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
)
Detention basins are
high land-take measures
used within the urban en-
vironment. The primary cost is therefore the cost of
land acquisition
or the
opportunity cost
of not using that land for development. This will depend on
the land values at the site. Geotechnical investigations are required to confirm the
land stability and underlying soil/geology conditions (€1k-€10k). Construction costs
range between €10 and 110/m
3
.
D
esign
Detention basins should be incorporated in a wider
sustainable drainage
system
. The size of a basin depends on the topography, the contributing area,
the relationship between the amounts of incoming and discharged water, and the
storage requirements
. CIRIA recommends a maximum depth of 3m, a flat
bottom and side slopes not greater than 1 in 4. Detention basins should not be
built where water storage may cause slope instability or foundation problems.
Regular inspection and maintenance is essential.
S
cale
Detention basins can be designed to
accommodate any volume of runoff.
The contributing area is unlikely to be
greater than 1 km
2
, since SuDS should
deal with runoff close to source.
Detention basins are effective when receiving runoff from
low permeability surfaces.
Detention basins are
vegetated depressions
designed to hold runoff from impermeable surfaces and allow the settling of
sediments
and associated pollutants. Stored
water may be slowly drained to a nearby watercourse, using an outlet control structure to control the flow rate. Detention basins can provide water quality benefits through physical
filtration to remove solids/trap sediment, adsorption to the surrounding soil or biochemical degradation of pollutants. They may provide ancillary
amenity
benefits.
Case studies: Sustainable stormwatermanagement inFornebu,Norway; LeidscheRijn sustainableurbandevelopment,Netherlands
©
S
u
s
d
r
a
i
n
