La coupure du Rhin pour l'aménagement hydro-électrique de Rhinau

The damming of the Rhine for the Rhinau hydro-electric scheme

¹ Chef du Groupe d'Hydraulique générale du C.R.E.C., E.D.F., Chatou.
² Chef de l'Aménagement de Rhinau à la R.E.H. Nord, E.D.F.

Résumé

The 1956 Franco-German convention on the development of the upper reaches of the Rhine between Basle and Strasbourg stipulated that a storage reservoir, a water intake and a tail race canal be provided with every new power station built. Furthermore, work on the river bed was on no account to interfere with the very busy international river traffic (7 million tons in 1960). The Marckolsheim and Rhinau projects were started in 1956 and were implemented in different ways. The former dam was built in the river bed, which took from 1958 to 1961, and the latter was erected beside the river, only a few days being necessary in September and October 1961 to put the various structures into service. The Rhinau scheme cost less to put into effect than the Marckolsheim scheme, added to which work on the site was much more straightforward and interfered less with river shipping. It is discussed in closer detail in this article. The operations required to put the Rhinau scheme into service-which were the only part of the work liable to interfere with shipping-were carried out after the main structures had been completed on dry land (especially the sluiceway). They included three phases : 1) the preparation of the river closure by making openings in the dykes immediatly upstream and downstream from the dam and downstream from the tail race canal and the construction of a cutoff spur on the left bank, 2) the diversion of shipping through the intake canal and the locks and the construction of the dyke across the river and 3) completion of the final closure dyke. Closure operations were carried out at low water in October, with 2,000 cu.m/sec. as the maximum permissible river flow. The main operations in this programme were investigated on scale models at the 'Laboratoire National d'Hydraulique' at Chatou. It was decided to start the opening-up of a navigation channel at the diversion entrance by making an opening near the intake canal centre line. This work proceeded along two 'fronts' one progressing up-river and the other down-river. The opening was completed in forty days and had a final width of 130 m. The dam gates remained shut during the work and were then gradually opened up after diverting shipping to enable the closure to be made. With the upstream part of the dyke completely removed, this was to ensure that no silting would occur in the new channel. It was also decided to make the flood water sluice downstream from the dam 200 m wide to prevent bank erosion on the German shore, and to build the initial cutoff spur to extend 60 m out from the left bank. The final closure dyke was to be built working from both banks out into the river, using 20 kg to 75 kg rock fill over a 1 m thick rock fill blanket on the river bed. Work on the Rhinau site began on the 22nd August 1963. The shipping channel at the diversion intake was completed by the 26th September, also the flood water sluice downstream from the dam, the initial closure spur and the tail race canal back into the Rhine. Shipping was diverted immediately. The full closure dyke was completed in four days (3rd October), being built on a rock fill protection blanket. 15,400 cu. m of rock fill were used altogether. The damming of the Rhine at Rhinau is an example of a composite scheme combining the usual 'horizontal layer' procedure and work carried out from the banks into the river. With the facilities available at the site, this enabled small rock fill to be used and operations to proceed in complete safety as no major erosion was experienced at the tips of the two closure spurs. In view of the successful completion of this work and its complete lack of interference with international river traffic, the same procedure is also to be followed in implementing further hydroelectric projects on the Rhine.