It’s become an axiom of stormwater management that denser is better. Although at first it may seem like a contradiction, densely populated urban neighborhoods—impervious though they may be—produce less runoff, and fewer pollutants, than would the same number of people living spread out in suburbia with the many roads, driveways, and rooftops of single-family homes that the suburbs entail. As John Jacob writes in his Stormwater article, “Watersheds, Walkability, and Stormwater,” “Ten percent imperviousness is obtained with as little as one house per 2 acres, and 25% imperviousness with as few as one to two houses per acre.” He also notes, “The kind of densities required for walkable urbanism may actually translate into less of a pollutant load, on a per capita basis, than that from an equivalent population at lower, suburban densities, and therefore less of a total pollutant load for a given population.”
This logic is now informing urban planning in many places, with an emphasis on infill development and on preserving open spaces within a watershed while concentrating development in a smaller area. But not everyone sees the value in that. A recent article in the Wall Street Journal, “In Praise of Urban Sprawl,” looks at the picture from another angle.
The article reviews a book called The Human City: Urbanism for the Rest of Us by Joel Kotkin, in which the author vigorously defends suburban expansion. His reasons are primarily economic ones; he points out that not only most residences but by now most jobs as well, are located in the suburbs. He also maintains that suburban living is more family-friendly (San Francisco has 80,000 more dogs than children), and that revitalized city centers in the US are becoming unaffordable for all but the very wealthy.
People have many reasons other than stormwater management, of course, to favor denser urban development, including an abundance of mixed-use communities, access to public transportation, and—as Jacobs notes—walkability. Some cities like Seattle rate the walkability (and bikeability) of their various neighborhoods. But a great many people also have strong preferences for the amenities of suburban life, something to which several generations of Americans have aspired. The author of the WSJ review, himself a professor of city planning and leader of the NYU Expansion program, extends the discussion to developing areas outside the US whose populations are growing more rapidly, and where people are flocking to the cities faster than the expansion of those cities is being thought out. “On average, the land area of cities in less developed countries can be expected to triple by 2050,” he writes. “Like the farsighted planners of New York City, we need to imagine and shape the urban areas of the world to organize their form even before anyone moves in.”
Stormwater management might be only a small part of the discussion, but one that should be considered. How does it fit into urban planning and municipal codes in your area?
