Changes

[[File:Dryponds map.PNG|thumb|link=https://goo.gl/68Ewnz|Click here to see map of Dry Ponds in Scarborough and surroundings]]

[[File:Dryponds map.PNG|thumb|link=https://goo.gl/68Ewnz|Click here to see map of Dry Ponds in Scarborough and surroundings]]

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Also known as infiltration basins or detention basins (according to their features). Dry ponds are a grassed alternative to [[bioretention]] cells. This permits the landscape to be accessed and used as an amenity space.  

Also known as infiltration basins or [[detention basins]] (according to their features). Dry ponds are a grassed alternative to [[bioretention]] cells. This permits the landscape to be accessed and used as an amenity space.  

==Overview==

==Overview==

Dry ponds are recommended as [[flood control]] structures to accommodate occasional excess overflow downstream of other structural BMPs. They should be integrated into the landscape as useful, accessible public space.

Dry ponds are recommended as [[flood control]] structures to accommodate occasional excess overflow downstream of other structural BMPs. They should be integrated into the landscape as useful, accessible public space.

Dry ponds are a useful tool for managing flooding during larger storm events. They are well suited to being placed downstream of other smaller distributed BMPs for occasional backup flood protection.  

Dry ponds are a useful tool for managing flooding during larger storm events. They are well suited to being placed downstream of other smaller distributed BMPs for occasional backup flood protection.  

Where possible they should be integrated into amenity space, given that users rarely wish to continue outdoor activities during such intense rainstorms.  

Where possible they should be integrated into amenity space, given that users rarely wish to continue outdoor activities during such intense rainstorms.  

===Risk===

===Risk===

==Design==

==Design==

{|{| class="wikitable"

{|{| class="wikitable"

|+Design parameters for dry ponds <ref name="MOE">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>

|+Design parameters for extended detention<ref name="MOE">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>

!Element  

!Element  

!Design Objective  

!Design Objective  

|style="text-align: left|Minimum 3 m above maximum water quality/erosion control water level

|style="text-align: left|Minimum 3 m above maximum water quality/erosion control water level

|}

|}

The bottom of a dry pond should be flat to encourage uniform ponding and infiltration across the entire surface. Recommended tolerance on base levels 10 mm in 3m.  

The bottom of a dry pond should be flat to encourage uniform ponding and infiltration across the entire surface. Recommended tolerance on base levels 10 mm in 3m.  

===Detention time===

===Detention time===

A detention time of 24 hours should be targeted in all instances. Where this necessaitates a very low outflow, a [[Flow control#Vortex valve|vortex valve]] or similar is recommended over an orifice or pipe restiction. The detention time is approximated by the drawdown time.

A detention time of 24 hours should be targeted in all instances. Where this necessaitates a very low outflow, a [[Flow control#Vortex valve|vortex valve]] or similar is recommended over an [[orifice]] or pipe restiction. The detention time is approximated by the drawdown time.

The drawdown time in the pond can be estimated using the classic falling head orifice equation which assumes a constant pond surface area<ref name="MOE"/>. This assumption is generally not valid, and a more accurate estimation can be made if the equation is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression:

The drawdown time in the pond can be estimated using the classic falling head orifice equation which assumes a constant pond surface area<ref name="MOE"/>. This assumption is generally not valid, and a more accurate estimation can be made if the equation is solved as a differential equation. This is easily done if the relationship between pond surface area and pond depth is approximated using a linear regression:

==External links==

==External links==

*[https://www.edmonton.ca/residential_neighbourhoods/PDF/handout_nov_ld.pdf Edmonton Dry Ponds]

*[https://www.edmonton.ca/residential_neighbourhoods/PDF/handout_nov_ld.pdf Edmonton Dry Ponds]

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[[category: Modeling]]

[[category: Modeling]]