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*Anticipating a multi-year vegetation establishment phase | *Anticipating a multi-year vegetation establishment phase | ||
*Shaping the wetland using existing topography and geology, if possible | *Shaping the wetland using existing topography and geology, if possible | ||
− | *Introducing plants with deep roots along slopes to prevent erosion, emphasizing <span title="A species that has been observed in the form of a naturally occurring and self-sustaining population in historical times. Non-natives do not meet this definition."> '''native species'''</span> (see [https:// | + | *Introducing plants with deep roots along slopes to prevent erosion, emphasizing <span title="A species that has been observed in the form of a naturally occurring and self-sustaining population in historical times. Non-natives do not meet this definition."> '''native species'''</span> (see [https://stormwater.pca.state.mn.us/index.php?title=Minnesota_plant_lists Plants for Stormwater Design]) |
*Selecting plantings suitable for the designed water depth and climate patterns | *Selecting plantings suitable for the designed water depth and climate patterns | ||
*Considering the land use in the drainage area and selecting pollution tolerant species (e.g. salt tolerant species if heavy winter maintenance occurs in the drainage area) | *Considering the land use in the drainage area and selecting pollution tolerant species (e.g. salt tolerant species if heavy winter maintenance occurs in the drainage area) |
This page provides guidance for operation and maintenance (O&M) of stormwater treatment wetland practices. These include any constructed basin designed to treat stormwater through sedimentation but that additionally provide other green infrastructure benefits.
Stormwater treatment wetland practices are constructed depressions and pools that are planted with vegetation that is adapted to grow in standing water or under periodic flooding. Wetlands typically remain wet due to relatively impervious sublayers and retain stormwater long enough to allow pollutants to settle out of stormwater and into the sediment. The vegetated pools can provide excellent wildlife and aquatic habitat, enhance nutrient cycling, sedimentation, sequester carbon, and offer aesthetic improvements to urban and rural areas if properly maintained.
Wetlands can provide stormwater and other ecosystem services for many years if they are properly maintained. Typical lifespans range between 25 and 75 years, depending on local conditions and ongoing maintenance to the systems (Torres et al., 2015). The most common O&M concerns for stormwater wetland practices include the following.
The sections below describe best practices to prevent or minimize these and other common problems.
Designers should design stormwater treatment wetland practices in ways that prevent or minimize O&M issues. In general, wetland designs should mimic natural wetlands and introduce few complex components. Design phase O&M considerations include he following.
Designers should consult and include any local requirements regarding green infrastructure. O&M considerations often depend on whether the practice is located on public land, private land, or in the public right of way. For example, exterior plantings in the public right of way that conflict with any traffic safety considerations (e.g. sight lines) could require increased O&M, such as pruning or complete removal.
Designers should also recognize the need to perform frequent landscaping maintenance to remove trash, check for clogging, and maintain vigorous and healthy vegetation. Designers can incorporate design solutions to facilitate maintenance activities. Examples include
The designer should also provide a site-specific O&M plan that includes the following.
For more design information for stormwater wetland practices, see the Design criteria for stormwater wetlands page.
Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include the following.
Effective short and long-term operation of stormwater treatment wetland practices requires dedicated and routine maintenance. Proper maintenance will not only increase the expected lifespan of the facility but will improve ecological function, aesthetics, and property value. Important post-construction considerations are provided below.
Link to this table
First Year of Operation | ||||
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Activity | Frequency | Time Period | Level of Effort | O&M Benefita |
Check that there is no ponding in the pre-treatment device. | At least twice after storm events > 0.5 inches | Within the first 6 months | 1-2 hours | 1 |
Check for evidence of clogging in the pre-treatment device and/or in any conveyance structures | At least twice after storm events > 0.5 inches | Within the first 6 months | 1-2 hours | 1 |
Maintain proper water level for establishing vegetation (may require supplemental source) | 1/week initially | During first 2 months | 1-2 hours | 2,3,4,5,6 |
As needed | First growing season | 1-2 hours | ||
Remove any stormwater diversion or barriers once seedlings are established. | Once | When plants are sufficiently established | 1-2 hours | 1,2,3,4,5 |
Install protective barriers (e.g. chicken wire) to protect growing vegetation from wildlife | As needed | First growing season | 8 hours | 1,2,3,5 |
Check for signs of burrowing animals and incorporate gravel or rock in problem areas to discourage burrowing. | As needed | First growing season | 1-2 hours | 5 |
Check that water is moving as planned through the wetland. Identify and fix any stagnant zones. | As needed | During first 2 months | 4 hours | 1 |
Mow dikes frequently to establish deep rooted ground cover | Biweekly or as needed | First growing season | 3,4 | |
Remove and replace dead plants | As needed | First growing season | 2-4 hours | 2,3,4,5,6 |
Spot reseeding of bare patches and eroding areas | As needed | First growing season | 2-4 hours | 1,2,3,4,5,6 |
After First Year of Operation | ||||
Activity | Frequency | Time Period | Level of Effort per Visit | O&M Benefita |
Check that there is no ponding in the pre-treatment device | Biannually | Any time when ground is not frozen | 1-2 hours | 1 |
Check for evidence of clogging in the pre-treatment device and/or in any conveyance structures. | Biannually | In spring and fall | 1-2 hours | 1 |
Remove trash and debris from the pre-treatment device and/or in the main treatment area. | Monthly | All year long | 1-2 hours | 1,5 |
Inspect for and remove excess sediment in the pre-treatment device and/or in the main treatment area. | Monthly | All year long | 4 hours if removal is needed | 1 |
Check and repair eroded areas | Annually | In fall or spring when vegetation has died down | 4 hours if repairs are needed | 1,2,3,4,5 |
Weed and remove invasive plantsb | Twice during growing season | During growing season | 1-2 hours | 2,3,4,5 |
Inspect plant composition and health and replace as needed to maintain >50% coverage. | Biannually | In fall or spring | 4-8 hours, more if plant replacement is needed | 2,3,4,5,6 |
Remove woody vegetation on or near embankments, forebays, spillways, and outlets | Annually | In fall or spring | 4 hours | 1,2,3,4,5,6 |
Check for signs of burrowing animals and incorporate gravel or rock in problem areas to discourage burrowing. | As needed | During growing season | 1-2 hours | 1,2,5 |
Inspect for and repair broken inlets, pipes, or other water control structures | Biannually | After high flows and ice breakup | 2 hours, more if repairs are needed | 1 |
Mow dikes and remove any shrubs or trees growing on dikes | As needed | During growing season | 1-2 hours | 1,5 |
Monitor operating range of water level | Daily (collect data continuously, use information to diagnose issues) | Any time | 1-2 hours | 1,2,4,6 |
Check that water is moving as planned through the wetland. Identify and fix any stagnant zones | Annually | During growing season | 4 hours | 1,2,3,4,5 |
Inspect sediment accumulation in forebay and treatment areas. Remove if hydrology is impacted or if less than 50% of forebay capacity remains. | Annually | Fall | 2 hours | 1,4,6 |
Harvest wetland plants | Once every 2-3 years | After growing season | 4-8 hours | 1,4,5,6 |
Remove sediment from forebay | Once every 2-7 years, or when less than 50% forebay capacity remains | As needed | Varies | 1,4,5,6 |
After 5+ Years of Operation (non-routine maintenance) | ||||
Activity | Frequency | Time Period | Level of Effort per Visit | O&M Benefita |
Remote inspection of all conveyance structures (e.g. pipes, underdrains, etc.) | Every 10 years | Any time | Varies | 1 |
After long term operation of the practice, some occasional and infrequent maintenance activities might be required, such as bigger repairs or redesign of key elements of the practice. Replacement of concrete components (e.g. pipes, risers, may be required after 25-50 years. | As needed | As needed | Could be significant depending on the activity | 1,2,3,4,5,6 |
aKey to Maintenance Benefits:
bRemove invasive species immediately and replace vegetation as needed. As a general rule, control of undesirable invasive species (e.g., cattail and Phragmites) should commence when their coverage exceeds more than 15% of a wetland cell area. Although the application of herbicides is not recommended, some types, such as Glyphosate, have been used to control cattails with some success. Extended periods of dewatering may also work, since early manual removal provides only short -term relief from invasive species. |
Common problems and how to troubleshoot them for wetlands
Link to this table
Symptom | Possible causes | Solution |
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Vegetation will not establish properly | Water levels need to be maintained per species specific growth patterns during establishment. A secondary water source and flow routing may be necessary to establish vegetation for a year. Soils may not have been properly decompacted during construction. Influent pollutant loads may be harming unestablished vegetation. Wildlife may harm unprotected vegetation. |
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Stagnant water | Significant erosion that has impacted hydraulics. Clogs in the conveyance network. Grading issues. |
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Mosquitos | Optimal breeding conditions |
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Wetland capacity is reduced | Sediment build up or vegetative overgrowth |
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Flow or water imbalance (more water coming in than going out), lower than expected water levels. | Unanticipated infiltration |
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Maintenance costs will vary on a number of factors, including but not limited to the following.
Preventative maintenance is key to minimizing major costs associated with repairs. A general rule of thumb for annual GI maintenance is 3%-6% of the total cost (Clary, 2017). Maintenance costs may be higher the first few years, while plants are being established or modifications to the design are required. Sediment removal may also be the most costly maintenance activity. A 2015 report by E2 Storm Project in Europe recently estimated maintenance costs to be between $41 and $72 per cubic foot of storage based on case studies, including those from the United States (Torres, 2015).