Influence of Grain Arrangement on Particle Mobility and Patterns of Variability Between Gravel Bed Rivers

Plain Language Summary: The way that gravel is arranged on the bed of river influences how much flow is required to move the gravels. This is important in channel management, because it gives insight into the sensitivity of a river to future change. However, the arrangement of channel bed material and its effect on bed stability is not well understood, because river gravels vary in size and shape, which also influence the arrangement of gravels on the bed, as well as their mobility. The arrangement of gravels also changes through time as grains are moved in response to different histories of flood and low‐flow periods. This study collects grain‐scale surface models from 45 river reaches across England and Wales to evaluate the variability of grain arrangement, and compares the force needed to move gravels with different shapes and structures. River beds with individual grains that are similar sizes, heights and orientations generally require more force to move. This can help to better predict the likelihood of channel bed change using easy‐to‐collect observations from the field.