View source for Aller (Germany)

{{short description|River in Germany}}
{{Use Oxford spelling |date=November 2024}}
{{Use dmy dates |date=November 2024}}
{{infobox river
| name = Aller
| mapframe          = yes
| mapframe-point    = none
| map_size = 
| map_caption = 
| pushpin_map        = 
| pushpin_map_size   = 
| pushpin_map_caption= 
| pushpin_map_alt    =
| image = Aller Vorsfelde.jpg
| image_size = 
| image_caption = The canalised and [[Populus|poplar]]-lined Aller in the [[Drömling]] near Wolfsburg-Vorsfelde
| subdivision_type1 = Country
| subdivision_name1 = [[Germany]]
| subdivision_type2 = States
| subdivision_name2 = [[Saxony-Anhalt]] and [[Lower Saxony]]
| subdivision_type3 = Reference no.
| subdivision_name3 = DE:&nbsp;48
| length = {{cvt|214.8|km}} {{GeoQuelle|DE-NI|UK}}
| width_avg = 
| depth_avg = 
| source1_location = in [[Eggenstedt]] near [[Seehausen (Börde)|Seehausen]] in the [[Magdeburg Börde]]
| source1_coordinates = {{Coord|52.1024528|11.2337028|type:river_region:DE-ST|format=dms|display=inline,title}}
| source1_elevation = {{Höhe|130|DE-NN|link=true }}
| mouth_location = [[Weser]] near [[Verden an der Aller|Verden]]
| mouth_coordinates = {{Coord|52.945825|9.1856139|type:river_region:DE-NI|format=dms|display=inline}}
| mouth_elevation = {{Höhe|10|DE-NN|link=true}}
| basin_population = 
| basin_landmarks = {{ubl
 | Cities: [[Wolfsburg]]
 | Large towns: [[Gifhorn]], [[Celle]], [[Verden an der Aller|Verden]]
 | Small towns: [[Oebisfelde-Weferlingen]], [[Rethem]]
 | Villages: [[Wefensleben]], [[Ingersleben]], [[Müden (Aller)|Müden]], [[Wienhausen]], [[Hambühren|Oldau]], [[Winsen (Aller)|Winsen]], [[Hodenhagen]], [[Hülsen (Dörverden)|Hülsen]], [[Westen (Dörverden)|Westen]]
 }}
| progression = {{RWeser}}
| basin_size = {{cvt|15,721|km2}} {{GeoQuelle|DE-NI|UK}}
| discharge1_location = 
| discharge1_min = 
| discharge1_avg = {{cvt|118|m3/s|cuft/s}}<ref name=wsvver>Wasser- und Schifffahrtsamt Verden (s. auch: http://www.wsa-verden.wsv.de/wasserstrassen/weser/index.html {{Webarchive|url=https://web.archive.org/web/20181004013641/http://www.wsa-verden.wsv.de/wasserstrassen/weser/index.html |date=2018-10-04 }})</ref>
| discharge1_max = 
| tributaries_right = [[Kleine Aller]], [[Ise (river)|Ise]], [[Lachte]], [[Örtze]], [[Meiße]], [[Böhme (river)|Böhme]], [[Lehrde]], [[Gohbach]]
| tributaries_left = [[Oker]], [[Fuhse]], [[Wietze (Aller)|Wietze]], [[Leine (river)|Leine]], [[Alpe (stream)|Alpe]], [[Wölpe]]
| waterbodies = 
| ports = 
| bridges = 
| custom_label = Navigable
| custom_data = {{cvt|117|km}}; from Celle Class II, from Verden Class III
}}
The '''Aller''' ({{IPA|de|ˈalɐ|pron|de-Alle.ogg}}) is a {{convert|215|km|mi|adj=mid|-long}} river in the states of [[Saxony-Anhalt]] and [[Lower Saxony]] in Germany. It is a right-hand, and hence eastern, tributary of the [[Weser]] and is also its largest tributary. Its last {{convert|117|km|mi}} form the Lower Aller federal waterway ({{lang|de|Bundeswasserstraße}}). The Aller was extensively straightened, widened and, in places, [[Levee|dyke]]d during the 1960s to provide flood control of the river. In a {{convert|20|km|mi|adj=mid|-long}} section near [[Gifhorn]], the river [[meander]]s in its natural river bed.

== History ==

=== Meaning of the name ===
The river's name, which was recorded in 781 as ''Alera'', in 803 as ''Elera'', in 1096 as ''Alara'', has two possible derivations:

# A shortened form of ''*Eleraha'', where ''*Eler'' in [[Old German]] ''*olisa'' or [[Proto-Slavic language|Old Slavic]] ''olsa'' (Polish: ''olsza'') would mean ''Erle'' ("alder") and ''aha'' (pronounced in German: ''Acha'') is an old word frequently used in river names to mean "water" (cf. the [[Latin]] ''aqua''). The name of the tree passed into [[Low German]] as ''Eller'', which is very close to the word ''Aller''. ''Aller'' would therefore mean something like ''Erlenwasser'' i.e. "alder water", which was probably due to the river banks being largely covered in [[alder]] trees that prefer wet locations.
# In [[Hans Krahe]]'s system of Old European hydronomy, the old name for the Aller, ''Alara'', is an example of a group of river names with the root ''al-'', which is very common over much of Europe and according to Krahe all go back to the [[Proto-Indo-European language|Indo-European]] root ''*el-/*ol-'', which means "flowing". Similarly related would be rivers such as the [[Alster]], [[Iller]], [[Elz (disambiguation)|Elz]]<!--intentional link to DAB page--> and [[Ilmenau (river)|Ilmenau]]. Krahe's hypothesis is, however, hotly disputed in language circles. [[Theo Vennemann]] used a modified version of Krahe's model in his [[Vasconic substratum theory]].
<!--Gewässergeschichte-->

== Course ==

=== Upper Aller ===
[[File:Skizze Allerkanal.png|thumb|upright=2|Section of the Upper Aller near [[Gifhorn]] with the [[Aller Canal]], the only remaining part of the river with tight [[meanders]]]]
[[File:Aller Flusssystem topo.png|thumb|upright=2|Rivers of Aller basin in blue, others in grey]]
The Aller rises in the state of Saxony-Anhalt in the west of the region known as the [[Magdeburg Börde]] near [[Seehausen (Börde)|Seehausen]] and north of [[Oschersleben (Bode)]]. It has several source streams that run down the northeastern side of the [[Hohes Holz]] within the municipal boundaries of [[Wormsdorf]] (part of Gehringsdorf), [[Ovelgünne]] (part of Siegersleben) and [[Eggenstedt]]. The Eggenstedt tributary is the most southerly of the source streams. The nearest large centres of population in the source region are [[Helmstedt]], about {{convert|20|km|mi}} northwest, and [[Magdeburg]] around {{convert|25|km|mi}} east.

Initially, the Aller flows rather like a canalised brook in a northwestern direction through low hills and intensively farmed arable fields. As it does, it passes the [[Flechtingen Hills]] to the east and another range of hills to the west that stretches from the [[Lappwald]] over the Hohes Holz as far as Oschersleben (Bode). The river passes the villages of [[Eilsleben]] and [[Weferlingen]]. After about {{convert|60|km|mi|adj=pre|river}}, it reaches [[Oebisfelde]] and the southern edge of the [[Drömling]]. After crossing the state border between Saxony-Anhalt and Lower Saxony, the Aller bends sharply southwest near [[Grafhorst]]. Here, the terrain is already only about {{convert|55|m|ft}} above [[Normalnull|sea level]]. Between here and its mouth, {{convert|150|km|mi}} away, its elevation drops by only about {{convert|40|m|ft}}, so that the speed of the current is considerably reduced in Lower Saxony. Near Grafhorst, the Aller meets the Breslau-Magdeburg-Bremen [[glacial valley]] and then, for the most part, follows it. From here on, the river mainly runs through [[grassland]].

Near [[Wolfsburg-Wendschott]], the Aller passes under the [[Mittelland Canal]] in a [[culvert]] where there is a barrier that is impassable to fish. The Aller swings northwest again from [[Wolfsburg]]. In the area of the town it crosses the [[Allerpark]] and flows past the [[Allersee]] before flowing past the [[Barnbruch]].

{{gallery
|width=180
|height=135

|File:Allerbeiwefensleben.jpg
|The Aller near [[Wefensleben]], about {{convert|10|km|mi|0}} below its source

|File:Aller Oebisfelde.jpg
|The Aller near [[Oebisfelde]]

|File:Allerbrücke.jpg
|Bridge on the Upper Aller in [[Wolfsburg-Vorsfelde]]
}}

South of [[Weyhausen]], the [[Aller Canal]] branches off the Aller. The canal was built between 1860 and 1863 and is about {{convert|18|km|mi}} long. It was supposed to drain the long-standing floods that were greatly feared at that time. The canal runs parallel to, and generally a few miles south of, the Aller, rejoining it near Brenneckenbrück (west of Gifhorn). The canal runs south past Gifhorn, whilst the Aller flows through the town. This {{convert|20|km|mi|adj=mid|-long}} section, which parallels the Aller Canal, is the only section of the Aller that meanders in its natural river channel. Elsewhere, the Aller has been straightened and widened along its entire length from source to mouth. East of Gifhorn near [[Osloß]] it crosses under the [[Elbe Lateral Canal]], which is carried over it on an [[Navigable aqueduct|aqueduct]]. After that it runs via [[Gifhorn]] to [[Müden (Aller)|Müden]], where it merges with the [[Oker]].{{clear}}

[[File:Aller Schleife.jpg|thumb|upright=2|Bend in the river on the Upper Aller in [[Dannenbüttel]]]]{{clear}}

=== Middle Aller ===
The {{convert|30|km|mi|adj=mid|-long}} section of the Aller from the mouth of the Oker to [[Celle]] is referred to as the Middle Aller ({{lang|de|Mittelaller}}). After passing [[Wienhausen]], it is navigable as far as Celle. Here, the river has so much water that there are [[barrage (dam)|barrage]]s and the water power is extracted from the river using [[weir]]s.
{{gallery
|width=180
|height=135

|File:PICT4952 Okermündung in Müden.JPG
|Confluence with the Oker (right) near [[Müden (Aller)|Müden]]

|File:Aller in Blumlage (Celle) IMG 2472.jpg
|The river in Celle

|File:Örzte Mündung Aller.jpg
|Mouth of the [[Örtze]] (left) near [[Winsen (Aller)]]
}}

=== Lower Aller ===
The section of the river known as the Lower Aller (''Unteraller'') begins at Celle and runs for {{convert|120|km|mi}} to the [[Weser]]. The Lower Aller is a designated federal waterway (''Bundeswasserstraße''). The river is navigable from here to [[Winsen (Aller)|Winsen]]. Near [[Eickeloh]] a [[reaction ferry]] crosses the Aller and it is here that the [[Leine (river)|Leine]] flows into the Aller. Upstream and downstream of [[Rethem (Aller)|Rethem]], there are two groups of impressive meanders. Below them it passes  [[Verden (Aller)|Verden]]. About {{convert|4|km}} northwest of the town, near Eißel, a village in the borough of Verden, the Aller finally discharges into the Weser. There are two ''Alte Allers'', i. e. old branches of the Aller. One is on the left bank opposite Verden. The other is on the right bank and is the former lowest part of the course of the river.

[[File:Verden aller.jpg|thumb|left|600px|Floods on the Old Aller near [[Verden an der Aller|Verden]]]]
{{clear}}

== Aller glacial valley ==
[[File:Allertal Wietze.jpg|thumb|upright=1.6|The Aller Valley near [[Wietze]]. In the background, the low hills of the [[Lüneburg Heath]]]]
[[File:Binnendüne Aller.jpg|thumb|upright=1.6|Inland dunes in the pine forest north of the Aller near [[Winsen an der Aller]]]]
After the Aller has passed through the hills of Saxony-Anhalt it enters the Wolfsburg area into the [[Last glacial period|ice age]] drainage channel of the Aller [[glacial valley]], part of the Breslau-Magdeburg-Bremen glacial valley. The valley is on average {{convert|20|km|mi}} wide and was formed during the penultimate ice age, the [[Saale glaciation]] about 200,000&nbsp;years ago, and drained [[meltwater]]s from the [[ice sheet]] into the [[North Sea]]. The present course of the Aller in the miles-wide glacial valley does not reflect the courses of numerous streams of earlier centuries and millennia. For a long time there was a system of interwoven water courses, which changed their location and size depending on the materials and quantities of water being carried. Today there is a large number of dry [[oxbow lake]]s, river beds and branches in the water meadows. Climatic conditions and [[erosion]] also changed the landscape around the streams of the glacial valley. For example the wind formed inland sand dunes parallel to the river, especially on the northern side of the valley, around which the river sometimes snaked in meanders.

Near Wolfsburg the level of the river bed scarcely dropped at all and during times of low water it became almost an area of standing water. The [[Wolfsburg Volkswagen Plant]] uses the river and also feeds waste water, after cleaning, into its own [[sewage works]].

Today, the landscape of the Aller valley between Celle and Verden is mainly utilised as [[grassland]]. The Aller depression there comprises valley floors lying close to the watertable, so that fertile wet areas may be found here with rich habitats for flora and fauna. The landscape is characterised by oxbows, potholes, copses and rows of bushes. The valley floors are widened by the depressions of the tributaries flowing into the Aller, so that fens and bogs can form. Around the lower reaches crops are cultivated on the clay soils. Around the upper course of the river, many pine forests are managed on the sandy soils.

== Tributaries ==

=== Rivers ===
The most important [[tributaries]] to join the Aller from its left-hand, southern, side facing the [[Harz mountains]], are the [[Oker]] near [[Müden (Aller)]], the [[Fuhse]] in Celle, and the [[Leine]] near [[Schwarmstedt]]. If the Leine is counted as a source stream for the Aller, it has a total length of {{convert|346|km|mi}}.

From the right, the Aller is joined by smaller rivers that predominantly drain the [[Lüneburg Heath]]. Those worth mentioning include the [[Kleine Aller]] fairly near [[Weyhausen]], the [[Ise (river)|Ise]] in Gifhorn, the [[Lachte]] east of [[Celle]] (near Lachtehausen), the [[Örtze]] near [[Winsen (Aller)]], the [[Meiße]] near [[Hodenhagen]] and the [[Böhme (river)|Böhme]] near [[Rethem]].

=== Streams of the Upper Aller ===
The Upper Aller has numerous tributary streams between its source and [[Müden (Aller)|Müden]]:

{|
|
*Riole
*Schölecke
*Spetze
*Rote Riede
*Lapau
*Katharinenbach
*[[Drömling]]sgräben
*[[Wippermühle|Wipperaller]]
*Steekgraben and Hehlinger Bach
*Hasselbach
*Kronriede
|
*Beverbach
*Springriede
*[[Sassenburg-Triangel|Triangel]] Moor Canal
*[[Barnbruch]]graben
*Gosebach
*Fulau
*Knesebach
*Emmerbach
*Kiekenbruchrönne
|
*Momerbach
*Kielhorster Graben
*Bruno
*Fischergraben
*Flotte
*Sauerbach
*Beberbach
*[[Neudorf-Platendorf|Platendorfer]] Moorgraben
|}

=== Streams of the Aller Canal ===
The [[Aller Canal]] runs parallel to the Upper Aller between Wolfsburg and Gifhorn. The canal was built in the mid-19th century to reduce flooding. It has the following tributary streams:

{|
|
*[[Mühlenriede]]
*Klein Brunsroder Riede
*[[Hehlenriede]]
*Rischmühlenriede
*[[Rötgesbütteler Riede]]
|
*[[Viehmoorgraben]]
*[[Vollbütteler Riede]]
*Wittesmoorgraben
*Allertalgraben
*Flettmarscher Abzuggraben
|}

=== Streams of the Lower Aller ===
From the left, the following small rivers and brooks feed the Aller: the [[Alpe (Aller)|Alpe]] and the [[Wölpe]] near [[Rethem]], the [[Lehrde]] near [[Kirchlinteln]]-Hohenaverbergen, the [[Gohbach]] near Verden-[[Eitze]] and, just before its mouth, the Halse near Verden-Dauelsen.

== Castles and monasteries ==
[[File:Hudemühlen Schloss Merian 1650.jpg|thumb|[[Matthäus Merian|Merian]] copper engraving from the Renaissance castle of [[Hodenhagen]]-Hudemühlen on the Aller, 1654<ref>{{cite Q |Q19230666 |page=T61 |mode=cs1}}</ref><ref>{{cite wikisource |wslink=de:Topographia Braunschweig Lüneburg: Hudemühlen |title=Topographia Braunschweig Lüneburg |first1=Matthäus |last1=Merian |author1-link=Matthäus Merian the Elder |first2=Martin |last2=Zeiler |author2-link=Martin Zeiler |year=1654 |language=de |page=T61 |publisher=Matthaei Merians Seel. Erben |location=Frankfurt }}</ref>]]
*[[Bartensleben Castle]], built as a [[water castle]]
*[[Oebisfelde Castle]], built as a [[lowland castle]] (''Niederungsburg'') probably in the 10th century on a sand bank in the Aller in a swamp area of the [[Drömling]]
*[[Wolfsburg Castle]], built as a [[tower house]] in the 14th century on the Aller and expanded into a water castle with fortifications
*[[Gifhorn Castle]], completed in 1581 with fortifications
*[[Wienhausen Abbey]], former [[Cistercian]] monastery from the 13th century
*[[Celle Castle]], built in the 10th century as a [[fortified tower]] by a ford over the Aller
*[[Uhlenburg]] near [[Essel, Lower Saxony|Essel]], built as a [[manor house]] in the 14th century
*[[Blankenburg Castle (Essel)|Blankenburg Castle]] near Essel
*[[Ahlden House]], built in 1549 as a water castle on the Aller; where the river bed became part of the [[Leine]] from 1618 when the Aller changed its course
*[[Bunkenburg]], built as a [[circular rampart]] on the Aller in [[Ahlden (Aller)]] in the 13th century
* Hudemühlen Castle in the [[Hodenhagen]] sector of Hudemühlen, built in the 14th century as a castle, converted in the 16th century into a [[Weser Renaissance|Renaissance]] ''[[schloss]]'' and demolished in the 19th century
*[[Bierde Castle]] near [[Bierde (Böhme)|Bierde]]
*[[Hodenhagen Castle]] near [[Hodenhagen]]
*[[Blankenhagen Castle]] near [[Grethem]]
*[[Rethem Castle]] in Rethem (Aller), built in the 13th century and expanded into a bastioned site in the 17th century
*{{ill|Verden Cathedral|de|Dom zu Verden|eo|Katedralo de Verden|it|Duomo di Verden|nl|Dom van Verden}}, built in the 12th century

== Culture and tourism ==
The Aller is one of the few{{snd}}at least to all appearances{{snd}}undisturbed larger rivers in Germany. From Celle as far as the Verden area it forms, together with the [[Leine]], the attractive landscape of the [[Aller-Leine Valley]]. The Aller flows gently through relatively natural surroundings alongside meadows and woods, small villages and country towns. As a result, it is of great importance for those seeking relaxation in Lower Saxony with almost 4 million people in the conurbation of the Hanover-Brunswick-Göttingen-Wolfsburg Metropolitan Region. The [[Aller Cycle Way]], which is around {{convert|250|km|mi}} long and generally follows the course of the river at some distance, is just one of the leisure attractions in the area. There are attempts to make tourism along the river more compatible with nature through the 'soft tourism' (''Sanfte Tourismus'') initiative, especially in the Aller-Leine Valley. Leisure options include canoeing or travelling by houseboat. [[Water skiing]] is allowed on short sections of the lower river.

== Hydrology ==
The [[river]] is the biggest tributary of the Weser. The [[drainage basin|catchment area]] of the Aller covers {{convert|15744|km2|sqmi}}, about one third that of the Weser itself. The water flow gauge at Rethem below the Aller's confluence with the Leine registers an average volumetric flow of {{convert|114|m3|cuft}} per second.

The Aller receives via the [[Oker]] about half the run off from the [[Harz mountains]] (the other half drains into the Elbe via the [[Saale]] and other tributaries). Consequently, the Aller was and is frequently flooded by its tributaries. Since the commissioning of the [[dam]]s in the Harz, it is now possible to limit the impact, especially of seasonal floods, e.g. by delaying and slowing down the release of meltwaters on the Oker and [[Ecker]], the [[Innerste]] and the [[Grane (river)|Grane]] in spring. As a result, the discharge of the Aller into the Weser can be largely controlled and, although the level varies, it can be kept within boundaries.

Very little of the Aller is shaded by woods (apart from the section along the [[Aller Canal]]). Direct sunlight on much of the river encourages the growth of [[aquatic plant]]s and, in the absence of shady trees along its banks, the water becomes quite warm during the summer months.

=== Water velocity ===
The water velocity of the Aller is very slow in places. In its upper reaches, at the height of the [[Drömling]], the water compares to a sluggish canal and, in some sections, it is almost like a stretch of still water. Its sluggishness is due to the very gradual slope of the channel, which in Lower Saxony averages a mere {{convert|10|–|20|cm/km}}. Even in the upper course of the river, the flow across the whole of the stream bed is uniformly slow, due to the river having been widened and straightened. Here, the bed is covered by a mixture of sand and mud.

=== Sewage ===
[[Sewage]] from about half a million people is piped into the upper reaches of the Aller between its source and Müden/Aller, both directly and via its tributaries. The sewage is treated by 40 large [[sewage plant]]s. Sewage from the town of Wolfsburg, the only city along the river, is not discharged into the river, but dispersed by [[sewage farm]]s. The chemical composition of the Aller shows that the sewage discharged into it has generally been treated sufficiently well.

=== Heavy metal pollution ===
The pollution of the Aller by [[heavy metal (chemistry)|heavy metal]]s has resulted from centuries of [[Mining in the Upper Harz|mining in the Harz mountains]]. Harz rivers, such as the Aller tributary of the [[Oker]], picked up heavy metals from the mines and their spoil heaps. These were mainly cadmium, zinc and lead compounds that were concentrated into the [[suspended solids]] in the river. In this way, these chemicals were transported by the Oker into the Aller and Weser where they were deposited in the slacker-moving sections as [[sediment]]s.

In 1999, investigations were carried out into the heavy metal content of the suspended material in the Aller near Verden. They showed that the Aller was polluting the Weser disproportionally with [[lead]], [[cadmium]], [[zinc]] and [[mercury (element)|mercury]].<ref>Dieter Steffen: ''Schwermetallfrachten der Aller und deren Auswirkung auf die Weser-Bilanzierung auf der Basis von Schwebstoffuntersuchungen des Jahres 1999''</ref>

=== Water quality ===
The Lower Saxon water quality report <ref>''Gewässergütebericht Aller / Quelle 2004'' des [[Niedersächsischen Landesbetriebs für Wasserwirtschaft, Küsten- und Naturschutz]]</ref> of 2004 assessed the chemical [[water pollution]] level of the Aller overall as moderately polluted (quality level II). Some individual indicators were rated as quality level I (unpolluted to very lightly polluted), some however showed heavy levels of pollution (quality levels III-IV). Heavy pollution is predominantly caused by [[nitrate]]s. Pollution by [[ammonium]] in places is ascribed to the unsatisfactory operation of certain sewage works. Raised [[phosphate]] values were put down to intensive arable farming near the source of the river. Its [[salt]] content today is above the critical level for [[aquatic plant]]s. Since 1990, the salt content has reduced considerably, which may be connected with lower discharges from the former [[East German]] area following the ''[[Die Wende|Wende]]'' in 1989. Biological [[Freshwater environmental quality parameters|water quality]], based on the research into its [[Saprobe|saprobian systems]], is generally rated as unpolluted to very lightly polluted. The only area that is critically contaminated is the region of Wolfsburg, where deposits of digested [[sludge]] in the river are responsible.

=== Flooding and historical flood protection ===
[[File:Droemling Hochwasser-02.jpg|thumb|Spring flood in 1987 in the [[Drömling]]: the Aller at the level of the poplar avenue]]
[[File:Aller Ohre Kanal.jpg|thumb|Start of the Aller spillway (right) near Grafhorst leading to the [[Ohre]]]]
In former times, there were frequently spring floods in the Aller depression that stayed for a long time. This was mainly due to the very gentle slope of the river from its entry into the ice age glacial drainage channel of the Breslau-Magdeburg-Bremen [[glacial valley]]. The river had to accept large quantities of water from the rivers [[Leine]] and [[Oker]] following [[snowmelt]] in the [[Leine Uplands]] and the [[Harz]]. In the upper courses the Aller filled the flat, swampy basin of the [[Drömling]] from which the water drained only slowly. In addition the [[Ohre]] river flowed diffusely through the Drömling. Because the [[Drainage divide|watershed]] between [[Weser]] and [[Elbe]] lay in the middle of the Drömling, the river could even change its course so that the waters of the Aller flowed into the Elbe. The [[Prussia]]n king, [[Frederick the Great]], had the Prussian-owned eastern part of the Drömling drained between 1780 and 1796 and cleared for settlers (''Kolonisten''). His neighbours in western Drömling, in the shape of the [[Duchy of Brunswick]] and [[Electorate of Brunswick-Lüneburg|Hanover]] did not join the drainage project and only began to drain and control the Aller from 1860 onwards. They built the {{convert|20|km|mi|adj=mid|-long}} Aller Canal from a place near [[Grafhorst]] to the area of [[Calvörde]], through which the waters of the Aller could flow into the Ohre. Another canal built to prevent floods was the{{snd}}equally named{{snd}}[[Aller Canal]], finished in 1863, which protected the Aller depression near [[Gifhorn]]. The construction of the [[Mittelland Canal]] in the 1930s enabled surplus water from the Aller to be drained off. That is achieved near Grafhorst by the Aller relief channel, a {{convert|3|km|mi|adj=mid|-long}} canal. In spite of these measures there were floods in the Aller valley even in the 20th century that led to heavy losses for agriculture in the region.

=== Current flood protection ===
In the years 1954–1962, there was increased flooding along the Aller, which caused considerable damage to its water meadows. The flooded areas in the Aller valley varied between {{convert|300|and|5000|m|ft}} wide, mainly due to the uneven flow of the river. In 1961, the [[Landtag of Lower Saxony]] decided to regulate the Aller by widening it. The aim was to protect settlements as well as the agricultural economy of the villages and towns along the course of the river which were generally poorly protected from flooding. Most of the measures to regulate the Aller were established in the 1960s. They were followed by the construction of a {{convert|15|ha|acre|adj=on}} [[retention basin]] near Gifhorn in the 1970s. By contrast, plans for a retention basin on the bend in the Aller near [[Grafhorst]] were scrutinised between 1993 and 1996 on environmental grounds.<ref>
[http://www.wpk-gbr.de/allerknie.htm Allernknie] {{webarchive|url=https://web.archive.org/web/20050824151819/http://www.wpk-gbr.de/allerknie.htm |date=2005-08-24 }}</ref> The planned {{convert|12.5|km2|sqmi|adj=on}} "Fahle Heide" basin west of Gifhorn was never built due to lack of funding. As part of the widening of the Aller the banks were reshaped along large stretches. The state purchased strips of land up to {{convert|12|m|ft}} wide from those living along its banks. The banks were made flatter and lined with stones. Willows, alder and reed beds were planted. The Upper Aller was widened to {{convert|15|m|ft}}, the Middle Aller to {{convert|30|m|ft}} and the Lower Aller from its confluence with the Leine to {{convert|50|m|ft}}. Flood embankments were built along the Lower Aller near [[Rethem (Aller)]], [[Westen (Dörverden)|Westen]] and [[Häuslingen]].

==== Flood protection in Celle region ====
[[File:AllerAltencelle.jpg|thumb|The canal-like widened Middle Aller near [[Altencelle]]]]
As early as the 1980s the town of Celle had drawn up a "Plan for Flood Protection of the Celle Region".<ref>[http://www.celle.de/media/custom/342_6602_1.PDF Rahmenentwurf zum Hochwasserschutz der Region Celle]</ref> This described a combination of widely varying measures, such as excavation of the river shore, flood basins and dykes. On 6 June 2005 the town received authority to start the first stage of the flood protection project. In 2006 work was begun.<ref>[http://www.nlwkn.niedersachsen.de/master/C14994627_L20_D0_I5231158_h1.html NLWKN: Start der Hochwasserschutzprojekte in Celle]{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> This first part of the work entailed excavation of the river shore between Boye and the confluence with the river Fuhse, which were intended to increase the cross-section of the Aller channel during high water periods.<ref>[http://cdl.niedersachsen.de/blob/images/C17829250_L20.pdf Übersichtskarte der Vorlandabgrabungen in der Region Celle]{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> The flood basins have an area of about {{convert|15|ha|acre}} and are {{convert|1.5|m|ft}} deep, requiring about {{convert|240000|m3|ft3}} of earth to be washed away. The cost of the project came to around {{Euro|2{{nbsp}}million}}. Only two years later, it was determined that these first interventions of the river system had resulted in sand being permanently deposited in the Aller producing shoals. In May 2009, the shipping channel was dredged for the first time in the vicinity of the new flood basins so that ships could once again pass through. Now,{{when |date=November 2024}} it is planned to redesign the basins and, in some cases to fill them in, in order to reduce the future dumping of sand.

=== Negotiability for fish ===
In straightening the Aller in the 1960s the slope increased as the shortest route was taken. Ledges (''Sohlabstürze'') were built on the river bed to reduce erosion; these have since been converted to rock ramps (''Sohlgleiten'') in order to enable water organisms to pass more easily. There is no longer a barrier to fish at the [[weir]] near [[Grafhorst]]—designed to raise the water level during summer droughts—since it has been given a [[fish ladder]]. The migration of fish is however prevented by weirs near Gifhorn and [[Müden (Aller)]] and the locks of the [[Mittelland Canal]] near Wolfsburg-[[Wendschott]]. The [[Elbe Lateral Canal]] near [[Osloß]] flows freely under the Aller, however.
<!--Wasserführung-->

== Shipping ==

=== History ===
[[Shipping]] has plied the Aller for hundreds of years. It contributed to the economic growth of [[Braunschweig|Brunswick]], because the control of river transport fell into the hands of Duke [[Henry the Lion]]. Metals from the [[Harz]] were transported from Brunswick to the North Sea initially down the Oker and then down the Aller and Weser. In the 14th century, Celle was the most important [[grain|grain loading point]] in the region that is today Lower Saxony. Around 1500, the ships on the Aller already had a capacity of about {{convert|60|t|e3lbs|abbr=off}}. The section of the Lower Aller between Celle and Verden had a particular high economic significance for shipping. Nevertheless, maintenance, repairs and modifications were very expensive. Between 1908 and 1918 the Aller was widened to provide permanent navigability between Celle and Verden. Four barrages were built, with locks for ships. At the beginning of the 20th century, potash salt, that had been extracted near Celle, was transported in large quantities on the Aller. Today there are no commercial ships left.

=== Today ===
Today, the Aller is a federal waterway from its mouth on the Weser to Celle. This section has a length of {{convert|117|km|mi}} and is known as the Lower Aller. The Verden Water and Shipping Office (''Wasser- und Schifffahrtsamt Verden'') is responsible for upgrades and new projects. With this authority, responsibility is further subdivided. The Oldau branch is responsible for the Aller from Celle to {{ill |Hülsen (Dörverden) |lt=Hülsen |de |Hülsen (Dörverden) |nl |Hülsen (Dörverden) }} {{convert|94.1|km}} further downstream. In contrast, the Verden branch covers the river from Hülsen to its confluence with the Weser near Verden-Eissel {{convert|117.1|km}} downstream from Celle.

Since the mid-1960s, only pleasure cruisers and sports boats have been used on the river above Verden towards its source.

=== Permitted ship sizes ===
* Mouth–Verden: waterway class III (length × width: {{cvt|67|x|9.50|m|disp=or}})
* Verden–Celle: waterway class II (length × width: {{cvt|58|x|9.50|m|disp=or}})
* Above Celle: not navigable

=== Locks ===
[[File:Aller (Fluss) Schleuse Oldau 2008 by-RaBoe 05.jpg|thumb|Oldau lock]]
[[File:Schleusenbecken Bannetze.jpg|thumb|Bannetze lock basin]]
In 1907, the [[Prussia|Prussian state]] decided to canalise the Aller from above its confluence with the Leine near [[Schwarmstedt]] downstream to Celle. In the years 1908 to 1918, the river was regulated by four barrages with locks and thus made navigable for larger inland ships. In particular, the Aller locks in Bannetze and Oldau enabled the transportation of crude oil from the [[oilfield]]s of [[Wietze]] to Celle. Likewise, grain was shipped to Celle for milling.

{| class="wikitable" 
! bgcolor="#FFDEAD"| Place
! bgcolor="#FFDEAD"| Location
! bgcolor="#FFDEAD"| Usable length
! bgcolor="#FFDEAD"| Usable width
! bgcolor="#FFDEAD"| Fall
! bgcolor="#FFDEAD"| Built
|-
| Oldau
| align="center" |{{cvt|14.7|km|disp=br()}}
| align="center" | {{cvt|159|m|disp=br()}}
| align="center" | {{cvt|10|m|disp=br()}}
| align="center" | {{cvt|3.21|m|disp=br()}}
| align="center" |1908–10
|-
| Bannetze
| align="center" | {{cvt|26.7|km|disp=br()}}
| align="center" | {{cvt|159|m|disp=br()}}
| align="center" | {{cvt|10|m|disp=br()}}
| align="center" | {{cvt|2.40|m|disp=br()}}
| align="center" |1909–12
|-
| Marklendorf
| align="center" | {{cvt|38.3|km|disp=br()}}
| align="center" | {{cvt|159|m|disp=br()}}
| align="center" | {{cvt|10|m|disp=br()}}
| align="center" | {{cvt|3.22|m|disp=br()}}
| align="center" |1914
|-
| Hademstorf
| align="center" | {{cvt|49.8|km|disp=br()}}
| align="center" | {{cvt|159|m|disp=br()}}
| align="center" | {{cvt|10|m|disp=br()}}
| align="center" | {{cvt|1.23|m|disp=br()}}
| align="center" |1914–18
|-
|}

=== Timber rafting ===
Timber rafting was probably being used on the Aller by the 14th century. The logs thus transported were used for construction as well as fuel. An early centre of timber rafting and the wood trade was the princely ''[[Residenz]]'' town of Celle. At first the nobility had the wood transported as fuel to heat [[Celle Castle]] and other royal buildings. The timber was felled in the royal forests. The transportation of logs by raft was roughly 10 times more efficient than moving it by horse and cart.

A major rafting operation took place on the Aller in 1680 when a large quantity of construction wood was floated down to the Weser and its mouth. The wood came from the southern [[Lüneburg Heath]] and was used to build around 100 houses in the Swedish [[fort]] of Carlsburg on the site of present-day [[Bremerhaven]].

From the 17th century, wood was also rafted down the Aller tributaries, such as the [[Ise (river)|Ise]] and [[Örtze]] to Celle. In Celle, the logs collected at a [[needle dam]] in the Aller Land and were stored in a wood yard. Rafts also ran past Celle and down the Weser to Bremen. After the death of [[George William, Duke of Brunswick-Lüneburg]] in 1705, timber rafting on the Upper Aller to Celle fell into decline. When the royal household moved to Hanover, Celle lost the [[baroque]] lustre of a Residenz town. Raft dealers took over the business. On the Lower Aller, timber rafting flourished again at the end of the 19th century during the ''[[Gründerzeit]]''. There was a large demand for wood in [[Bremen]], Bremerhaven and the [[Landkreis Wesermarsch|Weser Marshes]], where wood was used for the construction of houses and shipbuilding. In the years around 1895, about {{convert|8,000|m3||adj=pre|solid}} of wood were rafted down to the Weser. After the [[First World War]], timber rafting on the Aller dwindled to nothing.

== Water power ==
[[File:Aller (Fluss) Wasserkraftwerk Oldau 2008 by-RaBoe 02.jpg|thumb|Oldau waterworks]]
In upgrading the Aller between Celle and the mouth of the Leine near [[Schwarmstedt]] between 1908 and 1918, [[hydropower station]]s were built at two of the four new [[barrage (dam)|barrage]]s: [[Hambühren|Oldau]] and Marklendorf. They enabled the [[electrification]] of the [[Südheide Nature Park|Südheide]]. The Oldau station, with three [[Francis turbine]]s, was taken over in 1929 by [[PreussenElektra]]. In 1972, the power stations were closed as they were unprofitable. Whilst the structure in Marklendorf was demolished, the power station in Oldau was declared a technological monument and escaped destruction. After being modernised in 1983, it rejoined the grid. It has largely been preserved in its original state. Here, the water power of the Aller, with the aid of Francis turbines with a [[nominal power]] of 650&nbsp;kW, is used to generate 3 million [[kilowatt-hour|kWh]] per year of electric current.<ref>[http://www.niedersaechsische-muehlenstrasse.de/index.php?id=106 Wasserkraftwerk Oldau]</ref>

==See also==
*[[List of rivers of Saxony-Anhalt]]
*[[List of rivers of Lower Saxony]]

== References ==
{{reflist}}

== Sources ==
{{refbegin}}
* {{cite book |first=Jürgen |last=Delfs |title=Die Flößerei auf Ise, Aller und Örtze |trans-title=The Rafting on Ise, Aller and Örtze |location=Landkreis Gifhorn |publisher=Gifhorn |year=1995 |language=de |isbn=3-929632-24-1 |oclc=237345239 }}
* {{cite book |first=Wilhelm Christian |last=Kersting |title=Die ausgleichenden Maßnahmen des Umweltschutzes bei der Hochwasserregulierung der Aller |trans-title=The Compensatory Measures of Environmental Protection in the Flood Control of the Aller |year=1979 |publisher=Fritz Steiniger und Henry Makowski, Schweiger und Pick Verlag |location=Celle |language=de |oclc=8495528 }}
{{refend}}

== External links ==
{{Commons category}}
{{Wiktionary|Aller}}
* [https://archive.today/20070628072907/http://www.bfn.de/0311_landschaft.html?landschaftid=62702 Landscape fact file - Aller Valley]
* [https://archive.today/20120614221014/http://www.bfn.de/0311_landschaft.html?landschaftid=62701 Landscape fact file - Aller Flood Plain]
* [http://www3.ndr.de/programm/epghomepage100_sid-429633.html TV report ''Wassergeschichten: Die Aller''] on [[NDR Fernsehen|N3]]
* [http://cdl.niedersachsen.de/blob/images/C28224211_L20.pdf Water quality report on the Aller /Source 2004 from Lower Saxony state]{{dead link|date=July 2017 |bot=InternetArchiveBot |fix-attempted=yes }} (pdf, 1 MB)

{{Authority control}}
{{Rivers of Germany}}

[[Category:Aller basin| ]]
[[Category:Rivers of Lower Saxony]]
[[Category:Rivers of Saxony-Anhalt]]
[[Category:Lüneburg Heath]]
[[Category:Federal waterways in Germany]]
[[Category:Rivers of Germany]]