Flow basin

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In Pass basin polluted is rainwater or mixed water mechanically clarified and in the receiving water passed. In the separation system it is used in rain clarification basins and in the mixed system in rain overflow basins .


A flow basin has an inlet channel and an outlet channel. The drainage channel either has a small cross-section or a throttle device , so that only the amount of water that can be absorbed by the sewage treatment plant is passed on . The excess amount of water then falls into the sedimentation chamber via a clarifier overflow . The excess water is stored and clarified in the sedimentation chamber. Should the entire flow basin fill up, purified and highly diluted water is immediately led from the sedimentation chamber via a basin overflow into the receiving water.


  1. In dry weather and small rain events, the water is directed to the sewage treatment plant without accumulating.
  2. In rainy weather with little precipitation , the accumulating water is temporarily stored in the sedimentation chamber and, after the rain event, passed on to the sewage treatment plant in doses.
  3. In rainy weather with heavy precipitation ( thunderstorms ), the excess water is backed up and stored in the sedimentation chamber.

This means that the water is mechanically pre-cleaned (settling effect of the basin). If the water accumulates up to the basin overflow, it is immediately directed into the receiving water, but a proper clarification effect is still ensured. Due to the high proportion of rainwater, it is only very dilute water, so that the organism of the receiving water is not damaged.

operation area

In contrast to catch basins , continuous basins are built when the size of the catchment area suggests that the pollution will occur over a longer period of time and must therefore be treated continuously.