Rainwater retention basin
A rainwater retention basin (RRB) is an artificially created basin to temporarily store large amounts of rainwater for a short period of time, so that it is discharged more slowly into the downstream receiving water (drainage channel). It is often found in cities and on highways, where the drainage of large areas without intermediate storage would lead to an overload of the downstream drainage manifold. In contrast to the flood retention basin, rain retention basins are not located in or on a river.
While a rain overflow (in Austria also called rain or mixed water discharge ) only allows the separation into the inflow to the sewage treatment plant (7 to 15-fold wastewater discharge) and the discharge to the water body, in the retention basin the amount of water diverted is temporarily stored in the storage chamber and passed on with a delay ( Catch basin ) or after mechanical cleaning into the receiving water ( flow basin ).
Rain retention basins are built using earth and concrete construction. Advantages of earthworks are the lower construction costs and the possible natural design. The advantage of the concrete construction is the lower space requirement; the basin can also be built underground.
Rain retention basins usually have a usable volume of 150–250 cubic meters per attached hectare of paved area, but also more or less depending on local conditions.
Similar to the flood retention basins described above, there are also arrangements for rainwater retention basins in the main circuit or in the secondary circuit ; In the latter case, the constant flow of water flows past the pool and a subset is diverted into the pool during high water.
In Germany, rain overflow basins generally have 20–30 cubic meters, in individual cases 40 and more cubic meters of usable volume per hectare of attached paved area. Rain overflow basins usually relieve pressure about 30 to 40 times a year. Other standards may be common in other countries.
In 2002 there were around 24,000 rainwater retention basins in operation in Germany.
Underground rainwater retention basins
Underground rain retention basins are artificially created large chambers that are flooded during heavy rain and are often designed for 20 minutes of heavy rain.
During the filling process with liquid, room air escapes to the outside via exhaust air ducts. In order to keep the pressure difference low even with rapid filling, the cross-sectional area of the air duct must be dimensioned sufficiently large. If the chamber is emptied again later, the direction of the air flow is reversed.
As in general in sewers with a free liquid level, air shafts also have the function here that the water level can adjust hydraulically, i.e. below the flow gradient. Furthermore, the quality of the gas phase should remain both non- explosive (digester gas methane, evaporation of contamination with volatile flammable substances plus oxygen from the air) and breathable.
A central storage channel has been built in Graz since 2018 . The 2 parallel strands are divided into numerous chambers and run partly under the bed of the Mur river and also in the mud embankment below the Graz-Puntigam power plant, which was built at the same time .
- Rain retention system
- Rainwater retention basin in the Marzahn-Hellersdorf district
- Overflow threshold
- Wolfgang F. Geiger, Herbert Dreiseitl: New ways for rainwater . Handbook on the retention and infiltration of rainwater in building areas. 2nd Edition. Oldenbourg, Munich 2000, ISBN 3-486-26459-1 (first edition: 1995).
- Photos of an underground rain overflow and rain retention basin in Wuppertal on Wuppertaler-Unterwelten.de