Agenda - Planning Commission - 04/07/2016

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FUNCTION RANGE OF RIPARIAN BUFFER WIDTHS Environmental Law Institute (2003) Fischer and Fischneich (2000) Hawes and Smith (2005) Stream Stabilization 30-17o ft. 3o-65 ft. 30-98 ft. Water Quality Protection 15-30o ft. (remove nutrients) 10-40o ft. (remove sediment) 15-100 ft. 49-164 ft. (remove nutrients) 49-328 ft. (remove pesticides) Flood Attenuation 65-50o ft. 65-50o ft. Riparian/Wildlife Habitat 10 ft.-1 mile 10o ft.-0.3 mile 150-330 ft. Protection of Cold Water Fisheries >10o ft. (5 studies) 50—zoo ft. (1 study) 30-230 ft. Adapted from Rhode Island Low Impact Development Site Planning and Design Guidance Manual, 2011 and "A Scientific Foundation for Shaping Riparian Buffer Protection Regulations," Pennsylvania Land Trust Association, zo14 GEOGRAPHIC FEATURES One critical issue of floodplain management is that much new development has typically occurred on the fringes of metropolitan areas, where the local planning capacity is often weakest. Small towns and rural areas often acquire planning staff only after significant development has already occurred and growth makes this necessary. By then, flooding is- sues arising because of new development may already be embedded in the natural and man- made landscape that results. Many water bod- ies lack identified floodplains because, prior to development, they posed no problem and thus received no attention. Only one-third of rivers, streams, shore- lines, and coastlines in the U.S. have flood hazards identified along them, and only half of those have detailed flood data. While the FEMA flood maps are the world's most compre- hensive inventory of flood hazard areas, they are not complete. Further, because funding for mapping is limited and focused on existing areas of high flood risk (as defined by develop- ment), the lands most likely to be subdivided have been traditionally areas of low priority for flood mapping. Over zo percent of flood insur- ance claims and one-third of federal disaster assistance payments are for damages outside the FEMA-mapped too -year floodplains. Communities can remedy this by requir- ing mapping of the too -year floodplain and floodway for any area that could hold or con- vey water where a floodplain has not already been mapped. The basis for identifying these features can include (but is not limited to) U.S. Geological Survey blue line streams or identified water bodies, and historical flood- ing areas (good for depressional areas, karst topography, or other high-water areas). They can also use lower thresholds than National Over 20 percent of flood insurance claims and one-third of federal disaster assistance payments are for damages outside the FEMA-mapped ioo-year floodplains. Flood Insurance Program minimum standards (5o lots or five acres) for triggering the need to undertake a detailed flood study. For example, the threshold could be reduced to five tots and two acres, which would be much more effec- tive in most major subdivisions. Finally, they can require the use of future conditions, with regard to both land use and hydrology, when undertaking new flood mapping. The example of Charlotte -Mecklenburg County, North Caro- lina, in this regard is well documented, includ- ing a 2006 article in Zoning Practice by David Godschalk regarding build -out analysis, and a very thorough case study in PAS Report No. 56o (Hazard Mitigation: Integrating Best Practices into Planning, 2010). The most important landscape features with regard to managing flood risk are riparian areas, the corridors along the edges of rivers and streams that perform numerous ecologi cal, hydrological, and geomorphological func- tions. These areas are effectively the buffers that protect upland development from the raw energy of water flows during periods of high precipitation. Protection should be the goal for riparian areas in the best ecological condi- tion, while restoration is needed for degraded riparian areas. However, while many riparian areas can be restored and managed to provide many of their natural functions, they are not immune to the effects of poor management in adjacent uplands. Upslope management can significantly alter the magnitude and timing of overland flow, the production of sediment, and the quality of water arriving at a downslope riparian area, thereby influencing the capability of riparian areas to fully function. Therefore, upslope practices contributing to riparian deg- radation must be addressed if riparian areas are to be improved. Communities can accomplish this in at least four ways: • Prohibit development immediately adjacent to streams, rivers, lakes, wetlands, and other water bodies. Avoid land disturbance, pavement, and other impervious cover. Require restoration of any disturbances. • Require and maximize the width of riparian ZONINGPRACTICE 3.16 AMERICAN PLANNING ASSOCIATION I page 3