Inn (river)

• 1. Introduction

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  The Inn is a river that begins its life quietly in the Swiss Alps, west of St. Moritz, and travels 518 kilometers before finally surrendering its waters to the Danube at Passau. At that meeting point, something surprising happens. The Inn actually carries more water than the Danube when the two rivers converge. Yet it is still called a tributary. That paradox sits at the heart of what makes the Inn worth knowing.

  The river flows through three countries, Switzerland, Austria, and Germany, and along the way it passes through one of the only Swiss valleys whose waters drain not to the North Sea or the Mediterranean, but to the Black Sea. Its name is ancient, rooted in a Celtic word simply meaning water. Roman soldiers crossed it, noted it in dispatches, and named the towns they built along its banks.

  How does a river with more flow than the Danube end up classified as its tributary? And what happens when the Inn reaches its peak, as it did in the summer of 2013? Those questions will shape the chapters ahead.

• 2. A Name Older Than Nations

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  Sextilius Felix was sent to capture the banks of the Inn, which flows between the Rhaetian people and the Noric people. That sentence, preserved in the third book of Tacitus, from the years 105 to 109, is the first written mention of the river that would eventually be spelled with a double-n. At that point the Romans called it Aenus in Latin, or Ainos in Greek. Medieval Latin scribes wrote it as Enus or Oenus.

  The root of all these spellings traces back to old Celtic words, en and enios, both meaning water. The name was not a geographical description or a dedication to a deity. It was simply the word for the thing itself. A river called River.

  The shift from Enus to In came through old Bavarian speech, where the vowel e became i over time. Until the 17th century the river appeared in documents as In or Yn, and sometimes as Ihn or Yhn. The double-n that we recognize today appeared only in the 16th century. One early example of that spelling appears in the Tyrolean Landreim of 1557. The short vowel pronunciation has been standard since the 18th century.

  A document from 1338 offers an interesting aside: the river was listed by the thoroughly unsentimental name Wasser, which is simply the German word for water. It is the same meaning as the Celtic original, rendered into a different tongue centuries later. Scholars have also noted a possible connection between the name Inn and the name of the French river Ain, though this link remains speculative.

  The lower course of the river attracted Roman attention first, with references to the Tyrolean section appearing only later. Venantius Fortunatus, writing in the 6th century, was the first to apply the name Aenus to the Tyrolean stretch. The upper valley, known as the Engadine, preserves the older Romansh name En, reminding us that the river's name has been continuous for a very long time.

• 3. Mountains, Lakes, and a Long Journey

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  Lake Sils and Lake Silvaplana are among the first things the Inn meets after leaving its source. The river rises west of St. Moritz, in the Engadine region, and passes through these two lakes almost immediately, before settling into its long northeastward run toward Austria.

  The Engadine takes its name from the river itself. The Romansh version is Engiadina; the Latin form was vallis Eniatina, meaning the valley of the Inn. The highest point of the entire drainage basin stands here too: Piz Bernina, at 4,049 meters, is both the crown of the Inn's watershed and the highest point in the whole Danube drainage system.

  From Switzerland, the river enters Austria and bends eastward through the state of Tyrol. It passes through Innsbruck, whose own name reflects the river: Innsbruck means bridge over the Inn. The river then crosses into Bavaria near Kufstein, running north through Rosenheim and Wasserburg am Inn, then turning east through Mühldorf and Neuötting.

  Along this lower stretch, two major tributaries join the Inn: the Alz and the Salzach. The Salzach in particular is substantial, and together these additions swell the river considerably before it reaches Passau. From the Salzach confluence onward, the Inn forms the international border between Bavaria in Germany and Upper Austria on the Austrian side. The border towns along this final section include Marktl am Inn, Simbach on Inn, Braunau am Inn, and Schärding.

  At Passau, the Inn joins the Danube alongside a third river, the Ilz. Despite carrying an average discharge of 735 cubic meters per second at its mouth, more than the Danube at that same point, the Inn is designated the tributary. The Danube wins that classification by virtue of its greater total length, its larger drainage area, and a more consistent flow over time.

• 4. A Grid of Power Plants

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  Twenty-four hydroelectric power plants now line the course of the Inn, drawing on the river's steady drop from mountain source to lowland confluence. Seventeen of those plants are operated by Verbund AG.

  The installations range enormously in scale. Near the headwaters, the Islas plant generates just 4.3 megawatts and produces around 17 million kilowatt-hours per year. Higher-capacity stations emerge as the river gathers volume downstream. Pradella reaches 288 megawatts with an annual generation of roughly 1,000 million kilowatt-hours. Töging, further downstream, reaches 85 megawatts and produces over 564 million kilowatt-hours annually.

  The Braunau-Simbach plant, named for the border town shared between Germany and Austria, reaches 100 megawatts and generates around 550 million kilowatt-hours per year. Schärding-Neuhaus, near the mouth of the river, produces 96 megawatts and generates close to 542 million kilowatt-hours annually. The final plant before Passau, Passau-Ingling, generates 86 megawatts and roughly 505 million kilowatt-hours each year.

  The geographic spread of these stations, from alpine Switzerland through Tyrol and into Bavaria and Upper Austria, means the Inn's hydroelectric network spans the full journey of the river. The same current that once carried Roman descriptions from tribune to general now turns turbines across three countries.

• 5. The Flood of 2013

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  On the 3rd of June 2013 the Inn reached a discharge of 6,820 cubic meters per second at Passau, far beyond its typical average of 735. The water level climbed to 12.85 meters. That was the highest recorded flood level at Passau since 1501.

  Passau sits at the precise point where the Danube, the Inn, and the Ilz converge. The historic centre of the city, already squeezed between the rivers, was flooded severely. Three rivers arriving in flood at the same location created conditions the city had not experienced for more than five centuries.

  The 2013 event illustrated something the river's geography had always implied. The Inn drains a large alpine basin centered on the highest peaks in the Danube watershed. When snowmelt and heavy summer rain combine across that catchment, the Inn can transform within days from a steady, harnessed energy source into an overwhelming force. The dam and power plant at Passau-Ingling sits downstream of where the 2013 peak was measured, placing the full scale of that flood in the path of a river that, on a normal day, supplies electricity to the surrounding region.