Sec. 7.2.6. Stormwater Retention Ponds & Detention Basins

  1. Applicability
    All stormwater retention ponds and detention basins permitted, constructed or modified to a cumulative extent greater than 50% of their original size shall be screened for their entire length as set forth in Sec. 7.2.6.C. When amenity features are provided as set forth in Sec. 7.2.6.B., no screening of the stormwater control facility is required.
  2. Amenity Provisions
    Permanent stormwater retention ponds and detention basins may be supplemented with certain features which enable the facility to function as an amenity in addition to its primary function as a stormwater device. In situations where amenity features are provided consistent with these provisions, no screening of the stormwater control facility from on-site or off-site views shall be required. In the event a permanent stormwater retention pond or detention basin loses a feature by which the facility qualifies as an amenity, the feature shall be restored within 30 days or the facility shall be subject to the screening provisions listed in Sec. 7.2.6.C.
    1. Basic Amenity Features
      To qualify as an amenity, the following basic amenity features must be provided within any stormwater control facility.
      1. Integration of the permanent stormwater retention pond or detention basin into the design of public areas within the site or development through the use of appropriate placement, common building materials, textures, features or other treatments intended to lend architectural significance to the stormwater control facility. For the purposes of this section, "integration" shall mean at least two of the following 3 elements:
        1. Proximate placement of the stormwater facility to the principal structure;
        2. Provision of pedestrian access to the facility through installation of a delineated walk or trail from the principal structure; or
        3. Utilization of similar planting materials and building materials as used in the principal structure.
      2. 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.
      3. 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.
      4. 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.
      1. Permanent Retention (Wet) Ponds To be considered as an amenity feature, permanent retention ponds must;
        1. Retain water within a permanent pool;
        2. 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;
        3. Include horizontal curves or other sculptural elements within the shape of the facility so as to avoid a simple square or round shape; and
        4. Provide at least two of the following 4 features:
          1. Inclusion of an active water feature (i.e., aerator/fountain/ waterfall) within or adjacent to a permanent pool;
          2. 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;
          3. 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
          4. 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.
      2. Detention (Dry) Basins
        To be considered as an amenity feature, detention ponds must:
        1. Not contain water on a permanent basis;
        2. Provide a 100% vegetative cover capable of withstanding extended periods of inundation, except in spaces designed for specific recreational uses (e.g., baseball fields);
        3. 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
        4. Provide at least 2 of the following 3 features:
          1. Pedestrian access trails to the stormwater control facility from the existing and/or 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;
          2. 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; or
          3. Grading and slopes of 8:1 or shallower which will allow utilization of the facility as an area for recreation when not in use as a detention facility (except on the dam structure and as is necessary to tie the dam back to existing grades); 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.
    3. Incentives
      When a permanent stormwater retention pond or detention basin provides amenity features in compliance with the minimum requirements of this UDO, then the following provisions may also apply:
      1. The permanent stormwater retention pond and detention basin and related facilities, including amenity features, may be placed within required landscaping areas, including but not limited to: street protective yards, transitional protective yards and parking lot landscaping areas, (except in tree conservation areas adjoining thoroughfares, within areas zoned for resource management, tree protection areas and in natural protective yards); and
      2. When a permanent stormwater retention pond or detention basin is located within a required landscaping area, the portion of land associated with or adjacent to the stormwater control facility is only required to meet 80% of the minimum planting requirements of the required landscaping area.
  3. Screening Requirements
    When amenity features are not provided as set forth in Sec. 7.2.6.B., screening of the stormwater control facility is required as set forth below.
    1. All vegetative screening shall be 75% locally-adapted evergreen species.
    2. All vegetative material shall be planted so as to attain a screen occupying at least 75% of a vertical plane around the perimeter of the facility to an average mature height of 6 feet above grade.
    3. Screening shall be required around the base of the dam structure (as applicable), but not on the dam structure, with those plant materials in immediate proximity to the dam characterized by shallow, non-invasive root systems.
    4. Screening shall not be required within required facility inlets or facility outlets or within a maintenance access path provided that such path does not exceed 12 feet in  width; in all other instances, at an average mature height of planting, the maximum open horizontal space between vegetative screening materials shall not be more than 2 feet in width.
    5. Vegetative material composing the screen shall be selected and installed so as to exhibit variety in texture, color, spread and height by using ornamental or deciduous shade trees in combination with evergreen materials.
    6. In some cases, vegetative material may be placed in clusters or groups to add additional visual interest as well as to achieve intermittent levels of vertical height; and
    7. In situations where the stormwater control facility utilizes a fence, all vegetative material associated with screening the facility shall be located outside the fence.
    8. In situations where a fence and gate are proposed, the fence and gate shall be colored black, forest green, dark brown or similar dark color, unless the fence is constructed of masonry, wood or similar natural material, in which case it may be left to weather naturally.