Fluvial incision and channel downcutting as a response to Late-glacial andEarly Holocene climate change: the lower reach of the River Meuse (Maas), The Netherlands

Detailed fieldwork and new extensive C-14 dating of residual channel infill ings provide data for the reconstruction of the Late-glacial channel downcu tting and incision history of the Venlo-Boxmeer lower reach of the River Me use (= Maas) in the southern Netherlands. Within a period of 500-1300 yr af ter Late-glacial climatic amelioration, the Meuse responded to increased di scharges and decreased sediment supply by adjusting the width/depth ratio o f its channels. Two main phases of channel downcutting are followed by two main phases of floodplain lowering and narrowing, indicating net floodplain degradation by the fluvial system as a non-linear response to Late-glacial and Early Holocene climate change. Some 1300 yr after initial late-glacial warming, channels downcut rapidly d uring the Early Belling (13.3-12.5 kyr BP) and adopted a high-sinuosity mea ndering style. Channel downcutting paused around 11.9 kyr BP, possibly in r esponse to rising groundwater levels and/or the Older Dryas cooling event. Between 11.9 and 11.3 kyr BP a new floodplain was formed. Then, lateral ero sion look place and initialed a first phase of 2.6 m floodplain lowering du ring the Late Allerod. Gradual climate deterioration during the Allerod pro gressively broke up soils and vegetation cover, from 11.3 to 10.9 kyr BP. T he Meuse gradually adjusted to an increased ratio of sediment supply over t ransport capacity through higher width/depth ratios. Main channels became s hallower and adopted a low-sinuosity pattern, finally culminating in a brai ded river system during the Younger Dryas. The final Holocene warming resul ted, within 500 yr, in renewed rapid channel downcutting by a single low-si nuosity channel during the Early Preboreal, followed by a second phase of 1 .8-2.8 m floodplain lowering. Copyright (C) 1999 John Wiley & Sons, Ltd.