Hydrodynamics of flood


Morphological stream types

The single flow phenomenon cannot be assigned to the morphologic stream types in a unique way, but can occur in almost all of the 5 described stream types (compare figure on page 1). The rivers will be classified as follows:

  • v-shaped and rift valley rivers
  • meander valley rivers
  • flat valley rivers
  • lowland and coastal rivers
  • anthropogenically altered streams [*1]

Generally, several structural properties of a stream occur at the same time and place in nature, so that the choice of a model approach is usually not obvious.

The calculation in case of one or more flow properties that result in a multi-dimensional flow structure is not guaranteed to be multi-dimensional too, since the property of being multi-dimensional can be locally bounded and thus might not have an effect on the overall flow area.

A model approach must thus be scaled with an appropriate examination measure. The bigger the measure, the more important is the morphologic unsteadiness as a measured value of a more or less extended stream section. This value increases with the number of structural elements with multi-dimensional stream dominance.

A further criterion for the selection of a model is the required precision. It can vary a lot depending on the task.

A decisive factor is if absolute or relative flow variables are needed, while “relative” refers to the difference of flow factors between two stream states and “absolute” refers to the absolute value of the base stream factor for a state.
Type, Stream line, section, geometric variance in direction of flow, areas of backflow and retention, flow braiding and confluence, constructions in and at the stream, stream conditions.

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Flood modelling



*1 Otto, A (1991)



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