Canal De Haute Perche

The Haute Perche Canal ( ), despite its title, is a natural river, the , that has been slightly canalised to improve navigation between its mouth in the Bay of Bourgneuf at the port town of Pornic and the upstream settlements of , Chauvé and Arthon-en-Retz. It is located in the Pays de Retz in the Loire-Atlantique department and the Pays de la Loire region. It has also been known as the ' since the 16th century and was sometimes called the '. Historically, it was called the ''Rouet'', after the wheels of the water mills in the port..

Etymology

The is a village on the waterway between the towns of Arthon and Chauvé in the commune of Chaumes-en-Retz and was at times the navigable limit of the waterway.

Geography

The Canal de Haute Perche is located entirely in the Pays de Retz, south of the Loire in Loire-Atlantique. It extends over the municipalities of Pornic, Clion-sur-Mer, Chauvé and Chaumes-en-Retz.

Hydrography

The Haute Perche Canal drainage basin extends east of Pornic over and with its component tributaries totals in length. It is bordered by the basin to the north. To the east the basin of the Blanche links to the complex of rivers and canals associated with the Lac de Grand-Lieu: ( Acheneau and Tenu) and those of the Marais Breton (the Marais de Millac and the Falleron) to the south.
The river has its source in the commune of Chaumes-en-Retz (delegated commune of Arthon-en-Retz ) and it flows towards the west, emptying into the Bay of Bourgneuf at Pornic. It is one of the main sources of fresh water in the bay with the Falleron.

Ria

The mouth of the river is a ria (or ), eroded along a fault line in the Precambrian mica-schist rocks of the Armorican Massif which define the north coast of the Bay of Bourgneuf. It can be considered as the southernmost aber in Brittany. Formed mainly before the Pliocene era, it was inundated by the rise in sea level due to the Flandrian transgression and has gradually silted up since. The navigable part of the river upstream from the port was considered to be 11km or 12km, but the maximum length from source to port is . The distance between the causeway of the port and the mouth of the ria at the adds another .

Main tributaries

The course of the Canal de Haute Perche is fed by several streams whose SANDRE classification recognizes more than fifteen of 1 km or more. The banks of the canal are also connected with numerous lateral channels in the marshes. The largest tributaries on the right bank to the south include:

* The ''Ruisseau du Pontereau'', 5km, lies to the west of Arthon and is used by a wastewater treatment plant in the town. It delimits part of the border between Pornic and Chaumes-en-Retz. Its tributary, the ''Ruisseau du Port'', 5km, serves the village of Port to the west of Arthon (and not to be confused with the port of Pornic).
* the ''Gué'' flows from the hinterland of Bernerie-en-Retz and runs for 6 km.

The largest tributaries on the left bank to the north include:
* ''Ruisseau de la Basse-Chanterie'', 1.45 km, south of Chauvé.
* ''L’étier de l’écluse'', 4 km, and the ''Ruisseau du Pin'' and its tributaries extend over a vast area to the west and north of Chauvé. On its right bank stretches the ''le ruisseau des vieux moulins'' (the stream of the old mills), 5 km.
* the ''Rinais'', spread over 10 km, is the longest of the Canal de Haute Perche tributaries. It finds its sources in the south-east of the neighbouring town and commune of Saint-Michel-Chef-Chef. In the direction of Saint-Père-en-Retz, the Rinais was also blocked between 1866 and 1950, at the confluence with the ''Ruisseau de la Brégeonniere'', creating the lake of the ''Gros Caillou''. It covers .
* The ''Val Saint-Martin stream'' was blocked before 1866 and created the reservoir of the ''Etang du Val Saint Martin''. From the sluice at the foot of the dam, it flows for 0.54 km before its confluence with the river in the ria. It covers . Despite the installation of a fish ladder in 2012, the fish richness of the pond and stream upstream is considered poor by the local angling society: "Fishing Federation 44".
On the right bank of the ria near the mouth of the port, the ''Cracaud'' (or ''Cracault'' ) and the ''Dette'' streams flow in an arm of the ria which delimits the site of the Château de Pornic. Visible on Cassini's map, the mouth of this arm of the estuary has since silted up and most of these watercourses since buried, but the Cracault still flows visibly on the surface to the northwest of the pottery.

Hydrology

In the watershed, there are stations for measuring the flow, situated both on the main watercours and its tributaries. Some of them equip the river itself at the port, and in the ria.

Flow regulation

The sluice of the former lock at the causeway bridge in the port of Pornic is the main control point for the water level in the canal. Another sluice with three vertical check valves is located 1.25 km upstream in Boismain, near Pornic's wastewater treatment plant at Les Salettes. Operation of both of these was automated in 1987 and is controlled from Nantes, managed by Veolia Environnement for the city of Pornic. The artificial lakes of Val Saint-Martin and Gros Caillou are part of the water management control system. The Gros Caillou also serves as a drinking water reservoir.

History

Human influence on the river began in the 13th century during the time of , with the construction of the causeway in 1225 which linked the two banks and formed a dam equipped with four tide mills. The causeway provided a connecting road between the two shores of the port and formed the junction of the road north to Paimboeuf and south to Machecoul

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