Don't just let the valuable rainwater flow away in the sewage system, but store it in the ground where it rains where it rains and use it for plants and the climate: That is the goal behind the expression Offenbach's sponge city.

A new precipitation statute for Offenbach should now create a new regulatory basis for this.

Jochen Remert

Airport editor and correspondent Rhein-Main-Süd.

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According to its own statements, the city is reacting to developments that have been observed for years, starting with increasing overheating in the city because there is no cooling from evaporating rainwater.

In addition, according to the information, the groundwater level is also falling in Offenbach because the amount of precipitation is falling.

One of the most obvious consequences is the death of green structures, including tree diseases caused by drought, which often end in felling to avoid acute hazards.

rainwater as irrigation water

“Rainwater is not only useful and important to us, we also relieve the pressure on the sewage system and protect our city from flooding or mitigate the consequences of heavy rain events.

In this way we are also improving the situation for our trees and green spaces," explains Mayor Sabine Groß (Die Grünen).

It is important for property owners that rainwater should always be “managed” on their own property, for example as irrigation water or by allowing it to seep away and evaporate.

This can be done with rain barrels, cisterns or through infiltration, as the city says.

Green roofs could also temporarily store water and gradually release it back into the plants and the air.

Criticism of citizens' initiative

"By separating rainwater management from sewage disposal, we will on the one hand significantly improve the formation of new groundwater in Offenbach and also support the good biological status of Offenbach's water bodies, as required by law by the EU," said Sybille Schumann, leader of the Greens in the city council, in a message.

Schumann is a hydrologist.

The statute basically defines the handling of rainwater.

A central goal is that unpolluted precipitation is used for the formation of new groundwater and kept in the areas.

They should no longer flow through the sewage system into the sewage treatment plant.

Precipitation on roofs and green underground car parks with areas of 30 square meters or more are covered by the regulation.

From the time of the resolution, the statute applies only to new buildings, extensions and increases in height.

Meanwhile, the citizens' initiative Stadtfieber criticizes that Offenbach postulates the unsealing and storage of precipitation in green spaces with the sponge city project, but at the same time they are doing the opposite with a number of construction projects, namely the sealing of important green spaces and cold air corridors.

The initiative means, among other things, the planned extension of the federal highway 448 in the direction of the innovation campus, which would destroy parts of the Lohwald.

The city does not dispute that widening the existing path into a municipal road with a separate cycle and pedestrian lane will result in trees being felled.

However, she wants to unseal areas in the immediate vicinity, which, according to current planning, would mean more areas being unsealed than would be newly sealed for the construction of the road.

In addition, a trough between the roadway and the cycle path should allow water to seep away.

The city wants to have the question of fresh air and cooling clarified in a detailed climate report.