Unterläufe

Unterlauf is a geographic term describing the downstream portion of a river, from the end of the middle course to the river’s mouth. In plural form Unterläufe refers to the lower reaches of one or more rivers or to the lower stretches within a river’s basin.

In the Unterlauf, gradients are typically gentler than in upper courses, yielding slower flow, greater sediment deposition, and broader floodplains. The channel often shifts laterally, forming meanders; in some rivers the lower course shows braided patterns during floods. Sediment deposition can create levees, back swamps, and splay deposits; tidal influence and estuarine conditions may occur in the terminal stretch.

Hydrological and ecological importance: The Unterlauf controls flood dynamics, nutrient transport, and habitat connectivity. Human interventions such as river regulation, embankments, dredging, and navigation channels have significantly altered the natural morphology of many Unterläufe.

In German geography, the river profile is commonly described as Oberlauf, Mittellauf, and Unterlauf. The term Unterlauf is not tied to a specific distance but to the relative position within the river's course. In hydrological literature, Unterläufe may also refer to the lower reaches of tributaries within a drainage basin.