Unified Development Ordinance, 4th supplement, September 2017

Part 10A: Unified Development Ordinance City of Raleigh, North Carolina 7 – 20 Effective Date: September 01, 2013 Supp. No. 4 CHAPTER 7. ​GENERAL DEVELOPMENT STANDARDS | Article 7.2. ​Landscaping and Screening Sec. 7.2.6. ​Stormwater Retention Ponds & Detention Basins b. No fence may be installed around the permanent stormwater retention pond or detention basin that acts to prevent pedestrian access to the facility from the site or development where it is located; in cases where a fence is needed to restrict access, the fence shall be screened in accordance with the screening provisions described in Sec. 7.2.6.C. c. Rock riprap or other "hard armoring" is limited to 10% or less of the entire surface area of the stormwater control facility above the low pool line. d. Permanent stormwater retention ponds and detention basins must incorporate features designed to reduce mosquito populations through provision of non-chemical mosquito mitigation measures, including but not limited to: cyclical alteration of the pond level, installation of aeration/agitation features to disrupt larval growth, providing nesting boxes for mosquito-predacious birds or bats or stocking ponds with mosquito-predacious fish (e.g. Gambusia affinis holbrooki). 2. Supplemental Amenity Features In addition to the basic requirements described above, a permanent stormwater retention pond or detention basin must also provide supplemental features to be considered an amenity. The types of supplemental amenity features differ based upon the type of stormwater control facility. a. Permanent Retention (Wet) Ponds To be considered as an amenity feature, permanent retention ponds must; i. Retain water within a permanent pool; ii. Maintain slopes of 4:1 or shallower to a distance of 10 feet below the median pool line (beyond which slopes may become steeper); alternatively, a retaining wall may be incorporated into a portion of the facility, provided the design of walls are compatible with the principal building in terms of texture, quality, material and color; iii. Include horizontal curves or other sculptural elements within the shape of the facility so as to avoid a simple square or round shape; and iv. Provide at least two of the following 4 features: a) Inclusion of an active water feature (i.e., aerator/fountain/ waterfall) within or adjacent to a permanent pool; b) Pedestrian access trails to and around the stormwater control facility from the existing proposed pedestrian network associated with the site or development. Trails are not required to meet the minimum specifications for sidewalks or multipurpose trails as described within the City's standard specifications and details and may be constructed of any discernible, leveled, and stable surface material, including but not limited to: brick or masonry, gravel, mulch, wood chips, mowed grass or low groundcover; c) Provision of riparian plant materials throughout the stormwater control facility to prevent erosion and add visual interest and additional perimeter plantings consisting of at minimum 3 understory trees or 2 shade trees totaling 8 inches in caliper at time of planting, and four shrubs for every 100 linear feet equivalent to the pond's maximum pool circumference and located no more than 75 feet from the pond's maximum pool line; or d) Inclusion of other permanent, pedestrian-oriented features, including but not limited to: seating, dining tables and mounted trash cans, in areas around or proximate to the stormwater control facility. b. Detention (Dry) Basins To be considered as an amenity feature, detention ponds must: i. Not contain water on a permanent basis; ii. Provide a 100% vegetative cover capable of withstanding extended periods of inundation, except in spaces designed for specific recreational uses (e.g., baseball fields); iii. Maintain slopes of 4:1 or shallower; alternatively, a retaining wall may be incorporated into a portion of the facility, provided the design of provided the design of walls are compatible with the principal building in terms of texture, quality, material and color; and

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