Lift-locks on the "Canal du Centre" at Strépy-Thieu

In the afternoon the Spokesman of the Transport Category had organised a visit to lift-locks on the "Canal du Centre at Strépy-Thieu", which are situated some 30kms south of Brussels. These boat lifts are a feat of hi-tech civil engineering and they replace a series of locks which were otherwise required to span a height difference in this logistically important canal of 30m. Given the importance of Strépy-Thieu to Belgium's inland waterways, Jan Simons has wished to personally organise this small study tour for EESC Members, as part of his efforts to enhancing Members' knowledge of key infrastructure sites in the Benelux.

Brief introduction about the region

The canal known in French as the "Canal du Centre", some 18.65 km long, was originally constructed to link the canal from Condé-sur-l'Escaut to Mons, itself opened in 1818 and enlarged to accommodate 300-ton Frécinet-standard barges in the 1880s, with the branch to Houdeng at the summit level of the canal from Brussels to Charleroi which had been similarly enlarged by 1885. This involves a rise of some 90 metres from the former terminal basin at Mons to the summit level of 121 metres above sea level. As the "Canal du Centre" follows the natural route along the valley of the stream La Haine and its tributary, Le Tiriau du Luc, most of this rise is concentrated in the few kilometres nearest to Houdeng. Fortunately, this route lies just beyond the northern rim of the coalfield, and the canal was thus able to provide transport from the mines without running the risk of subsidence.
The growth in traffic to and from the local coal and iron industries, particularly following the creation of the European Community, led the Belgian government to decide in 1957 that the country's main navigable waterways should be enlarged to accept barges complying with the new international 1350-ton standard. A major programme of lock rebuilding, widening and deepening was drawn up, including complete replacement of the last part of the old route between Brussels and the summit level by a new direct canal with with the world's biggest inclined plane, 1432 metres long, at Ronquières. When this opened in 1968, with two tanks, each 85m5 x 11m6 and with its own counterweight, a total of 15 300-ton locks with an overall rise of 68 metres were eliminated, and through journey times were reduced by about half a day. The power needed for operation is minimised by having the counterweight somewhat lighter than the fully-loaded tank, and designing the system so that the level in each tank is about 30 cm higher during the descent than it is during the subsequent climb. A feeder stream beside the disused old canal via Arquennes keeps the lower pound full, and the adjacent electrically-powered pumping station supplies the upper pound when necessary.

First sight to be visited: the new lift-lock at Strépy-Thieu

West of Mons, a new 1350-tonne canal via Blaton to the Escaut/Scheldt at Péronnes, with a branch south to Condé via Pommeroeul, was excavated, while the first part of the old 300-ton canal to Condé was filled in so that it could be re-used for the E42 motorway to Valenciennes. But discussions on the best way to replace the historic lift-locks continued until 1980, when it was finally decided to build the world's biggest lift-lock nearby, at Strépy- Thieu. The construction work started in 1982, but although the first barge was raised to the upper level in November 2001, it took twice as long as originally foreseen and by the time the new canal entered service, in September 2002. It can lift each of the two independent tanks (120 x 12 metres with a draught of 3m75, which can accommodate a 2000-ton dumb barge and pusher), with a counterbalance having a total mass of 8500 tons, over the total rise of 73 metres to the summit level in about 7 minutes.

Second sight to be visited: "The historic lift-lock N° 1"

Navigation on the historic "Canal du Centre" is marked by 4 lift-locks. The "Canal" is open to 1350-ton traffic.
The visited lift-lock No. 1 has for a certain time been out of use since an accident has occurred in January 2002. Apparently the clamps that should hold the two lock chambers stationary while loading and unloading takes place failed to do so, and the lower chamber started to rise while a barge was on its way out. The barge grounded and was crushed against the 'guillotine' gates, which stopped the chamber from rising further. This is believed to be the first such accident since the lift locks were taken into regular operation in 1917.
Because the flight of lift-locks was granted world heritage status by UNESCO in 1998, the restoration work adopted the original procedures and special techniques that were employed during its construction in 1884.

A look into history - principles of operation of lift-locks

The lift-locks such as lift-lock N° 1 consist of a pair of tanks, each as large as a conventional lock chamber and closed at each end by a "guillotine" gate, which incorporates a sluice gate that can be opened when required. The adjacent ends of the upper and lower pounds of the canal are fitted with similar guillotine gates such that when the tank is clamped to either of them, which seals the sides and bottom of the gap between the gates, and the water levels in the tank and gap have been equalised with that in the pound, the gates can be raised together. Each tank is supported by a central column which acts like a piston in a deep vertical cylinder filled with water at high pressure, linked with that under the other column through a pipe with a valve that can be opened and closed as required. The total volume of water at high pressure is kept constant at the quantity needed to ensure that when the lower tank is correctly aligned for opening the gates from the lower pound, then the upper tank is similarly at just the right height for opening the gates from the upper pound.
As the total volume of water displaced by any vessel entering the tank has exactly the same mass as that vessel, the two tanks remain in equilibrium so long as the depth of water in them is the same. In order to take advantage of gravity to drive the lift-lock, the surface level of the upper pound must be set so that the depth of water in the upper tank is about 30 cm greater than that in the lower one when the guillotine gates between each of them and the adjacent pound are open. Once the tanks have been loaded, the gates are dropped, the clamps released, and when the valve in the connecting high-pressure pipe is opened, the unbalance is sufficient to make the initially upper tank descend to the lower level, thus raising the other tank to the position where it can be clamped to the upper pound; the valve is then closed again. As the water level in the upper tank is now about 30 cm below that in the upper pound, the sluice gates must be opened to allow water to flow from it into this tank until the levels are equal. Similarly, the excess water in the lower tank must be allowed to flow through the sluice gate into the adjacent pound. Then the guillotine gates can be opened and the cycle repeated.