2.1.1 Overflow from river channel or river floods

Of all river floods this is the one that is the most frequent.

The general factors affecting the river floods are: the intensity and the duration of the rainfall, the possibility of rivers and steams to let pass the rising waters, the condition of the land surface – soil and vegetation, topography and others. The river floods occur at the higher scale of rainfall system, where the permeability capabilities of the multitude of smaller tributaries are gradually filled up and the water peak is usually gradually collected and transported to the larger river.

These floods can be divided into two groups, depending on the form of the water-collection area and the length of the river:

  • The first group includes floods occurring in lengthy rivers /Nile, Danube, Euphrates, Mississippi, Rhine, and others.
  • The second group includes floods occurring in rivers with round shape of the water-collection basin /Congo/.

The lengthy rivers flow through flat terrain and the water movement speed is low. The same applies for the occurrence of a flood, the water peak is reached very slowly and afterwards it fades down very slowly over the course of few days to few weeks. Usually the reason for the flood is intensive and prolonged rainfalls occurring in other regions, often in other countries. The situation becomes even more complex when the heavy rainfall continues along the river. These floods can be predicted, they are usually of seasonal character and this allows establishing a proper organization to decrease the consequences.

In the case of rivers with round water-collection basin, after heavy rainfall the water peak reaches its highest value quickly and quickly decreases. Such floods usually happen in small and average sized rivers. Usually they are much more destructive because the water moves with higher speed. 

The above examples refer to smaller rivers with similar characteristics.