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LID SWM Planning and Design Guide β

Site assessment of residential

Understanding site conditions is critical when Screening LID Options. Gaining comprehensive knowledge of the proposed site requires a desktop review of relevant background information followed by field reconnaissance to verify the review and identify relevant site conditions not included in background information.

Desktop analysis

As you begin gathering and reviewing background information, determine any existing infrastructure gaps and planned upgrades, resident concerns, previous community greening efforts, past water usage and past problems with basement flooding. The following sources of information should be considered when conducting a desktop analysis:

  • Watershed studies
  • Subwatershed studies
  • Stormwater master plans
  • Sewershed delineation
  • Areas with identified storm sewer capacity issues
  • Areas contributing to combined sewer overflows
  • Areas of degraded water quality
  • Areas prone to flooding (both urban and riverine)
  • Water quality targets
  • Flow targets
  • Infiltration targets
  • The impact of planned development on existing infrastructure and watershed health
  • Source water protection plans
  • Wellhead protection areas (quantity and quality)
  • Surficial Geology
    • Soil characterization
    • Groundwater levels

Local bylaws and regulations

Be sure to know the relevant local bylaws before developing recommendations. Some LID features may contravene local regulations. Below are some examples of typical bylaws and their potential impact on LID planning:

Typical Bylaws General Provisions May Include: Impacts on LID Options:
Nuisance weeds and tall grass
  • Designates tall grass and weeds as a public nuisance:
  • Defines “tall grass” as grasses over a maximum height (typically 20 – 30 cm)
  • Requires tall grass to be cut to a height not exceeding the maximum height
  • Requires all nuisance weeds and weed seeds to be removed from a property by the owner
  • The municipality may carry out the work to bring properties into
  • Compliance and recovery costs from the land owner
Vegetated LID practices may be in violation of the relevant bylaw, e.g. landscape naturalization with prairie or ornamental grasses.
Property standards

Sets minimum requirements for privately owned properties

  • Restricts low-lying areas, including those that have been excavated and accumulate water, and requires that they be drained, filled and graded so that water drains to a storm sewer or ditch.
  • Requires that all landscaped areas be maintained in a reasonable condition relative to the neighboring environment
Can preclude the some LID practices, such as bioretention facilities designed be both low-lying and including ‘shallow’ surface ponding. Such bylaws can also prohibit other BMPs which rely on naturalizing landscapes.
Sewer use Although generally limited to sanitary sewers, many municipalities now include stormwater within this by-law. It generally requires all stormwater be discharged to an approved outlet and regulates the contents of the discharged water. May not permit direct discharge of roof water to the municipal storm sewer system. This can include overflow from rainwater harvesting tanks and similar devices.
Standing water

Prevents accumulation of water on an individual property within any depression

  • Often in response to mosquito breeding and West Nile Virus concerns.
  • Accumulation is typically defined by a determined period of time (e.g. 48 hours)

Infiltration trenches or chambers, bioretention, or swales may be prohibited.

Boulevard planting Regulates the type of vegetation that can be planted within the boulevard area Swales may be constrained by plant-type and plant-height restrictions along municipal boulevards
Roof leader policies (often part of property standards bylaws)

Regulates the collection and allowable discharge location of roof drainage

  • May specify outlet distance from building foundation and may prohibit discharge to storm sewers, impervious surfaces and property boundaries

Progressive roof leader policies can encourage the implementation of rain gardens, rain barrels and other LID practices.
See Downspout disconnection

Field reconnaissance

After concluding a desktop analysis, visiting the neighbourhood in question for field reconnaissance is be ideal. Be sure to look for:

  • Neighbourhood characteristics – general impressions
  • General lot characteristics:
    • Driveway sizes
    • Driveway types (% of asphalt, gravel, block pavers, etc.)
    • Percentage of property covered by house
    • Percentage of property covered by turf
    • Percentage of property covered by alternative landscaping
    • Percentage of property covered by trees
    • Percentage of property covered by curb
    • Location and general condition of gardens
    • Distribution and coverage of natural vegetation
    • Location of septic systems
    • Fencing style and location
    • Prevalence of irrigation systems
    • Roadside swales
  • Drainage characteristics
  • Rooftop / drainage characteristics
  • Best management practices info

This list is not meant to be exhaustive - keep your eyes open for other relevant factors, and let us know if there's anything we should add.

Once the analysis is complete, proceed to developing a list of recommended BMPs for implementation.