The frequent direct delivery of water and pollutants from impervious
surfaces to streams has a detrimental effect on stream health. Where
there is opportunity for attenuation of these inputs, that is, where
the link between impervious surfaces and streams is less direct,
the damage to stream health is mitigated. This suggests that improving
stream health, in areas subject to urbanisation, involves finding
ways to decrease the efficiency of water delivery from impervious
surfaces.
We have undertaken a feasibility study to examine options to reduce
the area of impervious surfaces that are directly connected to waterways.
These options include: rainwater tanks where the captured water is
used to replace a portion of the mains supply; permeable pavements
that reduce runoff from roads; and swale drains and bioretention
systems along roads rather than piped drainage direct to streams.
Models of the relationship between effective imperviousness and a
range of ecological indicators are used to assess the likely effect
of these options on stream health. A large-scale experiment is now
proposed to test this new approach to urban stream restoration.