Impact of abandoned water mills on Central European foothills to lowland rivers: a reach scale example from the Wurm River, Germany

摘要

This case study evaluates the changes of riverscape morphology that are caused by the abandonment of three water mills in a typical Central European foothill to lowland river for the period of 1810 to 2012 by the example of a short segment of the Wurm River, Germany. Based on a multi-temporal geographic information system analysis of historical maps, historical cross profiles, and the up-to-date high-resolution LIDAR DEM (1m), different tendencies of changes in the longitudinal profile and alteration of the channel planform have been distinguished. The results indicate (a) a mutual adjustment to a local base level during the active mill period, (b)a period of terrace formation in the inset floodplain following the mill demise, and (c) a heterogeneous pattern of lateral channel changes at the mill in the center of the study segment. Two other abandoned mills influenced channel incision depth, change of riverbed slope, and terrace formation. The reconstruction of the former river courses reveals limits of the applicability of historical maps on the scale of small catchments (approximate to 350km(2)) or on the study sub-catchment scale (approximate to 85km(2)) as details like channel width or the exact positions of river bends are documented imprecise. Furthermore, we determine factors that superimpose the geomorphological evidence by controlling discharge and affecting sediment availability, which is caused by the adjacent urban area of Aachen city in the headwater and the suburban area surrounding the study segment.