Vegetated Filter Strip Systems

From: Publication 826 Vegetated Filter Strip System Design Manual.

As you may recall, amendments in 2007 to Ontario Regulation 267/03 (as amended) allowed vegetated filter strip systems (VFSSs) to be engineered, constructed, and operated as a method for managing runoff from agricultural operations. Previously, a VFSS for runoff required a Certificate of Approval under the Ontario Water Resources Act issued by the Ministry of the Environment (MOE).

What is a Vegetated Filter Strip System:

A VFS system collects, temporarily stores, and transports agricultural runoff generated from an outdoor livestock yard/outdoor confinement area or a permanent solid manure storage facility to an infiltration area. The VFS system is composed of a series of components that serve the following primary functions:

1. Collect and temporarily store agricultural runoff (Figure 1)
2. Screen out solids from agricultural runoff (Figure 2)
3. Control rate of release of nutrients, organic matter, and pathogens in agricultural runoff (Figure 3)
4. Transport agricultural runoff to an infiltration area (via gravity or pump)
5. Distribute flow evenly across infiltration area (Figure 4)
6. Allow runoff to infiltrate into soil within infiltration area (Figure 5).

Figure 1: Barnyard with retaining wall that serves as temporary storage for runoff

Figure 2: Three screens to minimize solids from being pumped to the strip

Figure 3: Properly sized orifice plate behind screen to control flow rate

Figure 4: Distribution pipe with 1/2" holes at 17' intervals distribute runoff evenly across the strip

The infiltration area is a densely vegetated (planted) strip of land, engineered and constructed to accept and manage runoff through settling, filtration, absorption and infiltration processes. The VFS system is designed to be "zero discharge." This means the VFS system accommodates all of the agricultural runoff that it receives, without discharging any beyond the designed infiltration area.

Differences Between VFSSs and Permanently Vegetated Areas (PVA)

To use a VFSS for runoff:

• Engineering required: Yes
• Solid manure storage facility limited by dry matter or area of the facility: No
• Permanent outdoor confinement areas (OCA), limited by animal numbers or dimensions of the OCA: No
• Soil texture is an important consideration: Yes

To use a permanently vegetated area with flow path for runoff:

• Engineering required: No
• Solid manure storage facility, limited by dry matter or area of the facility: Yes
• Permanent outdoor confinement areas (OCA), limited by animal numbers or dimensions of the OCA: Yes
• Soil texture is an important consideration: No

Practical Considerations

Limitations on the use of the VFSS are largely related to the soil texture found on the farm, which becomes a key factor in determining the dimensions required for the strip. Using established engineering tables for infiltration rates of various soil textures (clay, sand, loam or silt) along with the flow rate of liquid delivered to the strip, the dimensions required for the VFSS can be calculated. Some of the VFSSs in operation currently have dimensions of 100' to 140' wide and 100' to 200' long. In practice, the VFSSs work well on "sandy-loam to loam to clay-loam" textured soils, typically referred to as a "medium" textured soil. The VFSSs do not tend to work well on either a coarse soil such as a "blow-sand" or a fine textured soil such as a "heavy" clay soil.

Assuming the site has a soil texture that allows for a reasonably compact and efficient VFSS, you will need the services of an engineer. A "drainage" engineer may be a good place to start since they are familiar with the soil properties in your area and a number of these engineers have had some technical training on VFSSs. OMAFRA is currently compiling a list of engineers for publishing that are willing to do VFSS design.

The two biggest variables that the engineer will address in the design are the volume/rate of liquid that the VFSS will be required to manage and the soil texture as discussed above. Volume of liquid produced will be based on the footprint or area of the uncovered manure storage and/or livestock yard and the rainfall expected from a one in 25 year storm event for the area.

While VFSSs are engineered and constructed only for runoff under the nutrient management regulations, these VFSSs projects do not require a NM strategy. Only if the operator is undertaking another initiative on the farm such as a project which requires a building permit for a livestock housing facility or manure storage with greater than 5 NU, would a NM strategy be required.

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Publication 826: Vegetated Filter Strip System Design Manual is available for $25 from OMAFRA Resource
Centres or download it for free from the OMAFRA website.

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Use of VFSSs During Winter Conditions

VFSSs are designed and constructed for year-round operation. Pipes that transport runoff to the strip are designed to either discharge liquid to the strip or drain back to the subsurface sump to prevent freezing. In addition, because runoff events are relatively infrequent during the winter and typically occur when the temperature is above the freezing point, runoff can infiltrate the strip during winter conditions or be trapped in the snow or vegetation cover.

Other Applications for VFSSs

OMAFRA is undertaking a field research project to examine the effectiveness of VFSSs for milking centre washwater starting in 2008. Because this is not "runoff", a VFSS for this application will require a Certificate of Approval from MOE.

For More Information on VFSSs, Contact:

Bob Stone, P. Eng. OMAFRA 613 475 5428 bob.stone@ontario.ca

Figure 5: Distribution pipe and vegetated strip area. The strip area is a slightly lighter shade of green because it consists of grasses whereas the rest of the field is predominantly alfalfa.