Agenda - Planning Commission - 07/12/2018

Home

event) flooding is increasingly common due to both sea -level rise and recent coastal development. There is no specific point in time that sea -level rise will suddenly take effect and permanently inundate a community. Rather, in the hear to medium term, a gradual rise in sea levels will have cumulative impacts in the form of more regular nuisance flood- ing and more extreme coastal flood events. According to the National Oceanic and Atmospheric Administration's (NOAA) 2017 publication Global and Regional Sea Level Rise Scenarios for the United States, the intermediate -high scenario of14 inches of local sea -level rise by 2030 (which NOAA considers increasingly likely) will increase instances of damaging or disruptive flood- ing 25-fold over the present baseline. This means that regular inundation during high tides, more extreme inundation during king tides, and inundation further inland during and after tropical disturbances are the likeli- est impacts that communities will need to plan for. The good news is coastal communi- ties may already be experienced in planning for coastal flooding. The bad news is that future flooding is likely to be of the more regular, and more extreme, variety. Zoning is a convenient and effective means of addressing coastal flood adapta- tion. At the building or lot scale, the zoning code can ensure that new and existing buildings are permitted to adapt to FEMA floodplain regulations. The zoning code can also build in additional requirements for buildings both in and outside of the floodplain to encourage additional adapta- tion to potential future sea -level rise or more extreme flood scenarios. The zoning code can also serve to enhance the local pedestrian experience in the case of build- ing elevations or dry floodproofingthrough design standards and incentives built into the zoning code. To this end, Mandeville, Louisiana, has developed a series of design standards for the elevation of buildings in historic districts intended to mitigate against the visual and practical impacts of elevation, and ensure that the character of the community and the experience of the citizen are preserved. At the district scale, zoning can play a consid- erable role in directing and incentivizing development away from high flood -hazard areas and toward parts of the jurisdiction capable of support- ing growth. Whether through existing zoning districts, new flood - specific overlays, or some combination of the two, map and code changes can effectively mitigate against the impact of flooding upon the community. Nor- folk, Virginia, is deeply engaged in the use of zoning to direct devel- opment away from its highest hazard areas, particularly in light of local sea -level rise impacts. In many cases, some combination of the two above strate- gies may be necessary. Over the last five years, New York City has taken a comprehensive look at how local zoning regulations can best permit attractive, con- textual, and resilient as -of -right develop- ment, while developing ways to accommodate coastal retreat and dedensification in the highest risk areas. 11111111111111 0 Retaining the historic character even after home elevation was a driving force behind Mandeville's design regulations and guidelines. MANDEVILLE, LOUISIANA Mandeville, Louisiana, is a city of about 12,00o people located north of New Orleans directly across Lake Pontchartrain. Though initially settled in the mid-19th century, the city experienced explosive growth toward the end of the loth century with the comple- tion of the Lake Pontchartrain Causeway, a pair of 24-mile-long bridges connecting Man- deville with the outskirts of New Orleans. With growth came considerable challenges, particularly around flood hazards. Much of the recent development was typical of mid-century slab -on -grade development popular elsewhere in the U.S., and few were elevated to accommodate floodwaters. Likewise, many new residents were unfa- miliar with flood hazards associated with Lake Pontchartrain. Much of Mandeville is located within a FEMA Special Flood Hazard Area, meaning both the enforcement of NFIP regulations and purchase of flood insurance for mortgage holders is required. Hurricane Katrina significantly impacted Mandeville, with 9.5 feet of storm surge off Lake Pon- tchartrain resulting in 423 NFIP claims and local damage costs of nearly $24 million. The historic context of Mandeville poses particular challenges for flood hazard mitigation. However, existing precedent for elevated pre -causeway historic homes did point a way forward. The problem to solve is essentially twofold: How does the local zon- ing code interfere with elevation, and what design standards are necessary to mitigate the visual impact of elevation? These queS-, tions have wide applicability beyond historic districts. Height requirements in residential districts would likely preclude elevation in ZONINGPRACTICE 6.18 AMERICAN PLANNING ASSOCIATION I page3