Line 169: Line 169:
 
</tr>
 
</tr>
  
Inspect the level spreader for sediment buildup and the vegetation for signs of erosion, bare spots, and overall health.
+
<tr>
Annually and after storm events larger than the 10-year return period
+
<td>Inspect the level spreader for sediment buildup and the vegetation for signs of erosion, bare spots, and overall health.
After winter and after storm events larger than the 10-year return period
+
<td>Annually and after storm events larger than the 10-year return period
1-2 hours
+
<td>After winter and after storm events larger than the 10-year return period
1,5
+
<td>1-2 hours
Mow the grass or vegetation only if needed. Avoid mowing when the ground is wet.
+
<td>1,5
As needed
+
</tr>
During growing season
+
 
1-2 hours
+
<tr>
1,2,3,4,5,6
+
<td>Mow the grass or vegetation only if needed. Avoid mowing when the ground is wet.
Inspect for and remove excess sediment in the pre-treatment device and/or in the main treatment area.  
+
<td>As needed
Monthly
+
<td>During growing season
All year long
+
<td>1-2 hours
4 hours if removal is needed
+
<td>1,2,3,4,5,6
1
+
</tr>
Remove sediment and debris from the toe of slope or level spreader.
+
 
Biannually
+
<tr>
In spring and fall
+
<td>Inspect for and remove excess sediment in the pre-treatment device and/or in the main treatment area.  
1-2 hours
+
<td>Monthly
1,5
+
<td>All year long
Remove trash and debris from the pre-treatment device and/or in the main treatment area.  
+
<td>4 hours if removal is needed
Monthly during rainy season
+
<td>1
All year long. Cleaning may need to be done more frequently during the summer storm season and less during the drier winter season  
+
</tr>
1-2 hours
+
 
1,5
+
<tr>
Mow grass in surrounding area to 3-4 inches
+
<td>Remove sediment and debris from the toe of slope or level spreader.
As needed
+
<td>Biannually
During growing season
+
<td>In spring and fall
1 hour
+
<td>1-2 hours
1,2,3,4,5,6
+
<td>1,5
Weed and remove invasive plants
+
</tr>
Twice during growing season
+
 
During growing season
+
<tr>
1-2 hours
+
<td>Remove trash and debris from the pre-treatment device and/or in the main treatment area.  
2,3,4,5
+
<td>Monthly during rainy season
Inspect plant composition and health and replace as needed
+
<td>All year long. Cleaning may need to be done more frequently during the summer storm season and less during the drier winter season  
Annually
+
<td>1-2 hours
In fall or spring
+
<td>1,5
4 hours if plant replacement is needed
+
</tr>
2,3,4,5,6
+
 
Reseed bare spots as needed.
+
<tr>
Biannually
+
<td>Mow grass in surrounding area to 3-4 inches
In spring and fall
+
<td>As needed
1-2 hours
+
<td>During growing season
1,2,3,4,5,6
+
<td>1 hour
Supplemental watering during drier periods, particularly if keeping stormwater offline until plant seedlings are established.
+
<td>1,2,3,4,5,6
As needed during extended dry periods
+
</tr>
Dry periods
+
 
1-2 hours
+
<tr>
2,3,4,5,6
+
<td>Weed and remove invasive plants
Spring cleanup (cut back and remove last year’s material)
+
<td>Twice during growing season
Annually
+
<td>During growing season
In spring
+
<td>1-2 hours
2-4 hours
+
<td>2,3,4,5
2,3,4,5
+
</tr>
Fall cleanup (removed excessive leaf litter, particularly in areas with lots of trees)
+
 
Annually
+
<tr>
In fall
+
<td>Inspect plant composition and health and replace as needed
2-4 hours
+
<td>Annually
2,3,4,5
+
<td>In fall or spring
 +
<td>4 hours if plant replacement is needed
 +
<td>2,3,4,5,6
 +
</tr>
 +
 
 +
<tr>
 +
<td>Reseed bare spots as needed.
 +
<td>Biannually
 +
<td>In spring and fall
 +
<td>1-2 hours
 +
<td>1,2,3,4,5,6
 +
</tr>
 +
 
 +
<tr>
 +
<td>Supplemental watering during drier periods, particularly if keeping stormwater offline until plant seedlings are established.
 +
<td>As needed during extended dry periods
 +
<td>Dry periods
 +
<td>1-2 hours
 +
<td>2,3,4,5,6
 +
</tr>
 +
 
 +
<tr>
 +
<td>Spring cleanup (cut back and remove last year’s material)
 +
<td>Annually
 +
<td>In spring
 +
<td>2-4 hours
 +
<td>2,3,4,5
 +
</tr>
 +
 
 +
<tr>
 +
<td>Fall cleanup (removed excessive leaf litter, particularly in areas with lots of trees)
 +
<td>Annually
 +
<td>In fall
 +
<td>2-4 hours
 +
<td>2,3,4,5
 +
</tr>
 +
 
 
After 5+ Years of Operation (non-routine maintenance)
 
After 5+ Years of Operation (non-routine maintenance)
 
Activity
 
Activity

Revision as of 20:56, 16 August 2021

Warning: This page is an edit and testing page use by the wiki authors. It is not a content page for the Manual. Information on this page may not be accurate and should not be used as guidance in managing stormwater.

Operation and Maintenance of Vegetated Filter Strips

Overview of Typical O&M Issues

Vegetated filter strips, 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 a pre-treatment practice to other practices like bioretention or 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 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:

  • Flow channelization and erosion.
  • Insufficient/inadequate vegetative cover.
  • Sediment and debris accumulation leading to practice clogging.

The sections below describe best practices to prevent or minimize these common problems.

Design Phase O&M Considerations

Designers should design these practices in ways that prevent or minimize O&M issues. Examples include:

  • Using a maximum drainage area to filter strip area ratio of 6:1
  • Limiting the lateral slope to less than or equal to 1%
  • 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 Plants for Stormwater Design) to enhance pollinator and wildlife habitat, improve infiltration and evapotranspiration, reduce urban heat island effect, provide optimized carbon sequestration, and provide climate adaptation. 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 hydrologic soil group, slope, and vegetation (PADEP 2006).
  • Providing pretreatment (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 pretreatment practice to meet the intent of the stormwater permit, as identified in sections 16 and 17, 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.
  • Prohibiting any kind of traffic through the installation of a visible barrier or signage.
  • Providing educational signage to increase public awareness.

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:

  • Incorporating multiple and easy site access points
  • Providing recommendations of vegetation appropriate to the location

The designer should also provide a site-specific O&M plan that includes the following:

  • Construction inspection schedule and checklists
  • Post-construction routine maintenance schedule and checklists
  • Operating instructions for the practice (if applicable)

For more design information for vegetated filter strips, click here.

Construction Phase O&M Considerations

Proper construction methods and sequencing play a significant role in reducing O&M problems. Some key items during the construction phase include:

  • Before construction begins:
    • Check the grading where the practice will be placed to enable sheet flow from the level spreader and throughout the filter strip. Grading must be uniformly perpendicular to the direction of flow to prevent channelized runoff.
    • Protect the proposed filter strip from the surrounding area by using upstream sediment traps or barriers and diversions to direct stormwater flows from the contributing drainage area away from the practice.
    • Install any needed erosion and sediment controls in your construction site and prepare a storm water pollution prevention plan (SWPPP).
    • Designate a stormwater supervisor to make sure someone is responsible for erosion and sediment control.
    • Hold a pre-construction meeting with the designer and the installer to review the construction plans and the sequencing of construction.
  • During construction:
    • Construct any pretreatment devices first.
    • Implement soil stabilization measures until permanent vegetation is established.
    • Use as much of the existing topsoil on the site as possible to enhance plant growth.
    • Prevent soil compaction by marking boundaries of the practice to ensure no construction traffic occurs on the practice. Foot traffic should be minimized if possible.
    • Ensure that the plant and vegetation mix conforms to the vegetation design plan.
    • Inspect the practice during construction to ensure that the vegetated filter strip practice is built in accordance with the approved design and standards and specifications.
  • After construction:
    • Verify that the vegetated filter strip practice was built in accordance with the approved design and standards and specifications.
    • Verify that the filter strip area is fully stabilized with vegetation prior to removing any barriers, diversions, or erosion and sediment control measures.
    • Verify that the practice directs flow as intended over the entirety of the practice. This serves as a verification that the practice is functional at the time of construction.
    • Use a detailed inspection checklists that include sign-offs by qualified individuals at the completion of construction, to ensure that the contractor’s interpretation of the plan is acceptable to the professional designer. An example construction phase inspection checklist is provided further down below.
    • Review and discuss the plant warranty/establishment period with the plant provider to understand the conditions under which failing plants will be replaced.
    • Determine if stormwater should be kept offline from the practice until the seedlings are established.
    • The design/construction team should provide the O&M team with the following information to be included in the O&M plan:
      • The plant warranty.
      • The “as-built” plans of the practice
      • A list of conditions that might cause failure of the practice if not properly maintained.

Post-Construction Phase O&M

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.

  • A site-specific Operations and Maintenance Plan should be prepared by the designer prior to putting the practice into operation. This plan should provide any operating procedures related to the practices. The plan should also provide clear maintenance expectations, activities, and schedules. Include photos if possible. Be clear about who is responsible for the maintenance and the type of expertise that will be needed for distinct O&M activities. The O&M plan should include an anticipated budget for O&M activities. The O&M plan should also include an example O&M inspection checklist and an example maintenance report. Example O&M plans and checklists are provided in the “Useful Resources” section.
  • A legally binding and enforceable maintenance agreement should be executed between the practice owner and the local review authority that provides adequate access for the inspection, maintenance, and necessary equipment. Example maintenance agreements are provided in the “Useful Resources” section.
  • Inspection and maintenance activities are distinct and can be done as separate activities or together. Inspection will typically assess the practice for any O&M issues, whereas maintenance will address the O&M issues identified by the inspection. A dedicated inspection effort on a large number of BMPs can help prioritize maintenance activities.
  • While maintenance is being conducted, ensure that no heavy vehicle traffic occurs on the vegetated filter strip and foot traffic is limited to avoid compaction.
  • Minimize use of any fertilizer.
  • Avoid mowing when the ground is wet. Doing so can create rutting from the wheels.
  • Vegetated filter strips should not be used for permanent snow storage because this will extend the duration of ineffective treatment caused by increased snowpack. Other snow and salting considerations can be found this is "here" the site needs to be build for the link.

The table below provides an overview and schedule of general maintenance activities.

After 5+ Years of Operation (non-routine maintenance) Activity Frequency Time Period Level of Effort per Visit O&M Benefit* 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: Proper stormwater flow and infiltration Creation and maintenance of wildlife habitat Creation and maintenance of pollinator habitat Nutrient cycling and storage Aesthetics and public enjoyment Carbon sequestration
First Year of Operation
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 months1-2 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
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
After First Year of Operation
Activity Frequency Time Period Level of Effort per Visit O&M Benefit*
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