Detailed Stormwater Management Practice Design - Tauranga City ...

The major difference between swales and filter strips is that swales accept concentrated
flow while filter strips accept flow as distributed or sheet flow. Filter strip performance
also relies on residence time that stormwater flows take to travel through the filter strip
and the depth of water relative to the height of vegetation. Good contact with vegetation
and soil is required to promote the operation of the various mechanisms that capture and
transform contaminants, so spreading flow in minimal depth over a wide area is
essential.
They are well suited for treating runoff from small impervious surfaces and for use as a
pre-treatment device for other practices such as a sand filter or wetland.
A key element of filter strips is that they rely on vegetation to slow runoff velocities. If
stormwater runoff is allowed to concentrate, it effectively short-circuits the filter strip and
reduces water quality benefits. As used in this guideline, filter strips are simple designs
that must withstand the full range of storm events without eroding.
Filter strips were used as part of the overall low impact design approach for the Mount
Greens Sports Bowls and Croquet Club and Cosmopolitan Club Development in
2010/11. The aim for stormwater management was to alleviate existing flooding, reduce
the stormwater running off the site as much as possible (due to downstream pipe
capacity issues) and provide quality treatment of the stormwater itself and creating a site
which was visually appealing through the use of plants/landscaping. This solution was a
cost effective, more environmentally beneficial and less disruptive solution for the
community than replacing the downstream stormwater system with larger pipework.
SMG 9 Figure 5b – Filter Strip (Mount Greens Car Park)
Page 15 Updated 01/11/2012