25 October 2004
out the gravel and then excavate to remove the sediment and uncover a layer of soils
that has sufficient infiltration capacity.
FILTER STRIPS are bands of dense vegetation planted downstream of a
Figure 8-4. Filter Strip
Most Appropriate Uses. The use of natural or engineered filter strips is
limited to gently sloping areas where the vegetative cover is well-established and where
channelized flow is not likely to develop. Filter strips are well suited for treating runoff
from roads and highways, roof downspouts, very small parking lots, and pervious
surfaces. They are also ideal components for the fringe of a stream buffer, or as
pretreatment for a structural practice.
Cost Data. A rough estimate of filter strip construction costs includes the
cost of seed or sod, approximately 30 per square foot for seed or 70 per square foot
for sod. This amounts to a cost of between ,000 and ,000 per hectare (,000
and ,000 per acre) for filter strips. The cost of filter strip construction may be higher
than other stormwater management practices, but the construction costs are offset by
low maintenance costs, roughly 5 per hectare (0 per acre) per year.25
Additionally, maintenance costs might overlap with regular landscape maintenance
Maintenance Issues. Filter strips require standard vegetation management,
such as mowing, irrigation, and weeding. Typical maintenance activities include
inspection of filter strips at least twice annually for erosion or damage to vegetation and
additional inspection after periods of heavy runoff. Recent research on biofiltration
swales indicates that grass height and mowing frequency have little impact on pollutant
Adapted from SWRPC, 1991.