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 physical removal of a single dam or weir in itself, particularly on smaller
channels, may not be very expensive, but it is often combined with other resto-
ration works, leading to higher costs overall. Costs may be higher if the facility
is not removed altogether but is
modified or reconstructed
(€0,05 to 1
million).
Investigations
are important to understand the impacts upstream and
downstream from removing a barrier: studies and maintenance costs can reach
15% of the capital cost.
D
esign
Some dams and weirs are constructed in order to control river flows and erosion.
Assessment
of the possible negative impacts of removing the dam and of the
feasibility of mitigation options is necessary. Every situation needs to be considered
individually. The measure could be
combined
with reconnection of floodplains,
oxbow lakes and other retention volumes in order to mitigate flood risk and to
further restore the natural erosion and sediment transport rates.
S
cale
The measure is applied predominantly to
small and medium sized rivers.Whilst it
is also applicable to large rivers, where
removal is not possible, improvements to
management of the dam may help to
re-establish some of the natural func-
tions.
Dams and other longitudinal barriers are obstacles that cut across the river section and cause discontinuities for sediment and fauna, as well as altering the
depths and dynamics of flow both upstream and downstream. Removing them involves
complete destruction of the obstacle,
restoring the slope and
longitudinal profile of the river, therefore allowing re-establishment of natural fluvial dynamics, as well as sediment and ecological continuity.
Case studies:Renaturationof theSeymaz river, Switzerland;ÓrbigoRiver ecological status improvement, Spain
HYDROMORPHOLOGY
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