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− | [[File:Kortright-farm-june-2011.jpg|thumb|Wetlands fed by stormwater at Kortright Farm, Vaughan ON]] | + | [[File:Kortright-farm-june-2011.jpg|thumb|500px|Wetlands fed by stormwater at Kortright Farm, Vaughan ON]] |
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| ==Overview== | | ==Overview== |
− | Constructed wetlands are similar to [[SWM ponds]] in function and design, with the most significant difference being that 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.
| + | 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. |
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| {{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. |
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| ==Planning considerations== | | ==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> |
| |- | | |- |
| !Free-water surface flow | | !Free-water surface flow |
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| !Vertical sub-surface flow | | !Vertical sub-surface flow |
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− | |[[File:Schematic of the Free Water Surface Constructed Wetland.jpg|frameless|300px]] | + | |[[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|300px]] | + | |[[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|300px]] | + | |[[File:Tilley et al 2014 Schematic of the Vertical Flow Constructed Wetland.jpg|frameless|upright=1.5]] |
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− | |Schematic of a free-water surface constructed wetland: It aims to replicate the naturally occurring processes, where particles settle, pathogens are destroyed, and organisms and plants utilize the nutrients.
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− | |Schematic of the Horizontal Subsurface Flow Constructed Wetland: Water flows horizontally through the bed.
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− | |Schematic of a vertical subsurface flow constructed wetland: Water flows through pipes on the subsurface of the ground through the root zone to the ground.
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− | |Soil
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− | |-
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− | |Underdrain||Common||Uncommon
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| |- | | |- |
− | |Maintenance||Medium to high||Low | + | |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 |
| |- | | |- |
− | |Stormwater benefit||High||Moderate | + | |style="text-align:left;"|'''Cons''' |
− | |- | + | *Requires larger land area |
− | |Biodiversity benefit||Increased with native planting||Typically lower
| + | *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>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> | + | |+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 |
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| |- | | |- |
| |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 |
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| |Pre-treatment | | |Pre-treatment |
| |style="text-align: left| | | |style="text-align: left| |
− | #Minimum depth: 1 m;
| + | *Minimum depth: 1 m; |
− | #Sized to ensure non-erosive velocities leaving forebay;
| + | *Sized to ensure non-erosive velocities leaving forebay; |
− | #Maximum area: 20 % of total permanent pool
| + | *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| | | |style="text-align: left| |
− | #Overall: minimum 3:1;
| + | *Overall: minimum 3:1; |
− | #Forebay: minimum 2:1
| + | *Forebay: minimum 2:1 |
| |- | | |- |
| |Permanent pool depth | | |Permanent pool depth |
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| |Safety | | |Safety |
| |style="text-align: left| | | |style="text-align: left| |
− | #5:1 For 3 m above and below permanent pool;
| + | *5:1 For 3 m above and below permanent pool; |
− | #Maximum 3:1 elsewhere
| + | *Maximum 3:1 elsewhere |
| |- | | |- |
| |Inlet | | |Inlet |
| |Avoid clogging/freezing | | |Avoid clogging/freezing |
| |style="text-align: left| | | |style="text-align: left| |
− | #Minimum 450 mm;
| + | *Minimum 450 mm; |
− | #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 |
| |- | | |- |
| |Outlet (See also [[flow control]]) | | |Outlet (See also [[flow control]]) |
| |Avoid clogging/freezing | | |Avoid clogging/freezing |
| |style="text-align: left| | | |style="text-align: left| |
− | #Minimum: 450mm outlet pipe;
| + | *Minimum: 450 mm outlet pipe; |
− | #Preferred pipe slope: >1%;
| + | *Preferred pipe slope: > 1 %; |
− | #If orifice control used, 75mm diameter minimum;
| + | *If orifice control used, 75 mm diameter minimum; |
− | #Minimum 100mm orifice preferable
| + | *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;
| + | *Provided to approval of Municipality; |
− | #Provision of maintenance drawdown pipe preferred
| + | *Provision of maintenance drawdown pipe preferred |
| |- | | |- |
| |Buffer | | |Buffer |
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| |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. | | 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]. |
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− | ===Modeling===
| + | 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]. |
− | '''[http://www.unep.or.jp/Ietc/Publications/Water_Sanitation/SubWet2/index.asp SubWet 2.0]''' is a modeling tool for subsurface flow wetlands (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 BOD5 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.
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| ==Gallery== | | ==Gallery== |
| {{:Wetlands: Gallery}} | | {{:Wetlands: Gallery}} |
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− | ==Construction==
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| ==See also== | | ==See also== |
| *[[SWM ponds]] | | *[[SWM ponds]] |
| *[[Dry ponds]] | | *[[Dry ponds]] |
| + | *[[Plants]] |
| | | |
| ==External links== | | ==External links== |
− | [https://www.ontario.ca/page/wetland-conservation-strategy Ontario's wetland conservation strategy] | + | *[https://www.ontario.ca/page/wetland-conservation-strategy Ontario's wetland conservation strategy] |
− | 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. | + | *[https://cawt.ca/ Centre for Advancement of Water and Wastewater Technologies at Fleming College] |
− | https://www.epa.gov/sites/production/files/2015-10/documents/constructed-wetlands-handbook.pdf
| + | |
| + | ===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). |
| + | ---- |