Urban Flash Floods

Urban flash floods after heavy rainfall can affect any municipality: sealed settlement areas are particularly at risk. But unlike floods there is no pre-warning during heavy rainfall: the mud flood comes from above, with a high flow velocity and high destructive force. If the water can neither seep away nor run off in a controlled manner, it makes its own way. News of washed-out streets and flooded cellars is becoming more and more frequent - even from previously spared communities. Often already during the clean-up work the population and politics ask the question about the "why".

By taking stock of the surface sealing on the basis of current aerial photographs, the sealing situation of each property is documented and problem areas are obvious.

On the basis of sealing and land use data we simulate different heavy rainfall events. In addition to the flow paths and directions of the flash floods, we plot floodplains, taking into account the capacity of the sewer system.  

Preventive road, green space and urban land use planning, adaptation of the canal network, unsealing measures, public relations work, municipal and private property protection and similar can now be targeted.

From the 3D aerial photographs or laser scan data, we create a terrain or surface model of the settlement areas. Sinks and potential flow paths of the surface water can now be identified. And hydraulic calculations become possible.

All data is analysed GIS-based. Hazard maps depict flow paths, sinks, water bodies, obstacles and bottlenecks, areas with unsealing potential, critical infrastructure such as hospitals, electrical supply facilities, landfills, protection and retention facilities, etc. This results in areas where action is required and the potential damage in the event of a case can be estimated.

The measures will be implemented under consideration of technical standards, such as the paper of the State Office for Nature, the Environment and Consumer Protection North Rhine-Westphalia on the "Recording of unsealing potentials in NRW". Fire brigades and disaster control also benefit from the hazard maps. They can optimize their schedules at an early stage and thus reduce response times.