Raining downtown, and that’s just fine. Photo by bobtravis.

Virginia is updating statewide stormwater regulations. A draft is open for public comment until August 21, 2009. Some people are concerned that the stricter caps on nutrient loads, as currently written, will promote low-density development and ultimately hurt the water quality and quantity of runoff in the Chesapeake Bay watershed.

Here’s a simple but realistic hypothetical scenario. Developer A wants to develop 100 dwelling units on 1,000 acres of land, and developer B wants to develop 100 dwelling units on 10 acres of land. Developer A will only need to cover 10% of her large site with impervious surface, while developer B will need to cover 70% of her small site with impervious surface. Developer A assumes that 100% of residents will use an automobile for transportation, while Developer B assumes 50% will primarily walk or use transit. Therefore, Developer A’s project will require twice as many parking spaces and approximately twice as much road width in the region, but will accommodate most of the parking off-site.

Under the stormwater regulations being proposed, Developer A will likely score an A+ with a pass to move forward, while Developer B will fail. This is because the standards are determined, site-by-site, on a per acre basis and not a per unit basis. Developer B may have the option of purchasing off-site water quality improvements or implementing a set of BMPs to offset the damage she is incurring, but she takes a hard look at her balance sheet and decides to join developer A as a business partner. What benefited the individual acres of the sites in question clearly was an overall loss for the watershed as a whole.

And considering opportunity costs makes the situation even dicier. What if these developers bypass infill redevelopment of an industrial site for a more compliant and cheaper greenfield development? (Stormwater controls will generally be more expensive for redevelopment than new development). Now you have impervious surfaces in two places, instead of one.

The economic market analysis, conducted for the Department of Conservation and Recreation by a Virginia Tech professor, bears this out in more detail.

Based on this site-by-site method, low density developments would produce less estimated phosphorus runoff than medium or high density areas. Very low density developments (1 dwelling unit per 3 to 5 acres) would unlikely face any water quality control requirements. Yet, on a watershed basis, low-density (“sprawl”) development increases dependence on auto transport (thus increasing emissions and roadway impervious surfaces). Highly impervious areas accompanied by dense population settlement can produce net water quality improvements, independent of whether stormwater controls are implemented ... Higher phosphorous control costs in high density developments create financial disincentives that may work at cross purposes with larger watershed objectives.

I’m no hydrologist. Most of the science and bureaucratic mechanisms behind this policy are pretty bewildering, and I don’t really have the time to try to figure them out. Furthermore, I thought it might be safe to assume that as glaring a potential problem as this is, somebody in the state offices must be working to sort it out. Then I read this comment from a member of the Technical Advisory Committee that helped craft the policy:

Stormwater management seeks to replicate the water quality and quantity benefits that are provided by a natural, undeveloped landscape. Development that contains more natural landscape (e.g. rural dev.) will consequently find it less costly to comply. This is not a fault of the stormwater management regulation; it is a natural consequence of the hydrologic cycle.

In other words: That’s life. Deal with it. He went on,

Stormwater codes should be judged on how well they manage runoff quantity and quality, not how well they do or don’t control growth ... Smart growth codes should be judged by how well they control sprawl.

This is where the trouble lies. Sometimes genuinely smart and well-intentioned people err by focusing intently on the piece of the puzzle they have been commissioned to solve, thereby missing the larger system within which their problem is embedded. It’s the classic widen-the-freeway-to-reduce-congestion scenario. It may solve the technical problem at hand, but it exacerbates the real problem.

The fact is that stormwater management and Smart Growth have everything to do with each other. Treating them separately and pitting one against the other is a losing game for both water quality and growth of development.

This was demonstrated pretty convincingly by a 2006 EPA report. Here are the three scenarios proposed by the study:

From the U.S. Environmental Protection Agency, Protecting Water Resources with Higher-Density Development.

They put this model to empirical tests and mined numerous other studies to back up their conclusions. Once again, the crux of difference:

The results indicate when runoff is measured by the acre, limiting density does produce less stormwater runoff when compared to the higher-density scenarios. However, when measured by the house, higher densities produce less stormwater runoff.

They show that this is the lapse in logic that lead so many regulatory agencies to assume that sprawl is good for controlling stormwater runoff:

Many communities assume that low-density development automatically protects water resources. This study has shown that this assumption is flawed and that pursuit of low-density development can in fact be counterproductive, contributing to high rates of land conversion and stormwater runoff and missing opportunities to preserve valuable land within watersheds.

And this report focuses exclusively on quantity of water runoff. If you look at the issue of quality and factor in the introduction of pollutants such as motor fuels, de-icing chemicals, vehicular exhaust, lawn fertilizers and pesticides, faulty septic systems, and more into the water supply, the case against promoting low-density development grows and grows.

Let’s not strike out on this one.

Crossposted at Discovering Urbanism.