Climate Change and the European Water Dimension - Agri ...

Chapter VI.F. Climate Change, Extreme Events, Dioxins and
the 2002 Flood in the River Elbe
Chapter VI.F.1. Introduction
Press and radio reporting during the late summer of 2002 was dominated by flooding
of the Rivers Elbe, Danube and Moldau catchments. Devastating damage of private
property, infrastructure, industrial and commercial enterprises and cultural
monuments, together with numerous fatalities, especially in the Elbe catchment,
eclipsed all flood damages ever experienced in central Europe.
Heavy floods are periodic natural phenomena as the climatic history of central
Europe shows. Their recurrence is foreseeable and consequently preventive
measures against floods have always been part of the human settlement history
along rivers. But the extent of damages caused by floods is rising as function of
urbanisation of the river catchments and even without any change of climatic factors,
urban areas are continuously moving towards a higher flood risk.
Several determining factors are known: Settlement areas on former floodplains
increase the amount of “economic damage” through floods, even though the flood
intensity remains the same. Straightening (channelling) of river courses and dikes
separate the river from its floodplains and alluvial forests, which before, acted as
natural buffers that temporarily absorbed floodwaters and flattened the flood peaks.
Overall, it is estimated that only 20% of Europe’s floodplains remain functional.
In addition the water storage capacity in soils of the river catchments has decreased
as a result of surface sealing in urban areas, deforestation, and soil compaction on
agricultural land. Consequently a given amount of precipitation moves comparatively
faster and at increasing floodwater levels through the river catchment of an urban
area. On top of these physical changes of the catchment properties, an increase of
intensity of precipitation has been observed in the recent years and is being
discussed in the context of climate change.
Besides various aspects of increasing physical damages related to floods the
mobilisation, distribution and fate of chemical pollutants and pathogens through
floodwaters have received public concern in the recent years. Past observations of
fish kills in floodwaters, caused by mobilization of anoxic sediments and the related
decrease of dissolved oxygen in the water, have demonstrated that large water flow
does not necessarily result in a dilution of pollutants. In contrast the complex
dynamics of sedimentation and re-suspension in riverbeds typically result in a “first
flush” of sediment born pollutants during flood events.
In addition, flooding of urban areas, especially behind broken dikes, affects industrial
sites, mining areas, sewage sludge plants, and waste deposits, and may result in
additional pollutant releases from terrestrial sources. The mobilisation of pollutants
during the Elbe flood in 2002 was addressed in the frame of an a issued by the
German federal ministry of Education and Research (Bundesministerium fuer Bildung
und Forschung - BMBF) involving various research institutes and federal institutions
in Germany and Czech Republic. The objective of this project 5 was the determination
of pollutants in water, soil, river sediment and floodwater sediments combined with
an assessment of related threats to the environment and human health.
5 The final report can be downloaded from http://www.ufz.de/data/HWEnd1333.pdf
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