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On a watershed scale, factors contributing to flooding include the total volume of stormwater, the peak flow and the duration of peak flow.
On a watershed scale, factors contributing to flooding include the total volume of stormwater, the peak flow and the duration of peak flow.
All low impact development facilities can help to prevent flooding by providing watershed distributed stormwater storage, and most feature some form of peak flow control device at the outflow or [[overflow]]. The limiting factors in the contribution that a system can make to flood control include the total storage and [[drainage time|the rate at which the system can be emptied between events]].
All low impact development facilities can help to prevent flooding by providing watershed distributed stormwater storage, and most feature some form of peak flow control device at the outflow or [[overflow]]. The limiting factors in the contribution that a system can make to flood control include the total storage and [[drainage time|the rate at which the system can be emptied between events]].
The smallest diameter orifice accepted by most municipalities to ensure that clogging does not occur in a stormwater system is 75 mm. The preferred minimum orifice size is 100 mm where the effects of freezing are a concern. It is recommended that this latter size be maintained for exposed outlet designs (i.e., reverse sloped pipes).
The smallest diameter orifice accepted by most municipalities to ensure that clogging does not occur in a stormwater system is 75 mm. The preferred minimum orifice size is 100 mm where the effects of freezing are a concern. It is recommended that this latter size be maintained for exposed outlet designs (i.e., reverse sloped pipes).
In instances where a perforated riser outlet is designed, the orifice is protected by the smaller perforations in the riser and a minimum orifice size of 50 mm is acceptable. Where small orifices are required, consideration should be given to providing an overflow outlet which would operate in the event that blockage of the primary orifice occurs.<ref>Ontario Ministry of Environment. (2003). Stormwater Management Planning and Design Manual. Retrieved January 15, 2017, from https://www.ontario.ca/document/stormwater-management-planning-and-design-manual/stormwater-management-plan-and-swmp-design</ref>
In instances where a perforated riser outlet is designed, the orifice is protected by the smaller perforations in the riser and a minimum orifice size of 50 mm is acceptable. Where small orifices are required, consideration should be given to providing an overflow outlet which would operate in the event that blockage of the primary orifice occurs<ref>Ontario Ministry of Environment. (2003). Stormwater Management Planning and Design Manual. Retrieved January 15, 2017, from https://www.ontario.ca/document/stormwater-management-planning-and-design-manual/stormwater-management-plan-and-swmp-design</ref>.
'''[[Flow through an orifice]]'''
==Weirs==
==Weirs==
https://books.google.ca/books?id=fTQWDQAAQBAJ&dq=Jefferies+Scotland+Swales+2004&source=gbs_navlinks_s
https://books.google.ca/books?id=fTQWDQAAQBAJ&dq=Jefferies+Scotland+Swales+2004&source=gbs_navlinks_s
==Multi-stage Risers==
==Multi-stage Risers==
*[http://echelonenvironmental.ca/stormwater/stormwater-flow-control/vortex-valves/ Echelon vortex valves]
*[http://echelonenvironmental.ca/stormwater/stormwater-flow-control/vortex-valves/ Echelon vortex valves]
*[https://www.hydro-int.com/en/hydro-brake-flow-control-series Hydrobrakes]
*[https://www.hydro-int.com/en/hydro-brake-flow-control-series Hydrobrakes]
==See also==
*[[Blue roofs]]
*[[Dry ponds]]
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