Kitsap County Department of Public Works CRAB – November 04, 2015 Bioretention Stormwater BMP Benson Burleson Design Engineer

Kitsap County Department of Public Works Stormwater BMPs Older approach to managing stormwater runoff.

Kitsap County Department of Public Works Low Impact Development (LID) A stormwater management strategy that focuses on maintaining or restoring the natural hydrologic functions of a site to achieve natural resource protection objectives and fulfill environmental regulatory requirements. Also referred to as: Green Stormwater Infrastructure and Natural Drainage Systems

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT POROUS PAVERS

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT POROUS PAVERS BIORETENTION CELL / SWALE ALSO CALLED RAINGARDENS

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT POROUS PAVERS BIORETENTION CELL / SWALE GREEN ROOFS

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT POROUS PAVERS BIORETENTION CELL / SWALE NOT A GREEN ROOF

Kitsap County Department of Public Works Low Impact Development (LID) New approach to managing stormwater runoff. POROUS PAVEMENT POROUS PAVERS BIORETENTION CELL / SWALE GREEN ROOFS PLANTER BOXES

Kitsap County Department of Public Works Bioretention Cells (Rain Gardens)

Kitsap County Department of Public Works Bioretention Cells (Rain Gardens) Shallow ponded area with compost amended soils and plantings to provide stormwater pollutant removal and flow control

Kitsap County Department of Public Works Bioretention Cells  Smaller footprint than stormwater wetponds  Recharges ground water  Provides aesthetic benefits  Reduces construction and maintenance costs  Reduces grading area required  Treats both stormwater quality and quantity Advantages:

Kitsap County Department of Public Works Bioretention Cells Disadvantages:  Does not infiltrate efficiently in glacial till soils  High seasonal groundwater areas not recommended  Does require a flat to gently sloped area  Shallow installation depths makes conveyance difficult  Requires a high degree of certainty for long-term design infiltration rates for Ecology minimum requirements  Not recommended for high vehicle traffic areas

Kitsap County Department of Public Works Bioretention Cell Design Considerations  Existing and proposed basin land use  Stormwater overflow discharge  Amended Soil  Suitable location for facility (SSC)  Size and geometry of facility  Long-term infiltration rate

Kitsap County Department of Public Works Bioretention Cell Design Example  Existing and Proposed Basin Land Use Forest A/B or C/D - Existing conditions Road and/or Sidewalks etc.. – Proposed conditions

Kitsap County Department of Public Works Bioretention Cell Design Example  Size and geometry of facility Begin with a square area for simplicity

Kitsap County Department of Public Works Bioretention Cell Design Example  Stormwater overflow discharge Enter riser information.

Kitsap County Department of Public Works Bioretention Cell Design Example  Amended soil onsPre-approvedMaterials/index.htm Using the City of Seattle specification for amended soil, SMMWW

Kitsap County Department of Public Works Bioretention Cell Design Example  Long-term infiltration rate For project that must comply with minimum requirements a geotech recommendation is the best course of action

Kitsap County Department of Public Works Bioretention Cell Design Example  Infiltration results

Kitsap County Department of Public Works Bioretention Cell Design Example  Point of Compliance (POC) report

Kitsap County Department of Public Works Bioretention Cell Design Example  Flow frequency report

Kitsap County Department of Public Works Bioretention Cell using WWHM2012

Kitsap County Department of Public Works Bioretention Cell Design Example  Suitable location for facility (SSC) Setbacks for buildings, property lines, wells, steep slopes Seasonal groundwater elevations Adequate fall to get catchment area to facility Land flat enough to avoid excessive grading Downstream conditions

Kitsap County Department of Public Works Bioretention Cell Design Example  Vegetation selection and quantities Native plants preferable. Three zone scheme typical. Zone 1 - Emergents and Plants tolerant of wet conditions, 1 to 3 foot O.C. Zone 2 – Plants tolerant of occasional standing water, 2 to 6 foot O.C. Zone 3 – Plants that prefer drier conditional, 2 to 6 foot O.C. Plant quantities determined from SF of zone area Quantity example: 500 sf of planting area in Zone 1 Using 3 different species, 1 at 3’ OC and 2 at 1’ OC 500 / 3^2 = 55 for 3’ OC 500 / 1^2 = 500 – 55 = 445 for 1’ OC

Kitsap County Department of Public Works Bioretention Cell Drawings

Kitsap County Department of Public Works Bioretention Cell Photo Sidney Road Project (4,350 sf NPGIS)

Kitsap County Department of Public Works Bioretention Cell Drawings

Kitsap County Department of Public Works Bioretention Cell Photo Bethel-Mullinex Project (>10,000 sf NPGIS)

Kitsap County Department of Public Works Bioretention Cell Drawings

Kitsap County Department of Public Works Bioretention Cell Photo Lincoln-Widme Project (>10,000 sf NPGIS)

Kitsap County Department of Public Works Bioretention Cell Drawings

Kitsap County Department of Public Works Bioretention Cell Photo Phillips-Mullenix Project (>1,000 sf NPGIS)

Kitsap County Department of Public Works Questions?