Résumé
Summary
At Locquirec’s Moulin de la Rive, the old aqueduct and undersized culvert on the Lapic blocked fish migration and sediment transport and created a drop that proved impassable, despite the site being a priority action zone for eel and sea trout. Rescue electrofishing during works confirmed the barrier effect, with far fewer eels and trout upstream than downstream. The project replaced the structure with a 20 m precast frame bridge set 60 cm lower than the former invert, restored a more natural bed with stone and blocks, and added a concrete control wall at the inlet so that high flows can safely spill into the upstream wetland reedbed. The design also integrates a faunal shelf for mammals and bat roosting blocks under the deck, and it secured vulnerable sewer lines that lay near the channel bed. Implementation required careful coordination around numerous underground utilities and a tight spring window to avoid the summer tourism season, combined with strong, proactive communication with residents, surfers and local associations. Traffic on RD64 was diverted from 17 March, and the route reopened ahead of schedule on 30 April 2025. Funding came from Agence de l’Eau Loire-Bretagne, Région Bretagne and Morlaix Communauté. Early observations show fish passage working, otter prints upstream and downstream, macrophyte recovery and rapid revegetation of disturbed zones. The project contributes to WFD ecological continuity targets in a basin facing multiple pressures, including agricultural pollution, hydrocarbons from runoff and intensive anthropogenic footprint.
Photo gallery
Vue d'ensemble
Year of issue
2025
Implementation status
Completed
Contact
Service Public de l’Eau An Dour
Location of the project
Moulin de la Rive, Locquirec, Finistère, on the river Lapic
Country
France
NUTS2 Code
Bretagne
Sponge measures implemented in the case study
Appropriate design of roads and stream crossings
Removal of dams and other longitudinal barriers
Objectives
Restore ecological continuity for eel and sea trout
Re-establish sediment transport
Reduce submersion risk at 30 and 100-year horizons while enabling flood expansion into the upstream reedbed
Protect vulnerable sanitation networks at the crossing
Re-establish sediment transport
Reduce submersion risk at 30 and 100-year horizons while enabling flood expansion into the upstream reedbed
Protect vulnerable sanitation networks at the crossing
Involved partners
| Authority type | Authority name | Authority role | Comments | Authority responsibility |
|---|---|---|---|---|
| Local water authority | An Dour (for Morlaix Communauté) | Initiation of the measure | Client, coordination, communication, works delivery | Responsible |
| Architects / Engineers | Verdi Environnement | Determination of design details of the measure | Pre-project diagnosis | Supporting |
| — | ING Concept | Determination of design details of the measure | Design and works phases, technical details, public procurement. | Supporting |
| Architects / Engineers | Colas | Implementation | Works execution including installation of the 20 m frame. | Supporting |
| National water authority | DDTM | Other | Regulatory support and validation. | Supporting |
| Regional / sub-national water authority | DDTM | Other | Regulatory support and validation. | Supporting |
| Other | Fisheries stakeholders | Other | Fédération de pêche du Finistère; AAPPMA Morlaix. Technical inputs, fish rescue, continuity. | Supporting |
| Local water authority | Locquirec Municipality | Implementation | Institutional partner and communication. | Supporting |
| Other | Morlaix Communauté transports | Other | Bus detours and schedule adjustments | Supporting |
| NGO | Local associations. | Other | Surfing Playa; Surfing Locquirec; Les Amis du Moulin de la Rive; FORCE5; local conservation groups. Local stakeholders engaged via meetings and communications. | Supporting |
Site Information
Climate Zone
Cool temperate moist
Precipitation
995.00 mm
Temperature (°C)
11.75 °C
Elevation range
0 - 10 m
Vegetation class
Reedbed and wetland upstream, macrophytes recolonising channel margins.
WFD Ecological status
Poor
WFD Chemical status
Unknown
Water quality status
Barrier to ecological continuity, agricultural pollution and siltation from vegetable production, hydrocarbon inputs from runoff on impervious surfaces, strong anthropogenic footprint at the crossing
Design and Implementation
Project scale
Micro
Project scale specifications
Single site intervention at one crossing on the Lapic
Project area
20 m long frame bridge.
Principles
Consensus-seeking design acceptable to local users
Lower-impact construction approach with sheet piles and limited earthworks to reduce nuisance
Frame set 60 cm lower than previous invert to restore grade
Inlet control wall to allow floodwater to spread onto the upstream reedbed
Faunal shelf under deck and bat roosting blocks
Channel bed recharge with stones and blocks for habitat diversity
Lower-impact construction approach with sheet piles and limited earthworks to reduce nuisance
Frame set 60 cm lower than previous invert to restore grade
Inlet control wall to allow floodwater to spread onto the upstream reedbed
Faunal shelf under deck and bat roosting blocks
Channel bed recharge with stones and blocks for habitat diversity
Factor constraints
High density of underground utilities and need to maintain service
Sandy soils
Busy departmental road requiring detours and bus rescheduling
Sandy soils
Busy departmental road requiring detours and bus rescheduling
Financing
Total cost
430857.00 €
Total cost information
Project management mission (ING Concept/Verdi Environnement) = €26,529:
Geotechnical Study (Kornog Géotechnique) = €7,782;
Preparatory Work (Kerne Pruning: Felling/Girobroyage) = €17,562
Works (COLAS SA) = €366,087;
Communication (Sky Arts/Norwest Design/Le Friant advertising) = €12,897
Geotechnical Study (Kornog Géotechnique) = €7,782;
Preparatory Work (Kerne Pruning: Felling/Girobroyage) = €17,562
Works (COLAS SA) = €366,087;
Communication (Sky Arts/Norwest Design/Le Friant advertising) = €12,897
Compensations
Non
Policy and Governance
Policy description
Part of a territory contract with the Water Agency aiming at achieving good status on three degraded water bodies by 2030.
Land ownership
Road: Département. Adjacent parcels: multiple private owners. Delegated project management arrangement with the Département to An Dour.
Target remarks
Restore ecological continuity and improve water quality at the crossing
Maintain service for transport and sanitation networks during works
Maintain service for transport and sanitation networks during works
Pressure remarks
Ecological barrier, agricultural pollution, hydrocarbons, intensive local footprint.
Part of a wider plan
Oui
Wider plan
| Wider plan type | Wider plan focus | Name |
|---|---|---|
| Catchment-based | Water | Territory contract with Agence de l’Eau Loire-Bretagne |
Public consultation
Oui
Consultation activities
| Activity stage | Activity type | Key issues | Comments |
|---|---|---|---|
| Implementation phase | Intensive communication | Broadly supportive public after intensive communication | Professional videos and social media series, photo exhibition, educational panels |
| Screening phase | Information meetings with local groups, municipal presentation, public meeting | — | With about 80 participants |
Has contractual arrangements
Oui
Contractual arrangements
| Arrangement type | Name | Role |
|---|---|---|
| Institutional arrangement | Delegation of project management with the Département. | Department is the road owner. It delegated to An Dour the project owning for this site and for a limited time. |
Impacts and Monitoring
Monitoring System
Monitoring parameters
Baseline biological indices IPR and I2M2 at state 0
Follow-ups planned at 2 and 5 years
Visual inspections of hydraulics and wetland expansion
Follow-ups planned at 2 and 5 years
Visual inspections of hydraulics and wetland expansion
Maintenance
Maintenance requirements
An Dour oversees for one year post-works, then the Département for road-related maintenance including debris and vegetation removal.
Impact Assessment Methodology
Biophysical impact assessment method
Qualitative observations to date; quantitative follow-ups planned through standard biological indices.
Socio-economic Impacts
Direct benefits
Positive site feedback on the amenity after works; RD64 reopened earlier than planned.
Biophysical impacts: Hydrology
Information on retained water
The undersized aqueduct–culvert and downstream drop have been removed. The new 20 m frame is set 60 cm lower to remove the hydraulic step and restore a continuous bed profile. An upstream regulating wall lets the Lapic pass up to about 3.2 m³/s through the frame; beyond that threshold the upstream reedbed intentionally takes flow, activating storage and reducing downstream peaks. Visual checks confirm upstream floodplain activation during high water. The upstream end block also narrows the section under flood to protect nearby houses, as designed. Overall effect: reconnect baseflows, re-engage flood storage on the wetland, and make high flows safer for people and infrastructure.
Biophysical impacts: Biodiversity
Information on improved biodiversity
Fish rescue during works found 160 eels and 81 trout downstream versus 60 eels and 30 trout upstream, confirming the former barrier effect. Barrier removal and a lowered invert now restore longitudinal connectivity for eel and sea trout. Bed recharge with stones/blocks increases habitat heterogeneity. A concrete faunal shelf below the deck provides safe passage for semi-aquatic mammals; blocks fixed to the soffit offer bat roosting features. Early post-works signs include visual fish passage, otter footprints upstream and downstream, macrophyte recolonisation below the structure, and rapid re-greening of worked areas by reeds and sedges.
Biophysical impacts: Water & Soil Quality
Information on water quality overall
The works secured vulnerable sewer lines that lay at bed level to prevent rupture risks after the bed lowering, with protective encasement and replacement of sections to limit parasitic inflows. Local authorities report that after the project, Lapic water quality is expected to improve from “poor” to “moderate,” with a basin-wide sanitary action order in preparation to jointly address bacterial sources (collective, individual, and agricultural). These steps complement the crossing redesign by reducing accidental pollution risk and improving flushing of fine sediments.
Lessons Learned
Key lessons
Know your upstream wetlands and hydraulic control points to right-size the crossing and safely reactivate flood storage. Engage early and communicate a lot to keep acceptance high when closing a key road. Plan around utilities and protect sanitation lines when lowering the channel. Prefer a sober, low-nuisance construction approach to cut truck movements, noise and pollution. Build fauna and roosting features into the crossing rather than treating them as add-ons. Align the site project with basin-scale programmes and transport services so detours and public service continuity are managed from day one.
Drivers
| Driver type | Driver role | Comments |
|---|---|---|
| Balancing different objectives | Main driver | Significant ecological and risk-management stakes |
| Organisation committed to it | Main driver | Availability of subsidies and a territory contract framework |
Success factors
| Success factor type | Success factor role | Comments |
|---|---|---|
| Existing staff and consultant knowledge | Main factor | Competent MOE and contractors |
| Public participation | Main factor | Early and sustained multi-stakeholder engagement, including owners and local groups |
| Communication activities | Main factor | Intensive, anticipatory communication |
| Successful coordination between authorities | Main factor | Good coordination across technical, financial and local actors |
Cost effectiveness
Qualitatively strong delivery with early reopening and reported lower works outturn than prevision in press coverage.
Transferability
Highly transferable as part of basin-wide continuity programmes, provided it is embedded in broader sponge strategy with agricultural partnerships and GI measures.
Sources
Sources