# 5 | Serial cofferdams between islets and the bank
In France, over 60,000 structures – dams, locks, weirs, mills – have been identified in watercourses (national reference document for water flow obstructions, March 2010); these pose a potential risk to ecological continuity. The European Water Directive (Directive 2000/60/EC – Ecological Water Framework Directive) sets December 2027 as the latest deadline for achieving environmental objectives.
River development works and the targeted removal of certain hydraulic structures are gathering pace to encourage the free movement of fish and the removal of sediment while respecting the biodiversity and identity of our regions.
TEMPORARY DIVERSION OF THE VARENNE RIVER (SEINE-MARITIME) USING A WATER-GATE COFFERDAM
Water-Gate was installed last July to facilitate works on the Varenne River: total removal of the hydraulic structure of the old spinning mill at Torcy-le-Petit and creation of three rip-rap weirs to compensate for the difference in height and reinforce the banks.
Works carried out by the company Nature Environnement Terrassement, based in Longueville-sur-Scie.
Works financed by the Seine-Maritime Water Agency and the Department.
Installation of three sections of Water-Gate cofferdams:
1 – Water-Gate WA 2850 cofferdam: height 71 cm x length 15 m
2 – Water-Gate WA 3950 cofferdam: height 100 cm x length 15 m
3 – Two Water-Gate WA 3950 twin cofferdams
- To ensure that sediment is carried along the river.
- To allow fish to migrate by removing an impassable obstacle and to encourage the return of emblematic species: sea trout, Atlantic salmon, sculpin, lamprey.
- To satisfy the regulatory obligations of the European Water Framework Directive.
- To manage the risks related to public safety.
See the full article HERE (Syndicat du Bassin Versant de l’Arques)
Weir to be levelled off | Fish ladder to be removed
Temporary water diversion using Water-Gate
New rip-rap weirs, reinforced banks