Navizence

The Navizence is a 23-kilometer-long Swiss river located in the Anniviers Valley, in the canton of Valais. It is a left-bank tributary of the Rhône River, joining it at Chippis. The river originates from the Zinal Glacier and flows northward and then north-northwest. It passes through several streams, particularly from Vissoie, where its bed lies at the bottom of a crevasse. Its main tributary is the Gougra. The water from the Navizence is utilized by multiple hydroelectric plants and can be pumped to the Moiry Dam via a system of galleries. The Navizence has encountered major floods in 1834 and 2018, resulting in extensive destruction in the Anniviers Valley and Chippis. The river is home to various benthic macroinvertebrates and brown trout.

Hydronymy In 1267, the river was referred to as aquam de la Navisenchy. Its name could have originated from an early "Anniviers" form, with the suffix -entia, forming Anavisentia. Another possibility is that the name derives from the Gaulish "nava," which means "deep valley, ravine" in Latin, with the suffix -ence. Philologist Paul Aebischer suggests a Gaulish root anavo-, conveying ideas of inspiration and wealth. The river has multiple spellings: "Navizance", "Navizence", "Navisance", or "Navisence". Its German name is Uzenz. In the local Arpitan dialect, it is referred to as Navijèïngtse.

Geography

Location

The Navizence flows through three municipalities in the canton of Valais: Anniviers, Chalais, and Chippis. The drainage basins of the Rèche surround it to the northwest, the Borgne to the west, the Viège from Zermatt to the south and southeast, the Turtmänna to the east, the Illgraben to the northeast, and the Rhône to the north.

Courses The Navizence originates at 2,100 meters, at the exit of the Zinal Glacier, at the bottom of the western branch of the Anniviers Valley. At this point, the river also collects water from other glaciers, such as the Moming Glacier and the Lée Glacier. It then flows through a narrow gorge about 600 meters long. At its exit, it passes through the Plat de la Lée where several small streams join it from the Roc de la Vache, the Tracuit Glacier, Les Diablons, or the Garde de Bordon. The Navizence then flows through the village of Zinal. About 2 km after Zinal, in Mottec, the watercourse descends sharply into a new stream with a direct and consistent slope. At this point, the river changes its direction from northward to north-northwest. Along its right bank, it is fed by water from the small Diablons Glacier, and further downstream in Ayer, it receives water from the Forcletta Pass. At an elevation of 1,287 meters above sea level, the river merges with its main tributary, the Gougra, which carries water from the Moiry Glacier and the Zozanne, Lona, and Marais lakes. Considerably swollen by the Gougra, the Navizence flows northward and then turns north-northwest after Saint-Jean. It merges with the Moulins stream at Vissoie, which originates from the snowfields of Pointe de Nava, Toûno, and Bella Tola. As the valley narrows from Vissoie, the Navizence disappears into a canyon, receiving water from two tributaries: one from the Orzival Valley under Pinsec and the other from Schwarzhorn at Fang.

At the site known as "des Balmes," the rocky spur of Pontis, located at the base of Illhorn, alters the river course once more, this time flowing northwestward. The Navizence, reaching an elevation of 535 meters east of Chippis, spans a distance of 23 km before merging with the Rhône.

Hydrology The Navizence basin covers an area of 255.5 km2, with the Zinal valley accounting for 114.7 km2 and the Gougra basin covering 57.1 km2. The watershed altitude ranges from 447 to 516 m, with an average altitude of 2,387 m. The surface composition of the watershed includes 27% rocks, 24% herbaceous vegetation, 21% forests (20% conifers and 1% mixed forests), 13% glaciers, and 9% loose rocks. The remaining area is divided among shrubby vegetation (3%), wetlands (2%), watercourses (1%), and urban areas (1%). From 1981 to 2010, the average annual rainfall in the watershed was 1,020 mm/year, with precipitation increasing with altitude. May receives the highest precipitation, averaging 125 mm, and has the highest snow water equivalent at 310 mm. The Navizence has different river regimes. It has a glacial regime from the Zinal Glacier to its confluence with the Gougra. From that point until it meets the Rhône, it is a snow-fed regime. The Strahler number of the Navizence is 5 until Vissoie, where the addition of the Moulins stream increases it to 6.

Two flow measurement discharges were established on the Navizence. The first station was located 250 m downstream of the Gougra mouth and operated from September 1928 to June 1935. The second station was situated 450 m downstream of the Vissoie road bridge and operated from January 1956 to December 1962. The average flow recorded during this period was 7.82 m3/s, with the lowest daily average of 0.89 m3/s recorded in 1959. From 1961 to 1980, the average annual flow of the Navizence was 6.19 m3/s at Vissoie and 7.21 m3/s at Chippis.

Weather

Developments The major developments along the Navizence are located from the Chippis mill to its confluence with the Rhône. In this section, the river has been straightened with rock blocks on the left bank and a stone wall on the right bank. The remaining part of the river has been preserved in its natural state, except for stabilizations around Mottec and near certain structures. Two compensation basins are situated along the Navizence, at Mottec and Vissoie. The first basin is utilized to regulate the flow towards Vissoie during the summer and can also pump water towards the Moiry Dam during off-peak hours. The Vissoie basin is designed to supply water to the Vissoie-Chippis open-flowing gallery.

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