Aare

The Aare (French Aar/Arole; Latin Arula/Arola/Araris) is the longest river running entirely within Switzerland. Its total length is 288 km, its gradient is 1665 m, its catchment area is 17,709 km² and its mean discharge is 525 m³/s (Untersiggenthal gauge, 2019). The Aare is the Rhine's most water-rich tributary, ahead of the Meuse and the High Rhine itself, and it carries more water than the Moselle and Main combined.

The Aare rises in the two Aar glaciers in the eastern Bernese Alps at Finsteraarhorn, west of the Grimsel Pass in central southern Switzerland. Its course leads through the cantons of Bern, Solothurn and Aargau. It first passes the Aareschlucht gorge, cut into a high rock bar, and then reaches the plain between Meiringen and the glacial Lake Brienz. Shortly before entering Lake Thun at Interlaken, it is canalised and leaves it to the northwest into the wide Aare valley. On the territory of Bern, it flows around the medieval town centre and reaches Lake Wohlen in a westerly direction. At Aarberg, it is channelled into Lake Biel via the Hagneck Canal and, after exiting, follows the course of the Jura mountains in a north-easterly direction. Below Brugg, it takes in the Reuss and the Limmat before flowing into the Rhine at Koblenz (CH).

In the course of geological development, the Aare was successively the upper course of the Danube, the Rhone and the Rhine.

Flood

Flood probability

The mean annual flood of the Aare at the Untersiggenthal monitoring station near Stilli is 1574 m³/s.

The highest annual peak measured so far was reached during the flood of the century in 2007 and amounted to 2656 m³/s.

The flood probability table:

Probability of occurrence of annual flood values (HQn) Measuring period 1904-2017 Measuring point: Aare - Untersiggenthal, Stilli - 2205
Annuality (years)	2	5	20	30	50	100
Discharge (m³/s)	1518			2221		2446
Note on HQn: the number corresponds to the flood flow (HQ = flood quantity) in m³/s, which is repeated - on average - with the specified annuality (n = number of years).

Historical floods of the Aare

The most severe surviving flood in the Aare river basin occurred during the Magdalen flood of 1480, which also affected other parts of the Rhine region, but not as extensive regions as the Magdalen flood of 1342. After a rainy May and June, a heat wave had accelerated the melting of snow in the Alps. Then heavy precipitation fell for days in the foothills of the Alps. The damage to the towns along the Aare is well documented in the late medieval chronicles. In Solothurn, part of the town and the Aare bridge were flooded.

Other exceptional floods occurred in the Aare in 1651, 1852, 1876 and 1999.

Possible extreme flooding

A report published in 2021 on behalf of the FOEN, SFOE, ENSI, FOCP, MeteoSwiss and carried out by the Swiss Federal Institute for Forest, Snow and Landscape Research WSL, the University of Zurich and the Paul Scherrere Institute PSI, among others, estimates the possible effects of floods with a return period of up to 100,000 years. This applies in particular to the Mühleberg, Gösgen and Beznau nuclear power plants, which are located on the Aare: At Mühleberg, a 100,000-year flood would inundate the site to a height of just under 1 m; at the Gösgen NPP, the water depth would be 1.15 m in the event of a 100,000-year flood, while at Beznau it would be approximately 1.1 m. In addition, at the Hagneck Canal, the water depth would be 1.5 m. This would mean that a flood of up to 1.5 m could occur. In addition, the old course of the Aare could be reactivated at the Hagneck Canal.

Flood June 2005, here in Olten with older flood marks

History of use and culture

Early use

In the Middle Ages, the Aare was an important border river: for example, it separated the tribal duchies of Burgundy and Alemannia, was a border section of the Carolingian divisions of the empire and also separated Hochburgund from the Roman-German Empire for a while. With the founding of the city of Bern at the end of the 12th to the 13th century, the character of the Aare changed, because from the middle of the 13th century at the latest, there were bridges across the river and contiguous dominions developed on both sides of the Aare.

The short border sections that deviate from the Aare bed at various points today are due to the former natural meanders that defined the border at the time and have now fallen dry.

For a long time, the Aare was important for timber rafting. Wood from the Emmental was transported to the Rhine and to its mouth in the North Sea. To commemorate this tradition, the cultural-historical rafting trail exists between Stilli and Laufenburg.

The stretch of the Aare from Nidau to Solothurn is navigable, as is Lake Biel. The Aare has been used for shipping since ancient times, as can be seen from a stone inscription by Roman shipmen in Avenches. Long-distance traffic on the river only came to a standstill at the end of the 19th century after the construction of the railway lines and the first river power stations.

Current use

Power stations

Hydropower

The waters of the Aare are used to produce electricity in numerous hydroelectric power stations. The headwaters of the Grimsel are home to the Kraftwerke Oberhasli (KWO) power plant group. With its storage power plants and pumped storage power plants, it processes the water from the Oberaar, Grimsel, Räterichsboden and Gelmer reservoirs into peak-load energy, which plays an important role in grid regulation. In the short term, a capacity of 1.3 GW can be called up, which is roughly equivalent to the capacity of the Leibstadt nuclear power plant.

From Interlaken to the mouth of the river, the water of the Aare is used to power several low-pressure run-of-river power stations.

Map

Brügg Schwa Ka Ba Beznau Felsenau Grimsel Handeck Hopflauenen Innertk Interlaken Mat Thun Klingnau Mü NiRdf Aarb Rupperswil Ruppoldingen Flu Wynau Hagneck Go Wildegg-Brugg A R

List of hydroelectric power stations on the Aare:

Name of the power plant	Owner	Type of power plant	Location	first commissioning	Flow rate m³/s	Height dif m	Turbine	Power MW	Energy per year GWh/a
Grimsel 1 Lake Oberaar	KWO	Storage power plant	Chessituren, Guttannen	1954	8	536	1 × Double Pelton	33,6	74
Grimsel 1, Grimselsee	KWO	Storage power plant	Chessituren, Guttannen	1974	20,2	142	1 × Francis	32,2	32,8
Grimsel 2	KWO	Circulation	Chessituren, Guttannen	1981	100		4 horizontal machine groups consisting of Francis + motor/generator + single-stage pump, of which one group with frequency converter	388	600
Grimsel Nollen	KWO	small run-of-river power station in the Grimselsee-Gelmersee connecting tunnel (replenishment turbine)	Spittelnollen, Guttannen	2017	2,5		1 × Francis	1,1	5
Hand corner 1	KWO	Storage power plant	Handegg, Guttannen	1932	10,5	680	2 × Pelton	45	168
Handeck 2 + 2a	KWO	Storage power plant	Handegg, Guttannen	1950		465	5 × vertical Pelton	215	262
Hand corner 3 (Isogyre)	KWO	Pumped storage power plant	Handegg, Guttannen	1976	14,3		1 × horizontal Isogyre pump turbine	55	39
Hopflauenen (drift)	KWO	Storage power plant	Hopflauenen, Gadmen	1967	23,6	463	2 × Double Pelton	81,6	245
Innertkirchen 1 + 1a	KWO	Storage power plant	Innertkirchen	1943	69		6 × Pelton	394	720
Innertkirchen 2	KWO	Storage power plant	Innertkirchen	1967	29,5	242	2 × Francis	54,8	161
Interlaken	IBI	Run power plant cottage industry	Ship canal, Interlaken	1897	30	3,6	3 × chaplain	0,82	5,1
Interlaken-Dotierzentrale	IBI	Doping center (small power plant)	Aare weir, Interlaken	1996	15			0,3	1,2
AAREwerk62	Energy Thun	Run-of-river power plant (diversion power plant)	Thun	1962	125		2 × vertical Kaplan	6,32	32
AAREwerk94	Energy Thun	Run-of-river power plant (run-through power plant)	Thun	1917	49,7		1 × S-Turbine	2,83	8,4
Thun	RUAG	small run-of-river power station of the munitions factory	Trade canal, Thun	1901	6			0,44	2
Mat	EWB	Run-of-river power plant (diversion power plant)	Mat, Bern	1891	40	2–3	1 × S-Turbine	1,16	6,8
Engehalde doting center	EWB	Doping center (small power plant)	Weir at Felsenau power station, Felsenau, Berne	1998	16			0,44	2,6
Felsenau	EWB	Run-of-river power plant (diversion power plant)	Felsenau, Bern	1909	100		1 × Pipe turbine	11,5	73
Mühleberg	BKW	Run-of-river power station at Lake Wohlen (continuous power plant)	Buttenried, Mühleberg	1919	291	20	1× Chaplain 6× Francis	45	160
Niederried-Radelfingen	BKW	Run-of-river power plant (diversion power plant)	Niederried Radelfingen	1963	170		2 × chaplain	15	81,2
Aarberg	BKW	Run-of-river power plant (run-through power plant)	Aarberg	1968	170		2 × chaplain	15	90
Kallnach	BKW	Run-of-river power plant (Expelling power plant)	Kallnach	1913	45		1 × Pipe turbine	8,1	49
Hagneck (old)	Lake Biel Power stations	old run-of-river power plant used as doping plant	Hagneck Canal, Hagneck	1900	40		3 × propeller 2 × chaplain	3	11
Hagneck	Lake Biel Power stations	Run-of-river power plant (run-through power plant)	Hagneck Canal, Hagneck	2015	280		2 × bulb turbine	21	99
Brügg	Lake Biel Power stations	Run-of-river power plant (Bay power plant)	Nidau-Büren Canal, Brügg	1995	219		2 × bulb turbine	5,2	21,3
Flumenthal	Alpiq	Run-of-river power plant (run-through power plant)	Flumenthal	1970	395	6–8.5	3 × Pipe turbine	23,4	147
Bannwil	BKW	Run-of-river power plant (run-through power plant)	Bannwil	1970	435		3 × Pipe turbine	28,5	149
Wynau	Onyx	Run-of-river power plant (run-through power plant)	Wynau	1996	220		1 × Pipe turbine	12	51
Blackhouses	Onyx	Run-of-river power plant (run-through power plant)	Blackhouses	1923	200		4 × propeller	8,2	41
Ruppoldingen	Alpiq	Run-of-river power plant (run-through power plant)	Boningen	2000	475	4–6.5	2 × bulb turbine	21,1	115
Gösgen	Alpiq	Run-of-river power plant (Expelling power plant)	Niedergösgen	1917	380	13–17.4	5 × chaplain	48.5	300
Aarau city	Eniwa	Run-of-river power plant (Expelling power plant)	Aarau	1893	394	5.3–7.4	9 × chaplain 2 × propeller 1 × Francis	16	102
Ruechlig	Axpo	Run-of-river power plant (Expelling power plant)	Aarau	1929	360	3.3–3.5	4 × bulb turbine	9	54
Ruechlig	Axpo	Doping center (small power plant)	Aarau	2014	40			1,2	8,1
Rupperswil-Auenstein	Axpo	Run-of-river power plant (Expelling power plant)	Auenstein AG	1945	492		2 × chaplain	40	221
Rupperswil	Axpo	Doping center (small power plant)	Rupperswil	1945	25			1,7	10
Wildegg-Brugg	Axpo	Run-of-river power plant (Expelling power plant)	Villnachern	1953	410		2 × chaplain	50	290
Wildegg-Brugg	Axpo	Doping center (small power plant)	Schinznach-Dorf	1953	11,5			0,6	3,5
Beznau	Axpo	Wehrkraftwerk	Döttingen AG	2001	140		1 × chaplain	6	36
Beznau	Axpo	Run-of-river power plant (Expelling power plant)	Döttingen AG	1902	418		11 × propeller	20	120
Klingnau	Axpo	Run-of-river power plant (run-through power plant)	Klingnau Gippingen	1935	810		3 × chaplain	38	230
Total								2501	4827

Nuclear power plants

The Swiss nuclear power plants Mühleberg, Gösgen and Beznau, whose cooling systems use water from the Aare, are located along the river.

Traffic

Sewerage system

In several sections, the course of the river was altered by major construction work. From the 18th century onwards, the cantons of Bern and Solothurn attempted to secure the banks, which were endangered by erosion, in numerous places and called in the Grisons specialist Richard La Nicca for this purpose. With the first Jura water correction, one of the largest river engineering projects in Switzerland in the 19th century, the federal government and cantons restored the marshy Bernese Seeland, which was threatened by frequent flooding, by diverting the Aare and its bedload into Lake Biel. Since 1939, the Port weir has controlled the water balance of the lakes and the Aare in the section at the southern foot of the Jura. The water level of the Aare, which is decisive for regulation, is measured at the gauging station near Murgenthal, because the water volume supplied by the Emme also has an effect there.

The second Jura water correction improved the effect of water level regulation around 1960.

The Working Group for the Protection of the Aare, founded in 1964, campaigned against the expansion of the river road through the planned Transhelvetian Canal.

Shipping

Today, the Bielersee-Schifffahrts-Gesellschaft AG, which emerged from a predecessor company in 1966 and is based in Biel, operates the courses on Lake Biel and the Aare.

Bridges

Numerous bridges cross the Aare. In the city of Bern alone, there are 18 of them. (→ List of bridges over the Aare)

Old Aare and guidance of the Aare through Lake Biel since 1878