Aa (Werre)

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Course of the Aa, called Johannisbach in the upper reaches

Course of the Aa, called Johannisbach in the upper reaches

Water code EN : 464
location North Rhine-Westphalia , Germany
River system Weser
Drain over Werre  → Weser  → North Sea
source At Uerentrup
52 ° 1 ′ 24 ″  N , 8 ° 29 ′ 44 ″  E
Source height approx.  199  m above sea level NN
muzzle In Herford in the Werre Coordinates: 52 ° 7 ′ 25 ″  N , 8 ° 40 ′ 13 ″  E 52 ° 7 ′ 25 ″  N , 8 ° 40 ′ 13 ″  E
Mouth height approx.  62  m above sea level NN
Height difference approx. 137 m
Bottom slope approx. 5.3 ‰
length 26 km
Catchment area 254.45 km²
Discharge at the Brake
A Eo gauge: 207.12 km²
MNQ 1983-2006
MQ 1983-2006
Mq 1983-2006
MHQ 1983-2006
428 l / s
865 l / s
3.64 m³ / s
17.6 l / (s km²)
46 m³ / s
73 m³ / s
Left tributaries Paderbach , Twellbach , Krebsbach , Schwarzbach , Moorbach , Jöllenbecker Mühlenbach , Jeipohlbach , Sieben-Teiche-Bach , Lubbenbach , Eickumer Mühlenbach
Right tributaries Schloßhofbach , Lutterbach , Milsebach , Hellebach , Flachsbach , Bowerre
Reservoirs flowed through Obersee near Schildesche
Big cities Bielefeld
Medium-sized cities Herford
Bridge of the former Bielefeld district railways over the Johannisbach in Schildesche
The Westphalian Aa in Herford near Bielefelder Strasse
Confluence of the Werre (left) with the Westphalian Aa in Herford during a light flood

The Aa (rarely: "Westphalian Aa"), in the upper reaches of Johannisbach , is a left tributary of the Werre in north-eastern North Rhine-Westphalia , in the urban areas of Bielefeld and Herford .


The Aa is also referred to as the Westphalian Aa to distinguish it from other rivers (mostly also located in Westphalia ) with the name Aa . Its upper course is called Johannisbach. Johannisbach and Aa are hydrogeographically identical and are continuously kilometered, although the lower and upper reaches are known under the two different names in local parlance and are therefore regarded as two different rivers. The additional designation "Westphalian" is now uncommon in local language as well as in map series. The Westphalian name Aa (Lower Saxony Aue , Schleswig-Holstein Au , High German Ach, Ache, Achen or Aach , Old High German Aha , Swedish A , Danish Å ) means water or river and possibly goes back to the Latin aqua . In the Middle Ages the Aa was called "Hardna".


The Johannisbach below the Obersee in Schildesche

The Johannisbach rises near Uerentrup in the Teutoburg Forest , west of the Bielefelder Pass . It initially flows in a north-westerly direction through a longitudinal valley of this mountain range, away from Bielefeld city center. At Großdornberg it leaves the mountains through a breakthrough in the northern ridge and then flows first northeast, then eastward through the Ravensberg hill country . He picks up Schwarzbach from Werther .

Below Schildesche , the Johannisbach has been dammed into the Obersee since 1982 (river kilometer 14), into which the Jölle originally flowed from Jöllenbeck in the north . Since 2009, most of the water in the Johannisbach has been diverted around the lake in a flood. The Jölle now also drains directly into this flood. A little to the east of it, the Hamm – Minden railway has crossed the Johannisbach valley on the Schildescher Viaduct since 1847 .

In the Milse district of Bielefeld , the Johannisbach joins the Lutter coming from the south , which took in the wind drift three kilometers earlier , and is referred to as Aa from this point on. The Aa then flows through the Brake district and reaches Herford , where it forms the border between the Elverdissen districts on the right and Stedefreund and Diebrock on the left. In the further course the Aa is the border river between Altstädter Feldmark and Radewiger Feldmark , between Old Town and Radewig and between Herford Neustadt and Radewiger Feldmark. In the Radewig / Neustadt area, the Aa is dammed by means of two weirs. Here the city moat branches off to the left, which, in contrast to the main arm, flows around the Radewig district to the west. Shortly before the moat joins the main arm again, the Bowerre joins the Aa from the right . After 26 km (8.6 km after the tributary of the Lutter) the Aa flows into the Werre at the Hansastraße bridge (Werre km 22.5), passing the MARTa Herford museum on the back just before the confluence .

Catchment area

Its catchment area covers an area of ​​254.5 km². Since Johannisbach and Lutter drain parts of the slope of the Teutoburg Forest, the Aa has a high flood potential .


On its way, the water includes the following waters when viewed downstream:

(All length information according to the Land Survey Office North Rhine-Westphalia)

L / R: Left or Right Inflow
KM: River kilometers measured from the mouth of the main river upwards
L: length of the tributary in kilometers
H: mouth heights in m according to DE-NN if known


The upper Johannisbachtal is under nature protection (NSG Oberes Johannisbachtal with side valleys).


The Aa or Johannisbach marked the border between France and the Kingdom of Westphalia between 1811 and 1815 . This happened when Napoleon annexed the German North Sea coast in 1811 as part of the continental blockade . Large parts of the department of the Weser , with the Johannisbach as part of the new border, were separated from the Kingdom of Westphalia and assigned to the department of the Upper Ems , one of the four newly created Hanseatic departments .

From 1939 to 1972 the Johannisbach was the northern border of the city of Bielefeld.

See also

Web links

Commons : Aa  - collection of images, videos and audio files

Individual evidence

  1. a b Topographic map 1: 25,000
  2. a b c Topographical Information Management, Cologne District Government, Department GEObasis NRW
  3. ELWAS-IMS Ministry for Climate Protection, Environment, Agriculture, Nature and Consumer Protection NRW