Filter strips: Performance

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Starting after TRIECA (end March) members of STEPSustainable Technologies Evaluation Program will be undertaking a literature review on the performance of our most popular BMPs. The results will be combined with the information we have to date from the development of the Treatment Train Tool and agreed performance metrics established. Until then, please feel free to continue to ask questions via email or the feedback box below.

Vegetated filter strips are primarily a practice used to achieve water quality improvements although some infiltration can occur, depending on the soil type and infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour..

Ability of vegetated filter strips to meet SWMStormwater Management objectives
Water balanceThe accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle. benefit Water quality improvement Erosion controlIncludes the protection of soil from dislocation by water, wind or other agents. benefit
Partial: depending on soil infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. Partial: depending on soil infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour. and length of flow path over the pervious area Partial: depending on soil infiltration rateThe rate at which stormwater percolates into the subsoil measured in inches per hour.

Water balanceThe accounting of inflow and outflow of water in a system according to the components of the hydrologic cycle.

Research indicates that runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. reduction from vegetated filter strips is a function of soil type, slope, vegetative cover and flow path length across the pervious surface. A conservative runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. reduction rate for vegetated filter strips is 25% for HSG C and D soils and 50% for HSG A and B soils. These values apply to filter strips that meet the design criteria outlined in this section.

Volumetric runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. reduction achieved by vegetated filter strips
Location RunoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. reduction, by length of strip
2 - 5 m 8 - 15 m
Guelph, ON[1] 20 % 62 %
California, USA[2] 40 % 70 %

Water Quality

Vegetated filter strips can provide moderate pollutant removal from runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface.. Research suggests that runoffThat potion of the water precipitated onto a catchment area, which flows as surface discharge from the catchment area past a specified point.Water from rain, snow melt, or irrigation that flows over the land surface. pollutant concentrations and loads decrease when treated with filter strips and that steady state pollutant levels are typically achieved within 5 m of the pavement edge [3]. Based on a synthesis of performance monitoring studies as of 2000, it was reported that pollutant removal efficiencies of vegetated filter strips are highly variable. For this reason, filter strips should be used in conjunction with other water quality best management practicesState of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include Source, Conveyance and End-Of-Pipe Controls. (e.g., as pretreatmentInitial capturing and removal of unwanted contaminants, such as debris, sediment, leaves and pollutants, from stormwater before reaching a best management practice; Examples include, settling forebays, vegetated filter strips and gravel diaphragms.).

Pollutant removal efficiencies of vegetated filter strips
Total suspended solids (TSSTotal suspended solids) 20 - 80 %
Total Nitrogen 20 - 60 %
Total Phosphorus 20 - 60 %
Total heavy metals 20 - 80 %

Performance of filter strips has also been evaluated based on the Roadside Vegetated Treatment Sites Study [2] and the BMPBest management practice. State of the art methods or techniques used to manage the quantity and improve the quality of wet weather flow. BMPs include: source, conveyance and end-of-pipe controls. Retrofit Pilot Study [4]. These studies concluded that concentration reductions consistently occur for TSSTotal suspended solids and total heavy metals and frequently for dissolved metals. Nutrients concentrations remained generally unchanged.

NOTE:Water quality performance declines when vegetation cover on the filter stripa gently sloping, densely vegetated areas that treat runoff as sheet flow from adjacent impervious areas. They function by slowing runoff velocity and filtering out suspended sediment and associated pollutants, and by providing some infiltration into underlying soils. falls below 80 %.
  1. Abu-Zreig, M. Rudra, M. Lalonde. H. Whitely and N. Kaushik. 2004. Experimental investigation of runoff reduction and sediment removal by vegetated filter strips. Hydrologic Processes. 18: 2029-2037.
  2. 2.0 2.1 Barrett, M. 2003. Roadside Vegetated Treatment Sites (RVTS) Study Final Report, Report # CTSW-RT-03-028. California Department of Transportation. Sacramento, CA.
  3. Barrett, M., Lantin, A., Austrheim-Smith, S. 2004. Stormwater pollutant removal in roadside vegetated buffer strips. Transportation Research Record. No. 1890, pp. 129-140.
  4. California Department of Transportation (Caltrans). 2004. BMP Retrofit Pilot Program, Final Report, CTSW-RT-01-050. Sacramento, CA.