The formation of alluvial fans and young floodplain deposits in the Lieser catchment, Eifel Mountains, western German Uplands: A study of soil erosion budgeting

Abstract

This study deals with the exploration and spatiotemporal quantification of the young Holocene, nearly skeleton-free floodplain sediments of the Lieser River, a tributary of the Mosel River in the Eifel Mts. The deposits are primarily a consequence of anthropogenic-triggered soil erosion in the catchment. To observe the phenomenon of corresponding soil erosion on multiple levels two small alluvial fans of tributary catchments were investigated. For comparison, one location in the neighboring Salm valley was described. The results were compared with those of other streams. With extensive fieldwork more than 100 drillings and pits were made at 12 locations. For dating the sediments OSL dating, 14C dating of organic contents and archaeological artifacts were used. In the floodplains of the Lieser and its tributaries, 35.1 × 106 t of overbank fines are stored. To achieve this, an average soil erosion of 61.4 mm in the whole catchment would have been necessary. About 28% of young floodplain sediments in upper and lower course were deposited before ad 1000. However, prehistoric deposits could not be positively proven. Only 18% of floodplain sediments were deposited between ad 1000 and 1320 (early and high Middle Ages) and 54% during late Middle Ages and early Modern Time (ad 1320–1850), respectively. The thickness of floodplain sediments is mostly independent of the valley gradient. The largest sediment thickness (> 5 m) was found by drilling in the upper reaches. However, a part of this could be dated to the early Holocene. In the narrow middle reaches, the maximum thickness of the skeleton-free deposits was only 1.2–2 m. The average thickness of the floodplain sediments rose again in the depression of Wittlich up to 2.4 m. The formation of the investigated small fans was quite different. Sedimentation occurred within limited periods as a result of single events.