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 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 Prussian 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 Hanover did not join the drainage project and only began to drain and control the Aller from 1860 onwards.
They built the 20 km 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 - equally named - 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 3 km 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.
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 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 Prussian 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 Hanover did not join the drainage project and only began to drain and control the Aller from 1860 onwards. They built the 20 km 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 - equally named - 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 3 km 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.
Aller (Germany)