Characteristics
The watershed is not a clearly defined divide. Tectonics, especially in the area that is now the Upper Rhine Plain, created the River Rhine. As its headward erosion is much stronger than that of the much older River Danube (see the upper river geology) (due to the Rhine’s gravity on its much shorter way to the North Sea), the Rhine and its tributaries intrude deeper into phreatic zones of the Swabian Karst and even capture the upper Danube and its surface tributaries.
It is expected that the Danube's upper course will one day disappear entirely in favour of the Rhine ("stream capture").
Read more about this topic: European Watershed