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Bioretention Designs to meet different goals by Jay Dorsey
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Bioretention Designs to Meet Different Goals
Jay Dorsey & John MathewsODNR-DSWRApril 16, 2014
Goals for Presentation Sizing Requirements for WQv
New Development Redevelopment
Base DesignDesign Modifications to Address Location
Specific Conditions/Limitations or Meet Watershed Specific Goals
Basic Design Example
Sizing Requirements for WQv- New Development -
From NPDES Construction Stormwater Permit
Sizing Requirements for WQv- New Development -
Target Drawdown Time, Td = 24 hr
Design Drawdown Assumption - Kfs of settled filter bed media
(planting soil) is between 0.5 to 2.0 in/hr[Maintenance required when Kfs < 0.5/in/hr]
Td = dWQv /Kfs = (12 in)/(0.5 in/hr) = 24 hr
Where: Td – drawdown time dWQv – equivalent depth of WQv Kfs – saturated hydraulic conductivity
Filter Bed Sizing Requirement If impervious area exceeds 25% of
contributing drainage area, filter bed area shall be a minimum 5% of contributing impervious area.
Filter Bed Sizing Requirement Example 1
Total contributing drainage area = 0.82 Ac Impervious percent = 45% (>25%) Contributing impervious area = (0.82 Ac)(0.45)
= 0.37 Ac = 16,073 ft2
Minimum filter bed area = (16,073 ft2)(0.05) = 803 ft2
Filter Bed Sizing Requirement If impervious area exceeds 25% of
contributing drainage area, filter bed area shall be a minimum 5% of contributing impervious area.
If impervious area makes up less than 25% of contributing drainage area, filter bed area shall be at least equal to the WQv divided by the one foot maximum ponding depth.
Filter Bed Sizing Requirement Example 2
Total contributing drainage area = 0.82 Ac Impervious percent = 15% (<25%) For 15% impervious,
C = (0.858)(0.15)3 – (0.78)(0.15)2 + (0.774)(0.15) + 0.04= 0.141
WQv = C*P*A = (0.141)(0.75 in)(0.82 Ac)(1 ft/12 in)= 0.007 Ac-ft = 315 ft3
Minimum filter bed area = (315 ft3)(1 ft) = 315 ft2
Filter Bed Sizing Requirement If impervious area exceeds 25% of
contributing drainage area, filter bed area shall be a minimum 5% of contributing impervious area.
If impervious area makes up less than 25% of contributing drainage area, filter bed area shall be at least equal to the WQv divided by the one foot maximum ponding depth.
Assumption - sediment storage requirement (20% of WQv) will be met with excess bowl volume
Filter Bed Area(%
)
Filter Bed Area
What about Redevelopment? For redevelopment projects, the full WQv
must be captured for all new/additional impervious area, but for existing impervious area the volume that must be captured is 20% of the WQv.
What about Redevelopment? A rule of thumb based on research shows an
optimal 10:1 to 20:1 ratio for contributing impervious drainage area to bioretention filter bed area (i.e. hydrologic loading ratio). If all best practices are used (pretreatment, energy dissipation, construction, etc.) a hydrologic loading ratio of 25:1 is probably okay for most sites.The filter bed area of the bioretention cell
should not be less than 4% of the contributing impervious area.
Redevelopment BRC Options For straight redevelopment (no new
impervious), capture and treat the full WQvfrom 20% of the site
For mixed redevelopment and new development, match the size of your bioretention cell to your contributing impervious area
Build a bioretention practice capable of capturing the full WQv from the entire site, and use the rest as credit toward reduction of stormwater fees or as mitigation
Bioretention Cell Components
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Base Bioretention Configuration
Base Bioretention Configuration
30”-36” Planting Soil
6” Filter
12” Aggregate
Base Bioretention Configuration
24” Planting Soil above Invert
6” (min) Planting Soil in IWS
Special Designs Pollutant Load Reduction Goals
Temperature Mitigation Nitrogen Removal Phosphorus Mitigation
Site Conditions or Limitations High Permeability Soils (> 1 in/hr) Very Low Permeability Soils (<0.05 in/hr) Depth Limitations Groundwater Pollution Potential
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
High Permeability Soils
If measured subgrade infiltration rate exceeds 1.0 in/hr, the underdrain, and aggregate and filter layers, can be eliminated
High Permeability Soils
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Source: Bill Hunt, NCSU-BAE
Temperature Mitigation
Planting soil media depth - minimum 36”Underdrain/outlet configuration
minimum 48” depth to drain; more is better upturned elbow with internal water storage
(IWS) layer, minimum 18” sump
Temperature Mitigation
Planting Soil36” Minimum
18” IWS Min.48” DrainDepth Min.
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Nitrogen Removal
Planting soil media depth - minimum 36”Underdrain/outlet configuration
upturned elbow with internal water storage (IWS) layer, minimum 18” sump with at least 6” IWS in planting media
if necessary, orifice on drain outlet to control discharge rate
Nitrogen Removal
Planting Soil36” Minimum
18” IWS Min.
6” Min. inPlanting Soil
Phosphorus Removal
Planting soil media depth - minimum 36” Planting soil phosphorus content – 15-40
mg/kg P by Mehlich3Recommend adding water treatment
residuals (WTR) or other iron or aluminum rich amendment
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Depth Limitations
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Low Permeability Soils or Impediments to Infiltration
If subgrade infiltration rate is less than 0.05 in/hr, or if shallow bedrock or seasonal high water table is present, there may be limited benefits and potential issues from the IWS; a level drain with 3” sump allows limited exfiltration
Low Permeability Soils or Impediments to Infiltration
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
High Groundwater Pollution Potential
In Karst areas or areas with shallow groundwater aquifers, water supplies are susceptible to contamination – use an impermeable liner
In sites with contaminated soils or pollution hot spots, bioretention cells should use an impermeable liner
Alternative configurations can still be used to mitigate temperature and nutrient impacts
GW Pollution Potential – Add Liner
Bioretention Decisions
Nitrogen Treatment
HSG D Soils(depending on
limitations)
Temperature
Base Design30-36” depth;
IWS LayerDepth Limitations
(e.g., Shallow Outlet, High Water Table)
36+” media depth; IWS Layer (>18”);48” depth to drain
Underdrain w/ 3” of cover & 3” of
bedding
36” media depth; IWS layer (>18”), outlet raised >6”
into planting media
24” mediadepth
High Water Table, Karst, Shallow
Bedrock or High Pollution Loads
Impermeable liner
HSG A Soils
If Kfs > 1 in/hr, may not require
underdrain, aggregate, filter
Base Bioretention Configuration
Design Example – Holden Arboretum
North WshedDA = 0.67 Ac%Imp (est) = 58%ImpArea = 0.39 AcABRC = 0.0195 Ac
= 850 sq ft~ 23 x 40 ft
South WshedDA = 0.48 Ac%Imp (est) = 59%ImpArea = 0.28 AcABRC = 0.014 Ac
= 610 sq ft~ 20 x 30 ft
Watersheds
North WshedDA = 0.67 Ac%Imp (est) = 58%ImpArea = 0.39 AcABRC = 0.0195 Ac
= 850 sq ft~ 23 x 40 ft
South WshedDA = 0.48 Ac%Imp (est) = 59%ImpArea = 0.28 AcABRC = 0.014 Ac
= 610 sq ft~ 20 x 30 ft
Watersheds
proposed bioretentionlocations
Design Example – Holden ArboretumNorth Bioretention Cell
Drainage Area = 0.67 AcImperviousness = 58%Impervious Area = 0.39 AcABRC = 0.05*0.39 Ac = 0.0195 Ac = 850 sq ftC = 0.394WQv = C*P*A = 0.394*(0.75 in)*(0.39 Ac)
= 0.016 Ac-ft = 719 ft3
Soil Map
PlateaHSG-D
PierpontHSG-C
proposed bioretentionlocations – measure infiltration rate at proposed depth of excavation ~48-54”
other potential samplinglocations – sample at ground surface
Infiltration Tests
Measured Kfs (in/hr)BRC1(N): 0.02, 0.02BRC2(S): 0.02, 0.08
Target Bioretention Configuration
36” Planting Soil
6” Filter
12” Aggregate
Bioretention Cell 1(N) - Section
Not to Scale
existing pavement
Lowest Pavement = 99.3’
All Elevations are Relative, Not MSL
Outlet Invert = 94.0’
existing 15”outlet
12” clean gravel (#57)
3” filter - clean gravel (#8)
3” filter – clean concrete sand
~36” bioretention soil
Bioretention Cell 1(N) - Section
Not to Scale
existing pavement
Lowest Pavement = 99.3’
All Elevations are Relative, Not MSL
freeboard = 0.5’
max ponding depth = 1.0’
Outlet Invert = 94.0’
existing 15”outlet
drain
drainoutfall
12” clean gravel (#57)
3” filter - clean gravel (#8)
3” filter – clean concrete sand
~36” bioretention soil
Bioretention Cell 1(N) - Section
Not to Scale
existing pavement
Lowest Pavement = 99.3’
All Elevations are Relative, Not MSL
freeboard = 0.5’
max ponding depth = 1.0’
Outlet Invert = 94.0’
existing 15”outlet
drain
drainoutfall
Bottom of Excavation = 93.3’
Proposed Overflow = 98.8’
Filter Bed Surface = 97.8’
Sand/Gravel Filter = 94.3’
Filter Bed Bottom = 94.8’
Drain Outfall = 95.1’
Scarifying Bottom of Cell
Underdrain w/Upturned ElbowCreating 21” Internal Water Storage (IWS) Zone or Sump
Waterproof Connection
Hydraulic Cement
12” #57 gravel
Water Table Monitoring Well
3” #8 gravel filter
3” clean C-33 sand filter
36” bioretention planting soil
Holden Bioretention Configuration
36” Planting Soil
6” Filter
12” Aggregate
Holden North Cell Drawdown Data
Drawdown Begin Date/Time
Drawdown End Date/Time
Beginning Stage (ft)
Ending Stage (ft)
Delta Stage (ft)
Delta time (days)
Drawdown Rate (ft/day)
Drawdown Rate (in/hr)
Infiltrated Volume (ft3)
10/7/2013 17:22 10/16/2013 0:30 2.099 1.17 0.929 8.30 0.112 0.056 26110/17/2013 6:42 10/17/2013 15:38 2.085 1.97 0.115 0.37 0.309 0.154 3210/18/2013 2:48 10/19/2013 12:20 2.084 1.721 0.363 1.40 0.260 0.130 10210/20/2013 12:12 10/21/2013 20:30 2.052 1.624 0.428 1.35 0.318 0.159 12010/22/2013 14:16 10/23/2013 7:02 2.07 1.783 0.287 0.70 0.411 0.205 8110/26/2013 18:36 10/26/2013 21:12 1.923 1.894 0.029 0.11 0.268 0.134 810/27/2013 12:56 10/31/2013 4:00 1.892 1.352 0.54 3.63 0.149 0.074 15111/2/2013 3:48 11/2/2013 9:22 1.883 1.815 0.068 0.23 0.293 0.147 1911/4/2013 1:30 11/6/2013 17:18 1.847 1.344 0.503 2.66 0.189 0.095 14111/9/2013 10:00 11/11/2013 17:46 1.851 1.355 0.496 2.32 0.213 0.107 13911/15/2013 7:16 11/17/2013 18:46 1.794 1.491 0.303 2.48 0.122 0.061 8511/19/2013 4:14 11/21/2013 21:28 1.789 1.279 0.51 2.72 0.188 0.094 14311/23/2013 21:28 12/9/2013 9:06 1.811 1.165 0.646 15.48 0.042 0.021 181
Avg drawdown rate: 0.125 ft/day TotalExfiltrated Volume: 1463Avg drawdown rate: 0.062 in/hrStandard Deviation: 0.0507
North Cell Well Drawdown Rates
Holden North Cell Drawdown Data
Drawdown Begin Date/Time
Drawdown End Date/Time
Beginning Stage (ft)
Ending Stage (ft)
Delta Stage (ft)
Delta time (days)
Drawdown Rate (ft/day)
Drawdown Rate (in/hr)
Infiltrated Volume (ft3)
10/7/2013 17:22 10/16/2013 0:30 2.099 1.17 0.929 8.30 0.112 0.056 26110/17/2013 6:42 10/17/2013 15:38 2.085 1.97 0.115 0.37 0.309 0.154 3210/18/2013 2:48 10/19/2013 12:20 2.084 1.721 0.363 1.40 0.260 0.130 10210/20/2013 12:12 10/21/2013 20:30 2.052 1.624 0.428 1.35 0.318 0.159 12010/22/2013 14:16 10/23/2013 7:02 2.07 1.783 0.287 0.70 0.411 0.205 8110/26/2013 18:36 10/26/2013 21:12 1.923 1.894 0.029 0.11 0.268 0.134 810/27/2013 12:56 10/31/2013 4:00 1.892 1.352 0.54 3.63 0.149 0.074 15111/2/2013 3:48 11/2/2013 9:22 1.883 1.815 0.068 0.23 0.293 0.147 1911/4/2013 1:30 11/6/2013 17:18 1.847 1.344 0.503 2.66 0.189 0.095 14111/9/2013 10:00 11/11/2013 17:46 1.851 1.355 0.496 2.32 0.213 0.107 13911/15/2013 7:16 11/17/2013 18:46 1.794 1.491 0.303 2.48 0.122 0.061 8511/19/2013 4:14 11/21/2013 21:28 1.789 1.279 0.51 2.72 0.188 0.094 14311/23/2013 21:28 12/9/2013 9:06 1.811 1.165 0.646 15.48 0.042 0.021 181
Avg drawdown rate: 0.125 ft/day TotalExfiltrated Volume: 1463Avg drawdown rate: 0.062 in/hrStandard Deviation: 0.0507
North Cell Well Drawdown Rates
Holden North Cell Drawdown Data
References ODNR. Rainwater and Land Development Manual. NCDENR Stormwater Manual. 2009. Hunt, Davis, and Traver. 2012. Meeting Hydrologic and
Water Quality Goals through Targeted BioretentionDesign. J. Env. Eng. 138(6): 698-707.
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.
Brown, Hunt, and Kennedy. 2009. Designing Bioretention with an Internal Water Storage (IWS) Layer. NCSU-CE.
CWP. 2012. West Virginia Stormwater Management and Design Guidance Manual.
Questions:
Jay DorseyWater Resources EngineerODNR, Soil & Water Resources(614) [email protected]