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Vegetative filter strips are areas of dense vegetation designed to slow stormwater runoff, trap sediments, and filter out pollutants before water reaches streams or other waterways. These strips are highly effective for reducing runoff, improving water infiltration, and removing contaminants like nutrients, sediments, and herbicides.
Key Benefits:
- Pollutant Removal: Can remove 90% of sediments, 50–80% of nutrients, and up to 100% of certain herbicides.
- Runoff Reduction: Reduces runoff volume by 25–50%, depending on soil type.
- Versatile Applications: Used in agriculture, urban areas, and along roadsides or parking lots to manage stormwater effectively.
- Wildlife Habitat: Provides habitat for wildlife while improving soil health.
How Do They Work?
- Slowing Water Flow: Dense vegetation reduces water speed, spreading it into a thin, even layer.
- Filtering Pollutants: Traps sediments and pollutants through physical and biological processes.
- Improving Infiltration: Enhances water absorption into the soil, reducing runoff and further filtering pollutants.
Why Maryland Needs Them:
Maryland’s proximity to the Chesapeake Bay makes stormwater management critical. Vegetative filter strips help reduce sediment and nutrient pollution, protecting waterways and supporting local conservation goals.
This article explains how vegetative filter strips work, their benefits, and design tips to maximize their effectiveness.
Filter Strip
How Vegetative Filter Strips Work
Vegetative filter strips handle stormwater through three main processes: slowing water runoff, filtering out pollutants, and improving soil infiltration. These processes work together to manage stormwater effectively.
Slowing Stormwater Speed
One of the key roles of vegetative filter strips is to reduce how fast stormwater moves. When water flows over hard, impervious surfaces, it speeds up and picks up various pollutants along the way. The dense vegetation in these strips – made up of stems, leaves, and roots – creates natural resistance, slowing the water down. This resistance helps spread the water out into a thin, even layer (called sheet flow) instead of allowing it to form concentrated streams. Research shows that these strips work best when water flow depths stay below 1 inch and speeds are under 0.5 feet per second[2]. To ensure they perform well, designers often limit the distance water flows into a filter strip to 75 feet from impervious surfaces and 150 feet from pervious surfaces[2].
Filtering Sediment and Pollutants
Once the water slows down, the next step is filtering out sediments and pollutants. Slower runoff allows physical and biological processes to trap and break down contaminants. Physical processes like sedimentation, filtration, and adsorption work alongside biological activities, including nutrient uptake by plants and microbial breakdown of pollutants[2]. Native perennial grasses play a key role here, forming a dense filtering layer that captures sediment effectively[5]. Additionally, the interaction between plant roots, soil, and beneficial microbes enhances this filtration process[1]. Well-designed vegetative filter strips can remove 60–65% of phosphorus and 30–45% of nitrogen[1]. Under ideal conditions, studies have shown these strips can achieve over 90% sediment removal, 50–80% nutrient reduction, and 44–100% removal of herbicides like atrazine[5].
Increasing Water Infiltration
Beyond filtering, vegetative filter strips also boost water infiltration into the soil, which reduces the overall volume of runoff. By slowing the water down, these strips give it more time to soak into the ground, where it undergoes further natural filtration. Filter strips with soils designed for better infiltration, achieving rates of 2 to 12 inches per hour, can retain water for at least nine minutes[1]. This can lead to significant reductions in runoff, with studies reporting decreases ranging from 40% to nearly 100%, depending on factors like soil type, vegetation, and storm intensity[6]. Forested strips, in particular, tend to perform better than grass-planted areas because their deeper root systems and added organic matter improve soil structure[1]. Together, these advantages make vegetative filter strips effective for managing storm events with a 1- to 2-year frequency[2].
Key Design Elements for Effective Vegetative Filter Strips
Vegetative filter strips are a practical solution for managing stormwater and filtering pollutants. Their effectiveness hinges on thoughtful design, including dimensions, plant choices, and soil conditions.
Length, Slope, and Placement
The size and placement of a filter strip play a major role in its ability to slow down runoff and trap pollutants. To achieve meaningful water quality improvements, the flow path across the strip should be at least 16.4 feet long [3]. Importantly, the flow path of the filter strip must be longer than that of the adjacent impervious surface [3].
To maintain proper sheet flow, the slope should be carefully designed. Tools like level spreaders or gravel diaphragms at the top of the slope can help evenly distribute water [3]. This design ensures better performance compared to swales, which rely on channelized flow [4].
Runoff reduction rates depend heavily on soil type. For example, clay-based or poorly draining soils (HSG C and D) can reduce runoff by about 25%, while sandy, well-draining soils (HSG A and B) can achieve up to 50% runoff reduction [3]. Additionally, factors like available space, topography, and existing flow patterns will influence the placement and size of the strip [3].
Equally important is selecting vegetation that complements these physical design features.
Plant Selection
The choice of plants directly impacts how well a filter strip removes pollutants. Native perennial grasses are often the backbone of successful designs, but certain species are particularly effective at tackling specific contaminants.
For instance, blue flag iris can remove up to 76% of chlorpyrifos, 94% of chlorothalonil, 48% of pendimethalin, and 33% of propiconazole from soil within three months [7]. This plant thrives in moist soils with full sun but can tolerate partial shade [7].
Eastern gama grass is another standout, excelling in areas with high levels of chlorothalonil, removing 95% of this fungicide and 47% of chlorpyrifos [7]. It grows best in well-drained to somewhat poorly drained soils under full sunlight. Similarly, big blue stem adapts well to challenging conditions, such as shallow soils or low pH levels. It has been shown to remove 91% of chlorothalonil and 52% of chlorpyrifos [7].
Plants that establish dense turf, improve soil infiltration, and have high transpiration rates are particularly effective. Additionally, robust root systems encourage microbial activity, which aids in breaking down pollutants [7].
While plant selection is critical, soil properties also play a pivotal role in the success of filter strips.
Soil and Drainage Considerations
The soil beneath a vegetative filter strip determines how efficiently it can absorb and filter water. The ideal infiltration rate for the soil is between 0.5 inches and 12 inches per hour [1]. Rates below 0.5 in./hr can hinder water penetration, while rates above 12 in./hr allow water to pass through too quickly, reducing filtration effectiveness [1].
To optimize soil performance, amendments like organic compost are often added to the top 18 inches of soil [1]. The amended soil should have a pH between 5.5 and 7.5 and a cation-exchange capacity above 5 millequivalents per 100 grams [1]. These conditions support plant growth and enhance pollutant retention.
Before installation, it’s essential to evaluate the existing soil. For example, rocky soils are unsuitable because they allow water to infiltrate too quickly without proper filtration [5]. Similarly, shallow water tables can limit the strip’s infiltration capacity [5]. In some cases, marl soils may be a better fit for filter strip applications [5].
Testing the infiltration rate of the native soil is a crucial step before adding amended soil. Imported soil and compost should also be free of weed seeds to avoid future maintenance challenges [1]. Additionally, replacing native soil with amended soil may trigger underground injection control requirements based on state regulations [1].
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Maintenance Requirements for Vegetative Filter Strips
Keeping vegetative filter strips in good condition is key to ensuring they continue to manage stormwater and filter pollutants effectively.
Regular Inspections
In the first two years after installation, make it a habit to inspect your filter strips at least four times a year and after any major storm (about 1 inch of rainfall). Once the system has matured, reduce inspections to twice a year – preferably in spring and fall – but still check after heavy storms.
During inspections, focus on the following:
- Confirm that at least 80% of the filter strip is covered with vegetation.
- Look for signs of damage, such as soil compaction, channelized water flow, or sediment buildup in pretreatment areas.
- Make sure there are no drainage problems like standing water, sinkholes, or animal burrows.
Trash and debris can block the filter strip’s function, so clear these out at least twice a year. After inspections, remove any sediment buildup promptly to keep the system working efficiently [8][9].
Sediment Removal
Sediment will naturally accumulate over time, and managing it quickly is critical. Remove sediment when it reaches about 1 inch deep or when it begins to cause channelized water flow. Wait for dry conditions to avoid compacting the soil during removal.
For light sediment buildup, sweeping may suffice. For moderate accumulation, use a rake or shovel, but avoid driving vehicles onto the filter strip to prevent soil compaction.
"If a significant amount of sediment accumulates on the pretreatment vegetated filter strip (more than 2 inches) and is not removed in a timely manner, the vegetation will die off and require reseeding/replanting" [10].
Staying on top of sediment removal minimizes the risk of costly repairs and keeps the system functioning as intended.
Plant Health
Healthy plants are the backbone of a well-functioning filter strip. For new plantings, water frequently over the first two months, then switch to biweekly watering for the first two growing seasons. Keep plants mowed to a height of 2 to 4 inches – too short can stress the plants, while letting them grow too tall can make maintenance harder.
Weed management is also important. Remove weeds regularly and ensure any imported soil is free from weed seeds. Replace any dead or struggling plants quickly to maintain at least 80% vegetation coverage. Prune or divide plants as needed to encourage dense, healthy growth.
Julie Newman, an environmental horticulture farm adviser with the University of California Cooperative Extension, emphasizes:
"Maintenance of vegetative buffers is necessary to sustain buffer function and effectiveness" [11].
When dealing with pests, avoid chemical treatments near filter strips, as these can harm nearby water systems. For areas with significant damage, re-grade and restore cover over animal burrows deeper than 4 inches or erosion rills longer than 12 inches to maintain proper water flow and filtration.
Why Vegetative Filter Strips Work Well for Maryland Landscapes
Maryland’s unique mix of landscapes, urban areas, and its proximity to the Chesapeake Bay creates a pressing need for effective stormwater solutions. Vegetative filter strips, with their ability to filter and slow down runoff, are a perfect fit for the state’s diverse environment.
Addressing Maryland’s Stormwater Challenges
Stormwater management is a significant issue in Maryland, especially with its commitment to reducing sediment and nutrient pollution in the Chesapeake Bay. According to the Chesapeake Bay Program, croplands are a major contributor, accounting for 27% to 53% of phosphorus and 60% to 70% of nitrogen loads during average and wet years, respectively [13]. This makes filtration systems like vegetative filter strips essential.
These strips are particularly effective in Maryland’s climate. Research shows they can remove 35–65% of phosphorus, 30–45% of nitrogen, and reduce runoff by up to 50% [1]. Agricultural studies have highlighted their efficiency: a 15-foot-wide grass buffer can filter out 50% of nitrogen, phosphorus, and sediment, while a 100-foot buffer increases removal rates to nearly 70% [14].
Maryland’s varied terrain is ideal for vegetative filter strips, which are most effective on slopes between 2% and 6%, helping to prevent concentrated water flow [14]. Additionally, these strips are a great option for protecting cold water streams, as they don’t raise water temperatures [14]. Their versatility allows them to handle runoff from a variety of sources, such as roads, highways, roof downspouts, and small parking lots [14]. Plus, their simple and cost-effective design makes them accessible for homeowners with different budgets [12]. However, proper installation and maintenance require specialized expertise, which is where local professionals come into play.
The Role of Pro Landscapes MD
Expertise is key when it comes to installing vegetative filter strips, and Pro Landscapes MD provides exactly that. They specialize in designing and installing filter strips that are customized to Maryland’s specific environmental needs, ensuring effective filtration and infiltration for stormwater management.
Their team of professional horticulturists carefully selects plants that can handle flooding and thrive in Maryland’s climate without relying on fertilizers, herbicides, or insecticides [1]. Pro Landscapes MD offers comprehensive drainage solutions, covering everything from initial design to long-term maintenance. They consider critical factors like sediment and nutrient loads, flow rates, plant density, and the slope and width of the filter strips to ensure optimal performance [13].
Pro Landscapes MD serves communities across central Maryland, including Howard, Montgomery, Carroll, Frederick, Prince George’s, and Baltimore Counties. Their local knowledge allows them to address the unique stormwater challenges of each area. By aligning their work with Maryland’s conservation goals, they help homeowners manage stormwater runoff while protecting the Chesapeake Bay.
To meet Maryland’s standards, Pro Landscapes MD ensures that filter strips are at least 25 feet long for water quality treatment. They also incorporate pea gravel diaphragms at the top of slopes to act as pretreatment devices and level spreaders [14]. Their expertise in selecting grasses that can handle high-velocity flows, as well as both wet and dry conditions, ensures long-lasting results for homeowners across the state.
Conclusion
Vegetative filter strips provide a straightforward and effective way to manage stormwater runoff while safeguarding Maryland’s waterways. By slowing water flow, trapping sediments, and filtering out pollutants, these strips play a critical role in improving water quality. When designed and maintained correctly, they can remove over 90% of sediments, 50–80% of nutrients, and up to 100% of atrazine [5].
Key Takeaways
The power of vegetative filter strips lies in their ability to reduce runoff speed, filter contaminants, and encourage water infiltration. Studies show they can remove 20–80% of total suspended solids, nitrogen, phosphorus, and heavy metals, while also reducing runoff by 25% on HSG C and D soils and 50% on HSG A and B soils [3]. Beyond their environmental impact, these strips can seamlessly fit into landscaping designs, provide visual screening, and treat runoff from roads, parking lots, and rooftops.
However, their effectiveness depends on proper design and consistent maintenance. Vegetation cover must stay above 80% to maintain performance [3], which means regular inspections, sediment removal, and plant care are essential [9]. Without these efforts, water quality benefits can diminish over time, making professional expertise a key factor in long-term success.
Call to Action
With such clear benefits, professional installation is essential to ensure vegetative filter strips work as intended. Experts can help with selecting the right plants, grading the area correctly, and installing level spreaders to maintain even water distribution [3].
Pro Landscapes MD specializes in designing and installing vegetative filter strips tailored to Maryland’s specific environmental needs. Their team of horticulture professionals knows how to choose salt-tolerant plants that thrive in varying conditions, set up maintenance schedules, and ensure your filter strips stay effective for years to come.
Given that annual maintenance costs typically range between $100 and $1,400 per acre [9], investing in professional services is a smart way to protect your property and Maryland’s waterways. Reach out to Pro Landscapes MD to create and maintain vegetative filter strips that not only manage stormwater but also enhance your landscape.
FAQs
What are vegetative filter strips and how do they help improve water quality?
Vegetative filter strips are patches of densely planted grass, shrubs, or other vegetation designed to intercept and filter stormwater runoff. By slowing down the flow of water, these strips give sediments, nutrients, and pollutants a chance to settle before the water moves into nearby streams, rivers, or other bodies of water.
These strips play a key role in reducing erosion, trapping contaminants, and encouraging water to soak into the soil. This makes them an effective way to improve water quality in both urban and agricultural areas. Especially in places prone to heavy rainfall or water pollution, they offer a practical and eco-friendly approach to managing runoff and safeguarding the environment.
How can I maintain vegetative filter strips to keep them effective over time?
To keep vegetative filter strips working effectively, regular upkeep is essential. Make sure the vegetation stays healthy and dense – aim for at least 85% ground cover. This can be achieved by mowing, replanting any bare patches, and controlling invasive species. Additionally, clear away trash, debris, and sediment buildup at least twice a year to maintain proper water flow and avoid blockages.
After heavy rainfall, take the time to inspect the filter strip for signs of erosion, uneven water flow, or any visible damage. If you notice erosion, address it quickly by adding barriers or leveling spreaders to ensure water distributes evenly across the area. Staying on top of these maintenance tasks can help extend the life of your vegetative filter strips while reducing runoff pollution and safeguarding water quality.
Why is choosing the right plants important for vegetative filter strips, and which ones work best?
Choosing the right plants for vegetative filter strips (VFS) is crucial because they play a central role in filtering stormwater runoff and reducing pollution. Plants with dense, fibrous root systems are particularly effective. They stabilize the soil, minimize erosion, and improve water infiltration, which helps the strip trap sediment and absorb nutrients more efficiently. For optimal pollutant removal and easier maintenance, aim for a vegetation density of at least 85%.
Some of the best choices for VFS are tall, perennial grasses like switchgrass, big bluestem, and eastern gamagrass. These grasses are excellent at capturing both sediment and nutrients. To enhance biodiversity and filtration, consider adding legumes such as Illinois bundleflower or wildflowers like black-eyed Susan. These plants not only improve water quality but also create habitats for local wildlife, making them an environmentally friendly and effective solution for filter strips.
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