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The rate of deformation of the longitudinal profile for a period of half a century in the sediment flow and riverbed morphology has been assessed by comparison of the leveling survey data on the longitudinal profile of a number of lowland rivers in Russia. This problem remains relevant in both the theoretical and practical aspects, especially for rivers in which a range of in-stream mines occupies kilometers and tens of kilometers and they have operated for decades. The removal of a large amount of alluvial material from the sediment transport and changes in the riverbed morphometric characteristics have given impetus to the leveling process of the sediment transport capacity along the river due to scouring. The result is lowering of the bottom and water surface. The scouring reaches 3–8 cm in rate and spreads 400–700 m/yr along the river. Retrogressive erosion (headcutting) is well-defined, whereas progressive erosion is less pronounced, because it is partially replaced by the mechanical removal of alluvial material. Under these deformations, the longitudinal profile has changed from convex or straight to concave, and there are no signs of recovery over the past decades, despite the fact that the mining has been relatively moderate for the past 30 years or has been completed in the rivers under consideration. [ABSTRACT FROM AUTHOR]

Various models have recently been developed to describe Arctic coastal erosion. Current process-based models simulate multiple physical processes and combine them interactively to resemble the unique mechanism of Arctic coastal erosion. One limitation of such models is the difficulty of including hydrodynamic forces. The available coastal erosion models developed for warmer climates cannot be applied to Arctic coastal erosion, where permafrost is a significant environmental parameter. This paper explains a methodology that allows us to use the models designed for warmer climates to simulate Arctic coastal erosion. The open-source software XBeach is employed to simulate the waves, sediment transport and morphological changes. We developed different submodules for the processes unique to Arctic coasts, such as thawing–freezing, slumping, wave-cut niche, bluff failure, etc. The submodules are coupled with XBeach to enable concurrent simulation of the two mechanisms of Arctic coastal erosion, namely thermodenudation and thermoabrasion. Some of the model's input parameters are calibrated using field measurements from the Arctic coast of Kara Sea, Russia. The model is then validated by another set of mutually exclusive field measurements under different morphological conditions from the study area. The sensitivity analysis of the model indicates that nearshore waves are an important driver of erosion, and the inclusion of nearshore hydrodynamics and sediment transport are essential for accurately modelling the erosion mechanism. [ABSTRACT FROM AUTHOR]