Effect of Soil Type and Static versus Dynamic Design Approaches on LID Facility Size and Cost

Presentation Overview:

Ministry of Environment, Conservation and Parks (MECP) draft guidelines for low impact development (LID) help to inform the sizing of LID facilities that aim to control the runoff generated by the regionally-specific 90th percentile rainfall event. Municipalities that seek to implement LID are often faced with site constraints in which a portion of the drainage area cannot feasibly be managed by LID. In these cases, “overcontrol” of LID is often practiced to compensate for the unmanaged area. However, consistent methods for calculating the degree of LID overcontrol needed to meet stormwater water quality or retention criteria have not been practiced to date. This project examined a set of right-of-way LID projects in the City of Kitchener. By calculating the nonlinear relationship between LID sizing depth and average annual retention volume, we demonstrated that the overcontrol needed to achieve criteria is much greater than a simple 1:1 offset in LID treatment depth. We next examined the effect of soil type by comparing results from a static design-based spreadsheet calculator, and the LID Treatment Train Tool with a dynamic design approach. We found that the degree of overcontrol needed is strongly influenced by soil type, and the selection of either a static or dynamic design approach. This has important cost implications for right-sizing LID infrastructure based on soil type, and potential adjustments for I/P ratios for different LID and soil types.

Learning Objectives:

  • Explore the nonlinear relationship between LID sizing depth and average annual retention volume, and understand the effect of soil type on LID sizing depth and average annual retention volumes.
  • Understand the degree of overcontrol required when LID is only feasible to manage a portion of catchment area runoff, and learn how water quality treatment measures in series (i.e. LID and OGS) can be sized jointly to achieve stormwater criteria.
  • Learn about examples of recently developed City of Kitchener LID standard drawings used to provide examples of the LID integration into the municipality’s complete streets initiative (road cross sections including LID features).


Matthew Wilson, City of Kitchener and Josef Kardos, Jacobs

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