Theoretical and numerical considerations of rivers in a tectonically inactive foreland

[摘要] Modeling the dynamics of alluvial rivers is theoretically and numericallymore challenging than modeling erosion of bedrock channels in activemountain ranges. As a consequence, the majority of the approaches developed in thecontext of alluvial rivers are one-dimensional. However, recent advances in thenumerics of fluvial landform evolution models allow for two-dimensional simulationsof erosion and sediment transport over time spans of several million years.This study aims atfinding out fundamental properties of rivers in a tectonicallyinactive foreland of a mountain range by investigating a simplereference scenario theoretically and numerically. This scenario consistsof a mountain rangeand a foreland in a quasi-steady state wherein the material erodedin the mountain range is routed through the foreland. In order tounderstand the properties of foreland rivers, a subdivision intotwo classes – carriers and redistributors – is introduced.Carriers originate in the mountain range and are thus responsiblefor the large-scale sediment transport to the ocean. In turn,redistributors are rivers whose entire catchment is locatedin the foreland. Using the concept of carriers and redistributors,it is shown that the drainage network in the foreland permanentlyreorganizes so that a steady state in the strict sense is impossible.However, the longitudinal profiles of carriers are described well bya steady-state approximation. Their concavity index is considerablygreater than that of rivers in the mountain range. Carrierspredominantly deposit sediment at high rates, while redistributorserode at much lower rates. Despite the low erosion rates,the sediment flux fromredistributors into carriers is a major component of the overall sedimentbudget and finally the main driver of the highly dynamic behavior ofthe carriers.

[学科分类] 土壤学