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
)
The primary cost of infiltration basins is
land acquisition
or the opportunity
cost of not using that land, which depends on land value. Geotechnical investi-
gations are also required. Construction costs range between €15 and 90/m
3
of
detention volume and there will also be some ongoing annual maintenance costs.
D
esign
Infiltration basins should not be used in areas where there is a pollution risk to
groundwater. Ground stability should be verified prior to construction. To guarantee
infiltration potential, the seasonally high
groundwater table
should be more
than 1m below the floor, which should be made as level as possible. An outflow
control structure and an emergency spillway should be included where required.
Regular inspection and maintenance is needed.
S
cale
In general, infiltration basins are designed
to treat small drainage areas, typically
covering a
number of properties
(from 2 to 20 hectares). They should
not be used as solutions for larger
drainage areas due to the increased risk
of sediment loading to the basin.
Infiltration basins are
vegetated depressions
designed to hold runoff from impervious surfaces. They allow the settling of sediments and associated pollutants, and allow water to
infiltrate
into underlying soils and groundwater. Infiltration basins are dry except in periods of heavy rainfall, and may serve other functions at other times (e.g. recreation). They
provide runoff storage and flow control as part of a
SuDS ‘train’
. Infiltration basins may also act as “bioretention areas” of shallow landscaped depressions, typically under-drained
and relying on engineered soils, vegetation and filtration to reduce runoff and remove pollution.
Case studies: LeidscheRijn sustainableurbandevelopment,Netherlands
©
S
u
s
d
r
a
i
n
