Agenda - Planning Commission - 04/07/2016

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buffers. White the minimum width needed depends to some extent on what benefits or ecosystem services are deemed impor- tant by the community, virtually all sources recognize that the wider the buffer the bet- ter the ecosystem services performance. • Inventory riparian areas as part of the sub- division process and preserve unimpaired riparian areas in natural conditions. • Require restoration of impaired riparian zones as a condition of subdivision ap- proval. LAYOUT AND DESIGN Cluster subdivisions are one of the most well- known techniques planners use to address many of the needs for better preserving the natural landscape and its functions. A cluster subdivision allows for the modification of dimensional requirements of the zoning law to group or "cluster" structures or lots at a higher density on the most suitable portion of land, leaving other areas open to preserve the natural and scenic quality of open lands. A conservation subdivision is a type of cluster subdivision that focuses on protecting large portions ofa site with important environmen- tal value. Usually, half or more of the site is preserved as open space. From a flood risk perspective, there is no other approach that has as much ability to reduce flood damages while simultaneously protecting the integrity of the floodplain ecosystem. PAS Report No. 473 recommends conservation subdivisions with no lots in the floodplain as the best policy for communities. Nothing has changed since 1997 to alter that view. However, some communities may have more difficulty implementing such an approach due to their geography or the fact that any remaining developable land is at higher risk from flooding. Here are the basic principles of conser- vation subdivision design that also apply in reducing flood risk and enhancing natural floodplain functions: • Ensure that floodplain areas are nonbuild- able, either laid out as areas that are non - buildable on lots, or set aside as reserve areas entirety (not contained within lots).. • Preserve riparian areas in perpetuity by making them reserve areas protected through permanent easements. This, in turn, protects or enhances the conservation of wildlife and aquatic resources. • Use smaller lots. • Allow for increasing density in developable areas to ensure a roughly equivalent lot yield that would otherwise be allowed if a more conventional subdivision design was applied to the site. • Be flexible in reducing setbacks from roads and increasing setbacks from floodplains or water bodies. Communities can accomplish this by prohibiting creation of new lots in the flood - plain and requiring that any flood -prone land not be included in any lot. Theycan also require that floodplain land be set aside as designated open space on the subdivision plat and preserved in perpetuity through permanent easements. If floodplain develop- ment is unavoidable, they can require that all lots created have adequate buildable area on natural high ground above the ioo-year base flood elevation. They can also require a flood protection elevation of at least two feet above the ioo-year flood elevation for any buildings or improvements on a lot, a standard used by Portland, Oregon. Finally, they can ensure that conservation subdivision submittals are meet- ing the following three goals at a minimum: • Protecting natural streams, water supplies, and watershed areas • Maintaining and enhancing the conserva- tion of wildlife, natural, or scenic resources • Promoting conservation of soils, wetlands, and other significant natural features Other considerations in layout and design include restrictions on problematic uses (e.g., storage or production of hazardous materials), dedication of land areas for public facilities and services, and providing adequate access, particularly where evacuation may be neces- sary or for the use of emergency vehicles. While not addressed here, these issues do receive attention in the forthcoming report. INFRASTRUCTURE In most subdivisions, roads and utilities are the two areas of concern with regard to devel- opment of infrastructure. The important ques- tions relate to establishing standards that will protect such infrastructure from damage from natural hazards, including floods. For roads and bridges, this primarily means sizing cul- verts and bridges to handle the ioo-year storm, and requiring the elevation of road surfaces above the base flood elevation —or allowing only a minimal flow of water over the road in such an event. Utilities typically include electric, natural gas, and water and wastewater installations, all of which must be protected from damage in the event of flooding, for example, by mounting transformers and similar facilities above flood CI A nonelevated pad mounted transformer in the floodplain, very close to the flooding source. ZONINGPRACTICE 3.16 AMERICAN PLANNING ASSOCIATION Ipage4