Description
Vegetated Filter Strips (VFS) are used adjacent to highways and parking areas. They include selected Bio-Sorption Activated Media (BAM) beneath the surface.
Runoff water enters the VFS as overland flow. After passing through the BAM, the water reappears and is assumed to discharge to a nearby surface water transport system, usually a ditch or swale.
The seasonal high-water table is typically greater than one foot below ground at the point of surface discharge.
Typically:
- 12 inches of BAM media is used
- Removal effectiveness is based on this depth
- Minimum width in the direction of flow = 10 feet
For the first 10 feet:
- The water table may intercept flow
- OR
- An impermeable membrane is used to redirect flow horizontally
Various BAM media must be used to receive removal credit (Chang, N., Dan Wen, Andrea Valencia, William Colona, and Martin Wanielista. (2019). Comparison of Biological Nutrient Removal via Two Biosorption Activated Media between Laboratory-scale and Field-scale Linear Ditch for Stormwater and Groundwater Co-Treatment. Water, Air and Soil Pollution Journal).
A vegetated cover must be used along with a minimum of 3 inches of topsoil with vegetation.
The topsoil infiltration rate must be greater than the infiltration rate of the BAM. Typical values range from 5–20 inches/hour.
The storage volume of the BAM depends on the type of BAM used.
If native soils are used, they must be:
- Homogeneously mixed
- Certified
Details on removal using BAM mixes in Florida are documented in:
Shokri, M., et al. (2021). Hydraulic and Nutrient Removal Performance of Vegetated Filter Strips with Engineering Infiltration Media for Treatment of Roadway Runoff. Journal of Environmental Management, Volume 300, December 15, 113747.
A schematic of the VFS is shown as:
Input Data
Required Parameters
Annual capture effectiveness is a function of:
- Vegetated filter strip width
- Width of the impervious catchment
- Type of BAM
- Slope of the VFS
- Rainfall zone
Important:
The VFS area must equal the catchment area.
Example calculation:
3000 ft × (18.56 + 25 ft) = 130,680 SF = 4 acres
Removal effectiveness is defined for:
- Width ≤ 30 feet
- Slope ≤ 20%
If slope is less than 2%, set slope = 2% for analysis.
Example Input
Using the Media Button, a 12-inch-deep B&G filter is selected.
Treatment time (passage through media) is typically greater than 2 hours.
Resulting Removal Effectiveness
For this site using a 12-inch BAM filter:
- Nitrogen removal = 58%
- Phosphorus removal = 83%
This meets the performance criteria of:
- 55% Nitrogen
- 80% Phosphorus
