The great hope of Mainaulass | Offenbach

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The city of Offenbach is expanding its sewer network in order to be able to cushion heavy rain events like on Sunday. However, sewer systems cannot be designed for very large amounts of water.

Bubbling water from manhole covers on Wilhelmsplatz, a flooded Mainstrasse and a number of full cellars and underground garages. Last Sunday afternoon, 60 liters of rain fell on every square meter in half an hour in a very limited area in Offenbach.

“No sewer network can be designed for such water masses – even pipes with a diameter of more than ten meters could not hold and transport such a quantity in such a short time”, explain the Offenbach public utilities. In a highly compacted soil like in a big city, in which numerous other supply lines have to be accommodated, there would be no space for it.

The fire brigade had to drive over 160 missions and was supported by the technical relief organization. In order to cushion such heavy rain events, the Offenbach municipal service is currently expanding the sewer network with a special canal. “The project is expected to be completed at the beginning of next year and will end with the so-called Main outlet,” the public utility company said. The outlet structure is being built at the level of the innovation campus next to the pipe bridge, which is a listed building. Among other things, this is intended to reduce the probability of the recurring flooding in Kettelerstraße before entering Bürgel to a minimum.

If the sewer then fills with heavy rain, water falls in a transfer structure on Kettelerstraße over a threshold into the new relief sewer with a diameter of two meters. This should then discharge the excess water directly into the river and relieve the canal system, which until now is only available for draining the water.

“In response to the fact that, statistically, there is no more rain falling in Offenbach, but more frequent cloudbursts fall over the urban area, the sewer system in Offenbach is continuously being adjusted,” says the municipal utility. However, the sewer pipes must not be too big. Otherwise there is a risk that they will no longer be adequately flushed out when there are no heavy rain showers.

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