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CHAPTER 7 DESIGN GUIDELINES
7.7.4 STORM-WATER BASINS & INFRASTRUCTURE Development has historically created large areas of impermeable surfacing in the urban environment causing environmental concerns in most municipalities in California. These include problems such as aquifer depletion, excessive surface runoff, flooding, erosion, and the pollution of rivers and other waterbodies. Regional agencies such as the Regional Water Quality Control Board have established strict regulations and policies that local agencies must follow. To comply with these policies, National City should adopt best management practices for storm-water capture and infrastructure for its public spaces and streets. A sustainable storm-water management system that captures and stores storm-water runoff could not only solve an array of environmental issues but also contribute to a greener urban environment that is more attractive to citizens and visitors. Runoff requirements should be integrated with urban forestry efforts throughout National City to boost water quality improvements, decrease runoff, and reduce the heat island effect. The aesthetic benefits of these strategies could simultaneously enhance National City’s image and improve its economic success. The two most established techniques for reducing the surface flow of water in urban areas, reducing impermeable surfacing, and slowing or capturing the surface runoff in landscape or other catchment devices, are both addressed in the following guidelines. For further information, consult the City’s storm-water standards manual.
7.7.4.1 Reducing Impermeable Surfacing The biggest factor affecting the quantity of runoff is the permeability of surfaces. To lower runoff quantity and to improve water quality, consider: A. All existing and proposed paved areas should incorporate permeable landscaped areas or a permeable surfacing material such as pervious asphalt/concrete, un-grouted pavers, grass pavers, tree grates, stabilized decomposed
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granite, or cobble to increase storm-water infiltration, sub-surface flow and aquifer recharge. Existing and future pervious asphalt and concrete surfacing should be cleaned periodically through dry-vacuuming and pressure washing treatments to preserve the water infiltration capacity of the surfacing. Without this periodic maintenance, the infiltration rates of permeable surfacing can decrease by 25 percent or more. B. Existing parkways and other landscaped areas should be preserved and expanded wherever possible. C. A permeable surfacing material should be used along gutters, at road edges, and as part of parking lot and street parking surfacing where possible. D. Street widths should be decreased where traffic flows allow to decrease impermeable surfacing and provide opportunities for planted areas, bike lanes, and other amenities. Pedestrian extensions, corner planters, bulbouts, and other pedestrian-friendly features can also be used to reclaim excessively wide streets at crossing points and intersections. E. Cluster development strategies which encourage the focusing of impervious surfaces and maximization of open space and permeable areas should be encouraged in new construction and development.
7.7.4.2 Capturing Surface Runoff Runoff should not be considered as a nuisance to get rid of. Water has beneficial uses, so it should be captured and used. Consider: A. All planted areas including parkways, bulbout planters, and medians should perform a storm-water detention or flow-through function through strategies such as bio-swales, detention ponds, percolation trenches, structural soils, or other methods.