Morphodynamics of supercritical flow in a linked river and delta system, Daihai Lake, Northern China

AbstractHistorically, the occurrence of Froude supercritical flow and preservation of its deposits was considered rare in natural systems. Over recent years, a growing body of evidence indicates that Froude supercritical flow is a significant formative flow across the terrestrial and marine landscapes, and responsible for much of the sedimentary record from rivers to deepwater systems. This riverbank, trench, ground penetrating radar and modern riverbed dataset from the Bantanzi stream in the Daihai Lake basin, northern China, documents a linked river and delta succession dominated by sedimentary structures formed by supercritical flow. This study links the sedimentary structures in river deposits to modern bedforms in the dry riverbed, and discusses how the sedimentary structures and the supercritical flow morphodynamics change from the river to the delta front. In addition to well‐known decimetre to metre‐scale sedimentary structures produced by supercritical flow in the river deposits, centimetre‐scale sedimentary structures were found on the delta front that were quantitatively linked to deposition from cyclic step migration, utilizing a theoretical framework. This work further documents two types of clinoform geometries in delta foresets. One of these clinoform geometries is consistent with deltaic processes controlled by hydraulic jumps at the river mouth, and the other with hydraulic jumps at the base of delta foresets. Comparison with flume experiments and quantitative assessment show that ephemeral rivers, like the Bantanzi stream, are likely to produce supercritical flow also on their delta fronts, and link the supercritical flow occurrences to the highly seasonal and intense monsoon precipitation in this semi‐arid region. This work sheds light on current fundamental understanding of sediment transport and deposition processes from river to delta and highlights the effect of cyclic steps in these processes.