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Wetlands (view source)

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[[File:Kortright-farm-june-2011.jpg|thumb|Wetlands fed by stormwater at Kortright Farm, Vaughan ON]]
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==Overview==
 
==Overview==
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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:  
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*Text A
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*Enhancing biodiversity
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*Text B
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*Providing a more aesthetic aquatic landscape
 
}}
 
}}
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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==
 
{|class="wikitable"
 
{|class="wikitable"
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|+ Types of Constructed Wetland
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|+ 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>
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|-
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!Free-water surface flow
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!Horizontal sub-surface flow
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!Vertical sub-surface flow
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|-
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|[[File:Schematic of the Free Water Surface Constructed Wetland.jpg|frameless|upright=1.5]]
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|[[File:Tilley et al 2014 Schematic of the Horizontal Subsurface Flow Constructed Wetland.jpg|frameless|upright=1.5]]
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|[[File:Tilley et al 2014 Schematic of the Vertical Flow Constructed Wetland.jpg|frameless|upright=1.5]]
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|-
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|style="text-align:left;"|'''Pros'''
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*Robust
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*Provides excellent water quality treatment
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*Resistant to temporary hydraulic overload
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*Can be beautiful
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*Sludge removal infrequent
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|style="text-align:left;"|'''Pros'''
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*Well established technology
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*May be natural looking, although often rectilinear in plan
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*Need little to no gradient
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*Provides buffer to discharge
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*Good pathogen removal from die off and predation
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*Minimal maintenance
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*Wide range of [[Wetland: list|plants]] suitable
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*Robust
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|style="text-align:left;"|'''Pros'''
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*High levels of treatment possible
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*May be run without power if significant gradient is available
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*Can be attractively designed to generate interest in the technology, may be any shape.
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*Maintenance is technically simple. Sludge easily removed
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*Biologically complex and robust
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*Failure tends to be gradual
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*Will function prior to establishment of vegetation
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|-
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|style="text-align:left;"|'''Cons'''
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*Requires larger land area
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*Sludge removal may be more difficult
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*Open water may generate more health and safety concerns.
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|style="text-align:left;"|'''Cons'''
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*Requires more land
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*Multiple substrate layers will promote stratification and channelization
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|style="text-align:left;"|'''Cons'''
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*Requires fall of at least 1.5 m to provide sufficient treatment
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*May be high cost
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*Sensitive to hydraulic overloading
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|}
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==Design==
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===Sizing free-water===
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{| class="wikitable"
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|+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>
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!Element
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!Design Objective
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!Criteria
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|-
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|Drainage Area
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|Sustaining [[Plants|vegetation]], volumetric turnover
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|style="text-align: left|5 Ha (≥10 Ha preferred)
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|-
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|Treatment Volume
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|Provision of appropriate level of protection
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|style="text-align: left|See [[#.|below]]
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|-
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|Active Storage
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|Detention
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|style="text-align: left|[[Total Suspended solids|Suspended solids]] settling 24 hrs (12 hrs if in conflict with min. orifice size)
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|-
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|Forebay
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|Pre-treatment
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|style="text-align: left|
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*Minimum depth: 1 m;
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*Sized to ensure non-erosive velocities leaving forebay;
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*Maximum area: 20 % of total permanent pool
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|-
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|Length-to-Width Ratio
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|Maximize flow path and minimize short-circuiting potential
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|style="text-align: left|
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*Overall: minimum 3:1; 
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*Forebay: minimum 2:1
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|-
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|Permanent pool depth
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|Vegetation requirements, rapid settling
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|style="text-align: left|The average permanent pool depth should range from 150 mm to 300 mm
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|-
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|Active storage depth
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|Storage/flow control, sustaining vegetation
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|style="text-align: left|Maximum 1.0 m for storms < 10 year event
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|-
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|Side slopes (See also [[berms]])
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|Safety
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|style="text-align: left|
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*5:1 For 3 m above and below permanent pool;
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*Maximum 3:1 elsewhere
 
|-  
 
|-  
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!Type A
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|Inlet
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!Type B
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|Avoid clogging/freezing
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!Type C
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|style="text-align: left|
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*Minimum 450 mm;
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*Preferred pipe slope: > 1 %;
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*If submerged, obvert 150 mm below expected maximum ice depth
 
|-
 
|-
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|Surface water||Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams
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|Outlet (See also [[flow control]])
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|Avoid clogging/freezing
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|style="text-align: left|
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*Minimum: 450 mm outlet pipe;
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*Preferred pipe slope: > 1 %;
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*If orifice control used, 75 mm diameter minimum;
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*Minimum 100 mm orifice preferable
 
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|-
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|Soil||Filter media required||Amendment preferable when possible
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|Maintenance access
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|Access for backhoes or dredging equipment
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|style="text-align: left|
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*Provided to approval of Municipality;
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*Provision of maintenance drawdown pipe preferred
 
|-
 
|-
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|Underdrain||Common||Uncommon
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|Buffer
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|Safety
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|style="text-align: left|Minimum 7.5 m above maximum water quality/erosion control water level
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|}
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===.===
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{| class="wikitable"
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|+Water volume storage requirements based on catchment type and receiving waters<ref name ="TRCA"/>
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!rowspan=2|Performance level
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!colspan=4|Storage volume (m<sup>3</sup>/Ha) required according to catchment impervious cover
 
|-
 
|-
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|Maintenance||Medium to high||Low
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!35%
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!55%
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!70%
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!85%
 
|-
 
|-
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|Stormwater benefit||High||Moderate
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|80 % TSS removal||80||105||120||140
 
|-
 
|-
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|Biodiversity benefit||Increased with native planting||Typically lower
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|70 % TSS removal||60||70||80||90
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|-
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|60 % TSS removal||60||60||60||60
 
|}
 
|}
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==Planning considerations==
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===Modeling sub-surface===
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==Design==
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'''[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.
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==Materials==
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===Planting===
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See [[Wetlands: Plants]]
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==Performance==
 
==Performance==
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==Construction==
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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.
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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>
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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.
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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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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].
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==Gallery==
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{{:Wetlands: Gallery}}
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==See also==
 
==See also==
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*[[SWM ponds]]
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*[[Dry ponds]]
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*[[Plants]]
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==External links==
 
==External links==
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*[https://www.ontario.ca/page/wetland-conservation-strategy Ontario's wetland conservation strategy]
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*[https://cawt.ca/ Centre for Advancement of Water and Wastewater Technologies at Fleming College]
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===Articles for review===
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#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.
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#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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