Modified drainage system
In these systems, attempts are made to keep rainwater out of the sewer network as much as possible. Rainwater that does not require treatment is either seeped away directly, semi-centrally or centrally, discharged into nearby bodies of water or temporarily stored on site in rain barrels or cisterns (for watering the garden, for flushing toilets). Rainwater in need of treatment (e.g. from polluted traffic areas) is diverted and clarified in the sewer network as in the conventional system. In the modified separation system , this water is passed through the rainwater sewer for further treatment; in the modified mixed system , this water is discharged as mixed water into the sewage treatment plant.
In addition to a reorganization of the sewer network, other requirements must also be taken into account for the development. These concern measures that contribute to a reduction in sealed areas (e.g. use of lawn paving stones ) and a slowdown in runoff, e.g. through roof greening .
By flattening the runoff peaks caused by precipitation, sewer networks and sewage treatment plants (in the case of mixed water systems) can be made smaller. Collected and used rainwater lowers drinking water consumption. In addition, the water cycle is improved, as rainwater that seeps away on site replenishes the groundwater reserves. Another advantage can be the improvement of the microclimate through the increased evaporation of precipitation. It can be problematic that the groundwater level rises locally in the event of rainwater seeping away.
Source in the network: Koster, Gorges, Biehler (2005): Decentralized rainwater management in urban areas ; Lecture in Esch-sur-Alzette