Bioretention rainwater treatment – technical design by ASLA
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9/6/2012 1 Jim Schuessler, ASLA James Urban, FASLA Kevin Robert Perry, ASLA JIM SCHUESSLER ASLA associate | landscape architecture BNIM berkebile nelson immenschuh mcdowell 106 West 14th Street Suite 200 Kansas City Missouri 64105 816.783.1608 American Society of Landscape Architects 2012 Annual Meeting Bio-retention Rain Water Management: Technical Design 2009 ASLA Honor Award James Urban, FASLA, ISA Urban Tree + Soils [email protected] Issues Introduction – The new rain water paradigm is a significant change in the way we view water and cities. Do we know what we are doing? Are we “experts” at this? Since ancient times, we have: Slowly evolved solutions to conflicts between rain water and human development. Any new water paradigm we must be sure to understand these conflicts and not reintroduce an old problem. Old paradigm Get the water away fast…… New paradigm Hold the water here for as long as possible……….. Steep slopes good Flat slopes bad Steep slopes bad Flat slopes good Minimum and maximum slope tolerance Slope tolerance 2 – 15% in planted areas Slope tolerance 0 – 1.5% in planted areas
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Transcript of Bioretention rainwater treatment – technical design by ASLA
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Jim Schuessler, ASLAJames Urban, FASLAKevin Robert Perry, ASLA
JIM SCHUESSLER ASLA associate | landscape architecture BNIM berkebile nelson immenschuhmcdowell 106 West 14th Street Suite 200 Kansas City Missouri 64105 816.783.1608
American Society of Landscape Architects2012 Annual Meeting
Bio-retention Rain Water Management:Technical Design
2009 ASLA Honor Award
James Urban, FASLA, ISAUrban Tree + [email protected]
gIssues
Introduction – The new rain water paradigm is a significant change in the way we view water and cities.
Do we know what we are doing? Are we “experts” at this?
Since ancient times, we have: Slowly evolved solutions to conflicts between rain water and human development.
Any new water paradigm we must be sure to understand these conflicts and not reintroduce an old problem.
Old paradigmGet the water away fast……
New paradigmHold the water here for as long as possible………..
Steep slopes goodFlat slopes bad
Steep slopes badFlat slopes good
Minimum and maximum slope tolerance
p
Slope tolerance 2 – 15% in planted areas
p g
Slope tolerance 0 – 1.5% in planted areas
I. Why are stormwater bioretention facilities important? x Infiltrate and Reduce Runoff x Filter Pollutants x Restore Ecological Function (Create Habitat) x Integrate Stormwater into the Landscape - Turn Problems into Beauty
II. How well do these facilities work?
x Design Components x Expectations of performance for stormwater bioretention facilities
Water Quality Value
Volume Reduction
Temperature Reduction
Oils/Floatables Reduction
Rain Garden <10 mg/l Significant Decrease Significant Infiltration Basin/Trench <10 mg/l Significant Decrease Significant Bioretention <10 mg/l Moderate Decrease Significant Pervious/Porous Pavement
10-20 mg/l Moderate Decrease Significant
Extended Detention Wetland
<10 mg/l Significant Unchanged Moderate
Vegetated Swales (Bioswale)
10-20 mg/l Moderate Unchanged Significant
Rain Garden Infiltration Basin/Trench Bioretention *Source: California Stormwater Quality Association, BMP Handbook, 2003/2009
Pervious/Porous Pavement Extended Detention Wetland Vegetated Swales (Bioswale)
*Source: California Stormwater Quality Association, BMP Handbook, 2003/2009 III. Measured Findings
x USGBC Stormwater Monitoring Research Results x Lessons learned from failures or under performance
1. Preservation of the existing landscape 2. Reducing disruption of site soils 3. How site characteristic inform design 4. Cost/stormwater benefit 5. Size and the problems of undersized systems 6. Mimicking Mother Nature 7. Plant selection 8. Design complexity 9. Low Cost Can Still be Effective 10) Stormwater Management Can be Beautiful
References
x California Stormwater Quality Association, BMP Handbook, 2003/2009 x APWA/MARC Best Management Practices Manual, 2009 x Hinman, C., “Bioretention Soil Mix Review and Recommendations for Western Washington”,
2009. x Hsieh, C., and A. P. Davis, “Multiple-Event Study of Bioretention for Treatment of Urban
Storm Water Runoff”, Diffuse Pollution Conference, Dublin, 2003. x Hunt, W.F., and W.G. Lord, “Bioretention Performance, Design, Construction, and
Maintenance”, North Carolina State Cooperative Extension Service, 2006.
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1. Water Into the System
2. Clogging at the Entry Point
3. Water Movement thru the soil
4 Areas of common mistakes in bioretention design
4. Water Out of the System
1. Water Into the SystemGrading toward the water access points
We assume this is the way the grades will fall…… But the grades do not always do that
Fall line
1. Water Into the SystemTurning the water into the catchment basin
Water does not want to turn 90°
Use gravity and or laminar flow to get water around the corner. Higher water velocity in the gutter will easily overcome laminar flow and gravity, letting the water flow past the entry.
Cheater curbs
Larger radius better
Too narrow
Too low and narrow
Making a better entry
1000 cf of loam soil treats 2,000 sf of paved surface (1.25 P storm)
1. Water Into the SystemSizing the system
1. Water Into the SystemSizing the system
Rain water systems are taking up increasingly larger amounts of urban space
Layered systems to improve land use ratio
1. Water Into the SystemSizing the system
Layered systems to improve land use ratio
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Perforated distribution pipe is installed to bring water from the catch basin through the Silva Cell system
Catch Basin
Queensway InstallationPutting the entire bioretention system under pavement
2. Clogging at the Entry PointFloatables and silt
2. Clogging at the Entry PointFloatables and silt
Rip rap caused clogged catchment
Steeper entry slope and larger unplanted fore bay needed.
Rip rap over opening to prevent velocity blow out
2. Clogging at the Entry PointDesigning for Maintenance
No covers over access channels
Thin, small cover over large opening
No tree at opening
No planting at water access zone for cleaning
Macro-pores
Micro-pores3. Water Movement thru the soilCapillary vs gravity water
Saturation Point Field Capacity Wilt Point
Gravity Water
20-25% of soil volume
Capillary Water
20-25% of soil volume
3. Water Movement thru the soilInfiltration rates are set by:
Soil type andSoil structure / preserved peds andSoil compaction
Unscreened sandy loam soil
Plants will grow best in unscreened sandy loam soils. Sandy loam soil with plants best captures pollutants.
Screened sandy loam soil mixSand/compost bio‐retention soil mix
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Fine grained soilInterface
3. Water Movement thru the soilSoil interface and water
Interface
Soil interface slowing the flow of water.
Upper layer must become saturated before water moves into lower layer.
Drainage rate in lower soil sets the total drainage rate for the two soils.
Coarse grained soil or compacted soil layer
3. Water Movement thru the soilWater drains too slow
Drains too slow!Too much water in?Too slow water out?Bio‐retention soil and still clogged?
3. Water Movement thru the soilWater drains too fast
Drains too fast!Piping and fine particle migration?Bio‐retention soil drains too fast?
Rain
Runoff RAISED overflow invert
Water head above soil
Soil
4. Water Out of the System
Stand Pipe Concept
Retention
Detention
To outfall
Perforatedsub drain line
Small amounts of Infiltration
Solid stand pipe
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