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
)
Retention ponds 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. Capital costs range
between €10 and 60/m
3
storage volume, and there will be ongoing relatively
minor maintenance costs.
D
esign
Retention ponds should be combined with
upstream sustainable drainage
components
, such as smaller detention basins and swales. Ponds would be sited
at a low point in the catchment where it can receive drainage by gravity. Soils
should be sufficiently
impermeable
to stop the water drying out. In areas of
contaminated soils or groundwater the pond should be fully sealed to prevent
transfers with the aquifer. Regular inspection and maintenance is important.
S
cale
The drainage area required to support a
retention pond can be as low as 0.03-
0.1 km
2
. There are no constraints on the
maximum drainage area, although SuDS
should treat runoff close to source.
Retention ponds are ponds or pools designed with
additional storage capacity
to attenuate surface runoff during rainfall events. Retained runoff is released at a controlled
rate. Ponds are created by using an existing natural depression, by excavating a new depression, or by constructing embankments. They can provide both storm water attenuation
and water quality treatment.Well-designed and maintained ponds can offer aesthetic, amenity and ecological benefits to the urban landscape.
Case studies:Retentionpond inChêneBougerie, Switzerland; Ecological adapted stormwater treatment inKretinga , Lithuania
©
S
u
s
d
r
a
i
n
