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

Detailed fieldwork and new extensive ¹⁴C dating of residual channel infillings provide data for the reconstruction of the Late-glacial channel downcutting and incision history of the Venlo-Boxmeer lower reach of the River Meuse (= Maas) in the southern Netherlands. Within a period of 500-1300 yr after Late-glacial climatic amelioration, the Meuse responded to increased discharges and decreased sediment supply by adjusting the width/depth ratio of 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 during the Early Bolling (13.3-12.5 kyr BP) and adopted a high-sinuosity meandering style. Channel downcutting paused around 11.9 kyr BP, possibly in response 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 erosion took place and initiated a first phase of 2.6 m floodplain lowering during the Late Allerod. Gradual climate deterioration during the Allerod progressively broke up soils and vegetation cover, from 11.3 to 10.9 kyr BP. The Meuse gradually adjusted to an increased ratio of sediment supply over transport capacity through higher width/depth ratios. Main channels became shallower and adopted a low-sinuosity pattern, finally culminating in a braided river system during the Younger Dryas. The final Holocene warming resulted, within 500 yr, in renewed rapid channel downcutting by a single low-sinuosity channel during the Early Preboreal, followed by a second phase of 1.8-2.8 m floodplain lowering.