The much-discussed and debated LEED v4 is set to roll out throughout 2013. I’m not sufficiently knowledgeable to write anything meaningful about earlier versions of LEED or their impact, although I’ve read enough to know they are mixed. Fortunately there are people out there eager to summarize and share the upcoming changes with the rest of us, and I have the people at Environmental Building News to thank for addressing some of the key ones. There are two that jumped out at me as being particularly relevant for those of us in green infrastructure:
1) New credit requirements to manage the 95th percentile of regional or local rainfall events direct LEED projects to address 95% of the average precipitation depth during a 24 hour period
2) LID tools are much more about mimicking pre-development hydrology than managing off-site flows (for example, rain gardens are preferred over swales)
In combination, it seems like these adjusted requirements encourage more truly sustainable site solutions. Specifically, ones that strike a better balance between managing both rainfall quantity and quality.
In a 2011 post, Diane Cameron of the Audubon Naturalist Society explained the eight basic hydraulic functions of forests and trees. These functions – interception, stem flow, leaf litter absorption, infiltration, evapotranspiration, hydraulic lift, groundwater recharge, and conveyance of large storms – are heavily degraded in urban environments. There are design solutions that can integrate them, however, even in ultra-urban sites defined by impervious paving. Green roofs, green walls, shade trees and forest protection/reforestation, soil decompaction, street trees, rain gardens, conservation landscaping and bioretention can provide many or all of these pre-development hydrologic functions, thereby diminishing the negative impact of polluted, “flashy” runoff on the surrounding environment and nearby water bodies.
Another item of note – not related to green infrastructure – was in the Materials and Resources (MR) category, where two new credits are available for publishing environmental impacts, even if the impacts are bad. So, they are rewarding transparency, regardless of how good or bad the information is, in the hope that improvements in materials sourcing and quality will follow. I have no idea how well that will work in practice, but I’m totally on board in theory and am curious about whether more responsible materials sourcing will result.