Dry ponds

File:Dry pond-labelled update.png|thumb|700 px|The following image showcases an extended detention dry pond. For more details click here. Ministry of the Environment. Stormwater Management Planning and Design Manual. https://dr6j45jk9xcmk.cloudfront.net/documents/1757/195-stormwater-planning-and-design-en.pdf. 2003. Accessed 3 September, 2021. A note: The following is an "image map", feel free to explore the image with your cursor and click on highlighted labels that appear to take you to corresponding pages on the Wiki.
rect 704 662 1517 837 Sediment Forebays
rect 165 1106 458 1269 Inlet
rect 676 1673 930 1761 Inlet
rect 34 1630 434 1987 Stone Erosion Control
rect 934 1661 1065 1848 Stone Erosion Control
rect 1879 1479 2474 1626 Forebay Berms
rect 2664 1535 2958 1689 Berms
rect 1514 349 2406 599 Vegetation
rect 2648 4 3565 178 Outlet
rect 3815 325 4072 539 Outlet
rect 3826 611 3886 480 Outlet Pipe
thumb|link=https://goo.gl/68Ewnz|Click here to see map of Dry Ponds in Scarborough and surroundings
See also Water squares
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==
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.
==Planning considerations==
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. 
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
===Infiltration===
For information about constraints to infiltration practices, and approaches and tools for identifying and designing within them see Infiltration.
For guidance on infiltration testing and selecting a design infiltration rate see Design infiltration rate.
===Risk===
Where temporary storage of water occurs on the surface the depth and rate of rise of the water should be sufficiently low that risks posed by the water body are minimized for site users (taking into account the temporary nature of the storage facility which will mean that the public are not accustomed to its presence). A risk assessment should be undertaken of the frequency and rate of flooding to a range of inundation depths in order that public safety is not jeopardised. Ballard, B. W., Wilson, S., Udale-Clarke, H., Illman, S., Scott, T., Ashley, R., & Kellagher, R. (2015). The SuDS Manual. London.
==Design==
Design parameters for extended detentionOntario 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
Element 	Design Objective 	Criteria
Drainage Area 	Minimum orifice size (see flow control) 	5 Ha (≥10 Ha preferred)
Treatment Volume 	Provision of appropriate level of protection 	See below
Active Storage 	Detention 	Suspended solids settling 24 hrs (48 hrs preferred)
Forebay 	Pre-treatment 	
*Minimum depth: 1 m;
*Sized to ensure non-erosive velocities leaving forebay;
Length-to-Width Ratio 	Maximize flow path and minimize short-circuiting potential	
*Overall: minimum 3:1; 
*4:1 preferred
Depth 	Safety 	Maximum 3 m
Side slopes (See also berms) 	Safety 	
*4:1 average
Inlet 	Avoid clogging/freezing 	
*Minimum 450 mm diameter inlet pipe; 
*Preferred pipe slope: > 1 %; 
*If submerged, obvert 150 mm below expected maximum ice depth
Outlet (See also flow control)	Avoid clogging/freezing 	
*Minimum: 450 mm diameter 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 	
*Provided to approval of Municipality; 
*Provision of maintenance drawdown pipe preferred
Buffer 	Safety 	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 side slopes should be no steeper than 1:3 to permit vegetation stabilization and access for maintenance and amenity. This may be relaxed where the pond area is very shallow (0.5 m). stepped or benched slopes are also a possibility, but consideration should be made of maintenance access. 
===Volume===
The surface storage volume of a dry pond (Ap) is determined:
A_{p}=\frac{RVC_T\times A_{c}}{f'\times t}
===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 necessitates a very low outflow, a 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. 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:
A_o=\frac{2A_{P}}{t\ C(2g^{0.5})}\left ( h_{1}^{0.5}-h_{2}^{0.5} \right )
C2
slope coefficient from the area-depth linear regression
C3
intercept from the area-depth linear regression
===Settling Velocity of Particulates===
The process of sedimentation is enacted when solids "settle" to the bottom of a sedimentation practice, from suspension in moving or retained water (in this case a dry pond BMP). Due to dry ponds having grassy channels and slopes they are able to over time decrease the velocity of incoming stormwater flow that enters the practice. This combined with the agility of the practice to allow for temporary storage and ponding of water (24 - 48 hr) allows excess sediments (sand, silts, clay and small aggregates) and associated pollutants to settle and be retained within the BMP (Weiss et al. 2010)Gulliver, J.S., A.J. Erickson, and P.T. Weiss (editors). 2010. "Stormwater Treatment: Assessment and Maintenance. University of Minnesota, St. Anthony Falls Laboratory. Minneapolis, MN. https://stormwaterbook.safl.umn.edu/. These sediments should be removed periodically to maintain as designed performance of the feature. The following calculations are for measuring the settling velocities of various solids.
====Stoke's Law for settling solids====
Stoke's Law measures solids settling in stormwater features and is applicable to fines, clay, silt, and sand in water. 
V = \left( \frac {g\left( \frac {p_1}{p} -1 \right)\ d^2}{18v} \right)
====Ferguson & Church (2004)Ferguson, R.I. and Church, M. 2004. A simple universal equation for grain settling velocity. Journal of sedimentary Research, 74(6), pp.933-937. for settling solids. http://geoweb.uwyo.edu/geol5330/FergusonChurch_GrainSettling_JSR04.pdf====
Ferguson & Church's calculation meanwhile allows for designers to include the relationship between settling velocity and particle diameter size. A relationship for settling velocity that incorporates larger particles, such as sands with Reynolds Number (RE) > 10. The equation becomes Stokes' Law when particles have smaller diameters and allows for a constant drag coefficient to be applied for larger particle diameters.
V = \frac{gRd^2}{18v + (0.75CgRd^3)^\frac{1}{2}}
See the table below for average settling velocities of different particle size ranges and particle types based on MOEE (1994)MOEE (1994). Stormwater management practices planning and design manual. Ministry of Environment and Energy, Ontario, Canada. and from Muschalla, 2014Muschalla, D., Vallet, B., Anctil, F., Lessard, P., Pelletier, G. and Vanrolleghem, P.A., 2014. Ecohydraulic-driven real-time control of stormwater basins. Journal of hydrology, 511, pp.82-91.
Visual Indicators Framework - Bioretention/Swales
Size Fraction (i)	Particle size range (µm)	Average settling velocity of particles in size fraction i, Vsi (m/s)	Fraction of total mass contained in size fraction i (%) - MOEE	Fraction of total mass contained in size fraction i (%) - measured
1 	x ≤ 20 	2.54E-06 	20 	83.4
2 	20 ≤ x ≤ 40 	1.30E-05 	10 	9.1
3 	40 ≤ x ≤ 60 	2.54E-05 	10 	4.4
4 	60 ≤ x ≤ 130 	1.27E-04 	20 	4.1
5 	130 ≤ x ≤ 400 	5.93E-04 	20 	-
6 	400 ≤ x ≤ 4000 	5.50E-03 	20 	-
===Excess flow control===
See Flow through riser
*https://www.fhwa.dot.gov/engineering/hydraulics/software/hy8/
*https://www.hydrologystudio.com/no-fail-detention-pond-design/
==Modeling==
==Materials==
==Gallery==
==External links==
*Edmonton Dry Ponds
*Calgary Braeside Dry Pond
*County of Fairfax Dry Ponds
**County of Fairfax Ponds
==References==
Category:Infiltration
Category:Green infrastructure
Category: Modeling