![]() ![]() Knowledge of the long-term geomorphological dynamics of wetlands is limited, so currently there is an inadequate scientific basis for assessing anthropogenically induced changes and for developing conservation, remediation, and/or sustainable management guidelines for these fragile ecosystems. Identification of the geological controls on meander and wetland formation provides information vital for the design of effective management guidelines for these ecologically rich habitats, and also contributes to a better understanding of rivers that are intermediate between fully alluvial and fully bedrock. In the longer term (greater than tens of thousands of years), however, vertical erosion will occur in the sandstone valleys as the downstream dolerites are lowered by erosion, resulting in channel incision, floodplain abandonment, and desiccation of the wetlands. The thickness of alluvial fill in the sandstone valleys is limited (<4 m), but the resultant meanders are naturally dynamic, with processes such as point bar deposition, cutoff formation and channel avulsion resulting in an assemblage of fluvial landforms. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. In these valleys, the river meanders (sinuosity up to ∼1♷5) on moderate gradients (0♰03), the river follows a much straighter course (sinuosity ∼1♱0–1♳4), and floodplains are restricted in width.Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. ![]() ![]() ![]() Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Results show the value of a combined modelling approach to automate the stochastic generation of facies distributions constrained by seismic interpretations.Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. We introduce a workflow to demonstrate how these two methods can be applied in combination to predict fluvial meander-belt facies distributions, using a subsurface dataset on a Pleistocene succession from the Gulf of Thailand where abandoned channels are visible on seismic time slices, but for which bar-accretion geometries and the exact timing of channel abandonment are unclear. With reference to case-study examples, we review, discuss and employ two of these methods: (i) ChaRMigS generates possible scenarios for channel evolution and meander cutoffs by a reverse migration process (ii) PB-SAND is a forward stratigraphic model which simulates fluvial point-bar geometry and facies distributions from known palaeo-channel geometries. Different methods exist to model such accumulated successions present in the subsurface by integrating knowledge of system evolutionary behaviour and geometries visible on seismic time or stratal slices. The sedimentary record of meandering rivers contains a diverse and complex set of lithological heterogeneities, which impact natural resource management. ![]()
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