stormwater best management practices - … · create/enhance habitat & bio-diversity •...
TRANSCRIPT
STORMWATER BEST
MANAGEMENT PRACTICES
Hans Arisz Associate Director
R.V. Anderson Associates Limited
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OUTLINE
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OUTLINE
• Urbanization Impacts • Storm Water Management Objectives • Storm Water Management Strategy • References • Best Management Practices
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URBANIZATION IMPACTS
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HYDROLOGIC EFFECTS
Source: CIRIA open space 2012
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HYDROLOGIC EFFECTS
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EFFECTS ON STORMWATER
• Increase in runoff flow rate • Increase in watercourse erosion • Construction erosion and sediment
discharges • Increase pollutants in runoff • Thermal enrichment of runoff
• Increased in runoff volume • Decrease in groundwater recharge • Decrease in evapotranspiration (ET)
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STORM WATER MANAGEMENT OBJECTIVES
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SWM OBJECTIVES
• Water Quantity • Reduce/control peak flows • Maintain low flows
• Water Quality
• Prevent pollution • Treat water • Maintain stream temperature
• Amenity
• Create/enhance habitat & bio-diversity • Maintain/enhance aesthetic value
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STORM WATER MANAGEMENT STRATEGY
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SWM STRATEGY
• Strategy components: • Minimize runoff:
• Store it and release it slowly (attenuation) • Allow it to soak into the ground (infiltration)
• Transport (convey) it slowly • Clean it (filter/settle pollutants)
• Different names • Low Impact Development (LID) - USA • Sustainable Urban Drainage Systems (SUDS) – UK • Water Sensitive Urban Design (WSUD) – Australia • Natural Drainage Systems/ Onsite Drainage
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SWM DESIGN FACTORS
• Effectiveness & site conditions (space & soils) • Cost (capital and O&M) • Robustness • Durability • Maintenance • Ownership/control
• Scale (small and many vs. large and few) • Climate
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REFERENCES
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REFERENCES
• “Stormwater Management Planning and Design Manual”, March 2003, Ontario MoE
• http://www.ene.gov.on.ca/environment/en/resources/ • Canadian/cold climate • Planning • Design criteria & examples • Infill Development • Operation, maintenance and monitoring • Capital and operating costs
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BEST MANGEMENT PRACTICES
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TREATMENT TRAIN
• Lot Level/Source Controls • Conveyance Controls • End of Pipe Controls
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LOT LEVEL/SOURCE CONTROLS
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SOURCE CONTROLS
• Dealing with water when and where it falls • Examples:
• Rainwater harvesting • On site ponding
• Rooftop storage • Parking lot storage • Green roofs • Super-pipe storage
• Infiltration • Rain gardens • Infiltration pits • Permeable surfaces
• Green roofs
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WATER BALANCE COMPUTATIONS
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RAINWATER HARVESTING
• To collect and store rain water
• Simple to complex • Rain barrels, tanks, butts • Rainwater systems for
domestic use (engineering design)
• Capacity considerations
• Purpose • Rooftop area X rainfall • Overflow
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ONSITE PONDING
• Backyard Ponds • Depressions that collect
stormwater for infiltration or evaporation.
• Maximum depths < 100 mm. • Flow paths altered to direct
overland flow to pond. • > 4 m from house
• For rooftop storage • Drains on flat roofs are raised • Max. ponding depth ~ 10 mm • Sized for 5-25 mm of rain
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GREEN ROOFS
• Advantages • Mitigation of
storm water runoff
• Protection of the roof
• Improved urban environment
• Consider • Plant types
(normally shallow roots)
• Structural requirements
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RAIN GARDENS
• A planted area for infiltration of stormwater from impervious urban areas
• Intended to capture initial flow of stormwater (reduce runoff)
• Intended generally to be surface drainage endpoint
• Not intended to have standing water
• Not intended to convey water elsewhere
• Natural filters: can reduce amount of pollution otherwise reaching streams
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INFILTRATION PITS
Figure From MOE Publication – Understanding Stormwater Management , An Introduction to Stormwater Management Planning & Design
• Rock drain material with filter liner
• Used for small runoff/ detention volumes
• Reduces surface ponding
• Design: • Infiltration area (surface)
to drain within 48 hrs • Total void volume based
on smaller storms (~ 2-year) considering material porosity
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ONSITE INFILTRATION
• Includes soakpits, infiltration areas
• Applicability • Groundwater table > 0.6
m of surface • Bedrock > 1.2 m of the
infiltration surface • Not overlying soils with
percolation rate < 1.3 mm.
Source: Alberta Drainage Guidelines
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PERVIOUS PAVEMENTS
• Objectives: • Maintain runoff rates from
developments at pre-development levels.
• Reduce the risk of causing pollution to controlled waters.
• Carry the required traffic loads without structural failure occurring.
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CONVEYANCE CONTROLS
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CONVEYANCE CONTROLS
• Transport runoff (slowly) • Examples of conveyance controls:
• Reduced lot grading • Enhanced roadside ditch/bioswales • Exfiltration / pervious pipe systems • Pervious catchbasins • Super-pipe (oversized sewer system)
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REDUCED LOT GRADING
• Purpose: Reduce runoff volume by increasing travel time
• Typical minimum lot grade of 2% to drain from buildings; 0.5% slope elsewhere
• Benefits: • Decrease runoff volumes • Local groundwater
recharge
Figures From MOE Stormwater Management Planning & Design Manual – March 2003
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BIOSWALES
• Bioswales slope to a destination, while rain gardens do not
• Drainage ditches may be handled like bioswales saving time and money on maintenance.
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ENHANCED SWALE
Figures From MOE Stormwater Management Planning & Design Manual – March 2003
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PERVIOUS CATCHBASIN
Figures From MOE Stormwater Management Planning & Design Manual – March 2003
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END OF PIPE CONTROLS
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END-OF-PIPE CONTROLS
Examples of end-of-pipe controls: • Wet and dry SWM ponds • Wet lands • Infiltration basins • Sand filter
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WET/DRY POND & WETLANDS
Figures From MOE Stormwater Management Planning & Design Manual – March 2003
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INFILTRATION SYSTEMS
Stormtech Infiltration System
Images obtained from Stormtech Website
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INFILTRATION SYSTEMS
“Matrix” Tanks by Atlantis
Images obtained from Atlantis Corp Website
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SAND FILTERS
Figures From MOE Stormwater Management Planning & Design Manual – March 2003
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QUALITY CONTROL
• Sediment and urban runoff contaminants impact quality of receiving waters
• Quality control design criteria are generally based on TSS (& oil) removal
• Other contaminants are indirectly addressed through TSS removal (suspended 50%)
• More stringent criteria also include phosphorous (LEED) and E. Coli (City of Toronto)
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QUALITY CONTROL
CDS Technologies SWM Tanks
Image obtained from www.cdstech.com
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CONCLUDING REMARKS
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CONCLUDING REMARKS
• “One size never fits” • (topography, space, usage and soils)
• 3 R’s • Reduce (retain, infiltrate and evaporate) • Re-use (rainwater harvesting, green roofs and rain
gardens) • Recycle (recharge groundwater)
• Easy does it & speed kills
