The Late Quaternary surface processes of a steep gully system in Central Europe occur mainly as multiple gully erosion and sedimentation cycles. These cycles depend largely on the relation between sediment supply and sediment transport capacity. The gully thalweg was aggraded during the Younger Dryas as a result of high sediment supply from the slopes and a diminished transport capacity in the channel instigated by a reduction in vegetation during this time. For the majority of the Holocene time period, phases of headward gully incision are the dominant process, which occurred as a result of internal hydrological and geomorphic thresholds under well-vegetated conditions. During this time sediment was also deposited on the gully fan.

The onset of intense human agricultural activity during medieval times led to large scale slope erosion due to vegetation removal and subsequent thalweg re-aggradation. In comparison with the natural hillslope sediment flux during the Younger Dryas, erosion from human driven slope instability was found to be at least ~2.3 times more efficient. More specifically, it is clear that different land use techniques on the catchment slopes, as reconstructed from the analysis of soil charcoal analysis, are the dominant control on overall hillslope erosion rates. The lowest erosion rate was found in an area where only small agricultural fields were maintained. The recovery of most of the catchment vegetation in the last ~500 years has re-stabilised the slopes and modified the internal threshold of sediment supply/sediment transport capacity, such that the gully has begun a new incision phase. Hence, sediment is again transported from the thalweg into the gully fan and floodplain of the adjacent trunk stream.

The quantification of sediment fluxes reveals that the most recent and continuing phase of sediment export is also the most geomorphically significant for the trunk stream, since it is the only time in the last ~15 000 years that a large percentage of the thalweg erosion budget is able to be incorporated into the alluvium of trunk streams. Because the gully system itself has a large storage capacity, sediment delivery from small headwater catchments to trunk streams generally does not occur until vegetation has re-stabilised the slopes, and allows sediment transport capacity to increase. The recent changes to high sediment delivery to the floodplain and adjacent streams are a possible explanation for the observed floodplain aggradation of trunk streams and the resulting changes of the river regime. However, it is also suggested that valley bottom damming for various purposes throughout this time is also a major factor controlling this large change in river behavior. The investigation of this direct human impact on the river landscapes of Central Europe remains a critical avenue of further research.

Dissertation available on:
http://eldiss.uni-kiel.de/macau/receive/dissertation_diss_00007685