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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.
Compared to wet ponds “Dry ponds… …are less expensive to install, require less maintenance and may involve less liability for the communities around them.”
https://www.fairfaxcounty.gov/soil-water-conservation/understanding-stormwater-ponds
===Risk===
===Risk===
===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]
==To review==
https://www.google.com/imgres?imgurl=http%3A%2F%2Fwww.calgary.ca%2FUEP%2FWater%2FPublishingImages%2FBraeside-Dry-Pond-610px.jpg&imgrefurl=http%3A%2F%2Fwww.calgary.ca%2FWWCDI&docid=RBtJ2qx0jhourM&tbnid=-OUrotj9LMYmfM%3A&vet=10ahUKEwjpwbyNt-bfAhXlguAKHS1pDtQQMwhjKBcwFw..i&w=610&h=299&bih=723&biw=1536&q=traplow%20stormwater&ved=0ahUKEwjpwbyNt-bfAhXlguAKHS1pDtQQMwhjKBcwFw&iact=mrc&uact=8
https://www.fairfaxcounty.gov/publicworks/sites/publicworks/files/assets/documents/drypond_1.pdf
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[[category: Modeling]]
[[category: Modeling]]