URBAN
Project funded
by theEU–DGEnvironment
L
andsurfacerelevant
forapplication
Artificial surface
Agriculture land
Forest and semi-natural areas
Wetlands
F
inancialcosts
(C
apital
,
operation
&
maintenance
)
Swales are
low land-take
measures and can often be incorporated within the
masterplan for new developments without significant opportunity costs for land use.
Cost ranges generally fall within €15 to 80/m
2
of swale area constructed. Ongoing
maintenance is required to maintain the functionality of the swale and ranges
between €0.50-€4.00/m² swale area. Where infiltration is intended, geotechnical
investigations may be required.
D
esign
Swales are most effective if applied at the
start of a SuDS ‘train’,
for example,
feeding in to a detention or infiltration basin. Generally, swales are efficient and
easier to construct and maintain if the channel is trapezoidal or parabolic in
shape, with shallow sides (between 1 in 3 and 1 in 4), shallow depths (less than
600mm) and a shallow gradient (between 1 in 100 and 1 in 300). They should
be located in
sun lit areas
to allow for vegetation growth. Regular inspection
and maintenance is essential.
S
cale
The contributing catchment area of
swales tends to be relatively small, for
example a car park, road surface or
small field
Swales can also be appropriatewhere there is runoff from
low permeability surfaces in other areas, e.g. agricultural.
Swales are broad, shallow, linear vegetated
channels
that can store or convey surface water (reducing runoff rates and volumes) and remove pollutants. They
can be used as conveyance features to pass runoff to the next stage of a SuDS treatment train, and can be designed to promote infiltration where soil and
groundwater conditions allow. There are three kinds of swale, giving different surface water management capabilities: standard conveyance swale, enhanced dry
swale (promotes infiltration) and wet swale (permanently wet base).
Case studies: Sustainable stormwatermanagement inFornebu,Norway; Water retention spaces in southernPortugal
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