Retention basins extend retention

A retention basin is used when the amount of water exceeds the capacity of cisterns. They are known especially in public space as a water reservoir for low precipitation periods. In the private sector they rarely play a role. The tanks, which are usually open at the top, must still be filtered when the cistern is fed.

Retention system for heavy rain

While a cistern is designed to catch and store normal rainfall, retention basins are set for heavy rain for up to twenty minutes. In the cistern, if there is excessive rainfall, the overflow would drain off the overflowing water and eventually cause soil softening, rinses and, in any case, the loss of excess water.

A retention basin serves as a short-term complete water reservoir, which takes over the principle of a retention cistern on a larger scale. Typical volumes are up to 250 cubic meters per hectare of rainfall area. The temporarily relatively large amounts of water can cause great damage to structural defects or improper installation of the retention basin.

Tests, checks and regulations

Unlike rainwater tanks, retention basins are legally defined as dams and are therefore subject to different regulations. While the approval and controls for cisterns in many cases only consist of the form of a disclosure requirement, retention basins must always be planned by qualified engineers and safety assessments must be provided.

The self-build a retention pool is almost impossible. Each owner and / or operator of a containment basin is under an obligation to submit periodic reports of incidental inspections to the lower water authority by unsolicited personnel.

The following tests must be carried out and documented at least once a year by a qualified engineer:

  • Visual inspection of the entire system
  • location measurements
  • Height and settlement measurement
  • Hydrometric measurement
  • Meteorological measurement / precipitation
  • Control of steel and machine components
  • Checking the functioning of the facility
  • Inflow, congestion, discharge and discharge measurement
  • Control of access and access security

Concealed retention basins

Often not recognized as storage spaces in the sense of a retention basin are the following water-storing installations:

  • garden ponds
  • fishponds
  • pond
  • fire extinguishing fires
  • settling tank
  • habitats
  • Brook and spring dams

They must also be reported to the lower water authority, as in the case of heavy rains they are exposed to the same load as a retention basin, without having to bring the building basics. Depending on the volume and type of installation, the respective lower water authority can define "dams of secondary importance". In the case of this classification, the scope of the mandatory annual examinations may be limited.

Cistern and restraints

In order to extract cistern water from retention basins, the feed must be regulated and provided with appropriate overflow and backflow protection mechanisms. In conjunction with a retention system, the water circuits and functional routes must be planned hydrologically and hydraulically.

Tips & Tricks

For individuals, retention basins are not recommended as they must meet extensive safety and construction requirements. If you expect extensive heavy rain, you should choose retention systems in the cistern building and create appropriately sized septic tanks.

Video Board: What is a detention area, the differences between Detention and Retention Ponds