Aa (Nethe)

	Aa
	The Aa at Herste
	Data
Water code	EN : 4526
location	North Rhine-Westphalia , Germany
River system	Weser
Drain over	Nethe → Weser → North Sea
source	On the eastern edge of the Eggegebirge , east of Altenbeken , above the Rehberg tunnel ; 51 ° 46 ′ 7 ″ N , 8 ° 58 ′ 34 ″ E
Source height	approx. 350 m above sea level NN
muzzle	Southwest of Brakel in the Nethe coordinates: 51 ° 42 ′ 5 " N , 9 ° 10 ′ 13" E 51 ° 42 ′ 5 " N , 9 ° 10 ′ 13" E;
Mouth height	approx. 133 m above sea level NN
Height difference	approx. 217 m
Bottom slope	approx. 11 ‰
length	20.6 km
Catchment area	80.153 km²
	In a dry summer, the weak stream below Reelsen runs dry in the rubble of the stream bed. Look upstream. (August 5, 2011)

The Aa is a 20.6 km long orographic left tributary of the Nethe in North Rhine-Westphalia , Germany . As a tributary of the Nethe, the Aa belongs to the Weser river system .

geography

The Aa rises on the eastern slope of the Rehberg ( 427.4 m ) belonging to the Eggegebirge at an altitude of 350 m above sea level. NN , about 2 km east of Altenbeken and above the east portal of the Rehberg tunnel in Bad Driburg - Langeland . Initially marked as Großer Wasser in the German Basic Map (DGK) (this name is taken up again as Großewasser for a parcel above Herstes ), the stream initially flows to the east and after about 2 km of the river it crosses the Herford – Altenbeken railway line . From here on it is also referred to as Aa in the German basic map. A little later, the Aa turns in a predominantly south-easterly direction and passes the village of Reelsen on its eastern edge. At Alhausen , the Rautebach flowing through the town flows out on the left , with the Aa flowing past the town a few hundred meters southwest.

East of Bad Driburg , the Schwallenbach coming from there flows into the Aa on the right. After crossing under the Altenbeken – Kreiensen railway line , the Hilgenbach also flows to the right . At Herste , the Katzbach flows again on the right side into the Aa, which is now flowing again in an easterly direction. At 8.2 km in length, the Katzbach is the longest tributary of the Aa. West of Istrup , the Escherbach joins the Aa on the left. After the river has flowed through the village of Riesel , it flows southwest of Brakel as a left tributary at 133 m above sea level. NN in the Nethe .

On its 20.6 km long path, the Aa overcomes a height difference of 217 m, which corresponds to a mean bed gradient of 10.5 ‰. The Aa drains a catchment area of 80.153 km². When there is heavy rainfall in the Egge Mountains, the Aa quickly carries large volumes of water through the Aatal.

Tributaries

Rautebach - 2.6 km long, left tributary at 193 m above sea level. NN
Schwallenbach - 5.0 km long, right tributary 181 m above sea level. NN
Hilgenbach - 5.5 km long, right tributary 172 m above sea level. NN
Katzbach - 8.2 km long, right tributary 155 m above sea level. NN
Escherbach - 4.9 km long, left tributary 149 m above sea level. NN

A special feature is the unnamed right side stream, only a few hundred meters long, at the southernmost point of the Johannes-Gelhaus-Weg near Reelsen, where it can be viewed well. As a tufa spring , it forms small sintered terraces with the participation of mosses. In summer it falls completely dry.

Mill ditches

Reelsen, Alhausen, Istrup and Riesel still have an old mill ditch.

Ashlar bridges

The Katzbach in Herste

There are still some preserved bridges made of ashlar along the Aa :

At the Josefsmühle. Round bridge with an arch (replaced by a simple concrete bridge)
Herste . Round arch bridge over the Katzbach with an arch on Heristiestraße, access
Istrup . Round arch bridge with four arches on Istruper Straße

photos

Probably the highest source of the Aa is located directly on the forest path when you descend from Rehberg to the source of the Emmer in Langeland.
Sintered terraces that have fallen dry
South of Reelsen, a wooden bridge leads Johannes-Gelhaus-Weg over the Aa. Look upstream. (August 5, 2011)
Bridge of the road In the stairs from Alhausen to Bad Driburg. Although the Aa below Reelsen had dried up on the surface at this point and the Rautebach was also dry, water is flowing here again. Look downstream. (August 5, 2011)