Spatial scales and their attributes 23widely disrupted. This results in flooding, bridge problems, water-supply degra-
dation, loss of fish populations, aquatic habitat loss, wetland loss, and so forth.
Stormwater washes a range of pollutants, such as heavy metals and hydrocar-
bons, from roads and vehicles into water bodies. Thus stormwater-mitigation
techniques and structures may be present, but are usually needed in much
greater abundance near roads. Basically, instead of accelerating stormwater flows
and pollutants in ditches and pipes directly to water bodies where several neg-
ative effects result, the stormwater can often be dispersed into the ground.
Forexample, common solutions include vegetated swales and detention basins,
where water flows can be slowed and reduced while chemical pollutants are
filtered and broken down (France2002,Brandtet al.2003,Hough2004).
Most likely, any road is a barrier or filter to crossing by some animals.
Hence the dense road networks in urban regions are particularly disruptive,
and divide the land up into little sections, often containing small populations
rather than the former large populations. However, busy multilane highways are
major barriers to crossing by wildlife, as well as to walkers and local residents.
In addition to the traffic-noise degradation or avoidance zone referred to above,
thehighway structure with moving traffic is intimidating and dangerous.
Thuswildlife underpassesandoverpassesare increasingly built to overcome the
highway barrier effect. These reconnect habitats on opposite sides of the road
and facilitate wildlife movement across the road (Rosell Pages and Velasco Rivas
1999,Formanet al.2003,Iuellet al.2003,Trocme et al.2003). Large and small
crossing structures, with or without water flows, are built in many creative
designs to aid different types of animals. The distance between wildlife-crossing
structures to reestablish landscape connectivity is a key dimension subject to
active research (Clevenger and Walth 2005). Major underpasses and overpasses
in places may also be designed for attractive, safe crossing by people, both local
residents and longer-distance hikers.
Managed roadsides cover a huge total land area, and could be used to address
awide range of societal objectives, in addition to stormwater and wildlife-
crossing issues (Formanet al.2003,Forman2005). Aesthetics, wood products,
habitats for biodiversity, carbon sequestration, enhanced traffic safety, enhanced
crossing by wildlife, and much more are addressable in roadsides. The overall
result would bevariegated roadsides,visually diverse vegetated strips alongside
roads which serve many objectives of society.
Streamcorridors
As the third example of a small structure widely repeated across the
land, the stream corridor offers special challenges and opportunities in an urban
region. In the natural landscapes present, stream corridors with wide continuous