Changes

==Performance studies on fine textured soils==

==Performance studies on fine textured soils==

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.  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.

   

   

Figure xx:  Facility wide infiltration rates for different LID practices installed in the Greater Toronto Area

Figure xx:  Facility wide infiltration rates for different LID practices installed in the Greater Toronto Area

Stormwater runoff volume reductions varied from site to site, 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 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 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 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.       

|Bioretention<ref name = "VS 2015"></ref>||Two growing seasons||Silty clay||10:1||<10 cm; flow rate control||90%

|Bioretention<ref name = "VS 2015"></ref>||Two growing seasons||Silty clay||10:1||<10 cm; flow rate control||90%

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|Permeable Pavement<ref>Van Seters, T. and Drake, J. Five year evaluation of Permeable Pavements, TRCA, Toronto, Ontario</ref>||Five growing seasons||Silty clay||1:1||<10 cm; flow rate control||45%

|Permeable Pavement<ref>Van Seters, T. and Drake, J., 2015, Five year evaluation of Permeable Pavements, TRCA, Toronto, Ontario</ref>||Five growing seasons||Silty clay||1:1||<10 cm; flow rate control||45%

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|Bioretention||One growing season||Silty clay||10:1||<10 cm; flow rate control||83%

|Bioretention<ref>STEP study ongoing (2017)</ref>||One growing season||Silty clay||10:1||<10 cm; flow rate control||83%

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|Bioretention||Two years||Silty clay||11:1||<10 cm; flow rate control||91%

|Bioretention <ref>Van Seters T and Graham C, 2014, Performance Evaluation of a Bioretention System, TRCA, Toronto, Ontario</ref>||Two years||Silty clay||11:1||<10 cm; flow rate control||91%

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|Infiltration chamber||Two years||Sandy silt||20:1||Approx.: 1.2 m||90%

|Infiltration chamber<ref name = "DY 2013">Young D, Van Seters T, Graham, C, 2013, Evaluation of Residential Lot Level Stormwater Practices – tech brief</ref>||Two years||Sandy silt||20:1||Approx.: 1.2 m||90%

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|Infiltration trench||Two years||Clayey silt||64:1||2 m||36%

|Infiltration trench<ref name = "DY 2013"></ref>||Two years||Clayey silt||64:1||2 m||36%

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|Infiltration trench||Two years||Clayey silt||155:1||2 m||16%

|Infiltration trench<ref name = "DY 2013"></ref>||Two years||Clayey silt||155:1||2 m||16%

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|Infiltration trench||Two years||Clay to clay silt till over silty sand till||Approx: 7:1||0.65 m||>90%

|Infiltration trench<ref>SWAMP, 2005.  Performance Assessment of a Perforated Pipe Stormwater Exfiltration system, Toronto, Ontario, TRCA, Toronto, Ontario</ref>||Two years||Clay to clay silt till over silty sand till||Approx: 7:1||0.65 m||>90%

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|Infiltration trench||Two years||Silty sand with clayey silt deposits||Approx: 4:1||1 m||89%

|Infiltration trench<ref>SWAMP, 2002, Performance Assessment of a Swale Perforated Pipe Stormwater Infiltration System, TRCA, Toronto Ontario</ref>||Two years||Silty sand with clayey silt deposits||Approx: 4:1||1 m||89%

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|Permeable pavement + bioretention||Four years||Clayey silt on silt till||Approx: 6:1||?||80%

|Permeable pavement + bioretention<ref>CVCa</ref>||Four years||Clayey silt on silt till||Approx: 6:1||?||80%

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|Bioretention||Four years||Silty clay||Approx.: 10:1||?||92%

|Bioretention<ref>CVCb</ref>||Four years||Silty clay||Approx.: 10:1||?||92%

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|Bioretention||Four years||Silty clay fill over clay till||30:1||?||72%

|Bioretention<ref>CVCc</ref>||Four years||Silty clay fill over clay till||30:1||?||72%

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|Permeable pavement||Four years||Silty clay fill over clay till||1:1||?||?

|Permeable pavement<ref>CVCd</ref>||Four years||Silty clay fill over clay till||1:1||?||?

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<nowiki>*</nowiki>Represents depth of sump below underdrain or outflow pipe.  In some cases, a flow control device was installed to slow outflow rates and enhance infiltration

<nowiki>*</nowiki>Represents depth of sump below underdrain or outflow pipe.  In some cases, a flow control device was installed to slow outflow rates and enhance infiltration

==References==

==References==

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