Retention basin

Flood retention basin

At the planning stage, watercourse extensions, the use and development of flood-prone areas, land sealing and the development of new areas must be examined. As local areas must be protected for a statistical 100-year flood event in accordance with the provisions of the state water law, flood protection will continue to have to be ensured by technical means (e.g. flood retention basins).

A flood retention basin is always a dam that temporarily stores the discharge volume of a watercourse during floods and releases a defined discharge volume to the downstream course via a so-called throttle. This discharge volume depends on the different and sometimes combined water management functions of the flood retention basins. As a rule, however, the flood retention basins are dimensioned so that they can store a 100-year precipitation event.

Flood retention basins essentially fulfill two main tasks:

A Equalization of the water flow

Sealing (roads, houses, etc.) and drainage systems result in more concentrated discharges into a body of water compared to the natural, uninfluenced state. These smaller unnatural floods, which occur more frequently, are released to the lower course in a controlled manner by the flood retention basins. In this way, near-natural discharge conditions can be established and habitats (flora and fauna) along the watercourses can be sustainably protected.

B Flood protection

Due to the retention effect (storage of runoff peaks) of the basins, the runoff in the lower reaches of the dam can be reduced in such a way that properties and residential buildings - and thus ultimately people and their belongings - can be protected from flooding up to a specified design level (HQ 100).

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Rainwater retention basin

A rainwater retention basin (RRB) is an artificial basin designed to temporarily store large quantities of rainwater over a short period of time so that it can be released into the downstream watercourse at a slower rate. It is often found in residential areas (sealed surfaces) in order to release the rainwater from the residential area into the watercourse at a slower rate. Examples from Aachen include three rainwater retention basins in the Breitbenden residential areas. However, there are also rainwater retention basins to protect the sewer system from flooding (e.g. Johannisbach at Pottenmühlenweg or in Preußwald near a supermarket)

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