LID Site Criteria and Constraints

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LIDLow Impact Development. A stormwater management strategy that seeks to mitigate the impacts of increased urban runoff and stormwater pollution by managing it as close to its source as possible. It comprises a set of site design approaches and small scale stormwater management practices that promote the use of natural systems for infiltration and evapotranspiration, and rainwater harvesting. Stormwater Management Practice Depth to High Water or Bedrock (m)[1] Typical Ratio of
ImperviousA hard surface area (e.g., road, parking area or rooftop) that prevents or retards the infiltration of water into the soil. Drainage Area
to Treatment Facility Area
Native Soil Infiltration Rate (mm/hr)[2] Head (m)[3] Space % [4] Slope % [5] Applicable in Pollution Hotspots [6] Set Backs Water Table [7] Wellhead Protection Area[8]
Rain Barrel Not applicable [5 to 50 m2] Not applicable 1 0 NA Yes None None None
CisternTank used to store rainwater (typically roof runoff) for later use. Not applicable 1:1 Not applicable 0 0 0 Yes None None None
Roof Downspout Disconnection Not applicable [5 to 100 m2] Amend if < 15 mm/hr 0.5 5 to 20 1 to 5 Yes Building Foundation None None
SoakawayA pit into which liquids may flow and then percolate slowly into the subsoil.An excavated area lined with geotextile filter cloth and filled with clean granular stone or other void forming material, that receives runoff and allow it to infiltrate into the native soil; can also be referred to as infiltration galleries, French drains, dry wells or soakaway pits., Infiltration Trench or Chamber 1 5:1 to 20:1 Not a constraint 1 to 2 0 to 1 <15 % No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
1 m 2 yr
BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. 1 5:1 to 15:1 UnderdrainA perforated pipe used to assist the draining of soils. required
if < 15 mm/hr
1 to 2 5 to 10 0 to 2 No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
1 m 2 yr
BiofilterBiofilters (FiltrationThe technique of removing pollutants from runoff as it infiltrates through the soil. only BioretentionA shallow excavated surface depression containing prepared filter media, mulch, and planted with selected vegetation. Design) Not applicable 5:1 Not applicable 1 to 2 2 to 5 0 to 2 Yes Building Foundation, Trees None None
Vegetated Filter Strip 1 5:1 Amend if < 15 mm/hr 0 to 1 15 to 20 1 to 5 No None None None
Permeable Pavement 1 1:1 to 1.2:1 UnderdrainA perforated pipe used to assist the draining of soils. Required
if < 15 mm/hr
0.5 to 1 0 1 to 5 No 4m-Underground Utilities
Drinking Water Wellhead
Protection Areas
1 m 2 Yr
Enhanced Grass SwaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. 1 5:1 to 10:1 Not applicable 1 to 3 5 to 15 0.5 to 6 No 4m- Building Foundation
Underground Utilities
1 m None
Dry SwaleA shallow constructed channel, often grass-lined, which is used as an alternative to curb and channel, or as a pretreatment to other measures. Swales are generally characterized by a broad top width to depth ratio and gentle grades. (BioswaleLinear bioretention cell designed to convey, treat and attenuate stormwater runoff. The engineered filter media soil mixture and vegetation slows the runoff water to allow sedimentation, filtration through the root zone, evapotranspiration, and infiltration into the underlying native soil.) 1 5:1 to 15:1 UnderdrainA perforated pipe used to assist the draining of soils. Required
if < 15 mm/hr
1 to 3 5 to 10 0.5 to 6 No 4m (3m if impermeable liner
is used)Building foundation,
Underground utilities, drinking
water wellhead protection areas
1 m 2 Yr
Perforated Pipe System 1 5:1 to 10:1 Not a constraint 1 to 3 0 < 15% No 4m- Building Foundation
Underground Utilities, Trees,
Drinking Water Wellhead
Protection Areas
1 m 2 Yr
  1. Minimum depth between the base of the facility and the elevation of the seasonally high water table or top of bedrock
  2. Infiltration rate estimates based on measurements of hydraulic conductivity under field saturated conditions at the proposed location and depth of the practice
  3. Vertical distance between the inlet and outlet of the LID practice
  4. Percent of open pervious land on the site that is required for the LID practice
  5. Slope at the LID practice location
  6. Suitable in pollution hot spots or runoff source areas where land uses or activities have the potential to generate highly contaminated runoff
  7. Separated from the seasonally high water table or top of bedrock elevation
  8. |Time-of-travel within wellhead protection areas