18J.15.170 Stormwater Facilities.
A. Applicability. The following standards apply to development proposals for attached single-family, multi-family, civic, utility, commercial, industrial, land divisions, use permits, and site development permits. The standards set forth in this Section are supplementary to the requirements of the Pierce County Stormwater Management and Site Development Manual.
B. Exemptions.
1. Resource uses where the principal use of the property is for animal, crop or forestry production or mineral extraction (e.g., surface mines) shall not be subject to these standards.
2. Residential developments designed to accommodate 9 or fewer dwelling units shall not be subject to these standards.
C. Design Objective. Minimize visual impacts of stormwater facilities with landscaping, contouring, and other techniques, including vegetated LID BMPs.
D. Standards.
1. General.
a. Stormwater facilities that are proposed to be dedicated to the public may be subject to additional requirements related to maintenance, security, and other considerations as set forth within the Pierce County Stormwater Management and Site Development Manual.
2. Storm drainage facilities shall be designed to comply with one of the following design standards, in order of preference:
a. Design storm features as a site amenity. Stormwater facilities are deemed site amenities when:
(1) Fencing is not required;
(2) Side slopes do not exceed 4 to 1;
(3) Ponds are lined with a mix of low-maintenance native plant materials;
(4) Uses such as recreation, walking or sitting, and picnicking are allowed; and
(5) The pond is designed in a curvilinear, non-rectangular shape.
b. Place storm drainage detention into underground vaults, and underground retention systems; or
c. If subsection D.2.a or b is not feasible, storm drainage features shall include a complete visual screen on the outside of any fencing facing the public right-of-way, adjacent development, or other public areas with evergreen shrubs at a rate of 1 per 5 lineal feet and evergreen trees at a rate of 1 per 8 lineal feet, with a minimum planting width of 10 feet. Minimum mature height for trees shall be 16 feet. Screening of stormwater ponds shall not be required when the pond is surrounded by a 6-foot tall solid board fence. Screening of public ponds should be outside of the public tract, on private property.
E. Guidelines.
1. Urban Facility Design.
a. Design the pond in an aesthetically-pleasing manner along with other landscape features;
b. Capture treated storm water and other non-potable water for use in irrigation;
c. Utilize pervious paving surfaces, such as porous pavement and pavers, for roads, driveways, parking lots, or other types of drivable or walkable surfaces.
2. Rural Facility Design.
a. Design and vegetate wetponds and detention ponds to simulate natural wetland features in conjunction with required landscape areas;
b. Direct rooftop runoff to infiltration areas, full dispersion systems, or to cisterns for non-potable reuse, or utilize vegetated roof systems to evaporate and transpire stormwater;
c. Design storm drainage facilities at schools, churches, and similar uses to accommodate recreational elements, such as sport fields, walking, and picnic areas, with the understanding that at times throughout the year, these areas may be wet or totally unusable;
d. Minimize changes to natural topography. Limit grading and clearing disturbance to road, utility, building pad, and landscape areas to the minimum area needed to maneuver equipment during construction; and
e. Maintain surface roughness on the site to reduce flow velocities and encourage sheet flow on the development by preserving native vegetation, forest litter, and micro surface topography.