Rainwater Infiltration

Installation and maintenance of infiltration trenches

The effects of land sealing are becoming noticeable throughout Germany in the form of rising drinking water and wastewater prices as well as flood damage. In particular, the topic of rainwater infiltration is highly topical for many new buildings, conversions and renovations.

Today's state of the art ensures near-natural management of the rainwater that accumulates. In this sense, decentralized infiltration on site (e.g. with the help of infiltration troughs) is increasingly demanded by the approval authorities.

What is decentralised rainwater infiltration?

When rainwater that has not been polluted with harmful substances infiltrates directly onto the property, this is referred to as “decentralised rainwater infiltration”. The technical issues in this context are regulated by the DWA-A 138 worksheet.

What is a storm drain?

An infiltration trench is an underground trench in which rainwater can infiltrate. Infiltration trenches are mainly planned because of limited space and the relatively simple realisation.

Infiltration trenches can be installed under paved paths and areas accessible by lorries. They can be combined with other techniques, e.g. above-ground depressions (swales).

Amendment of the Water Resources Act

According to the amended German Water Resources Act (WHG), more rainwater is to be infiltrated instead of being drained into the sewage system as was previously the case. According to § 55 para. 2 WHG, the mixing of rainwater and wastewater is to be avoided. In fact, this regulation means the end of the principle of mixed sewerage.

Furthermore, rainwater infiltration systems are increasingly prescribed in development plans. Modern infiltration trenches offer various advantages over classic rainwater infiltration (troughs, gravel):

  • High storage and infiltration capacity (only 30% of the gravel volume is required for the same capacity).
  • Less land required (less excavation)
  • Hardly any restriction on surface usability (in contrast to swale infiltration)

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