| Navizence Navisence, Navizance | |
|---|---|
 Navizence inZinal. | |
 | |
| Location | |
| Country | Switzerland |
| Region | Valais |
| Physical characteristics | |
| Source | Zinal Glacier |
| • location | Anniviers |
| • coordinates | 46°04′53″N7°38′02″E / 46.08139°N 7.63389°E /46.08139; 7.63389 |
| • elevation | 2,100 m |
| Source confluence | Rhône |
| • location | Chippis |
| • coordinates | 46°16′57″N7°32′30″E / 46.28250°N 7.54167°E /46.28250; 7.54167 |
| • elevation | 522 m |
| Length | 23 km |
| Basin size | 255,5 km2 |
| Basin features | |
| Landmarks | Rhône |
| Tributaries | |
| • left | Gougra |
| • right | Torrent des Moulins |
TheNavizence is a 23-kilometer-longSwissriver located in theAnniviers Valley, in thecanton of Valais. It is a left-banktributary of theRhône River, joining it atChippis.
The river originates from theZinal Glacier and flows northward and then north-northwest. It passes through severalstreams, particularly fromVissoie, where its bed lies at the bottom of acrevasse. Its main tributary is theGougra.
The water from the Navizence is utilized by multiplehydroelectric plants and can bepumped to theMoiry 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 variousbenthic macroinvertebrates andbrown trout.
In 1267, the river was referred to asaquam de la Navisenchy. Its name could have originated from an early "Anniviers" form, with the suffix -entia, formingAnavisentia. Another possibility is that the name derives from theGaulish "nava," which means "deep valley, ravine" inLatin, with the suffix -ence.[1]PhilologistPaul Aebischer suggests a Gaulish rootanavo-,[2] conveying ideas of inspiration and wealth.[3]
The river has multiplespellings: "Navizance", "Navizence", "Navisance",[4] or "Navisence".[5] ItsGerman name isUzenz.[4] In the localArpitan dialect, it is referred to asNavijèïngtse.[6]
The Navizence flows through three municipalities in thecanton of Valais:Anniviers,Chalais, andChippis.[8] Thedrainage basins of theRèche surround it to the northwest, theBorgne to the west, theViège from Zermatt to the south and southeast, theTurtmänna to the east, theIllgraben to the northeast, and theRhône to the north.[9]
The Navizence originates at 2,100 meters, at the exit of theZinal Glacier, at the bottom of the western branch of theAnniviers Valley.[4][10] At this point, the river also collects water from other glaciers, such as theMoming 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 smallstreams join it from theRoc de la Vache, the Tracuit Glacier,Les Diablons, or theGarde de Bordon. The Navizence then flows through the village ofZinal.[4]
About 2 km after Zinal, in Mottec, the watercourse descends sharply into a newstream 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 inAyer, it receives water from the Forcletta Pass. At an elevation of 1,287 meters above sea level, the river merges with its main tributary, theGougra, which carries water from theMoiry Glacier and the Zozanne, Lona, and Marais lakes.[11]
Considerably swollen by the Gougra, the Navizence flows northward and then turns north-northwest afterSaint-Jean. It merges with the Moulins stream atVissoie, which originates from thesnowfields of Pointe de Nava,Toûno, andBella Tola. As the valley narrows from Vissoie, the Navizence disappears into acanyon, receiving water from two tributaries: one from the Orzival Valley underPinsec and the other from Schwarzhorn atFang.[12]
At the site known as "des Balmes," the rocky spur of Pontis, located at the base ofIllhorn, alters the river course once more, this time flowing northwestward. The Navizence, reaching an elevation of 535 meters east ofChippis, spans a distance of 23 km before merging with theRhône.[11]
The Navizencebasin covers an area of 255.5 km2, with the Zinal valley accounting for 114.7 km2 and theGougra 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%).[13]
From 1981 to 2010, the average annualrainfall in the watershed was 1,020 mm/year, withprecipitation increasing with altitude. May receives the highest precipitation, averaging 125 mm, and has the highest snow water equivalent at 310 mm.[13]
The Navizence has differentriver regimes. It has aglacial regime from theZinal Glacier to its confluence with the Gougra. From that point until it meets theRhône, it is asnow-fed regime.[14] TheStrahler number of the Navizence is 5 until Vissoie, where the addition of the Moulins stream increases it to 6.[15]
Two flow measurementdischarges 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.[16] 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.[17] From 1961 to 1980, the average annual flow of the Navizence was 6.19 m3/s atVissoie and 7.21 m3/s atChippis.[18]
| Data | Station | Jan. | Feb. | Mar. | Apr. | May. | Jun. | Jul. | Aug. | Sep. | Oct. | Nov. | Dec. | Year |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Mean maximum temperatures (°C) | Evolène/Villa (1,825 m)[19] | 0.7 | 0.9 | 4.4 | 8 | 11.8 | 15.7 | 18 | 17.5 | 13.7 | 10.1 | 4.7 | 1.8 | 8.9 |
| Grächen (1,605m)[20] | 0.9 | 1.5 | 5.4 | 9.3 | 14 | 18.3 | 20.4 | 19.8 | 15.5 | 10.8 | 4.7 | 1.4 | 10.2 | |
| Zermatt (1,638 m)[21] | 0.8 | 1.7 | 5.7 | 9.8 | 13.9 | 17.8 | 20 | 19.6 | 15.4 | 11.2 | 5.1 | 1.5 | 10.2 | |
| Mean minimum temperatures (°C) | Evolène/Villa (1,825 m) | -5.5 | -6.0 | -3.5 | -0.8 | 2.9 | 6.3 | 8.2 | 8.6 | 5.3 | 2.3 | -2.1 | -4.6 | 0.9 |
| Grächen (1,605 m) | -5.4 | -5.6 | -2.7 | 0.4 | 4.3 | 7.9 | 9.8 | 9.9 | 6.5 | 3.2 | -1.4 | -4.4 | 1.9 | |
| Zermatt (1,638 m) | -7.4 | -7.3 | -4.0 | -0.7 | 3.2 | 6.6 | 8.3 | 8.3 | 5 | 1.4 | -3.1 | -6.3 | 0.3 | |
| Precipitation (mm) | Evolène/Villa (1,825 m) | 49 | 40 | 41 | 50 | 81 | 81 | 88 | 85 | 55 | 54 | 55 | 55 | 734 |
| Grächen (1,605 m) | 42 | 31 | 37 | 47 | 69 | 58 | 56 | 62 | 43 | 57 | 56 | 50 | 607 | |
| Zermatt (1,638 m) | 42 | 30 | 33 | 40 | 77 | 70 | 59 | 68 | 51 | 57 | 65 | 47 | 640 | |
| Sunshine (hours) | Evolène/Villa (1,825 m) | 110 | 119 | 159 | 164 | 178 | 192 | 212 | 194 | 169 | 143 | 104 | 96 | 1,840 |
| Grächen (1,605 m) | - | - | - | - | - | - | - | - | - | - | - | - | - | |
| Zermatt (1,638 m) | 94 | 109 | 151 | 147 | 155 | 171 | 185 | 176 | 156 | 133 | 89 | 83 | 1,648 | |
| Source:MeteoSwiss. | ||||||||||||||
The major developments along the Navizence are located from theChippis mill to itsconfluence with theRhône. 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.[22]
Two compensation basins are situated along the Navizence, at Mottec and Vissoie.[22] The first basin is utilized to regulate the flow towards Vissoie during the summer and can also pump water towards theMoiry Dam duringoff-peak hours. The Vissoie basin is designed to supply water to the Vissoie-Chippisopen-flowing gallery.[23]
In samplings conducted in the 1980s, 32taxa ofbenthic macroinvertebrates were recorded in the Navizence. These taxa mainly consist ofinsect larvae, including species ofTricladida, one ofHydrachnidia, and two ofOligochaeta.Phyla involved arePlatyhelminthes (Crenobia alpina),Annelida (Lumbricidae andTubificidae), andarthropods from theordersEphemeroptera,Plecoptera,Coleoptera,Trichoptera, andDiptera.[24]
The rapids at the entrance of theAnniviers Valley pose a challenge for fish migration. In the 1930s,brown trout (Salmo trutta fario) populations were introduced by catching them in the Rhône Valley and releasing them in various locations in the Anniviers Valley.[25] From 2012 to 2014, 15,000 brown trout were released annually into the Navizence River from theSierrefish farm.[26]
The Navizence experienced twofloods that resulted in a significant overflow. The first flood occurred in August 1834, caused by the obstruction of the river's flow at theZinal Glacier by aproglacial lake. This obstruction was a result of an exceptionally dry summer, heavy rainfall, and a south wind. When the lake suddenly burst, it swept away several bridges, barns, stables, and mills inAyer.[27] InChippis, the river deposited a layer ofsand andsilt measuring between 1 and 2 meters.[12]
In July 2018, a new overflow occurred due to a violentthunderstorm covering 35 km2 and the melting of large amounts ofsnow.[28] The Navizence reached a 120 m3/s flow, which is half theRhône nominal flow.[28] The overflow impacted various areas betweenZinal and Chippis: the FC Anniviers football stadium was submerged, and a bridge in Chippis had to be urgently demolished by rescuers.[29][30] The sewage treatment plant in Anniviers atFang suffered significant damage, leading to the direct discharge of wastewater from Zinal and Grimentz into the Navizence.[31] The estimated damage from the event was between 30 and 40 millionSwiss francs.[32]
Water from the Navizence has been utilized for hydroelectric power generation since 1908 inChippis by the "Navizence"hydroelectric plant. This plant initially suppliedelectricity to theAlusuisse factory in Chippis from a water intake inVissoie. A new plant harnessing the Navizence was constructed in Vissoie in 1909,[33] and the "Navizence" plant underwent renovation in the 1950s. TheMoiry Dam was constructed between 1954 and 1958 on theGougra River, along with a network of galleries in theAnniviers Valley,[34] enablingwater to be pumped from the Navizence from Mottec to the dam.[35] Local hydroelectric operators have a total of nine intakes in the Navizencebasins.[36] The maintenance of aminimum discharge at each intake is regulated by the Federal Law on Water Protection of January 24, 1991.[37] At the Vissoie intake, the Navizence flow must be at least 470 l/s before abstraction.[35]
There are tengroundwaterdrinking water intakes in the Navizence watershed. Additionally, water is extracted at eight locations along the banks of the Navizence to supply irrigation channels (bisses): the Gillou alp, the Sarrasin channel inSaint-Jean andChalais, the Briey channel inSaint-Luc and Chalais, the Chararogne and Ricard channel in Chalais and Chippis, as well as the Lacher, Tinda, and Neuf Bénou channel. Furthermore, asewage treatment plant releases treated water into the Navizence atFang.[38]
Since 1922, theNiouc suspension bridge has spanned the Navizence River at a height of nearly 200 meters. Visitors can cross the bridge and participate in activities such asbungee jumping orpendulum jumping. In 2021, avia ferrata route was made accessible either by crossing the suspension bridge or starting fromChippis.[40]
Two sectors of the Navizence watershed are classified in the federal inventory of alluvial areas of national importance: the Plat de la Lée (30.85 ha) and the Zinal Glacier (186.09 ha).[41][42][43] Additionally, the downstream part of the watershed intersects thePfynwald-Illgraben area, which is included in theFederal Inventory of Landscapes and Natural Monuments.[22][44]
Among theaquifers in the watershed, 34% are highly vulnerable to pollution penetration, while 24% have a high vulnerability. This indicates that these aquifers lack adequate protection from low-permeability layers.[45]
Fishing is prohibited in the section of the Navizence between the mouth of the Pinsec stream and the Vissoie accumulation basin, as it is designated as a reserve. However, fishing is permitted downstream of theGougra mouth with a cantonal permit.[46]
The theater troupe inVissoie is called "Les Compagnons de la Navizence."[47] In 1993, an exhibition titledOh! Navizence, conceptualized by Jean-Jacques Le Joncour, was held inSierre. The exhibition depicted the banks of the Navizence in a post-apocalyptic future scenario set in 2009.[48]
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