Integration of shelf evolution and river basin models to simulate Holocene sediment dynamics of the Humber Estuary during periods of sea-level change and variations in catchment sediment supply
Three modelling elements and sedimentary evidence provide an understanding of sediment characteristics, river basin processes, tidal regimes and sea-level changes to explain sediment supply to the Humber Estuary through the Holocene (the last 10,000 years). An upscaled cellular catchment model simulates water and sediment fluxes from river basins, illustrating significant variations in response to climate change, especially precipitation and vegetation changes, principally deforestation. Much of the sediment mobilised remains in stores within the catchment and only a small fraction reaches the Humber tidal system. An empirical model helps to explain sediment erosion, transport and deposition from the offshore and coastal zones through the Holocene and sea-level rise caused the transgression of the continental shelf of the North Sea. Comparison with the sediment fill of the lowlands around of the Humber estuary, that represent the extent of the estuary during the Holocene, demonstrates that most of the fill (approximately 95-98%) was derived from non-fluvial sources. A shelf evolution model, with reconstructions of sea level, palaeogeography and palaeobathymetry for 1,000 year time steps through the Holocene predicts significant changes in tidal regimes, first over wide areas of the coast as the transgression of the continental shelf progresses. The most significant changes occur with the inner reaches of the palaeo-estuaries, especially those of the Humber and the Fenland. Throughout the mid-Holocene they are characterised by significantly lower tidal ranges (MWHST approximately 2.5 m less than present) and low tidal currents. The simulated patterns of tidal currents concur with the transport of fine grain sediment from the coastal zone into the estuaries. The major tidal range changes revise estimates of late Holocene and ongoing relative sea and land level changes.