River Landscapes in the Dijle Catchment: From Natural to Anthropogenic Meandering Rivers

In this chapter the changing river landscapes in the Dijle catchment since the Late Glacial are discussed in terms of climatic and anthropogenic changes. Climatic changes in the Late Glacial triggered the incision of large meanders in Weichselian braided-river deposits in the downstream part of the study area, which still form one of the most prominent landforms in this region. During the early Holocene period, peat accumulation, which initiated in the now-abandoned meanders, characterized floodplains lacking a clearly defined river channel. The landscape was covered with a deciduous forest, while floodplains were mainly covered with an alder carr forest. Although agriculture started in the region in the Neolithic (~6200 cal BP), it is only from the Bronze Age onwards that anthropogenic deforestation on the hilly loess slopes caused an increase in soil erosion and sediment delivery. In the upstream part of the Dijle catchment, this resulted in accelerated floodplain sedimentation that halted peat growth and covered the Late Glacial landforms entirely. Rivers developed again a meandering channel pattern with much smaller amplitude compared to the Late Glacial meanders, whilst also levees and colluvial fans were formed. During the past 250 years, many of these channels were artificially or naturally cut off, and they remain visible in the current floodplain as oxbow lakes or shallow depressions. In this chapter we demonstrate how this evolution is the result of a change from a climate-dominated to a human-dominated fluvial landscape.