A flood plain is a zone around a waterway, lake or inland sea that is subject to flooding over the course of a year, due to rising groundwater and waterline levels.

Increasing settlement and industrialisation in Germany have resulted in these natural drainage areas being sealed off, effectively removing the availability of natural reserve capacity. Particularly in autumn, heavy rainfall in these regions often leads to severe flooding; recent examples in inland Germany have been commonly referred to as the 'Oder flood' or the 'flood of the century'. Today, we know that re-opening artificially sealed areas like these is the only effective measure against flooding.