Strong Towns Critique of LID
May 16, 2012 § 2 Comments
Creek Freak has written about LID – Low Impact Development. It’s basically a sort of “green building” standard that requires new buildings to detain and/or infiltrate rainwater. While I think that LID is a step in the right direction, at least compared to development as usual, it’s nowhere near the end of the work on getting to healthy creeks and streams.
I read a good concise critque of LID (also LEED and green building in general) at Strong Towns today. Strong Towns is a site I’ve been enjoy a lot lately; it’s written by an engineer who has a lot of common sense. He mostly critiques heavily car-centric development patterns.
Here’s an excerpt from Strong Towns on LID:
I see LID being applied almost exclusively to new projects, which are largely themselves on greenfield sites. The stormwater ponds and other such approaches are used to mitigate the negative impacts of the development. This is a sub-optimal outcome because, in almost every instance I have ever seen, the development is the result of a series of government policies that favor greenfield development.
Read the full Strong Towns critique here. I think I am going to track down the The Original Green by Steve Mouzon. See also my earlier parenthetical musings on limitations of LID, and LEED critiques in Green Metropolis by David Owen (mentioned briefly in this earlier overly-long post.)
My problem with LEED has been that it more heavily weights good products than good design. For instance, you get points for efficient windows and points for efficient mechanical, but you only get a couple of points for the overall design So if you design with no south facing windows, overhangs, east and west facing baffles, etc that only gets treated like using insulated glass even though the impact can be far greater.
I noticed that too, back when I was still working in architecture, and – at the risk of sounding too cynical – was disillusioned by what I saw as cooptation of sustainability by catering to corporate interests, emphasizing a products-based approach over, as you say, design. I was pooh-poohed a lot for raising that point at the time, and so have kept my distance from the issue.
The post makes an interesting point about the limited lifespan of permeable pavements etc. I was recently at a site that had been paved with permeable asphalt, and someone in passing observed that permeable asphalt is so efficient at absorbing runoff that even after it’s been silted in it will still absorb rainfall for pretty significant rainstorms (I can’t recall the exact storm event, I think it exceeded a 10-year storm). What’s a reasonable lifespan for an infiltration-based treatment?
My concern with LID is that it may not account for the variability of a watershed and its soils – nor, if applied truly across a watershed, account for the need for channel forming flows in natural streams and rivers. The goal in my opinion wouldn’t be to retain all flows, and certainly not channel-forming flows, but to address the rates of runoff and mimicking natural “background” rates of infiltration while improving water quality. An old post, Going Bananas over Water Quality in Orange County, discusses this and related concerns. https://lacreekfreak.wordpress.com/2009/09/08/going-bananas-over-water-quality-in-orange-county/
But, short of addressing legacy and industrial pollutants, one of the best ways to improve the water quality for the majority of our pollutants (urban runoff) will be to remove the concrete and reestablish natural processes in our actual streams. Streams naturally do all the things that biotreatment does (biotic and chemical processes, infiltration, biofiltration, floodplain storage and detention…etc). So why isn’t this the primary approach?