Abflussbahn

Abflussbahn is a hydrological term that describes the path along which surface runoff travels from its source areas across a catchment toward rivers or streams. It represents the network of overland flow routes through which rainfall water moves before entering the drainage system or, in some cases, directly reaches stream channels.

The formation and evolution of an Abflussbahn depend on terrain morphology, land cover, surface roughness, and soil infiltration characteristics. Runoff can initiate by infiltration-excess processes (Hortonian overland flow) on dry soils with high rainfall intensity, or by saturation-excess processes on already moist soils. Once runoff begins, it tends to concentrate along slope shadows, depressions, and existing microtopography, progressively forming concentrated flow paths, rills, and eventually larger channels. The Abflussbahn is not fixed; it changes with rainfall patterns, antecedent moisture, vegetation, and land use, leading to dynamic routing of water through the landscape.

In modeling and analysis, the Abflussbahn can be treated as a network or a set of potential flow paths rather than a single fixed line. It can be derived from high-resolution topography, remote sensing, or tracer measurements and integrated into distributed or semi-distributed hydrological models to simulate runoff generation, routing, and delivery to the drainage system.

Applications of understanding Abflussbahnen include flood forecasting, assessment of erosion and sediment transport, water quality studies, and land-use planning. The concept emphasizes how landscape structure controls where and how quickly rainfall becomes surface runoff on its way to streams.