Difference between revisions of "Wetlands"

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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|150 px|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.]]
|[[File:Schematic of the Free Water Surface Constructed Wetland.jpg|frameless|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.]]
|[[File:Tilley et al 2014 Schematic of the Horizontal Subsurface Flow Constructed Wetland.jpg|frameless|150 px|Schematic of the Horizontal Subsurface Flow Constructed Wetland: Water flows horizontally through the bed.]]
|[[File:Tilley et al 2014 Schematic of the Horizontal Subsurface Flow Constructed Wetland.jpg|frameless|Schematic of the Horizontal Subsurface Flow Constructed Wetland: Water flows horizontally through the bed.]]
|[[File:Tilley et al 2014 Schematic of the Vertical Flow Constructed Wetland.jpg|frameless|150 px|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.]]
|[[File:Tilley et al 2014 Schematic of the Vertical Flow Constructed Wetland.jpg|frameless|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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|Surface water||Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams
|Surface water||Minimal<br>Any surface flow can be slowed with check dams||Ponding is encouraged with check dams

Revision as of 23:00, 29 September 2018

Wetlands fed by stormwater at Kortright Farm, Vaughan ON

Overview[edit]

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.

Wetlands are an ideal technology for:

  • Text A
  • Text B
Types of Constructed Wetland
Free-water surface flow Horizontal sub-surface flow Vertical sub-surface flow
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. Schematic of the Horizontal Subsurface Flow Constructed Wetland: Water flows horizontally through the bed. 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.
Surface water Minimal
Any surface flow can be slowed with check dams		 Ponding is encouraged with check dams
Soil Filter media required Amendment preferable when possible
Underdrain Common Uncommon
Maintenance Medium to high Low
Stormwater benefit High Moderate
Biodiversity benefit Increased with native planting Typically lower

Planning considerations[edit]

Design[edit]

Element Design Objective Criteria
Drainage Area Sustaining vegetation, volumetric turnover 5 Ha (≥10 Ha preferred)
Treatment Volume Provision of appropriate level of protection (Table 3.2) See Table 3.2
Active Storage Detention Suspended solids settling 24 hrs (12 hrs if in conflict with min. orifice size)
Forebay Pre-treatment
  1. Minimum depth: 1 m;
  2. Sized to ensure non-erosive velocities leaving forebay;
  3. Maximum area: 20 % of total permanent pool
Length-to-Width Ratio Maximize flow path and minimize short-circuiting potential
  1. Overall: minimum 3:1;
  2. Forebay: minimum 2:1
Permanent Pool Depth Vegetation requirements, rapid settling The average permanent pool depth should range from 150 mm to 300 mm
Active Storage Depth Storage/flow control, sustaining vegetation Maximum 1.0 m for storms < 10 year event
Side Slopes Safety
  1. 5:1 For 3 m above and below permanent pool;
  2. Maximum 3:1 elsewhere
Inlet Avoid clogging/freezing
  1. Minimum 450 mm;
  2. Preferred pipe slope: >1%;
  3. If submerged, obvert 150 mm below expected maximum ice depth
Outlet Avoid clogging/freezing
  1. Minimum: 450mm outlet pipe;
  2. Preferred pipe slope: >1%;
  3. If orifice control used, 75mm diameter minimum;
  4. Minimum 100mm orifice preferable
Maintenance Access Access for backhoes or dredging equipment
  1. Provided to approval of Municipality;
  2. Provision of maintenance drawdown pipe preferred
Buffer Safety Minimum 7.5 m above maximum water quality/erosion control water level

Performance[edit]

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.

STEP (under previous name SWAMP) conducted their own research into the performance of stormwater wetlands, the project page and report can be viewed here.

Modeling[edit]

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.

Gallery[edit]

  • Wetlands on the Rouge River, Toronto ON. Photo credit: Vlad Litvinov (flickr)

  • Emergent wetland vegetation supported by stormwater runoff at Kino Environmental Restoration Project. Photo by Matthew Grabau, US Fish and Wildlife Service

  • Azalea Park, Charlottesville VA - "This side of the park, formerly located along a runoff channel that led into Moore's Creek, has been converted into a wetland which supports a surprising amount of insect and amphibian life." -Credit and Photo: Scott Clark (certhia on Flickr).

  • Walberswick Mill sluice, part of the water level control and coastal defence infrastructure within the marshes, UK

Construction[edit]

See also[edit]

External links[edit]

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://www.epa.gov/sites/production/files/2015-10/documents/constructed-wetlands-handbook.pdf

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.

A vegetated area such as a bog, fen, marsh, or swamp, where the soil or root zone is saturated for part of the year.

Structures constructed of a non-erosive material, such as suitably sized aggregate, wood, gabions, riprap, or concrete; used to slow runoff water. Can be employed in practices such as bioswales and enhanced grass swales.

The engineered soil component of bioretention cell or dry swale designs, typically with a high rate of infiltration and designed to retain contaminants through filtration and adsorption to particles.

A perforated pipe used to assist the draining of soils.

The temporary storage of stormwater to control discharge rates, and allow for sedimentation.

A pretreatment basin at the inlet of a practice that allow settling out of sediment and associated contaminants suspended in urban runoff.

A pretreatment basin at the inlet of a practice that allow settling out of sediment and associated contaminants suspended in urban runoff.

Includes the protection of soil from dislocation by water, wind or other agents.

A body of water smaller than a lake, often artificially formed.

The technique of removing pollutants from runoff as it infiltrates through the soil.

Sustainable Technologies Evaluation Program

Shallow, constructed pools that capture stormwater and allow for the growth of characteristic wetland vegetation.

The portion of water precipitated onto a catchment area, which then flows as surface discharge from the catchment area past a specified point.

Water from rain, snow melt, or irrigation that flows over the land surface.

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