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Origin and history

The Vias Lock Dam is part of the Libron, a unique structure designed to allow the Canal du Midi to cross the Libron River near Agde. Originally, frequent floods of the Libron (about 20 per year) blocked the canal with silts and debris. To remedy this, a temporary system, the Libron Radeau, a wooden bulkhead barge, was placed in the canal during the floods, blocking river traffic to the riverhead. This system, in place since the opening of the canal in 1681, was replaced in 1855 by the current structures, designed for the permanent coexistence of the two watercourses.

The Urban engineer Maguès imagined a structure dividing the Libron into two canalized arms, crossing the Canal du Midi via six doors on each side of a 30.5 metre protected area. Normally, the Libron flows under the channel through a gutter. In flood, its waters are directed through the six locks, whose stone walls guide the flow while limiting mud deposits. This system also allows vessels to cross the Libron tracks safely: a vessel on approach stops temporarily, allowing another vessel to pass through the protected area, while the flow of the river is regulated by sliding doors.

The books of the Libron, listed as historical monuments in 1996 and classified as a UNESCO World Heritage Site, illustrate the hydraulic ingenuity of the 19th century. Their operation is based on a precise balance between the water levels of the canal (slightly raised) and the Libron (at sea level), making it impossible to use a conventional aqueduct. The solution combines stone wall, lock and buffer zone, ensuring both navigation and flood protection, while avoiding sediment accumulation.

Before 1855, the Libron flood regularly interrupted traffic on the Canal du Midi, requiring manual interventions to place or remove the raft. The Maguès project removed these constraints by automating flow management. Today, these works testify to the adaptation of historical infrastructures to geographical challenges, while preserving the integrity of the canal, a major work by Pierre-Paul Riquet opened in 1681, a year after his death.

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