National Id
Site name
Hermance river
Hermance is a French/swiss transboundary river. From 2006, in the frame of a transboundary river management program, the SYMASOL has been implementing restoration measures along river in order to decrease flood risk downstream, supported amongst other by Geneva Canton. The river mouth have been widenned, the river has been remeandered, 2,3km of the river have been renaturated and vegetation have been planted back on banks. The Mermes marshland water retention power has been exploited through the creation of a retention pond. In addition to flood risk reduction for a hundred houses, the renaturation and restoration of a path along the river provided social benefits: people happen to appropriate again their river.
Light or indepth?
RBD code
Data provider
Anaí¯s HANUS, ACTeon
Climate zone
cool temperate moist
Mean rainfall
Mean rainfall unit
Average temperature
Case Study Info
Vegetation class
Predominant vegetation classes are crops and forests
Monitoring impacts effects
Monitoring location
Monitoring parameters
Water quality (pesticides, nitrogen and metals) is monitored. Water flow and ecological quality are measured punctually
Monitoring upstream station
There is a project of settling down a station upstream
Monitoring downstream station
HER 379 and HER380
Performance impact estimation method
Catchment outlet
Performance impact estimation information
Comparison to the state before the implementation of the measure
Application scale
Installation date
Performance timescale
1 - 4 years
Area (ha)
Area subject to Land use change or Management/Practice change (ha)
Size unit
No performance evaluation has been done after the measure was imlemented. Effects are hard to assess.
Favourable preconditions
Areas relevant to retain water have been identified; the Mermes marshland appeared as an interesting retention place.
Management change from
artificialised courses
Management change to
natural courses / change in management practices in order to improve water retention
Crop rotation
crops are mostly vineyards and fruit plantations without rotation
Outflow volume
Outflow volume unit
Peak flow rate
Public consultation
Contractural arrangements
Design contractual arrangement
Arrangement type Responsibility Role Comments Name
Contractual agreement
Contractual arrangements have been signed with private owners about banks management
Contracts with private owners
Design consultation activity
Activity stage Key issues Name Comments
Design phase
Information letters
Screening phase
Private interviews
Screening phase
Public meeting
Implementation phase
Public meeting
Design land use change
Land use change type
Water courses
Design authority
Authority type Role Responsibility Name Comments
Local water authority
Local water authority created to manage weter in the concerned watershed and impelement the River contract
Canton de Genève DIAE
swiss Canton of Geneva
Key lessons
The case study provides an example of a bundle of measures which can be implemented to achieve several purposes; it does not gives much facts on biophysical impacts but provides interesting elements about succes and barrier factors; in this case as in many others, dealing with private owners in order to implement the measures on their properties have been the main difficulty.
Financing mechanism
Financing difficulties
Success factor(s)
Success factor type Success factor role Comments
Successful coordination between authorities
main factor

coordination between stakeholders, particularly in a transboundary watershed, was essentiel to guarantee the success of the implementation

Financing possibilities
main factor

Existing financing posibilities, including one from Geneva Canton, was a main succes factor

main factor

Contractors change for the different works; the SYMASOL considers that it is a good thing

Financing type Comments
Sub-national funds
Sub-national funds were provided by water authority (Agence de l'Eau) and other authorities (Conseil régional rhí´ne Alpes, conseil général Haute Savoie).
Local funds
Local funds are water authority funds (SYMASOL) and other local authority funds (Canton of Geneva, Thonon town)
EU-funds: Rural development funds
EU contributed through FEADER fund
EU-funds: Cohesion and regional development funds
It also contributed through PSADER fund
Barrier type Barrier role Comments
Attitude of relevant stakeholders
main barrier
The main barrier has been dealing with land property; private owners were not ready to give away constructible lands and even in the case of existing regulations, they would not take away their fences. Negociations with private owners had to be done.
Attitude of the public
secondary barrier
At the beginning of the project, people were not convinced; after several achievements, they understand better.
secondary barrier
The property issue has been considered to late; it needs to be anticipated.
Limited staff and consultant knowledge
secondary barrier
The design consultant was not aware of the local context in terms of vegetation for instance; it proposed to plant trees which were not adapted to the local climate
Driver type Driver role Comments
Balancing different objectives
main driver
Local authorities decided to deal with their rivers management after some studies that showed the pressure of urbanisation and the need to restore water quality. They made a first preliminary dossier that led them to implement a River contract and create the SYMASOL
Legal obligations
secondary driver
Objectives fixed by the SDAGE asked for implementing a management strategy
Financing share
Financing share type Share Comments
European funds
National funds
Policy description
Main targeted problem is flood risk in urban areas downstream; erosion and habitats protection are also targeted
Quantified objectives
The objectives are renaturing 4,4km of artificialised river, improving water retention capacity of a 5ha marshland
Part of wider plan
Policy target
Target purpose
Peak-flow reduction
Increase Water Storage
Erosion Control
Improved Biodiversity
Oher Societal Benefits
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
Contrat de rivière transfrontalier Sud Ouest Lémanique
The plan defines water maagement strategy on rivers located in a watershed
SDAGE Rhí´ne Méditerranée
The SDAGE defines the main objectives and strategies necessary to reach the good status for water bodies in 2021
Policy requirement directive
Requirement directive Specification
Direct benefits information
The main benefit is social: people walk along the river and walkaways enable them to link the two sides of the city. People seem to make again the river their own and to became more aware of river management issues.
Costs investment
Costs investment information
343800€ have financed the creation of retention areas along the Hermance river
Costs land acquisition
Costs land acquisition unit
€ (total value)
Costs operation maintenance
Costs operation maintenance
About 96000€ have been spent for restoring the banks of the Hermance river and 1000800€ have been spentto restore and renature the riverbed. 134331€ have been spent for widenning a discharge section. 5128€ have been spent for implementing grass buffer strips in the vineyards above the river, 10 000e/year are spent on haying in retention ponds.
Costs operational
Costs operational information
About 96000€ have been spent for restoring the banks of the Hermance river (9,63€/m), corresponding to about 16 000€/year during six years. 166800€ have been spent per year during six years to restore and renature the riverbed. 134331€ have been spent for widenning an discharging section, that is to say 22400€ per year. About 100€/year have been spent on supporting grass buffer implementation in the vineyards above the river
Costs maintenance
Costs maintenance information
About 96000€ have been spent to manage the newly planted vegetation along the Hermance riverbanks. Moreover, haying in retention ponds require about 10 000€/year.
Costs total
Compensations annual
Compensations annual information
About 14000€ have been received by farmers for income losses
Compensations nr beneficiaries
Compensations nr beneficiaries information
Information on Economic costs - income loss
Famers have received indemnisations for yield losses
Ecosystem improved biodiversity
Information on Ecosystem improved biodiversity
The river renaturation, banks restoration and riverbed works have benefited to natural habitats; fish population status have improved along the river: it passed from disturbed to excellent in one station, and to good in another one, between 2002 and 2011. Moreover, new plants can now be observed along the river.
Ecosystem impact climate regulation
No information available
Ecosystem erosion control
Water quality overall improvements
Negative impact-WQ deterioration
Information on Water quality overall improvements
Water quality has decreased during the implementation of the measure, but his can be linked to other factors (pressures...). Only hydrobiological quality (downstream) and metals (mouth) have stayed at the same level.
Soil quality overall soil improvements
Not relevant for this application