stormwater best management practices - … · create/enhance habitat & bio-diversity •...

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

Hans Arisz, Associate Director Tel: 506-455-2888 Fax: 506-455-0193

harisz@rvanderson.com

Questions?