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Line 1: − + − + − − + − + + + + − + − + − + − + − + + + − + + + + + + + + + + + + + + + + + + + + + + + − + − |-+ − |Maintenance||Medium to high||Low+ − + − |Stormwater benefit||High||Moderate+ − |-+ − |Biodiversity benefit||Increased with native planting||Typically lower+ + + + + − ==Planning considerations== + + + Line 37:
Line 69: − + − + − + − + − #Minimum depth: 1 m;+ − #Sized to ensure non-erosive velocities leaving forebay; + − #Maximum area: 20 % of total permanent pool+ − + − #Overall: minimum 3:1; + − #Forebay: minimum 2:1+ − + − + − + − + − #5:1 For 3 m above and below permanent pool; + − #Maximum 3:1 elsewhere+ − #Minimum 450 mm; + − #Preferred pipe slope: >1%; + − #If submerged, obvert 150 mm below expected maximum ice depth+ − + − #Minimum: 450mm outlet pipe; + − #Preferred pipe slope: >1%; + − #If orifice control used, 75mm diameter minimum; + − #Minimum 100mm orifice preferable+ − + − #Provided to approval of Municipality; + − #Provision of maintenance drawdown pipe preferred+ Line 100:
Line 132: + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + − ==Construction== + + + + + + + + + + +
no edit summary
[[File:Kortright-farm-june-2011.jpg|thumb|Wetlands fed by stormwater at Kortright Farm, Vaughan ON]]
[[File:Kortright-farm-june-2011.jpg|thumb|Wetlands fed by stormwater at Kortright Farm, Vaughan ON]]
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==Overview==
==Overview==
Free-water surface flow wetlands are most commonly employed for stormwater treatment and are similar to [[SWM ponds]] in function and design The most significant difference is the extent to which they are designed to incorporate shallow zones for wetland [[plants]]. A facility is normally characterized as a wetland if shallow zones (<0.5 m deep) make up more than 70 % of its volume.
{{textbox|Wetlands are an ideal technology for:
{{textbox|Wetlands are an ideal technology for:
*Text A
*Enhancing biodiversity
*Text B
*Providing a more aesthetic aquatic landscape
}}
}}
Sub surface flow systems provide generally lower health and safety risks and are sometimes employed to handle stormwater in combination with another wastewater stream.
==Planning considerations==
{|class="wikitable"
{|class="wikitable"
|+ Types of Constructed Wetland
|+ Types of Constructed Wetland<ref>Grant, N., M. Moodie, and C. Weedon. 2000. Sewage Treatment Solutions. p. 35–67. In Sewage Solutions: Answering the Call of Nature. Centre for Alternative Technology Publications.</ref><ref name="EPA">United States Environmental Protection Agency. 1995. A HANDBOOK OF CONSTRUCTED WETLANDS: A guide to creating wetlands for agricultural wastewater, domestic wastewater, coal mine drainage and stormwater.</ref><ref>Jacques Whitford Consultants, 2008. CONSTRUCTED & ENGINEERED WETLANDS p. 1-21</ref>
|-
|-
!Type A
!Free-water surface flow
!Type B
!Horizontal sub-surface flow
!Type C
!Vertical sub-surface flow
|-
|-
|Surface water||Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams
|[[File:Schematic of the Free Water Surface Constructed Wetland.jpg|frameless|upright=1.5]]
|[[File:Tilley et al 2014 Schematic of the Horizontal Subsurface Flow Constructed Wetland.jpg|frameless|upright=1.5]]
|[[File:Tilley et al 2014 Schematic of the Vertical Flow Constructed Wetland.jpg|frameless|upright=1.5]]
|-
|-
|Soil||Filter media required||Amendment preferable when possible
|style="text-align:left;"|'''Pros'''
*Robust
*Provides excellent water quality treatment
*Resistant to temporary hydraulic overload
*Can be beautiful
*Sludge removal infrequent
|style="text-align:left;"|'''Pros'''
*Well established technology
*May be natural looking, although often rectilinear in plan
*Need little to no gradient
*Provides buffer to discharge
*Good pathogen removal from die off and predation
*Minimal maintenance
*Wide range of [[Wetland: list|plants]] suitable
*Robust
|style="text-align:left;"|'''Pros'''
*High levels of treatment possible
*May be run without power if significant gradient is available
*Can be attractively designed to generate interest in the technology, may be any shape.
*Maintenance is technically simple. Sludge easily removed
*Biologically complex and robust
*Failure tends to be gradual
*Will function prior to establishment of vegetation
|-
|-
|Underdrain||Common||Uncommon
|style="text-align:left;"|'''Cons'''
*Requires larger land area
*Sludge removal may be more difficult
|-
*Open water may generate more health and safety concerns.
|style="text-align:left;"|'''Cons'''
*Requires more land
*Multiple substrate layers will promote stratification and channelization
|style="text-align:left;"|'''Cons'''
*Requires fall of at least 1.5 m to provide sufficient treatment
*May be high cost
*Sensitive to hydraulic overloading
|}
|}
==Design==
==Design==
===Sizing free-water===
{| class="wikitable"
{| class="wikitable"
|+Design parameters for free-water surface flow wetlands <ref name="TRCA">Toronto and Region Conservation Authority (TRCA), and CH2M Hill Canada. 2018. Inspection and Maintenance Guide for Stormwater Management Ponds and Constructed Wetlands (T van Seters, L Rocha, and K Delidjakovva, Eds.).</ref>
!Element
!Element
!Design Objective
!Design Objective
|-
|-
|Drainage Area
|Drainage Area
|Sustaining vegetation, volumetric turnover
|Sustaining [[Plants|vegetation]], volumetric turnover
|style="text-align: left|5 Ha (≥10 Ha preferred)
|style="text-align: left|5 Ha (≥10 Ha preferred)
|-
|-
|Treatment Volume
|Treatment Volume
|Provision of appropriate level of protection (Table 3.2)
|Provision of appropriate level of protection
|style="text-align: left|See Table 3.2
|style="text-align: left|See [[#.|below]]
|-
|-
|Active Storage
|Active Storage
|Detention
|Detention
|style="text-align: left|Suspended solids settling 24 hrs (12 hrs if in conflict with min. orifice size)
|style="text-align: left|[[Total Suspended solids|Suspended solids]] settling 24 hrs (12 hrs if in conflict with min. orifice size)
|-
|-
|Forebay
|Forebay
|Pre-treatment
|Pre-treatment
|style="text-align: left|
|style="text-align: left|
*Minimum depth: 1 m;
*Sized to ensure non-erosive velocities leaving forebay;
*Maximum area: 20 % of total permanent pool
|-
|-
|Length-to-Width Ratio
|Length-to-Width Ratio
|Maximize flow path and minimize short-circuiting potential
|Maximize flow path and minimize short-circuiting potential
|
|style="text-align: left|
*Overall: minimum 3:1;
*Forebay: minimum 2:1
|-
|-
|Permanent Pool Depth
|Permanent pool depth
|Vegetation requirements, rapid settling
|Vegetation requirements, rapid settling
|style="text-align: left|The average permanent pool depth should range from 150 mm to 300 mm
|style="text-align: left|The average permanent pool depth should range from 150 mm to 300 mm
|-
|-
|Active Storage Depth
|Active storage depth
|Storage/flow control, sustaining vegetation
|Storage/flow control, sustaining vegetation
|style="text-align: left|Maximum 1.0m for storms < 10 year event
|style="text-align: left|Maximum 1.0 m for storms < 10 year event
|-
|-
|Side Slopes
|Side slopes (See also [[berms]])
|Safety
|Safety
|style="text-align: left|
|style="text-align: left|
*5:1 For 3 m above and below permanent pool;
*Maximum 3:1 elsewhere
|-
|-
|Inlet
|Inlet
|Avoid clogging/freezing
|Avoid clogging/freezing
|style="text-align: left|
|style="text-align: left|
*Minimum 450 mm;
*Preferred pipe slope: > 1 %;
*If submerged, obvert 150 mm below expected maximum ice depth
|-
|-
|Outlet
|Outlet (See also [[flow control]])
|Avoid clogging/freezing
|Avoid clogging/freezing
|style="text-align: left|
|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
|Maintenance access
|Access for backhoes or dredging equipment
|Access for backhoes or dredging equipment
|style="text-align: left|
|style="text-align: left|
*Provided to approval of Municipality;
*Provision of maintenance drawdown pipe preferred
|-
|-
|Buffer
|Buffer
|style="text-align: left|Minimum 7.5 m above maximum water quality/erosion control water level
|style="text-align: left|Minimum 7.5 m above maximum water quality/erosion control water level
|}
|}
===.===
{| class="wikitable"
|+Water volume storage requirements based on catchment type and receiving waters<ref name ="TRCA"/>
!rowspan=2|Performance level
!colspan=4|Storage volume (m<sup>3</sup>/Ha) required according to catchment impervious cover
|-
!35%
!55%
!70%
!85%
|-
|80 % TSS removal||80||105||120||140
|-
|70 % TSS removal||60||70||80||90
|-
|60 % TSS removal||60||60||60||60
|}
===Modeling sub-surface===
'''[http://www.unep.or.jp/Ietc/Publications/Water_Sanitation/SubWet2/index.asp SubWet 2.0]''' is a modeling tool for <u>sub-surface flow wetlands</u> (both 100% constructed and naturalized/adapted). It can be used to simulate removal of nitrogen (including nitrogen in ammonia, nitrate and organic matter), phosphorus and BOD<sub>5</sub> in mg/l and the corresponding removal efficiencies (in %). Although the model has been calibrated already with data from cold and warm climates, users can further calibrate and validate it using local data observations.
==Materials==
===Planting===
See [[Wetlands: Plants]]
==Performance==
==Performance==
Relative to a wet pond, a constructed wetland may offer added pollutant removal benefits due to enhanced biological uptake and the filtration effects of the vegetation.
Early stage wetlands readily sorb phosphorus onto substrates and sediments. Phosphorus removal in wetland systems is usually carried out by incorporating alum sedimentation ponds or [[sand filters]] as cells of the system, and/or by polishing wetland effluent in an iron-dosed mechanical filter.<ref>Jacques Whitford Consultants, 2008. CONSTRUCTED & ENGINEERED WETLANDS p. 1-21</ref>
Freezing temperatures in winter and early spring can reduce treatment if the wetland either freezes solid or a cover of ice prevents the water from entering the wetland. If under-ice water becomes confined, water velocities may increase, thereby reducing contact times<ref name="EPA" />. Runoff in excess of maximum design flows should be [[Overflow#routing|diverted]] around the wetland to avoid excessive flows through the wetland.
STEP (under previous name SWAMP) conducted their own research into the performance of stormwater wetlands, the project page and report can be viewed [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/conventional-stormwater-management/constructed-wetlands/performance-assessment-of-an-open-and-covered-stormwater-wetland-system-aurora-ontario/ here].
STEP (under previous name SWAMP) conducted their own research into the performance of stormwater wetlands, the project page and report can be viewed [https://sustainabletechnologies.ca/home/urban-runoff-green-infrastructure/conventional-stormwater-management/constructed-wetlands/performance-assessment-of-an-open-and-covered-stormwater-wetland-system-aurora-ontario/ here].
Central Lake Ontario Conservation Authority have been undertaking a coastal wetland monitoring project across Durham region, see [https://www.cloca.com/lwc/monitoring_coastal.php here].
==Gallery==
==Gallery==
{{:Wetlands: Gallery}}
{{:Wetlands: Gallery}}
==See also==
==See also==
*[[SWM ponds]]
*[[Dry ponds]]
*[[Plants]]
==External links==
==External links==
*[https://www.ontario.ca/page/wetland-conservation-strategy Ontario's wetland conservation strategy]
*[https://cawt.ca/ Centre for Advancement of Water and Wastewater Technologies at Fleming College]
===Articles for review===
#Kennedy, G., and T. Mayer. 2002. Natural and Constructed Wetlands in Canada: An Overview. Water Qual. Res. J. Canada 37(2): 295–325. doi: 10.2166/wqrj.2002.020.
#Bendoricchio, G., L. Dal Cin, and J. Persson. 2000. Guidelines for free water surface wetland design. EcoSys Bd 8: 51–91. http://www.pixelrauschen.de/wet/design.pdf (accessed 9 May 2018).
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