Flood risk or more safety?
Press review: an article in the Darmstädter Echo
2025/07/15 by Jürgen Buxmann
Streams such as the Seeheimer Elsbach flow predominantly in pipes in the municipal area – unlike in Bickenbach, for example. Where they flow openly, they eventually disappear into a pipe again. And the entrances are usually barred. This is to prevent children from crawling in while playing and putting themselves in danger. However, in the event of heavy rainfall, the water levels in the streams can rise sharply and branches, trunks and undergrowth can then collect in front of the entrances and block them. The consequences can be devastating.
An even greater rise in the water level, flooding where it can cause considerable damage: in basements and first floors of nearby houses, for example.
The Local Agenda 21 Group (LA21) is currently addressing the issue of flood protection. And the municipal council responded to their concerns. “There has been a weighing up of interests,” a representative of the administrative body told the LA21 people. After all, the grilles could be folded up if necessary. The LA21 group doubted whether this could be done reliably when the water level of the streams rises very quickly – especially at night. The conflict of interest between the safety of children at play and the protection of citizens from flooding was not resolved.
But there is a solution. The Echo asked an expert in hydraulic engineering from the Technical University of Darmstadt (TUD). Boris Lehmann is an engineer and university lecturer in the TUD's “Civil and Environmental Engineering” department, where he works in the field of “Hydraulic Engineering and Hydraulics”. He advises the use of gratings with inclined bars as opposed to vertical gratings. These are suitable for catching floating debris and thus quickly reducing or even completely blocking the flow of the watercourse. The inclined bars should be shaped in such a way that they form a plateau in the upper part. The inclined part ensures that the floating debris is pushed upwards towards the catchment area by the water pressure. In technical terms: It shears off upwards – where the catchment plateau is. As a result, the actual inflow into the pipe to be protected remains free due to the inclined bars – the water can continue to flow through. And branches and other floating debris are pushed upwards and do not block the inlet.
At the Seeheimer Grundweg – to which the Elsbach runs parallel in part – and also at the forest pond, such flotsam-shedding grids have already been installed. According to Lehmann, they are not necessary at pipe outlets.
Folding away when necessary often does not work
This leaves the additional precaution that the municipal council cites as a possible solution to the problem: Folding away the grids at the pipe inlets when necessary – in other words, during floods. However, research by the Echo has revealed this: In areas where such foldable devices are installed, it was often not possible to fold the grids away in time during floods. This was mostly due to a lack of personnel and coordination problems during emergency situations, which often prove to be hectic and require a high degree of flexibility.
There are no legal requirements for converting to grating with inclined elements. However, one has already been installed at the pipe entrance to the Elsbach at Seeheimer Grundweg.
This is an excerpt from the original article that appeared in Darmstädter Echo.
