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

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Location: 45° 52' 34.21" N, 0° 3' 11.24" E

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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

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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.

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this 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 Edit 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) 33 m <br />0.003 km <br />300 cm <br /> Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) 0.050.05 m³/s <br />50 l/s <br /> Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 300 m0.3 km <br />30,000 cm <br /> 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 Edit reasons for 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 Edit 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 Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit 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 Edit 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 Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Case study description by ONEMA (French National Agency for Water and Aquatic Environments) (in French) Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information