Case study:Removal of the pont Paillard weir on a secondary arm of the Aume

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Location: 45° 52' 34", 0° 3' 11"
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Project overview

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Status Complete
Project web site
Themes Flood risk management, Hydromorphology, Monitoring
Country France
Main contact forename Julien
Main contact surname Blancant
Main contact user ID
Contact organisation Syndicat intercommunal d’aménagement hydraulique du bassin Aume - Couture
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
projects
No
The pont Paillard weir, during the works.

Project summary

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The Aume is a 32 km long tributary of the Charente. It has great potential for eel, sea trout and brown trout. Its watershed is primarily agricultural. The Aume has undergone many morphological alterations. Between 1960 and 1995, the river was straightened, dredged and its cross-section modified in order to drain the marshes and make the cultivation of corn possible. This caused riverbed incision and lowering of the groundwater table. In order to try to stop this process raising the water level a series of 20 weirs made with planks was built. However, they caused silting, favoured eutrophication and induced longitudinal fragmentation. The plank weirs are kept open during the winter (October 15 to early May), except for the pont Paillard one, which had remain closed for ten years. The “Syndicat de rivière intercommunal d’aménagement hydraulique du bassin de l’Aume – SIAHBAC” (grouping of local administrations for the hydraulic management of the Aume basin) is the owner and manager of all of these works. As part of the new strategy of SIAHBAC, which aims to meet the objectives of the Water Framework Directive, it was decided to test the removal of planks at the pont Paillard site. The objectives of the action were to restore ecological continuity (for fish and sediment) and a more natural flow regime; moreover, to educate local stakeholders in this type of operation, to promote further restoration activities. The work, on a secondary, disconnected arm of the Aume, consisted in the mere removal of the wooden planks of the weir, entailing practically no costs. The concrete structure is retained, in order to make the measure reversible in case of failure (not all the farmers supported it). No planting or any other action in the riverbed was performed, in order to follow the natural evolution of the river.

Monitoring surveys and results

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Unfortunately no baseline was established before the measure was implemented and so far only a photographic monitoring was carried out, therefore environmental benefits cannot be quantified. However, a reduction of eutrophication was experienced, vegetation quickly recolonized the banks and the bed granulometry became more heterogeneous. A quantitative monitoring is foreseen, especially of the river morphology and of the groundwater level. A quantitative assessment will support the implementation of similar actions in other sites using the same approach.

Lessons learnt

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Image gallery


The pont Paillard weir, before works, in June 2008.
The opening of the pont Paillard weir, in June 2008.
About 150 meters upstream the weir, on the 30 June 2008.
The old reservoir just upstream the weir, after the removal of the wooden planks of the weir, on the 30 June 2008.
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Catchment and subcatchment

Catchment

River basin district Adour Garonne
River basin Charente

Subcatchment

River name Aume
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m)
Dominant geology Siliceous
Ecoregion Western Plains
Dominant land cover
Waterbody ID



Site

Name Paillard bridge at Fouqueure
WFD water body codes FRFR5
WFD (national) typology
WFD water body name
Pre-project morphology Straight, Single channel
Reference morphology Single channel, Sinuous
Desired post project morphology
Heavily modified water body No
National/international site designation
Local/regional site designations
Protected species present No
Invasive species present No
Species of interest
Dominant hydrology Quick run-off, Groundwater
Dominant substrate Gravel, Cobble, Boulders
River corridor land use Extensive agriculture, Grassland
Average bankfull channel width category 2 - 5 m
Average bankfull channel width (m) 3
3 m
0.003 km
300 cm
Average bankfull channel depth category 0.5 - 2 m
Average bankfull channel depth (m)
Mean discharge category
Mean annual discharge (m3/s) 0.05
0.05 m³/s
50 l/s
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)


Project background

Reach length directly affected (m) 300 m
0.3 km
30,000 cm
Project started 2008/06/01
Works started 2008/06/01
Works completed 2008/06/01
Project completed
Total cost category
Total cost (k€)
Benefit to cost ratio
Funding sources

Cost for project phases

Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname
Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring



Reasons for river restoration

Mitigation of a pressure Reservoir impoundment
Hydromorphology Quantity & dynamics of flow
Biology Fish: Species composition, Fish: Abundance
Physico-chemical
Other reasons for the project Landscape enhancement, Flood risk management, Community demand


Measures

Structural measures
Bank/bed modifications Planting, Weir removal
Floodplain / River corridor
Planform / Channel pattern
Other
Non-structural measures
Management interventions
Social measures (incl. engagement)
Other Participation in monitoring, Participation in maintenance, Information provision, Consultation


Monitoring

Hydromorphological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Fish: Species composition Yes Yes Awaiting results
Fish: Abundance Yes

Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Any other monitoring, e.g. social, economic

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative


Monitoring documents



Additional documents and videos


Additional links and references

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Supplementary Information

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