View source for Radolfzeller Aach

{{Short description|River in Germany}}
{{Infobox river
| name              = Radolfzeller Aach
| custom_label      = TVC
| custom_data       = DE/2172
| image             = Aachtopf-2014-06-17.jpg
| image_caption     = Aachtopf, view from the Radolfzeller Aach source in the direction of the flow
| map               = Radolfzelleraach.png
| map_caption       = Map, with place names in [[Alemannic German|Alemannic]]
| progression       = {{RRhine}}
| basin_size        = {{convert|255|km2|sqmi|abbr=on}} {{GeoQuelle|DE-BW|LUBW}}
| length            = {{convert|32.0|km|mi|abbr=on}} {{GeoQuelle|DE-BW|LUBW}}
| discharge1_avg    = {{convert|10|m3/s|cuft/s|abbr=on}}
| source1_location  = [[Aachtopf]] in [[Aach (Hegau)|Aach]]
| source1_coordinates= {{coord|47|50|48|N|8|51|29|E|region:DE-BW}}
| source1_elevation = {{convert|475|m|ft|abbr=on}}
| mouth_location    = into [[Untersee (Lake Constance)|Untersee]] between [[Radolfzell]] and [[Moos, Baden-Württemberg|Moos]] 
| mouth_coordinates = {{coord|47|42|57|N|8|56|28|E|region:DE-BW|display=inline,title}}
| mouth_elevation   = {{convert|395|m|ft|abbr=on}}
| subdivision_type1 = Country
| subdivision_name1 = [[Germany]]
| subdivision_type2 = [[States of Germany|State]]
| subdivision_name2 = [[Baden-Württemberg]]
| subdivision_type3 = [[Districts of Germany|District]]
| subdivision_name3 = [[Konstanz (district)|Konstanz]]
| subdivision_type4 = Cities
| subdivision_name4 = {{hlist|[[Radolfzell]]|[[Singen]]}}
}}
The '''Radolfzeller Aach''' (also known as '''Hegauer Aach''') is a right or north [[tributary]] of the [[Rhine]] in the [[Hegau]] region, southern [[Baden-Württemberg]] ([[Germany]]). It is approximately {{cvt|32|km}} long and drains into [[Untersee (Lake Constance)|Lower Lake Constance]]. Most of its waters derive from the [[Danube]] river through the [[Danube Sinkhole]].

== Course ==
The source of the [[river]] is the ''[[Aachtopf]]'' in [[Aach (Hegau)|Aach]], the largest [[spring (hydrosphere)|spring]] in [[Germany]], at a height of 475&nbsp;m above [[sea level]].  The water emerges from a [[karst]] cave.  About two thirds of the water originates in the headwaters of the [[Danube]].  Between [[Immendingen]] and [[Möhringen an der Donau]] and in [[Fridingen]], water from the Danube disappears underground (this is known as the [[Danube Sinkhole]] or {{lang|de|Donauversinkung}}); this water reappears in the Aachtopf.

The river first flows through a number of nature reserves in the [[Hegau]] area.  This segment of the river is known as ''Hegauer Aach''.  It then flows South to [[Singen]], where it is known as ''Radolfzeller Aach''.  The last six kilometers of the lower course flow through a nature reserve called ''Radolfzeller Aach Ried''.  It flows into the northwestern part of Lake [[Untersee (Lake Constance)|Untersee]] (the ''Zellersee'') between [[Radolfzell]] and [[Moos, Baden-Württemberg|Moos]].  At the mouth, the average discharge is 10&nbsp;m<sup>3</sup>/s, making it the fourth largest contributor to Lake Constance.

== Catchment area ==
The Radolfzeller Aach drains a [[Drainage basin|watershed]] of 255&nbsp;km<sup>2</sup>.{{GeoQuelle|DE-BW|LUBW}}  If one includes the catchment area of the Danube upstream of the [[Danube Sinkhole]] ({{langx|de|Donauversinkung}}), then the Radolfzell Aach drains an area of 1560&nbsp;km<sup>2</sup> on days when all of the Danube's water disappears into the Danube Sinkhole.

== Hydrology ==
In the past, the fast flowing water of the Radolfzeller Aach drove many [[watermill]]s. Today, it drives several [[hydropower]] stations.  In some areas, [[nature restoration]] projects are being carried out, for example in [[Beuren an der Aach]], where the borough of [[Singen]] has set up a [[sediment]] catching facility, catching sediments and gravel carried by the river.  Plans to release the sediments upstream of Volkertshausen were abandoned.

== Fauna ==
Several endangered species of waterfowl can be found at the Radolfzeller Aach, including [[snipe]], [[sandpiper]] and [[green sandpiper]].<ref>[http://vorort.bund.net/bawue/themen-projekte/radolfzeller-aach/erfolge.htm BUND Project Radolfzeller Aach] {{webarchive|url=https://web.archive.org/web/20070929090813/http://vorort.bund.net/bawue/themen-projekte/radolfzeller-aach/erfolge.htm |date=2007-09-29 }}</ref>  In the estuary, beavers established themselves in 1998, after having been absent for 200 years.<ref>[http://www.xfaweb.baden-wuerttemberg.de/nafaweb//berichte/inf00_3/in30048.html International Symposium on Beavers in Lake Constance] {{webarchive|url=https://web.archive.org/web/20070929095835/http://www.xfaweb.baden-wuerttemberg.de/nafaweb//berichte/inf00_3/in30048.html |date=2007-09-29 }}</ref>  Hydromorphologically, the Radolfzeller Aach is the lower end of trout and mullet territory.  The dominant fish species in the Aach is the brown trout, as grayling are less shy and consequently more exposed to the feeding pressure of the large [[cormorant]] colony in the Radolfzeller Aach Ried.  There are also noticeable stocks of some other endangered fish species, such as [[lamprey]] and [[European bullhead]], who enjoy their protection close to the bottom of the river.  In the lower reaches, we also find other species from Lake Constance.

== Communities ==
Villages on the Radolfzeller Aach include [[Aach (Hegau)|Aach]], [[Volkertshausen]], [[Beuren an der Aach]], [[Friedingen (Singen)|Friedingen]], [[Hausen an der Aach]], [[Singen]], [[Rielasingen-Worblingen]], [[Bohlingen]] and the Rickelshausen district of [[Radolfzell]].

== Water sports ==
Canoeing is possible all year round, due to the strong Aachtopf spring.  Canoeing in the section between Aachbad Singen and Bohlingen, however, is not advisable on account of the many water discharges and heavy industrialization.  The lower reaches of the Aach are a nature preserve and closed to water sports year round.

== See also ==
*[[List of rivers of Germany]]
**[[List of rivers of Baden-Württemberg]]

== References ==
{{Reflist}}

{{Rhine Tributaries}}
{{Lake Constance}}
{{Authority control}}

[[Category:Rivers of Baden-Württemberg]]
[[Category:Tributaries of Lake Constance]]
[[Category:Geography of Hegau]]
[[Category:Rivers of Germany]]