“Light Imprint New Urbanism” initiative is launched

Tom Low and others at Duany Plater-Zyberk & Company (DPZ) have created a matrix of more than 60 “Light Imprint New Urbanism” tools that can help new urbanists incorporate “sustainable” engineering methods into their designs. The “Light Imprint Storm Water Design Transect Matrix” indicates how the tools — which range from pervious asphalt to landscaped tree wells to bio-retention swales — can be used in settings across the urban-to-rural Transect. Low, head of DPZ’s Charlotte, North Carolina, office, presented the matrix at CNU XV in Philadelphia in May. A new CNU initiative on Light Imprint New Urbanism (LINU) has been formed to develop and exchange information on the topic. The tools can improve the ecological soundness of new urban developments (see Dec. 2006 and Jan.-Feb. 2007 New Urban News). Besides telling where the tools can be used, the matrix ranks the tools on cost of installation and maintenance. Organizers say a light-imprint strategy “significantly lowers construction and engineering costs, and allows for additional focus on conservation and environmental efficiency without compromising design priorities such as connectivity and the public realm.” The matrix is posted at www.cnu.org/node/1209. Low has compiled answers to frequently asked questions, some of which are condensed below: Q: What if a developer wants to stick to his detention-pond-behind-the-homes way of doing things? A: For most conventional developers, the current path of least resistance is “inlet, pipe, and pit.” We want to replace that method with “storage, swale, and filter” as a simple use framework. Q: A developer worries that neither the municipalities nor the homeowners will maintain bio-swales, rain gardens, etc., which will eventually lead to silt collecting in them. This reduces the drainage capability of the bio-swales and rain gardens, and leads to water collecting for more than 48 hours, possibly becoming a mosquito breeding ground and health hazard. A: Supportive developers have told us that they already spend a substantial sum on landscape maintenance to compete with the perfectly landscaped environs of the suburbs. Even they believe that the costs of folding Light Imprint New Urbanism into a regular maintenance program would be marginal. Our approach also distributes the rain gardens over a much larger area, resulting in better infiltration capacity and better evapotranspiration potential compared to a single detention pond. Since the system is distributed over the site, the health hazard and mosquito breeding potential of this approach will be less than with a conventional pond. Another set of benefits has to do with better aquifer recharge and better management of the retained water. Q: Pervious concrete and pavers can get caught up with silt and therefore need maintenance throughout the year. Who incurs that cost? A: As the benefits of Light Imprint New Urbanism become evident, we hope municipalities will take on more maintenance responsibility, recognizing this as a viable alternative to conventional engineering. Pervious concrete and pavers may require minimal maintenance. If they need to be replaced, this is easily done — on a small incremental basis. The City of Miami has installed turf blocks throughout the city in parking lanes, with successful results. Depending on the particular needs of a project, there is a wide range of tools with differing costs. Q: Another concern is drought. Plants that thrive on wet conditions will become dingy and brown and eventually die, thus needing replacement. A: Landscape aesthetics is very important. Designers need to do a better job of providing the right plant material for different situations. We want a selection of plants that would perform as well as those in other areas of the community. Recycled water can benefit the plants’ health. Xeriscape planting or plants requiring minimal irrigation are usually recommended. Maryland and other states and cities have identified indigenous plant material that can endure both drought and flood conditions and require minimal maintenance.