Channel evolution processes in a diamictic glacier foreland. Implications on downstream sediment supply: Case study Pasterze/Austria

Abstract. Global warming and glacier retreat are affecting the morphodynamics of proglacial rivers. In response to changing hydrology, their altered hydraulics will significantly impact future glacifluvial erosion and proglacial channel development. This study analysis proglacial channel evolution processes at the foreland of Austria’s biggest glacier Pasterze by predicted runoff until 2050. A high-resolution digital elevation model was created by an unmanned aerial vehicle, channel bathymetry was sampled, a one-dimensional hydrodynamic-numerical model was generated, and bedload transport formulas were used to calculate the predicted transport capacity of the proglacial river. Due to the fine sediment composition near the glacier terminus (d₅₀ < 49.6 mm), the calculation results underline the process of headward erosion in the still unaffected, recently deglaciated river section. In contrast, an armor layer is already partly established by the coarse grain size distribution in the already incised river section (d₅₀ > 201 mm). Furthermore, already occurring exposed non-fluvial grain sizes combined with decreasing flow competence in the long term are indicators for erosion-resistant pavement layer formation and landform decoupling in the vertical direction. The presented study clearly shows that subsystems of ‘developed channels’ exhibiting pavement formation of non-fluvial deposits are found at the investigated glacier foreland. Thus, an extension accompanied by a refinement of the fluvial system in the sediment cascade approach was developed as a central result.