Rigole d'Hilvern

An integral part of the Canal de Nantes à Brest, this "artificial watercourse" brought water from upstream on the Oust to the Bosméléac dam, the highest point on the canal, to maintain a constant level in the Hilvern divide for smooth river navigation.

Between 1828 and 1838, men and women with pickaxes, shovels and wheelbarrows moved millions of cubic metres of earth and stones to dig, earthwork and level this 65-kilometre-long channel.

The Rigole d'Hilvern required a great deal of engineering prowess and ingenuity to create this veritable technical work of art. With a regular slope of 0.3 millimeters per meter, the Hilvern channel follows a furtive, life-size contour, with a 45-degree slope, a 1.20-meter base opening and an average depth of 1.20 meters.

This aqueduct enabled the hamlet of Hilvern to deliver 30 to 33,000 m2 of water in 24 hours. To waterproof the channel, a clay lining was carefully applied to the bottom of the trench, and in the meanders, more exposed to the friction of the water, an assembly of cut dry stones was sealed with mortar and lime.

The cuttings were used as backfill to create the embankments along the banks and the three-meter-wide service road. Each side of the Rigole was then lined with trees (beech, chestnut, maple, plane, poplar, elm) to reduce bank erosion and reduce evaporation of the water conveyed.

This unusual work of art, now "dry", is an excellent cordon for exploring inland Brittany on foot, horseback or mountain bike along its towpath, which has been rehabilitated as a greenway. The mountain bike route from Saint-Caradec is available as a PDF file.