Friday, April 24, 2009

Draft Code: Stormwater Facility Design

The aesthetic impacts of stormwater facilities will be improved with the following Code amendments. Planning Commission will be reviewing these at their next meeting Tuesday April 28th.

This is entirely new Code language, and will be part of the Design Standards Chapter; how/where it will fit within the revised Chapter still needs to be determined.

XXX.XX.XX1 Stormwater Facility Location and Design. Stormwater facilities shall be located and designed with consideration to aesthetics, and to incorporate the facility as an amenity to the land division with features such as landscaping and natural building materials. The provisions in this section apply to all subdivisions and Planned Residential Developments proposed within Oak Harbor. The following design requirements shall apply to the location and design of stormwater facilities.
(1) Locations. Where feasible, open spaces and tree retention tracts within subdivisions and Planned Residential Developments shall be located adjacent to stormwater facilities to create the visual effect of larger open space areas. .
(2) Materials. Structural materials utilized within stormwater facility design must have regard for natural aesthetic principles.
a) Gabion baskets, and gabion rock are not permitted in stormwater facility designs.
b) All structural elements of ponds shall utilize stone or other natural material that have decorative finishes. Use of concrete in stormwater facilities is prohibited unless the concrete has a decorative finish and is combined with screen plantings to reduce the visual impact of these facilities. The use of ecology block in pond construction is prohibited.
(3) Design. To limit the need for safety fencing resulting from steep slopes, stormwater facilities shall be designed with shallow internal slopes (recommend 3:1 or flatter) whenever feasible. If it is demonstrated that safety fencing is required it must:
(a) be decorative or ornamental in nature. Chain-link fencing with slats is not permitted, although vinyl clad chain-link fencing is acceptable if screened by plantings and,
(b) for safety reasons, not completely limit visibility to the pond. Ponds shall be designed such that safety fencing is not required on more than two sides of the pond or 50% of the circumference, whichever is less.

XXX.XX.XX2 Stormwater Facility Landscaping. Landscaping shall be required for all stormwater facilities within land divisions. The purpose of the landscaping is to improve visual quality and provide screening of the stormwater facilities from streets, public areas, and neighboring properties. The following standards shall apply to the landscaping for stormwater facilities.
(1) Landscape Design. A landscape plan that meets the standards of this section shall be designed by a Landscape Architect certified in the State of Washington and submitted as part of the preliminary plat or the preliminary PRD development plan application.
(2) Landscape Perimeter. A perimeter landscape area, of minimum 10 feet wide, is required adjacent to all stormwater ponds. This area shall be delineated on the face of the plat and associated landscape plan. The perimeter landscape area shall include:
(a) evergreen ground cover, shrubs and bushes, to provide 100% ground cover of the perimeter area within two (2) years; native species and low-maintenance varieties are preferred. If a trail or pedestrian path is included around the stormwater facility, the area outside the trail or pedestrian path, but within the 10-foot landscape area must have 100% groundcover within two (2) years.
(b) a mix of evergreen and deciduous trees to provide visual interest, with a planting density of at least one tree for every 250 square feet of Landscape Perimeter.
(c) natural vegetation may be used to fulfill the landscaping requirements. However, all trees which pose a safety hazard and are subject to wind throw and blow down, must be removed.
(3) The perimeter landscape area may include a trail or pedestrian path for recreational purposes, provided that the side slopes of the pond are not steeper than 3:1.
(4) In the event that a trail, open space, or park has been identified and/or required by the City of Oak Harbor adjacent to, or integrated with a storm water facility, it shall be installed above the maximum extended detention level or five year storm level, which ever is greater, in order to prevent frequent flooding.
(5) Plantings must be designed and constructed not to conflict with the function of the stormwater facility as defined in the DOE Stormwater Manual.
(6) If a pond with two or more cells for treatment is proposed, one or more of the cells must be planted.
(7) No more than 50% of the pond circumference may have berming.

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