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Line 102: − 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. − The drawdown time in the pond can be estimated using Equation 4.10. Equation 4.10 is the classic falling head orifice equation which assumes a constant pond surface area. This assumption is generally not valid, and a more accurate estimation can be made if Equation 4.10 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. − − <math>A_O=\frac{2A_{P}}{t\ C(2g^{0.5})}\left ( h_{1}^{0.5}-h_{2}^{0.5} \right )</math> − t = start fraction 2 A subscript p over C A subscript o left-parenthesis 2 g right-parenthesis superscript 0 point 5 end fraction left-parenthesis h subscript 1 superscript 0 point 5 minus h subscript 2 superscript 0 point 5 right-parenthesis+ + + − or if a relationship between Ap and h is known (i.e., A = C2h + C3)+ − + + + + + + + + − where: − − t − drawdown time in seconds − Ap − surface area of the pond(m²) − C − discharge coefficient (typically 0.63) − A0 − cross-sectional area of the orifice(m²) − g − gravitational acceleration constant (9.81,/s2) − h1 − starting water elevation above the orifice (m) − h2 − ending water elevation above the orifice (m) − − <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 riser}}+ − + + Line 81:
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→External links
[[File:Dryponds map.PNG|thumb|link=https://goo.gl/68Ewnz|Click here to see map of Dry Ponds in Scarborough and surroundings]]
See also [[Water squares]]
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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.
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===
==Design==
==Design==
{|{| class="wikitable"
|+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
!Design Objective
!Criteria
|-
|Drainage Area
|Minimum orifice size (see [[flow control]])
|style="text-align: left|5 Ha (≥10 Ha preferred)
|-
|Treatment Volume
|Provision of appropriate level of protection
|style="text-align: left|See [[#.|below]]
|-
|Active Storage
|Detention
|style="text-align: left|[[Total Suspended solids|Suspended solids]] settling 24 hrs (48 hrs preferred)
|-
|Forebay
|Pre-treatment
|style="text-align: left|
*Minimum depth: 1 m;
*Sized to ensure non-erosive velocities leaving forebay;
|-
|Length-to-Width Ratio
|Maximize flow path and minimize short-circuiting potential
|style="text-align: left|
*Overall: minimum 3:1;
*4:1 preferred
|-
|Depth
|Safety
|style="text-align: left|Maximum 3 m
|-
|Side slopes (See also [[berms]])
|Safety
|style="text-align: left|
*4:1 average
|-
|Inlet
|Avoid clogging/freezing
|style="text-align: left|
*Minimum 450 mm;
*Preferred pipe slope: > 1 %;
*If submerged, obvert 150 mm below expected maximum ice depth
|-
|Outlet (See also [[flow control]])
|Avoid clogging/freezing
|style="text-align: left|
*Minimum: 450 mm outlet pipe;
*Preferred pipe slope: > 1 %;
*If orifice control used, 75 mm diameter minimum;
*Minimum 100 mm orifice preferable
|-
|Maintenance access
|Access for backhoes or dredging equipment
|style="text-align: left|
*Provided to approval of Municipality;
*Provision of maintenance drawdown pipe preferred
|-
|Buffer
|Safety
|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.
===Outlet===
===Outlet===
http://www.iowastormwater.org/documents/filelibrary/files/infiltration_bmps/Outlet_Structures_48B13497A39A1.pdf
===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.
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:
<math>A_o=\frac{2A_{P}}{t\ C(2g^{0.5})}\left ( h_{1}^{0.5}-h_{2}^{0.5} \right )</math>
t = start fraction 0 point 66 C subscript 2 h superscript 1 point 5 + 2 C subscript 3 h superscript 0 point 5 over 2 point 75 A subscript o end fraction
{{plainlist|1=Where
* ''t'' = Drawdown time (s)
* ''A<sub>p</sub>'' = Surface area of the pond(m<sup>2</sup>)
* ''C'' = Discharge coefficient (typically 0.63)
* ''A<sub>o</sub>'' = Cross-sectional area of the orifice(m<sup>2</sup>)
* ''g'' = Gravitational acceleration constant (9.81 m/s<sup>2</sup>)
* ''h<sub>1</sub>'' = Starting water elevation above the orifice (m)
* ''h<sub>2</sub>'' = Ending water elevation above the orifice (m)}}
C2
C2
slope coefficient from the area-depth linear regression
slope coefficient from the area-depth linear regression
C3
C3
intercept from the area-depth linear regression
intercept from the area-depth linear regression
===Excess flow control===
===Excess flow control===
See [[Flow through riser]]
https://www.hydrologystudio.com/no-fail-detention-pond-design/
*https://www.fhwa.dot.gov/engineering/hydraulics/software/hy8/
*https://www.hydrologystudio.com/no-fail-detention-pond-design/
==Modeling==
==Modeling==
==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]]