Stimulated by the increasing occurrence of extreme floods in the last years worldwide the flood research has been intensified leading to a better understanding about the phenomenon of flood. The physical processes contributing at its generation have been analysed and new refined mathematical methods have been developed.
While at the beginning floods were regarded only as surface runoff in the meantime we understand that various flow processes on the surface and in the underground contribute to its formation. The impact of anthropogenic changes on the water balance and flood flow became aware and has been studied in many national and international research programmes.
In the meantime climate change has been detected as the main uncertainty in determining the probability of flood. Meteorological models have been used to develop different scenarios of future climate condition. They show an increase of extreme weather conditions like droughts and heavy storm events. These scenarios have been used as input to hydrological models to determine the effect of climate change on the water balance in catchments and on the flood situation in rivers. Still research is at the beginning on that field. More refinement of modelling capabilities will be needed like the coupling of hydrological and meteorological models.
It is the objective of this chapter to present today’s knowledge about the hydrological processes participating at the formation of flood. An overview will be given on mathematical models to simulate these processes. They are divided into hydrological and hydraulic models. While the first group of models addresses the flow processes in the catchment, the second group simulates the transport processes of runoff in channels and rivers. At the end deficiencies of today’s knowledge on floods and modelling instruments will be discussed and needs for research are formulated.