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Line 31: − + + + + + − Stormwater runoff volume reductions vary between sites, primarily due to factors other than the native soil infiltration rate. For instance, the infiltration trenches and chambers shown in the Figure xx had similar native soil infiltration rates (3.1 to 5.1 mm/h), but runoff reduction values varying from 16 to 90%, chiefly due to site to site differences in the I:P ratio (reference definition), which ranged from 10:1 to 155:1. + − − − − The studies below clearly indicate that significant volume reduction through infiltration is feasible on low permeability soils. If geotechnical investigations indicate that volume loss through infiltration is not possible, or would provide more limited benefits than found in these studies, the project should focus on reducing runoff through vegetative evapotranspiration. See here for a list of options, and their relative potential to reduce runoff through evapotranspiration.
→Performance studies on fine textured soils
[[File:Infiltration_rates_studies.png|thumb|400 px|Facility wide infiltration rates for different LID practices installed in the Greater Toronto Area]]
[[File:Infiltration_rates_studies.png|thumb|400 px|Facility wide infiltration rates for different LID practices installed in the Greater Toronto Area]]
A number of field studies of LID practices have been conducted in southern Ontario on fine textured soils. Several of these studies have yielded data that allow for calculation of the facility wide infiltration rate during natural rain events of varying sizes. These are summarized in Figure xx. Infiltration rates on silty clay, clayey silt and sandy silt textured soils had a median value of 3.3 mm/h and a range between 0.3 and 17.8 mm/h. Permeable pavements had lower values in part due to compaction of the subsoils to accommodate traffic loading.
A number of field studies of LID practices have been conducted in southern Ontario on fine textured soils. Several of these studies have yielded data that allow for calculation of the facility wide infiltration rate during natural rain events of varying sizes:
*Infiltration rates on silty clay, clayey silt and sandy silt textured soils had a median value of 3.3 mm/h and a range between 0.3 and 17.8 mm/h.
*Permeable pavements had lower values in part due to compaction of the subsoils to accommodate traffic loading.
*Stormwater runoff volume reductions vary between sites, primarily due to factors other than the native soil infiltration rate. For instance, the infiltration trenches and chambers shown in the Figure xx had similar native soil infiltration rates (3.1 to 5.1 mm/h), but runoff reduction values varying from 16 to 90%, chiefly due to site to site differences in the I:P ratio (reference definition), which ranged from 10:1 to 155:1.
*The configuration of the outflow was also an important consideration. In systems where the outlet is elevated above the native soil, runoff reduction levels tend to be considerably higher than systems with underdrains located at the native soil interface, even if outflow rates from the non-elevated drains are controlled by orifices or flow control valves.
The studies, tabulated below, clearly indicate that significant volume reduction through infiltration is feasible on low permeability soils. If geotechnical investigations indicate that volume loss through infiltration is not possible, or would provide more limited benefits than found in these studies, the project should focus on reducing runoff through vegetative evapotranspiration. See here for a list of options, and their relative potential to reduce runoff through evapotranspiration.
The configuration of the outflow was also an important consideration. In systems where the outlet is elevated above the native soil, runoff reduction levels tend to be considerably higher than systems with underdrains located at the native soil interface, even if outflow rates from the non-elevated drains are controlled by orifices or flow control valves.
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