs, perennials and grasses—manage stormwater the best? Can we breed plants that are stormwater workhorses? Performance data about plants currently being used for green infrastructure would help position plants within project specifications so that stormwater facilities and features are right sized, not over engineered. We also need to know which engineered soils perform over time and how maintenance and care of those affects performance.
North Carolina Green Industry Council Water Symposium presentation:
Cultivate ’15 handout:
NewTerrain newsletter July 30, 2015