Fonserannes lock staircase

Fonserannes lock staircase:
view from below, chamber 7 in the foreground

The Fonserannes lock staircase ( French Échelle d'Écluses de Fonserannes ) is a lock staircase on the Canal du Midi . It is located in the municipality of the French city of Béziers in the Hérault department in the Occitanie region . With six chambers, it overcomes a height difference of 13.60 meters. The lock staircase is classified as a monument historique and one of the most visited attractions in the city.

etymology

The name of the lock staircase was spelled differently over the centuries: Fonceranes, Fonseranes, Foncerannes (with or without an accent). Today the spelling Fonserannes is common.

Development of the structure

17th century

The structure was built in the 17th century and went into operation together with the Canal du Midi planned and built by Pierre-Paul Riquet (section to Béziers). The lock staircase originally consisted of eight interconnected lock chambers with a length of approx. 300 meters in total with a height difference of 21.18 meters. Another double lock (Écluse de Notre Dame), which was no longer counted as part of the lock staircase, was just before the connection to the Orb River, about a kilometer away . The ships were allowed to descend to the river via the lock staircase and the following double lock. The ships then had to travel around 700 meters down the river. There, on the left bank of the river, in front of a weir, was the exit to the continuation of the Canal du Midi.

19th century

Canal bridge over the Orb (flowing to the right)

Chamber 8 of the lock
staircase (detail at the upper gate): Increase by Δh when the staircase is connected to the bridge canal over the Orb , in the background the gate against the bridge canal of the likewise elevated chamber 7

Since the Orb's water flow was very uncertain, a canal bridge was built over the river in the mid-19th century . This is located approximately in the middle of the section of the Orb that was previously used for shipping. The position of the new bridge canal is slightly higher than the headwater of the previous lock chamber 7, which has therefore been raised, expanded to the east and connected to the bridge canal.

The lock chamber 8 and the double lock on the river are no longer needed. However, in order to enable traffic to the old canal port of Béziers and, if necessary, via the Écluse de Notre Dame to the Orb, the lower / upper gate of lock 7/8 was also increased, and the bridge channel connection to lock chamber 7 was also increased provided a barrier gate.

East of the canal bridge, two new double locks (Écluse de l'Orb and Écluse de Béziers) were built, with which the level of the earlier canal continuation was reached. The new port of Béziers was built between these two locks. At the end of the 20th century, both new double locks were converted into single-stage locks that are double-length but can be shortened using a central gate.

The new route was put into operation in 1858 and in this form represents the current state of construction of the lock staircase. The six lock chambers used today raise and lower the ships to a height of 13.6 meters. The chamber 7 normally has a constant water level, it is always filled and thus part of the bridge channel.

20th century

Upper attitude , to the right of the branch to the Water slope

Plan of the lock staircase (right) and the water channel (left)

In 1983, an extraordinary boat lift , the Fonserannes water wedge lift , was built right next door to speed up the passage and possibly remove the lock staircase . This is an inclined channel in which the ship is transported in wet conditions . A shield that closes the channel on the valley side is pushed upwards by a tractor together with the wedge-shaped volume of water that forms in front of it, on which the ship floats, or is driven down to the valley with the brakes. However, the operation of this elevator was not accompanied by success. As a result of constant technical problems and the decline in commercial freight traffic, it was used very little, the last time in 1999. The lock staircase was always in operation in parallel and is still in service today.

Current use of the lock stairs

View from the upper chamber

The cargo shipping has almost completely disappeared on the Canal du Midi. Today, sports boats and houseboats , passenger ships for excursions and péniches converted into floating hotels operate on it in large numbers: the lock staircase is passed by around 10,000 such tourist watercraft every year, with up to 60 per day in the holiday months of July and August could be.

In order to be able to cope with this amount, a one-way system was introduced, in which the waiting watercraft are either only pushed downwards or only upwards several times a day during fixed time periods. Three of the usual tourist boats fit into each chamber. Locking a group of ships takes about 30 minutes downwards and 45 minutes upwards. During the downward lock, the groups of ships are moved downwards together with a single chamber filling. When moving upwards, one chamber filling is used for each stage. To speed up the process, each chamber is filled from the second higher chamber. The water exchange happens faster because of the increased level difference. However, an additional chamber filling is also lost.

The locks are operated by employees of the French waterway administration Voies navigables de France (VNF). The costs of the lock are covered by the mandatory purchase of the ship's vignette to use the canal. In 2016/17 a large car park and a visitor center were built.