Morphodynamics of alternate bars in the Alpine Rhine River: Methods for the applicability of mathematical models using felds observations

The process of formation and initial development of alternate bars in rivers has been studied since the 1950s and linear theories, based on perturbed solutions of the shallow water equation over an erodible bed, have been developed between the 1960s and the 1990s. Although these theories have received strong support from controlled laboratory experiments in their ability to predict bar formation conditions and morphological evolution, up to now feld data on the actual morphodynamics of alternate bars in channelized streams are relatively scarce. Constraints posed by the long time and spatial scales needed to observe alternate bar dynamics limited felds investigations and observations. This work aims to make a frst step in flling the gap between theoretical studies and feld observations of alternate bars morphodynamics in real rivers. It proposes a novel approach to the application of existing theories to compare their outcomes with feld observations on bar wavelength, migration and stability conditions. To this purpose, the study focuses on the Alpine Rhine River reach between Switzerland, Austria and Liechtenstein, an almost unique combination of a long channelized reach (>40 km, equivalent to 40-60 bar wavelengths) with almost uniform channel width and slope. 30 years of LANDSAT images and a hydrological dataset that covers more than 60 years provide ideal conditions to study the multi-decadal dynamics of alternate bars.