Sub-grade

The term “sub-grade” refers to the excavated bottom of native soils that forms the bottom of a ground-level LID practice. Excavation to the subgrade will differ depending on whether the design is for an infiltrating or a non-infiltrating LID system. If it’s an infiltrating practice, the sub-grade should be as level as possible to promote even infiltration across the facility’s footprint. For non-infiltrating practices, excavate sub-grade slopes to the design grade in the direction of the underdrain, typically 1 to 5 %. As with all infiltrating LID practices, avoid compaction of sub-grade soils whenever possible. However, depending on the design and the local municipality, compaction of the sub-grade may be required.

Low 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.

A perforated pipe used to assist the draining of soils.