During the 1990s, frequent occurrences of disastrous floods throughout the world have motivated experts, journalists, politicians, citizens and others to identify reasons for the formation of these floods. Even among experts the reasoning seems fairly subjective at times. Often, under the actual impression of catastrophic damages, basic process understanding gets lost and is replaced by all kinds of irrational assignments of guilt and responsibilities. Some publications and media even suppose that such factors as urbanisation are more important than rainfall for the formation of rare flood events. Quite astonishing is the criticism uttered by individuals and representatives of communities hit by flood damages, even though they have settled, more or less consciously, in the areas endangered by high flood risk, e.g. on flood plains. Yet it has to be clearly remembered that except in few cases, floods are caused by extreme rainfall events. However, anthropogenic impacts related to land use have an influence on the intensity of flood discharge. It must be remembered that each flood event has its own set of causes, which can be categorised as anthropogenic and natural event dependent (meteorology) and event independent. In this paper, results of a model based sensitivity analysis will be presented with respect to quantifying these impacts on floods. The model structure provides an opportunity to consider anthropogenic impacts like land use changes and river training. Some control measures, which appeared suitable to compensate for the anthropogenic impacts, were applied in two case studies.
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