Rainwater and Land Development Manual Bioretention Design Specification Updates Jay Dorsey & John Mathews ODNR-DSWR June 18, 2014
Why Change? Improved Design -> Better Performance, Fewer Failures; Based on: Bioretention Practice Inspections/Observations Research Scientific Knowledge Base Ability to Target Specific Pollutants or Stormwater Management Goals Temperature, Nitrogen, Phosphorus Facilitate Design, Review and Inspection Runoff Volume and Peak Discharge Reduction Credits (under Development)
Primary References Hunt, Davis, and Traver. 2012. Meeting Hydrologic and Water Quality Goals through Targeted Bioretention Design. J. Env. Eng. 138(6): 698-707. Hunt and Lord. 2005. Bioretention Performance, Design, Construction and Maintenance. NCSU-CE. Brown, Hunt, and Kennedy. 2009. Designing Bioretention with an Internal Water Storage (IWS) Layer. NCSU-CE. NCDENR Stormwater Manual. 2009. Wardynski and Hunt. 2012. Are Bioretention Cells Being Installed per Design Standards in North Carolina? A Field Assessment. J. Env. Eng. 138(12): 1210-1217. CWP. 2012. West Virginia Stormwater Management and Design Guidance Manual.
Grassed Bioretention aka Dry Enhanced Water Quality Swale Third Federal Bank, North Olmstead Source: Dan Bogoevski, Ohio EPA
Overhaul or Tweaks?
Updates Pretreatment Requirements Planting Soil Media Specifications Planting Soil Media Depth Filter Layer between Planting Soil and Gravel Drainage Layer Underdrain and Elevated Outlet (Internal Water Storage) Sizing and Drawdown Requirements Bioretention Data Submittal/Review Sheet Coming Update Runoff Reduction Credits
Pretreatment Requirements
Clogging of Filter Surface Source: Bill Hunt, NCSU-BAE
Source: Brad Wardynski, NCSU-BAE
Pretreatment Requirements Pretreatment is required Grass Filter Strip Gravel Verge plus Grass Filter Strip Grass Swale Sediment Forebay
Planting Soil (Filter Bed Media) PARAMETER OLD NEW Texture Class Sandy Loam, Loamy Sand >72% Sand, <10% Clay Loamy Sand >80% Sand, <10% Clay ph Range 5.2 7.0 5.2 8.0 Organic Matter 5-20% (no specification whether by weight or volume) 3-5% by Weight Phosphorus Content Soil P-Index between 15 and 40 15-60 mg/kg P by Mehlich3 Soil Test Certification Soil mixes must be certified by a qualified laboratory (1 test/100 yd 3 soil) Soil mixes must be certified by a qualified laboratory (1 test/100 yd 3 soil)
Planting Soil Mix or Recipe To get the appropriate planting soil mix (loamy sand; >80% sand, <10% clay when considering only mineral fraction; 3-5% OM by weight) a good place to start is a 5:1:1 mix (70% sand, 15% topsoil, and 15% organic matter by volume). The sand shall be clean and meet AASHTO M-6 or ASTM C-33. Good (lower P) sources of aged organic matter include leaf compost, pine bark fines, or mulch fines.
Planting Soil Media Depth 30 to 36 bioretention soil (typical) [24 bioretention soil minimum] 2-3 filter clean concrete sand 2-3 filter - clean gravel (#8) 12 clean gravel (#57)
Planting Soil Media Depth Pollutant removal - minimum 24 filter media depth provides excellent treatment for most pollutants Exceptions Temperature, Nitrogen, Phosphorus Plant/landscaping needs - planting soil depth needs to be adjusted to accommodate expected rooting depths of bioretention vegetation recommend 30-36 for most applications; coordinate with landscape architect and/or horticulturalist
Filter Layer between Planting Soil and Gravel Drainage Layer 30 to 36 bioretention soil (typical) [24 bioretention soil minimum] 2-3 filter clean concrete sand 2-3 filter - clean gravel (#8) 12 clean gravel (#57)
Filter Layer between Planting Soil and Gravel Drainage Layer Geotextile fabric filters no longer allowed mounting evidence that filter fabric clogs causing >24 failure bioretention of soil practice 2-3 filter clean concrete sand 2-3 filter - clean gravel (#8) 12 clean gravel (#57)
Underdrain & Elevated Outlet
Enhancing Performance through Outlet Configuration Source: Bill Hunt, NCSU-BAE
Underdrain & Elevated Outlet
Holden Arboretum, Kirtland
Outlet Options to Allow Drainage of IWS
Elevation of Overflow Catch Basin Soil Media (Underdrain with Upturned Elbow for Reservoir) Pea Gravel Layer Gravel Layer
Elevation of Overflow Catch Basin Soil Media (Underdrain with Riser in Catch Basin for Reservoir) Pea Gravel Layer Gravel Layer Screw Cap to Allow IWS Drainage for Maintenance
Underdrain Configuration For Basic BRC Installation 30 36 Media Depth Elevated outlet recommended for all HSG-A, B, C soils with K fs > 0.1 in/hr - 18 + for Temp, N & Volume Reduction D soils 3 gravel bedding acts as sump
Special Designs Temperature Mitigation Nitrogen Removal Phosphorus Mitigation
Sizing and Drawdown Requirements Assumptions K fs of settled filter bed media (planting soil) is between 0.5 to 2.0 in/hr [Maintenance required when K fs < 0.5 in/hr] 20% of WQv sediment storage requirement will be met with excess bowl volume
(%) Filter Bed Area
Filter Bed Area
Design Drawdown T d drawdown time d WQv equivalent depth of WQv K fs saturated hydraulic conductivity Td = d WQv /K fs = (12 in)/(0.5 in/hr) = 24 hr
Bioretention Design Checklist and Review Sheet
Questions: Jay Dorsey Water Resources Engineer ODNR, Soil & Water Resources (614) 265-6647 jay.dorsey@dnr.state.oh.us