Screening LID options

From LID SWM Planning and Design Guide
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Process for selecting a suite of LID Options[edit]

Process Diagram for Screening LID Options

Site Conditions[edit]

Complete definition of pre-development site conditions is essential prior to screening of

potential stormwater BMPs. The designer should prepare maps describing site

conditions, to ensure that all environmental features and functions that need

consideration in accordance with provincial, municipal and conservation authority

development regulations are identified. This includes watercourses and small drainage

features, floodplains, important recharge areas, steep slopes, wetlands, natural heritage

conservation areas and significant wildlife habitats. In addition, information regarding

native soil types, infiltration capacity and depth to water table must be determined.


Define Design Criteria[edit]

A detailed description of the design criteria that need to be defined is provided in the

respective CVC and TRCA Stormwater Management Criteria documents. If outside jurisdictional

boundaries, criteria developed should have requirements to:

  • preserve groundwater and baseflow characteristics;
  • prevent undesirable and costly geomorphic changes in the watercourse;
  • prevent any increases in flood risk potential;
  • protect water quality; and ultimately,
  • maintain an appropriate diversity of aquatic life and opportunities for human uses

The design criteria required to protect, enhance or restore the environmental resources

can be grouped under the following five categories.

  • Flood Protection;
  • Water Quality;
  • Erosion Control;
  • Recharge; and
  • Natural Heritage Systems or green infrastructure


Screen Potential LID Options[edit]

A number of factors need to be considered when screening the suitability of a given

location within a development site for application of stormwater BMPs. Table 3.4.1

summarizes site constraints associated with some general types of structural LID

practices for stormwater management that should be considered. Further

information regarding constraints to the design of various end-of-pipe BMPs can be

found in the Ontario Ministry of the Environment Stormwater Management Planning and

Design Manual (2003). The use of LID BMPs should be considered first to meet the

design criteria before the use of end-of-pipe BMPs.


Structural Requirements or Site Constraints[edit]

Performance Requirements[edit]

Operations and Maintenance Requirements[edit]

Life Cycle Costing Requirements[edit]

Select LIDs (Conceptual Design)[edit]

In order to assess if the selected suite of BMPs effectively meet the design criteria

either computer models or simple spreadsheet models should be used. Model selection

will be based on the size and type of development. A wide range of simple to complex

computer models such as Visual OTTHYMO, SWMM, SWMMHYNO, HSP-F and

QUALHYMO are available.

Assess Effectiveness[edit]

Once the suite of best management practices have been selected and the models have

been run, a comparison of the results and the environmental design criteria can be

made. An iterative approach, which involves adjusting the size or adding/deleting BMPs

should be used until the environmental design criteria are met. The project can then

proceed to the detailed design stage.