This post is intended to serve as a brief review of the debate between site-based and context-based stormwater management practices in the United States, with an emphasis placed on the negative side effects of site-based stormwater treatment and the solutions presented by context-based stormwater treatment. Both sides advocate for a reduction in the levels of non-point source pollution, with the shared goal of a healthy watershed. However, stormwater treatment plays one of the most influential roles in determining the physical character of a city, and as such, requires to be considered along with its side-effects. Site-based stormwater management requires treatment of stormwater at its point of entry into the system, the parcel. This mode requires every parcel to include water treatment designs into the site plan, such as a holding area for wastewater, thus promoting a more spread-out urban fabric, suburban sprawl. Context-based stormwater treatment allows for a more flexible approach to stormwater management. Incorporating the urban context into stormwater management decisions allows for a more dense setting in an urban area while at the same time, allowing site-based water treatment for more sub-urban areas. By replacing on-site remediation requirements in an inner city with off-site treatment options, density can be preserved and promoted. The debate between site-based and context-based stormwater management is a debate between sprawl vs. urbanism.
After WWII, the emigration of returning service-members from cities to the suburbs in pursuit of the “American Dream”, coupled with affordable automobiles and a federally subsidized national interstate system, led to an explosion of low-density developments surrounding the American city. This new paradigm of suburban growth was subsidized by the federal government and still remains the dominant pattern of settlement in the United States. City administrators in the 1950’s began observing an increase in flooding and determined that an additional need for stormwater management policies that discouraged density and promoted open space due to a lack of pervious surface cover was necessary (Aurbach, 3). This was a shortsighted and misguided interpretation made by civil engineers in the mid- 20th century that we now know to be based on the assumption that all development is bad, which in reality a distinction must be made between bad growth (sprawl) and good growth (traditional urban).
These restrictions that promote low density development are still in place today, and along with a variety of water quality standards set by both the Clean Water Act in 1972 and through the Nonpoint Discharge Elimination System (NPDES), municipalities are forced to address the issue of non-point source pollution with little to no federal funding in a regulatory environment that promotes low-density sprawl. Site-based stormwater management is more affordable on the surface because of the tendency to compare water quality and volume on a per-acre basis rather than a per-capita basis. Due to the perceived cost savings, municipalities continue to revert to conventional site-based stormwater management practices (Keeley).
The importance of density
On a regional scale, building compact urban entities reduces the stress and fragmentation of the watershed caused by roads, infrastructure and impervious cover (Low et al., 1). The landscape, in its unaltered form, is best at dealing with stormwater. Natural wetlands are much better able to filter stormwater than a series of holding ponds. Higher density “saves open space, with its natural cleansing abilities” (Jacob, 34). These realities illustrate the need to conserve as much land as feasible from low-density development throughout the watershed. According to John Jacob, while per-acre, the pollutant load of runoff from a suburban development is less than that of a more dense development, more people live in the more dense development that consumes less land, therefore, the per-capita pollutant load is less than in a suburban setting. “Higher density actually reduces pollutant loadings per capita (and thus total loadings for a given population)” (Jacob, 34).
Almost just as important, the level of density does not have to be too high for the area to begin to espouse the benefits of density. The breaking point in terms of pollutant load per capita is between 16 and 24 dwelling units per-acre (DUA), similar to a residential neighborhood with attached townhomes, with a 50% reduction in pollutant load per-acre versus a suburban development with four DUA (Jacob, 38). The benefits of density are not limited to the freeing up of habitat and farmland around the city but also a host of other issues, including auto-dependence. “You can’t have walkability without proximity. But higher density also means more impervious surface cover per acre, resulting in a higher pollutant load per acre. Recent research, however, shows that 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” (Jacob and Lopez, 687-701).
The importance of context
Urban areas vary in density. Along the edge of a city, development may be less dense, while, downtown, development will be more dense. A same-size-fits-all approach when it comes to stormwater management does not work in all areas. Many cities in the United States do not recognize the need for discretion when implementing stormwater management policies and thus apply suburban drainage standards to an urban area, disfiguring the urban fabric of the inner city.
Developed by urban planners Andrés Duány and Elizabeth Plater-Zyberk, the rural-to-urban transect serves as a way to visualize the ascending levels of density in an urban environment.
“Based on environmental transect theory, the rural to urban transect can be used to integrate regional scales down to the block size, reconcile several different zoning codes in one watershed, and provide a technique for developing context-sensitive designs and regulations” (Crabtree, Deluca, and Vandaveer, 3).
By adopting form-based building codes as illustrated above, the process of developing stormwater management plans for communities across the country will fall into place. With the advent of an appreciation for the context in which infrastructure is to be placed by planners and civil engineers, a more effective and cohesive stormwater management plan can be enacted.
Stormwater Management Zones play the same role as the rural to urban transect mentioned earlier, but focusing on stormwater infrastructure. These zones, meant to coincide with the different transect zones, are able to better manage stormwater treatment in an urban environment than conventional suburban models.
According to John S. Jacob, “Stormwater is best managed at the watershed scale. It is watershed health, not the state of any one particular site, that should concern us most. Watershed health is directly related to the water quality of the receiving streams.” Due to the importance of ensuring the conservation of open land for stormwater remediation around a city, planners and policy makers must take necessary steps that will allow for more dense development in the urban center, and discourage low-density sprawl. When the goal is to reduce the pollutant load of a given population, the inverse relationship of density and pollutant load will serve to provide sufficient impetus for change.
Almost as important as open land, and in fact inextricably interconnected, the importance of designing stormwater management systems that respect the surrounding urban fabric is one of the main issues within the site-based vs. context-based discussion. In order to provide a pedestrian-friendly and environmentally sustainable urban experience, distinctions will need to be made between what would be beneficial and what would be detrimental to a traditional urban environment.
|A collection of bioswales along Gaines Street in Tallahassee FL do not treat runoff as well as a natural landscape would; if anything, they send a mixed signal to pedestrians and drivers, that the street is confused about whether it is located in the middle of a city, or running through a swamp. By attempting to address two issues in the same context, walkability and stormwater treatment, the street does not adequately address either.|
|The Water Conservation Areas of South Florida treat stormwater and runoff more effectively than an incoherent network of sub-par holding ponds and bioswales spread throughout suburbia and also help, to a certain extent, limit uncontrolled sprawl into the Everglades.|
Aurbach, Laurence. "Dense and Beautiful Stormwater Management." Ped Shed. 14 May 2010. Pg. 3. Web. 20 Apr. 2012.
Keeley, Melissa. "Using Individual Parcel Assessments to Improve Stormwater Management." Journal of the American Planning Association 73.2 (2007): 149-60. Print.
Low, Tom, Stephen L. Davis, Andrés Duany, Patrick Kelly, Guy Pearlman, and Georgio Tachiev. Light Imprint New Urbanism - A Framework for Urban and Environmental Sustainability. Rep. Chicago: Congress for the New Urbanism, 2008.
Jacob, John S. "Watersheds, Walkability, and Stormwater The Role of Density." Stormh2o.com. Jan. 2011. Web. 20 Apr. 2012.
Jacob, John S., and Ricardo Lopez. "Is Denser Greener? An Evaluation of Higher Density Development as an Urban Stormwater-Quality Best Management Practice." JAWRA Journal of the American Water Resources Association 45.3 (2009): 687-701. Print.
Crabtree, Paul, Joe Deluca, and Tracy Vandaveer. "A Perfect Storm for a Regional Watershed Management Plan." Www.stormh2o.com. May 2011. Web. 20 Apr. 2012. <http://www.stormh2o.com/SW/SWhome.aspx>.