Is Denser Greener? An Evaluation of Higher Density Development as an Urban Stormwater‐Quality Best Management Practice¹

Abstract

A simple spreadsheet model was used to evaluate potential water quality benefits of high-density development. The question was whether the reduced land consumed by higher density development (vs. standard suburban developments) would offset the worse water quality generated by a greater amount of impervious surface in the smaller area. Total runoff volume and per acre loadings of total phosphorous, total nitrogen, and total suspended solids increased with density as expected, but per capita loadings and runoff decreased markedly with density. 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.(KEY TERMS: urban areas; watersheds; urbanization; water policy; modeling; best management practices; stormwater management; watershed management.)

Evaluating the Impact of Low Impact Development (LID) Practices on Water Quantity and Quality under Different Development Designs Using SWAT

“…Before applying LID practices to urban developments, UHD land use might be the best choice for minimizing the impact of urbanization on surface runoff and pollutant loadings, as shown in other studies [17,18,35]. Jacob and Lopez [18] mentioned the advantage of higher density development outperforming traditional stormwater BMPs in pollutant reductions, due to the decrease of a runoff-generating area. However, after the application of LID practices to urban developments, all post-LIDs scenarios performed better than the UHD scenario (Table 5).…”

“…Seo [17] investigated how the amount of runoff and pollutant loadings were generated differently under three different urban planning designs and presented the compact high-density urban type as the most effective urban type. Jacob and Lopez [18] also evaluated the benefits of high density development for the reduction of water quality loadings in comparison with standard suburban developments, mentioning it as an effective approach more than traditional BMPs under their study conditions. Such studies imply that the effects of the application of LID practices could vary with different urban patterns.…”

Sources, Fate and Effects of Contaminant Emissions in Urban Areas

“…Well-planned urban areas potentially can support the lowest per capita quantities of chemical emissions possible for human settlements (e.g. Jacob and Lopez, 2009). Thus, urban areas can be managed to minimize environmental impacts, outside obvious point source regulations.…”

Modeling Sewer Overflow of a City with a Large Floating Population

“…They also reported that combined sewer overflow (CSO) and stormwater effluents contribute 4 to 23% to the indicator bacteria concentrations of the Tama River. A simple spreadsheet model was used to evaluate potential water quality benefits of high-density development in the United States [36]. They concluded 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.…”