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*Checking that the maximum groundwater level is 2 to 4 ft below the filter strip | *Checking that the maximum groundwater level is 2 to 4 ft below the filter strip | ||
*Providing a vegetation design plan, emphasizing erosion resistant and native plantings (see [https://www.pca.state.mn.us/water/plants-stormwater-design Plants for Stormwater Design]) to enhance pollinator and wildlife habitat, improve <span title="Infiltration Best Management Practices (BMPs) treat urban stormwater runoff as it flows through a filtering medium and into underlying soil, where it may eventually percolate into groundwater. The filtering media is typically coarse-textured and may contain organic material, as in the case of bioinfiltration BMPs."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_infiltration_Best_Management_Practices '''infiltration''']</span> and <span title="Loss of water to the atmosphere as a result of the joint processes of evaporation and transpiration through vegetation"> '''evapotranspiration'''</span>, reduce urban <span title="an urban area having higher average temperature than its rural surroundings owing to the greater absorption, retention, and generation of heat by its buildings, pavements, and human activities."> '''heat island'''</span> effect, provide optimized <span title="The process of capturing and storing atmospheric carbon dioxide.> '''carbon sequestration'''</span>, and provide <span title="Adjustments in ecological, social, or economic systems in response to actual or expected climatic stimuli and their effects or impacts."> '''climate adaptation'''</span>. Site-specific plant selections should take into account sun exposure, shade, proximity to traffic corners (visibility issues), interior vs exterior plantings, salt-tolerant plants, etc. The selection of plantings suitable to their immediate surroundings will minimize long-term care and replacement frequency. | *Providing a vegetation design plan, emphasizing erosion resistant and native plantings (see [https://www.pca.state.mn.us/water/plants-stormwater-design Plants for Stormwater Design]) to enhance pollinator and wildlife habitat, improve <span title="Infiltration Best Management Practices (BMPs) treat urban stormwater runoff as it flows through a filtering medium and into underlying soil, where it may eventually percolate into groundwater. The filtering media is typically coarse-textured and may contain organic material, as in the case of bioinfiltration BMPs."> [https://stormwater.pca.state.mn.us/index.php?title=Stormwater_infiltration_Best_Management_Practices '''infiltration''']</span> and <span title="Loss of water to the atmosphere as a result of the joint processes of evaporation and transpiration through vegetation"> '''evapotranspiration'''</span>, reduce urban <span title="an urban area having higher average temperature than its rural surroundings owing to the greater absorption, retention, and generation of heat by its buildings, pavements, and human activities."> '''heat island'''</span> effect, provide optimized <span title="The process of capturing and storing atmospheric carbon dioxide.> '''carbon sequestration'''</span>, and provide <span title="Adjustments in ecological, social, or economic systems in response to actual or expected climatic stimuli and their effects or impacts."> '''climate adaptation'''</span>. Site-specific plant selections should take into account sun exposure, shade, proximity to traffic corners (visibility issues), interior vs exterior plantings, salt-tolerant plants, etc. The selection of plantings suitable to their immediate surroundings will minimize long-term care and replacement frequency. | ||
− | *Designing the filter strip length based on the <span title="A soil classification system (Natural Resource Conservation System) based on runoff potential. Groups include A soils (coarse textured with very low runoff potential), B soils (medium coarse textured with low runoff potential), C soils (fine to moderate textured with moderate runoff potential), and D soils (fine textured with high runoff potential)."> '''[https://stormwater.pca.state.mn.us/index.php?title=Design_infiltration_rates hydrologic soil group]'''</span>, slope, and vegetation (PADEP 2006). | + | *Designing the filter strip length based on the <span title="A soil classification system (Natural Resource Conservation System) based on runoff potential. Groups include A soils (coarse textured with very low runoff potential), B soils (medium coarse textured with low runoff potential), C soils (fine to moderate textured with moderate runoff potential), and D soils (fine textured with high runoff potential)."> '''[https://stormwater.pca.state.mn.us/index.php?title=Design_infiltration_rates hydrologic soil group]'''</span>, slope, and vegetation ([http://www.depgreenport.state.pa.us/elibrary/GetFolder?FolderID=4673 PADEP], 2006). |
*Providing [https://stormwater.pca.state.mn.us/index.php?title=Pretreatment pretreatment]</span> (e.g. gravel trench spreader) if necessary. Pretreatment can be used to dampen the effects of high or rapid inflow, dissipate energy, provide additional storage, and prevent the BMP from becoming overloaded by sediment. Pretreatment is a required part of infiltration and filtration practices covered under the Minnesota Construction Stormwater General Permit. Vegetated filter strips are often used as a [https://stormwater.pca.state.mn.us/index.php/Overview_for_pretreatment_vegetated_filter_strips pretreatment practice]</span> to meet the intent of the stormwater permit, as identified in [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit sections 16 and 17]</span>, but are designed with a different set of standards when they are a standalone structural practice. | *Providing [https://stormwater.pca.state.mn.us/index.php?title=Pretreatment pretreatment]</span> (e.g. gravel trench spreader) if necessary. Pretreatment can be used to dampen the effects of high or rapid inflow, dissipate energy, provide additional storage, and prevent the BMP from becoming overloaded by sediment. Pretreatment is a required part of infiltration and filtration practices covered under the Minnesota Construction Stormwater General Permit. Vegetated filter strips are often used as a [https://stormwater.pca.state.mn.us/index.php/Overview_for_pretreatment_vegetated_filter_strips pretreatment practice]</span> to meet the intent of the stormwater permit, as identified in [https://stormwater.pca.state.mn.us/index.php?title=2018_Minnesota_Construction_Stormwater_Permit sections 16 and 17]</span>, but are designed with a different set of standards when they are a standalone structural practice. | ||
*Installing berms where necessary to direct the flow and prevent bypassing. | *Installing berms where necessary to direct the flow and prevent bypassing. |
This page provides guidance for operation and maintenance (O&M) of filter strips. Filter strips are designed to filter suspended solids from runoff as water passes over the filter strip. Most filter strips are vegetated, with grass and perennial native vegetation most widely used.
Supplemental information can be found on the page called Operation and maintenance of filter strips - supplemental information. Supplemental information includes the following.
Vegetated filter strip, also known as buffer strips or buffers, are vegetated land areas between a pollutant source and a surface water body. They can be stand-alone practices or used as pretreatment to other practices like bioretention practices or wet ponds. They reduce the flow velocity of water and filter and infiltrate pollutants such as sediment from stormwater. Vegetated filter strips may be subject to high public visibility, trash loads, sedimentation, pedestrian traffic, and even vehicular traffic or loads. Vegetated filter strips can provide ecosystem services such as nutrient cycling and storage, carbon sequestration, climate adaptation, and habitat for bees, butterflies, and other insects and small animals that pollinate.
Vegetated filter strips require dedicated and regular maintenance to ensure proper and long-lasting operation, and in most cases a vegetated filter strip should be designed to be effective for at least 10 years (NRCS, 2010). The most frequently cited O&M concerns for vegetated filter strips include
The sections below describe best practices to prevent or minimize these common problems.
Designers should design these practices in ways that prevent or minimize O&M issues. Examples include the 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, plantings in the public right of way that conflict with any traffic safety considerations could require increased O&M, such as pruning or complete removal.
Designers should also recognize the need to perform frequent maintenance to remove trash or excess sediment, check for clogging, and if necessary perform practice cleaning. 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 on vegetated filter strips.
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 vegetated filter strips requires a dedicated and routine maintenance plan with clear guidelines, expectations, and schedules. Proper maintenance will not only increase the expected lifespan of the facility but will improve aesthetics and property value. A maintenance plan clarifying maintenance responsibilities should be required for all practices.
Some important post-construction considerations are provided below along with recommended maintenance standards.
Overview and schedule of general maintenance activities for vegetated filter strips
Link to this table
Activity | Frequency | Time period | Level of effort | O&M benefita |
---|---|---|---|---|
Inspect the level spreader for sediment buildup and the vegetation for signs of erosion, bare spots, and overall health. | At least twice after storm events 0.5 inches | Within the first 6 months | 1-2 hours | 1,5 |
Check for evidence of clogging or failing of the inlet, outlet, and bypass pipes. | At least twice after storm events 0.5 inches | Within the first 6 months | <1 hour | 1 |
Remove any stormwater diversion or barriers once seedlings are established. | Once | When plants are sufficiently established | 1-2 hours | 1,2,3,4,5 |
Supplemental watering during drier periods, particularly if keeping stormwater offline until plant seedlings are established. | 1/week initially | During first 2 months | 1-2 hours | 2,3,4,5,6 |
As needed | First growing season | 1-2 hours | 2,3,4,5,6 | |
Mow grass in surrounding area to 3-4 inches | As needed | During growing season | 1 hour | 1,2,3,4,5,6 |
Removal of sediment and debris from the toe of slope or level spreader. | Biannually | In spring and fall | 1-2 hours | 1,5 |
Reseed bare spots as needed. | As needed | First growing season | 2-4 hours | 1,2,3,4,5,6 |
Activity | Frequency | Time Period | Level of Effort per Visit | O&M Benefita |
Inspect the level spreader for sediment buildup and the vegetation for signs of erosion, bare spots, and overall health. | Annually and after storm events larger than the 10-year return period | After winter and after storm events larger than the 10-year return period | 1-2 hours | 1,5 |
Mow the grass or vegetation only if needed. Avoid mowing when the ground is wet. | As needed | During growing season | 1-2 hours | 1,2,3,4,5,6 |
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 |
Remove sediment and debris from the toe of slope or level spreader. | Biannually | In spring and fall | 1-2 hours | 1,5 |
Remove trash and debris from the pre-treatment device and/or in the main treatment area. | Monthly during rainy season | All year long. Cleaning may need to be done more frequently during the summer storm season and less during the drier winter season | 1-2 hours | 1,5 |
Mow grass in surrounding area to 3-4 inches | As needed | During growing season | 1 hour | 1,2,3,4,5,6 |
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 | Annually | In fall or spring | 4 hours if plant replacement is needed | 2,3,4,5,6 |
Reseed bare spots as needed. | Biannually | In spring and fall | 1-2 hours | 1,2,3,4,5,6 |
Supplemental watering during drier periods, particularly if keeping stormwater offline until plant seedlings are established. | As needed during extended dry periods | Dry periods | 1-2 hours | 2,3,4,5,6 |
Spring cleanup (cut back and remove last year’s material) | Annually | In spring | 2-4 hours | 2,3,4,5 |
Fall cleanup (removed excessive leaf litter, particularly in areas with lots of trees) | Annually | In fall | 2-4 hours | 2,3,4,5 |
Activity | Frequency | Time Period | Level of Effort per Visit | O&M Benefita |
After long term operation of the practice, some occasional and infrequent maintenance activities might be required, such as bigger repairs, soil regeneration, regrading, or redesign of key elements of the practice. | As needed | As needed | Could be significant depending on the activity | 1,2,3,4,5,6 |
Key to Maintenance Benefits:
|
Common problems and how to troubleshoot them for vegetated filter strips
Link to this table
Symptom | Possible Causes | Solution |
---|---|---|
Channelization of flow | Improper grading | Install infiltration trench or level gravel spreader trench upstream of practice |
Erosion | Improper (too steep) grading and/or plant loss | Correct for drainage and flow path issues to make sure flows are evenly distributed. Make sure the flow paths are unobstructed |
Vegetation is not able to establish | Plant selection is inappropriate for the site | Consult with a landscaper or horticulturist. Check that plants are suited to the local conditions. Make sure BMP is protected from snow storage or salt application. |
Maintenance costs will vary on a number of factors, including but not limited to:
Preventative maintenance is key to minimizing major costs associated with repairs. The annual cost of maintaining filter strips (mowing, weeding, inspection, litter removal, etc.) is generally between $100 and $1,400 per acre (based on 2006 cost estimate, PADEP 2006). Maintenance may be higher the first few years, while plants are being established.
More detailed information regarding specific maintenance activities are provided in the Vegetated filter strip detailed maintenance activity description page
Topics discussed include:
MPCA has compiled publicly available O&M resources (Excel format) related to green infrastructure. This non-exhaustive catalog is intended as a resource to practitioners.
Example O&M plans, checklists, reports, and maintenance agreements for vegetated filter strips
Link to this table
Document | Link |
---|---|
Operation and maintenance plan | O&M Plan for commercial building in Fairhaven, MA |
Construction phase inspection checklist | Fairfax County, VA |
Virginia DEQ BMP Clearinghouse | |
O&M inspection checklist | MPCA Checklist |
University of Kentucky | |
City of Roseville, CA | |
City of Durham, NC | |
O&M example report | Milwaukee Metropolitan Sewerage District (MMSD) |
Metropolitan St. Louis Sewer District (MSD) | |
Maintenance Agreements | Example Maintenance Agreement 1 |
Example Maintenance Agreement 2 | |
Example Maintenance Agreement 3 |