Agenda - Planning Commission - 12/02/1997

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I :!!I ~) ~I L_____ and site plan reviews in flood hazard areas; which are the focus of Subdivision Design in Flood Hazard Areas. Often, however, the land involved in such proposed developments is a mixture of both upland soils and floodplain. While it is always possible to reduce density in a floodplain with high minimum lot sizes, that approach does not address the fundamental problem of where buildings are actually located. Both the PAS Report and a number of good FEMA publications, however, contain excellent illustrations of how site plan and ,--..,~.. subdivision review can be used to minimize structural intrusion into the floodplain while preserving the development value oflarge sites containing flood-prone property. One common means of accomplish- ing this is to reduce density through larger lot sizes and to require building placement on the lots to be at higher elevations. For nonresidential or Cluster Plan: All floodplain lands and other sensitive lands kept as open space; net density remains equal to conventional plans; lot sizes reduced to protect natural features; all homesites are on natural high ground. CLUSTER PLAN A Matter of Design As the Wake County requirements suggest, the larger the encroachment into a floodplain, the greater the need for strict oversight of the resulting development, if development is allowed at all. The same logic applies to subdivision controls >3-. multifamily apartment buildings, this is largely a matter of build- ing configuration, elevation, and/or floodproofing to be considered during site plan review. The floodplain management ordinance can specifY standards for accomplishing these goals. For residential development, however, clustering is receiving growing attention as an alternative solution. For example, a 100-acre site might contain 36 acres within the regulated floodplain and 64 outside, with the latter varying from slight elevation above BFE [0 those with insignificant flood potential or none at all. Residential development can be concentrated in smaller lots on higher ground, while an easement can maintain most or all of the floodplain lands in permanent open space (see illustration). Wetmore observes, however, that including such development restrictions for flood-prone land in the ordinance may be essential in order for the community to qualify for CRS credits because FEMA will want some clear indication that this approach will not yield greater density in the future. The best overall guide to the concept of cluster development is probably Randall Arendt's Conservation Design for Subdivisions (Washington, D.C.: Island Press, 1996). His treatment of the use of conservation easements in subdivision design can be applied as profitably [0 floodplains as to any other environmental resource. Arendt specifically recommends in floodplains the use of internally transferable development credits, which would allow the developer [0 regain on high ground the development credits being sacrificed in flood-prone pares of the overall site. In floodplains, however, the issue in subdivision design is not purely one of lot configuration for conservation purposes; it is a matter of public safety. As a result, planners need to consider . 'l-. .. ~,'''' ,I ,..; Il ','...>. YJ t....i'f ':~.::;:-'~ ~~ :~?J . .':..~:. '. .~- ,~t~ . ~,~ Ct. ,.,.' .>J:" )~', ti ...,..... '. ~ -, ~ 3 :;- 'f" ~'... f"