Low Impact Development (LID) Techniques Associate BD Presentation, October 7, 2014
Low Impact Development (LID) Techniques What are LIDs? Why are they used? Where are they used? How are they designed or implemented? Recent example Business opportunities
What is LID? LID is a acronym for Low Impact Development LID is a SWM strategy that seeks to mitigate the impacts of increased runoff and stormwater pollution by managing runoff as close to its source as possible. Set of site design strategies that minimize runoff through techniques that that mimic natural or predevelopment hydrology through the processes of infiltration (retention), evapotranspiration, harvesting, filtration and detention of stormwater. Effectively shown to reduce the volume and intensity of stormwater flows and remove nutrients, pathogens and metals from runoff. It is a sustainable alternative or complementary technique to conventional SWM infrastructure
What is LID? For Stormwater Management, they aid in: Stormwater quantity control (peak rate reduction) Stormwater quality control (TSS, TP reduction) Stormwater retention (water balance, reduction in runoff volume) LIDs can be a significant benefit to site SWM and the environment Help a site mimic the natural hydrologic cycle through infiltration and evapotranspiration Filtering runoff as runoff infiltrates into the ground removing many contaminants instead of end-of-pipe solutions (i.e. TSS, TP, TN) Delay and reduce peak discharge rates Can replace some of a site s conventional SWM infrastructure Reduce downstream erosion More vegetation Reduction in urban heat island effect Reduction in downstream erosion
What are LIDs? Common LIDs: Rainwater harvesting (i.e. using captured runoff for irrigation) Permeable pavers Infiltration systems (i.e. soakaway pits, infiltration trenches, chambers, etc) Green roofs Bioretention systems
What are LIDs? Common LIDs: Porous Asphalt Permeable Pavers Pervious Concrete
Why are LIDs Used? To meet regulatory requirements (municipal/conservation) LEED accreditation General environmental consciousness (non-regulatory)
Where are LIDs Used? Not large enough end-of-pipe facilities exist Whereas LID measures are commonly at source type measures and therefore commonly used on sites, they can also be incorporated in municipal ROWs i.e. Enhanced roadside ditches, gutter inlets into boulevard retention basins, perforated pipes
Design of LIDs Some LIDs rely on soil infiltration rates i.e. Permeable pavers, porous concrete, infiltration systems Soil Permeability Source of Runoff (Surface, Site Servicing) Maximum Drawdown Time (48-72hrs) Minimum 4.0m from foundation of nearest building Separated 1m Vertically from Seasonal High Water Table Some LIDs are Generally Accepted as being able to Treat/Control a Tributary Area 5 times their Size Some LIDs rely on captured runoff reuse rates and evapotranspiration i.e. Rainwater harvesting (irrigation systems, toilet flushing, laundry, car washing), bioretention, green roofs Type of Vegetation Source of Runoff (Surface, Site Servicing) How Many Fixtures/Usage Case to use captured Runoff CSA (B128 for Design and Installation of Non-Potable Water Systems/Maintenance and Field Testing of Non-Potable Water Systems) and OBC requirements Note: Not all LIDs are practical for every site
Design Example Edward Gardens Site is located at the southwest corner of Leslie Street and Lawrence Avenue in the City of Toronto, adjacent to Wilket Creek, a tributary of the Don River Project goal: avoid use of conventional SWM infrastructure as much as is reasonable, i.e. OGS units, detention systems, etc) Address stringent City of Toronto SWM Criteria (per Wet Weather Flow Management Guidelines) Protect the downstream watercourse (Wilket Creek) from erosion
Design Example LIDs Used: Permeable pavers Biofilter/Bioretention facilities (with Open Granular Inlets ) river Chosen based on parking lot size, aesthetic and cost
Design Example Pre-Reconstruction Conditions Erosion from uncontrolled flow draining down into Wilket Creek
Design Example Post-Reconstruction Conditions All runoff drains toward permeable pavers Permeable pavers placed only in south parking stalls Can treat an area 5 times their size Runoff not infiltrated by permeable pavers will drain into the subdrain located along the length of the curb and then into storm sewer located along west side of parking lot
Design Example Post-Reconstruction Conditions Open Granular Inlets capture runoff not captured by permeable pavers, runoff will drain into adjacent bioretention facilities Drainage Depressed curb at edge of permeable pavers/asphalt
Design Example Open Granular Inlets Above Biofilter/Bioretention Facilities Post-Reconstruction Conditions All Runoff Captured by Permeable Pavers and Open Granular Inlet will Drain into Biofilter/Bioretention Facilities Beneath Traffic Island Runoff that is not captured by Permeable Pavers or Open Granular Inlet will be Captured by a Catchbasin at West End of each Parking Space Row Catchbasins are connected to a small storm sewer system that is capable of conveying runoff in case of very large storm event or failure of LIDs
Design Example Post-Reconstruction Conditions Biofilter/Bioretention facility underneath traffic islands and adjacent permeable pavers
Design Example Result: The vast majority of storm events can be controlled and treated on site through the use of LIDs Less conventional SWM infrastructure used The LIDs that were used helped achieve the project s goals and demonstrated that they are an effective way to achieve the City of Toronto s stringent SWM WWFM Guidelines. Erosion has been significantly reduced along Wilket Creek bank (downstream)
Opportunities Most design and construction projects can benefit from LIDs So far most projects involving LIDs have been incorporated into our private development assignments but there is no reason why LIDs wouldn t be useful in other kinds of projects (i.e. municipal clients, treatment plant project sites) Current SWM criteria will become more stringent over time and so reliance on LIDs will become greater. In many municipalities and conservation authorities (closer to Toronto and GTA) it is only possible to obtain SWM approval with the use of LIDs due to stringent SWM criteria. This will likely be true far outside of the GTA soon. i.e. more push from conservation authorities for use in road ROWs LIDs can reduce the reliance on or size of conventional SWM infrastructure cost/benefit issues, clients may not yet understand. LID SWM Manual was developed by CVC and TRCA, originally released as draft in October 2009. It is anticipated that the next revision to the MOE SWM Guidelines will focus on these type of approaches. 18