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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===

|Avoid clogging/freezing  

|Avoid clogging/freezing  

|style="text-align: left|

|style="text-align: left|

*Minimum 450 mm;  

*Minimum 450 mm diameter inlet pipe;  

*Preferred pipe slope: > 1 %;  

*Preferred pipe slope: > 1 %;  

*If submerged, obvert 150 mm below expected maximum ice depth

*If submerged, obvert 150 mm below expected maximum ice depth

|Avoid clogging/freezing  

|Avoid clogging/freezing  

|style="text-align: left|

|style="text-align: left|

*Minimum: 450 mm outlet pipe;  

*Minimum: 450 mm diameter outlet pipe;  

*Preferred pipe slope: > 1 %;  

*Preferred pipe slope: > 1 %;  

*If orifice control used, 75 mm diameter minimum;  

*If orifice control used, 75 mm diameter minimum;  

===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]]