Line 372: | Line 372: | ||
<td>Vegetation will not establish properly | <td>Vegetation will not establish properly | ||
<td>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. | <td>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. | ||
− | <td>*Consult with the designer to check what water depths should be maintained for the planted vegetation. | + | <td> |
+ | *Consult with the designer to check what water depths should be maintained for the planted vegetation. | ||
*Consult an engineer to ensure proper decompaction occurred during construction. | *Consult an engineer to ensure proper decompaction occurred during construction. | ||
*Install chicken wire or other barriers to deter wildlife from young plantings. | *Install chicken wire or other barriers to deter wildlife from young plantings. | ||
Line 381: | Line 382: | ||
<td>Stagnant water | <td>Stagnant water | ||
<td>Significant erosion that has impacted hydraulics. Clogs in the conveyance network. Grading issues. | <td>Significant erosion that has impacted hydraulics. Clogs in the conveyance network. Grading issues. | ||
− | <td>*Remove any sediment or soil that has sluffed into the treatment pools due to erosion. | + | <td> |
+ | *Remove any sediment or soil that has sluffed into the treatment pools due to erosion. | ||
*Check and remove debris or clogs from all conveyance structures. | *Check and remove debris or clogs from all conveyance structures. | ||
*Consult the designer or an engineer to identify grading or other hydraulic issues. | *Consult the designer or an engineer to identify grading or other hydraulic issues. | ||
Line 397: | Line 399: | ||
<td>Wetland capacity is reduced | <td>Wetland capacity is reduced | ||
<td>Sediment build up or vegetative overgrowth | <td>Sediment build up or vegetative overgrowth | ||
− | <td>*Remove accumulated sediment | + | <td> |
+ | *Remove accumulated sediment | ||
*Harvest vegetation | *Harvest vegetation | ||
</tr> | </tr> | ||
Line 404: | Line 407: | ||
<td>Flow or water imbalance (more water coming in than going out), lower than expected water levels. | <td>Flow or water imbalance (more water coming in than going out), lower than expected water levels. | ||
<td>Unanticipated infiltration | <td>Unanticipated infiltration | ||
− | <td>*Check the integrity of any impermeable barriers or linings that were installed beneath the growth media. | + | <td> |
+ | *Check the integrity of any impermeable barriers or linings that were installed beneath the growth media. | ||
</tr> | </tr> |
Operation and Maintenance of Stormwater Treatment Wetland Practices
Stormwater treatment wetland practices are constructed depressions and pools planted with emergent aquatic or wetland vegetation. Wetlands typically remain wet due to relatively impervious sublayers and have retention times that allow pollutants to settle out of stormwater and into the sediment. The vegetated pools can provide excellent wildlife habitat, enhance nutrient cycling, 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 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:
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 wetlands 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:
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.
First Year of Operation | ||||
---|---|---|---|---|
Activity | Frequency | Time Period | Level of Effort | O&M Benefit* |
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 Benefit* |
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 plants | 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 Benefit* |
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 |
Key to Maintenance Benefits:
|
Symptom | Possible Causes | Solution |
---|---|---|
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. |
|
Stagnant water | Significant erosion that has impacted hydraulics. Clogs in the conveyance network. Grading issues. |
|
Mosquitos | Optimal breeding conditions | *Address stagnant water
|
Wetland capacity is reduced | Sediment build up or vegetative overgrowth |
|
Flow or water imbalance (more water coming in than going out), lower than expected water levels. | Unanticipated infiltration |
|