Recently, 3 weirs with very large flap gates have been built on the Seine River near Paris for VNF-DTBS (Voies Navigables de France- Seine Basin): Chatou, 2nd weir downstream of Paris finished in 2013, Le Coudray finished in 2012, and Vives-Eaux finished in 2017, 4th and 5th weirs upstream of Paris. The 3 old weirs had been built about 80 years ago to increase navigation depth on Seine river. They had lift gates (Chatou) or wicket « Aubert » gates.
The flap gates operated each by 2 hydraulic jacks are remarkable because they are out of or just at the limit of the proven optimal scope of flap gates compared to other types, according to 2006 PIANC report (design of movables weirs and storm barriers), because of the torsional rigidity limit, or out of the range indicated by standard design guide for flap gates made by VNF-Cerema in 2009. There is no example of both larger and higher flap gate (Erbisti). The main dimensions (water height x span in meters) of these gates are: 7.8 x 32.5 (Chatou), 6 x 34 (Le Coudray) and 4.8 x 30 (Vives-Eaux), the gate height in Chatou is 9 m. However, the reasons why this kind of gates has been chosen are mainly aesthetic, liability, precise regulation and price.
The main design, construction or operating constraints have been gates the structure, the energy dissipation basin, the cofferdam, the maintenance bulkhead, and fish passes.
The flap gate design will be compared: use of torsion tube or traditional fish belly shape, design and installation of hinges and Cardan suspensions. The large gates have been installed in several parts assembled on place with bolts. The hydraulic jacks’ rods have unusual long strokes, 9.25 m for Chatou weir. Using these 3 examples, the limit of optimal scope of flap gates will be discussed.
For Le Coudray Weir, a laboratory physical model (scale 1/12) has been made and has improved the calculations and design, for discharge, hydrodynamic forces, energy dissipation basin, hydraulic jump and downstream protection, aeration and vibrations prevention.
The hydraulic winter conditions imposed to remove or to be able to remove the cofferdam every winter. In addition the soil conditions were difficult: hard limestone or chalk. So, innovative sheet-piles cofferdams have been made: cofferdam without concrete plug in Chatou, sheet-piles set on riverbed with bored piles and injections in rock in Le Coudray to insure stability and watertighting.
For the 3 weirs, the maintenance upstream bulkhead will be floating ones which leads to some difficulties in design and operations, because of the large dimensions.
Fish ladders with pools are made on these weirs to insure ecologic continuity.
The 2 first weirs have been commissioned 4 years ago. So a first feedback can be made about operation and maintenance.
Precise regulation of water level is necessary for navigation and fish passes, especially because of the Paris reach which needs stability.