Changes

*wet ponds;

*wet ponds;

*[[dry ponds]];

*[[dry ponds]];

*infiltration facilities with quantity control component; and,

*[[infiltration]] facilities with quantity control component; and,

*low impact development practices with quantity control component.

*low impact development practices with quantity control component.

Infiltration facilities and low impact development practices (such as [[bioretention]] and [[rainwater harvesting]]) are typically designed to manage more frequent and lower magnitude rainfall events. However, should these practices be designed for year round functionality, with sufficient flood storage capacity, the volume reductions associated with these practices will only be recognized where the local municipality has endorsed the use of these practices and has considered long term operations and maintenance.

Infiltration facilities and low impact development practices (such as [[bioretention cells]] and [[rainwater harvesting]]) are typically designed to manage more frequent and lower magnitude rainfall events. However, should these practices be designed for year round functionality, with sufficient flood storage capacity, the volume reductions associated with these practices will only be recognized where the local municipality has endorsed the use of these practices and has considered long term operations and maintenance.

==Background Research==

Background Research

TRCA undertook modeling excises to evaluate effectiveness of different stormwater management measures (LID and Ponds) in mitigating impacts of development on the peak flow and runoff volume. A sub-catchment in Humber River was selected that has an area of 35.71 ha. The existing land use in the sub-catchment is agriculture and the proposed future land use is employment land with 91% total imperviousness.

TRCA undertook modeling excises to evaluate effectiveness of different stormwater management measures (LID and Ponds) in mitigating impacts of development on the peak flow and runoff volume. A sub-catchment in Humber River was selected that has an area of 35.71 ha. The existing land use in the sub-catchment is agriculture and the proposed future land use is employment land with 91% total imperviousness.

Hydrological model run were carried out by integrating different stormwater management measures (LID and SWM Pond) for 2-year and 100-year 6-hr AES design storms.

Hydrological model run were carried out by integrating different stormwater management measures (LID and SWM Pond) for 2-year and 100-year 6-hr AES design storms.

Scenarios evaluated include:

Scenarios evaluated include:

1. LID measures that provide 25 mm on-site retention

#LID measures that provide 25 mm on-site retention

2. SWM pond to control post-development peak flows to pre-development peak flows.

#SWM pond to control post-development peak flows to pre-development peak flows.

3. Combination of scenario 1 and scenario 2

#Combination of scenario 1 and scenario 2

Runoff volume and peak flow reductions were calculated. The figures and tables below show hydrographs extracted and the calculated change runoff volume and peak flow .

Runoff volume and peak flow reductions were calculated.  

 

===Peak Flow===

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Peak Flow

25 mm on-site retention using LID measures can reduce post-development peak flows generated from 2 to 5 year design storms by over 26%, whereas for 50  and 100 year design storms it reduces only 4%  and 1% respectively. This shows that LID will not reduce significantly the post-development peak flows generated  from major storms.

25 mm on-site retention using LID measures can reduce post-development peak flows generated from 2 to 5 year design storms by over 26%, whereas for 50  and 100 year design storms it reduces only 4%  and 1% respectively. This shows that LID will not reduce significantly the post-development peak flows generated  from major storms.

Runoff Volume

===Runoff Volume===

25 mm on-site retention using LID measures can reduce post-development runoff volume generated from 2 to 5 year design storms by over 52 %, whereas for 50  and 100 year design storms it reduces only 33%  and 30% respectively. This shows that the post-development runoff volume generated from major storms  going to receiving features can be reduced considerably by implementing LID to retain 25 mm.   

25 mm on-site retention using LID measures can reduce post-development runoff volume generated from 2 to 5 year design storms by over 52 %, whereas for 50  and 100 year design storms it reduces only 33%  and 30% respectively. This shows that the post-development runoff volume generated from major storms  going to receiving features can be reduced considerably by implementing LID to retain 25 mm.   

Finally, LID as standalone cannot control post-development peak flows to pre-development peak flows under major storm events.  

Finally, LID as standalone cannot control post-development peak flows to pre-development peak flows under major storm events.  

Therefore, in order to meet flood control requirements, LID need to be augmented by some flood storage measures such as dry/park ponds, underground storage.  

Therefore, in order to meet flood control requirements, LID need to be augmented by some flood storage measures such as dry/park ponds, underground storage.  

 

==Literature Review==

Literature Review/Identify examples

Review examples of where LID practices with quantity control components have been used for achieving flood control  

Review examples of where LID practices with quantity control components have been used for achieving flood control  

Example 1: Costco Distribution Centre

Example 1: Costco Distribution Centre

Final erosion control provided within the stormwater management facility, controlling release rates to maintain the existing condition erosion exceedance values.

Final erosion control provided within the stormwater management facility, controlling release rates to maintain the existing condition erosion exceedance values.

Final design required both LIDs to reduce the overall runoff volumes, but also sub-surface storage chambers to provide quantity control for rare storm events up to the 100-year design storm. Due to large area required for truck parking, limited opportunities for more landscaping to promote evapotranspiration, runoff volumes increased beyond ability of LIDs to negate the need for quantity control.

Final design required both LIDs to reduce the overall runoff volumes, but also sub-surface storage chambers to provide quantity control for rare storm events up to the 100-year design storm. Due to large area required for truck parking, limited opportunities for more landscaping to promote evapotranspiration, runoff volumes increased beyond ability of LIDs to negate the need for quantity control.

Example 2. West Gormley, Town of Richmond Hill

Example 2. West Gormley, Town of Richmond Hill

Residential development consisting of low and medium density land-use is implemented on the site. Average site imperviousness is approximately 60%;

Residential development consisting of low and medium density land-use is implemented on the site. Average site imperviousness is approximately 60%;

Water balance/Erosion Control – Retention of 5 mm event on-site

Water balance/Erosion Control – Retention of 5 mm event on-site

Stormwater Strategy

==Stormwater Strategy==

Large portion of the roof proposed as green roof and cistern proposed in underground parking to capture remaining volume to meet 5 mm target.  Water to be used for irrigation and carwash stations.

Large portion of the roof proposed as green roof and cistern proposed in underground parking to capture remaining volume to meet 5 mm target.  Water to be used for irrigation and carwash stations.

Quality target achieved as majority of site is ‘clean’ roof water or directed to pervious area. Underground storage tank provided to satisfy municipal release rates to receiving storm sewer system.

Quality target achieved as majority of site is ‘clean’ roof water or directed to pervious area. Underground storage tank provided to satisfy municipal release rates to receiving storm sewer system.

Overall Conclusions

===Overall Conclusions===

Final design required both LIDs to reduce the overall runoff volumes, but also sub-surface storage chambers to provide quantity control to meet municipal requirements.

Final design required both LIDs to reduce the overall runoff volumes, but also sub-surface storage chambers to provide quantity control to meet municipal requirements.

Due to underground parking limited opportunities for infiltration LIDs but used green roof to promote evapotranspiration, and cistern to reduce runoff volumes.  

Due to underground parking limited opportunities for infiltration LIDs but used green roof to promote evapotranspiration, and cistern to reduce runoff volumes.  

 

==Data Analysis/Modelling==

 

Data Analysis/Modelling

Suggest detailed modelling to evaluate how source and conveyance controls could provide a flood control function

Suggest detailed modelling to evaluate how source and conveyance controls could provide a flood control function

Fieldwork

Fieldwork