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The Malpas tunnel on the Canal du Midi
The Malpas tunnel on the Canal du Midi

The Malpas tunnel was excavated in 1679 under the colline d'Ensérune in Herault, allowing the passage of the Canal du Midi. It was Europe's first navigable canal tunnel and a monument to the determination of Pierre-Paul Riquet, the chief engineer.

There was great disappointment when the works reached the colline d'Ensérune. A few metres of digging in hard rock revealed a very brittle sandstone subject to slippage. Colbert, the prime minister halted the works when he was made aware of the situation. The portal was blocked and the workings re-sited. Riquets detractors took advantage of this situation to impede the project. Colbert announced that he would send royal commissioners to decide the canals future. The advice of the chevalier de Clerville, architect to Louis XIV, was to cross the River Aude rather than tunnel through the hill. Riquet however, maintained his preference for a tunnel because of the extra problems that crossing the Aude would create.

Riquet's response was to ask his master mason Pascal de Nissan to continue tunneling in secret despite the risk of collapse. In less than eight days the tunnel was complete with a concrete ceiling throughout. The tunnel is 165m long and removed the necessity for an extra lock.

Under the Malpas tunnel there are two others at different levels. One is for the Béziers to Narbonne railway line built in the nineteenth century and the other is a tunnel dug to drain the étang de Montady.

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[edit] The Inclined Planes

The four original inclined planes are in order from the summit level downwards, Buczyniec (Buchwalde) with a rise of 20.4m and a length of 224.8m, Katy (Kanten) with a rise of 18.83m and a length of 225.97m, Olesnica (Schönfeld) with a rise of 21.97m and a length of 262.63m and Jelenie (Hirschfeld) with a rise of 21.97m and a length of 263.63m. The fifth incline was Calony Nowe (Neu-Kussfeld) with a rise of 13.72m, it was built to replace five wooden locks close to Elblag.

The canal worked independently of other waterways and as a result the boats were designed within the limits of the inclines. The boats had a maximum length of 24.48m, a maximum width of 2.98m and a maximum draught of 1.1m, they carried loads of about 50 tonnes.

The inclines all consist of two parallel rail tracks with a gauge of 3.27m. Boats are carried on carriages which run on these rails. The inclines rise from the lower level of the canal to a summit and then down a second shorter incline to the upper canal level. The first part of the main incline and the short upper incline were both built at a gradient of 1:24. A carriage is lowered down the incline to counterbalance an upward moving carriage. Once the downward moving carriage has reached the summit and started down the main incline its weight helps pull up the upward moving carrige. This allowed the slope of the incline for this section to be built at a higher gradient of 1:12.