Irenée Heyse

The Flemish Valley: Response of the Scheldt drainage system to climatic and glacio-eustatic oscillations

Beyond its focus on the climatic and eustatic controls of the Flemish Valley evolution, this chapter explores more broadly the Plio-Quaternary history of the Belgian part of the Scheldt basin, in which the Flemish Valley is essentially a buried incised-valley system that once drained the Scheldt area. The Scheldt is typically a lowland river flowing across a subdued hilly topography in its middle course and on the flat plain chiefly made of its own alluvial deposits in the lower course. We first describe the terraces located on the interfluves and valley sides of the Middle Scheldt region, providing also a tentative chronology of their development. Then, the morphology and the sedimentary infill of the Flemish Valley are described in relation to alternating erosional and aggradational episodes since the Saalian. The transition from stepped terraces to cut-and-fill processes at the Flemish Valley level is attributed to the waning of the tectonically driven uplift of the area during the Middle Pleistocene and the bedrock incision episode that lastly created the Flemish Valley is tentatively related to the base level fall induced by the catastrophic breaching of the Dover Strait dam during the Late Saalian. Finally, the Late Glacial and Holocene fate of the Flemish Valley is evoked, emphasizing the role of the Late Pleniglacial/Late Glacial coversand morphology in deflecting the river’s former NNW-striking course to the east and over Antwerp and pointing to the first impact of human activities on the Scheldt behaviour in the last third of the Holocene.