National Id
Luxembourg_2
Site name
Ernz Blanche renaturation at Larochette
Summary
The Ernz Blanche (Luxembourg) river restoration project aimed at erasing the effect of the river chanelling, which caused the river uniformisation and floods downstream. The project consisted in a remeandering, increase of the base level of the river and widening of the riverbed.
Light or indepth?
Light
NUTS Code
Luxembourg
RBD code
LU RB_000
Transboundary
0
Data provider
Alexandra Rossi, ACTeon
Source(s)
Restauration des prairies humides le long de l'Ernz Blanche entre Altinster et Larochette
Interview with Micha Bunusevac
NWRM(s) implemented in the case study
Re-meandering
Wetland restoration and management
Longitude
6.2194
Latitude
49.7837
Climate zone
cool temperate moist
Mean rainfall
853
Mean rainfall unit
mm/year
Average temperature
9,2
Type
Case Study Info
Average slope range
2-5%
Performance impact estimation method
Edge of Field/Plot
Performance impact estimation information
A hydrological study was realised in order to measure the impact of the NWRM.
Application scale
River
Installation date
2002
Performance timescale
> 20 years
Area (ha)
6596000
Size
10
Size unit
km
Design capacity description
NWRM aimed at reducing the maximum peak flow.
Basis of design
The NWRM was designed to reduce the peak flow for a 10-years storm (from 18.8 m3/s to 15 m3/s).
Constraints
No main constraint identified.
Favourable preconditions
Land next to the river is owned by the Grand Duchy of Luxembourg.
Peak flow rate
18,7999992370605
Contractural arrangements
0
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Design consultation activity
Activity stage Key issues Name Comments
Design land use change
Land use change type
Design authority
Authority type Role Responsibility Name Comments
Other
Initiation of the measure
Environment Ministery
National environment authority
Key lessons
The natural water retention measure was more cost effective than a classical measure. The possibility of building a rainwater retention reservoir was considered but costs amounted to about 10M€. The cost of the wetland restoration project was about 2,9M€.
Success factor(s)
Success factor type Success factor role Comments
Other

The land next to the river was owned by the Grand Duchy of Luxembourg. In consequence, no land acquisition was necessary (which can need a lot of time).
Financing
Financing type Comments
National funds
Barrier
Barrier type Barrier role Comments
Driver
Driver type Driver role Comments
Financing share
Financing share type Share Comments
Policy description
Larochette is a village located along the Ernz Blanche River. It is regularly flooded, leading to damages on houses and community facilities. Classical flood protection measures (dikes, river banks, etc.) exacerbate the flood risk down stream.
The overall flood risk is due to urbanisation and the river canalisation upstream from Larochette, as well as river realignments.
Policy target
Target purpose
Peak-flow reduction
Increase Water Storage
Improved Biodiversity
Policy pressure
Pressure directive Relevant pressure
Policy area
Policy area type Policy area focus Name Comments
Policy impact
Impact directive Relevant impact
Policy wider plan
Wider plan type Wider plan focus Name Comments
Policy requirement directive
Requirement directive Specification
Direct benefits information
The benefits could in theory be assessed based on the costs of avoided damages due to floods in Larochette. This assessment has not been done.
Costs investment
2940000
Costs investment information
The investment costs cover all the earthworks and structures.
Costs operation maintenance
The maintenance costs were not assessed in the feasability document. However, we can assume that they are low and that there are no extra maintenance costs compared to a usual river management.
Costs total
2940000
Ecosystem improved biodiversity
1
Information on Ecosystem improved biodiversity
Wetland restoration is beneficial for the aquatic biotope.
Ecosystem impact climate regulation
No specific impact
Information on increased water storage
The NWRM increased the volume of water retained up to 110 000m3.
Peak flow rate reduction
15
Peak flow rate reduction unit
m3/sec
Water quality overall improvements
Positive impact-WQ improvement
Information on Water quality overall improvements
The wetland restoration leads to the improvement of self-purifying properties. This leads to improved overall water quality. Though, no assessment has been realized.
Soil quality overall soil improvements
N/A info