Using form-based codes for watershed protection

Berg, Hannah and Todd BenDor.  2010.  “A Case Study of Form-Based Solutions for Watershed Protection.”  Environmental Management  46:3 September 2010.  pp. 436-451.
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Despite numerous policies at  the federal and state level aimed at regulating stormwater discharges, engineered solutions enacted by local governments often fail to meet water quality standards (Albrecht 2005;  National Research Council 2008).

Land-use planning strategies to direct the location, rate, and extent of urban development are often overlooked as critical initial steps to improving water quality (Clayton 2000).  Dispersed patterns of development lead to increased per-capita impervious surface levels, thus diminishing the land's ability to absorb and treat water naturally (NALGEP 2003).

Although planner have begun to recognize that sustainable planning techniques...are aligned with stormwater management...many local governments lack ordinances and codes through which to fully integrate stormwater into broader urban planning processes.

Describes potential for form-based codes...especially reducing sprawl and requiring site-specific standards like vegetation or building placement.

A growing literature has long demonstrated a clear linkage between impervious surface cover and water quality at the watershed scale (Dunne and Leopole 1978; Schueler 1994; Arnold and Gibbons 1996; NRDC 2000; EPA 2008b).

While minimizing the impacts of development in areas adjacent to water supplies is vital, large lot, low-density development is often misconstrued as low-impact development (EPA 2006).    Form of development important, too.

While BMPs such as rain gardens, cisterns, and bioretention ponds help to mitigate stormwater impact of new development, they do little to address the broader issue of unsustainable development patterns (Hirschman and Kosko 2008; Low Impact Development Center 2008).

Link between sprawling development patterns and declining water quality (Arnold and Gibbons 1996; Knaap 2002; EPA 2004)

...Some evidence, however, indicates that new urban site design may have some advantages over conventional low-density development in protecting water resources. For example, Berke and others (2003) found that new urban, greenfield developments pave over less land, use more BMPs, and protect and restore more sensitive areas than conventional developments. A study in Charleston, South Carolina compared runoff impacts of a conventional low-density development scenario to a new urban development scenario in the same watershed (South South Carolina Coastal Conservation League 1995). Results indicate that for the same amount of development, the conventional neighborhood consumed eight times more land and generated 43 percent more runoff, three times more sediment, and markedly higher nitrogen and phosphorus loadings. However, Girling and others (2000) found that new urbanist developments are only effective at better managing peak flow when they are clustered on sites in way that protects hydrologically sensitive open spaces.

Stormwater Best Management Practice Standards
Additional components can be included in a form-based code to address community-specific needs, including specific standards for stormwater management. Mitigation through BMPs should be considered a final alternative, after managing growth to avoid sensitive areas and designing neighborhoods and parcels to minimize the amount of impervious surfaces. Stormwater standards could mirror those set forth in existing BMP manuals that describe appropriate environmental conditions for proper function of a given BMP (examples include soil drainage, depth to water table, steep slopes, space requirements, etc.; NCDWQ 2007d). In this respect, BMPs could be added to the transect model, showing BMPs that fit into the specific character of each zone (Table 1). For instance, grass swales and large dry pond detention basins may be appropriate in some zones, but certainly not in the most urban areas.
The space required and the costs of installing and maintaining many BMPs are high. Moreover, BMPs can be ineffectual at slowing water flow and filtering pollutants beyond their engineering specifications (EPA 2009a). Therefore, the integration of BMPs into a broader framework of watershed protection is crucial. Table 2 summarizes how each component of a form-based code fits within a larger watershed protection framework to avoid sensitive areas, minimize impervious coverage, and finally, mitigate the impacts of development using stormwater BMPs.

Table 2 Summary of form-based code components and watershed protection framework
Strategy FBC Component Effects on Watershed
1) Avoid sensitive areas  - Regulating Plan
• Assign transect zones based on ecological factors
• Designate high intensity districts away from wetlands, riparian habitats,
highly erodible soils, steep slopes, etc.
2) Minimize impervious coverage - Public Space Standards; Building Form Standards
• Design street width according to context
• Match the variety of civic spaces with the activities and the intensities they are used for
• Require sidewalks only where appropriate
• Minimize lot widths
• Allow mixed use
• Allow for shared driveways
3) Mitigate development impacts - Stormwater Standards
• Match BMPs with appropriate environmental conditions and development context

Although advocates assert that form-based codes present a viable environmental alternative to traditional zoning practices, a more explicit integration of watershed protection into the code’s framework would strengthen their argument. To accomplish this, the literature suggests a four pronged approach: (1) design a regulating plan at the watershed level, designating different zones of urban intensity based on their relationship with vital ecological features; (2) create public space standards for streets and civic spaces that both reduce impervious surfaces where contextually appropriate and contribute to a high quality public realm; (3) outline building form and lot standards that preserve permeable surfaces or, depending on the transect context, cluster permeable surfaces together in order to preserve permeable open spaces; and (4) outline suitable stormwater mitigation devices for each transect zone.