Denser development reduces watershed impact

Benefits of smart growth

Elizabeth Campbell, Jun 15, 10.

Findings by a Houston researcher suggest that compact neighborhood development built to a walkable scale reduces the amount of pollutants that end up in watersheds due to stormwater runoff, writes Kaid Benfield. The report, written by John Jacob, the director of the Texas Coastal Watershed Program and Ricardo Lopez, a faculty member at Baylor College of Medicine, “quantifies the per-capita impacts of different residential densities on watersheds, finding that the benefits of relative density (compared to sprawl patterns) begins at around 8 units per acre, increase substantially up to around 32 units per acre, and then continue but at diminishing rate of increase after 64 units per acre. “

The study reports:

For a constant or given population, then, higher density can result in dramatically lower total loadings than more diffuse suburban densities. The model showed that a simple doubling of standard suburban densities [to 8 dwelling units per acre (DUA) from about 3 to 5 DUA] in most cases could do more to reduce contaminant loadings associated with urban growth than many traditional stormwater best management practices (BMPs), and that higher densities such as those associated with transit-oriented development could outperform almost all traditional BMPs, in terms of reduced loadings per a constant population.

Because higher density is associated with vibrant urban life, building a better city may be the best BMP to mitigate the water quality damage that will accompany the massive urban growth expected for the next several decades.

While some have thought stormwater regulations to be discouraging of such dense development, this study confirms that it is better, in fact, if water quality officials encourage the development of communities with more walkable and transit-supportive densities.

Dr. Jacob will report on his findings at Houston Tomorrow’s Livable Houston meeting on Wednesday, June 23, at noon at the Houston-Galveston Area Council.
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