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Abstract

Time-variable mass bodies with mostly linear geometry, such as the regulated rivers in central Europe, yield effects on the local gravitational potential and acceleration. Currently, observation methods are limited. Permanent gravimetry stations offer a high temporal resolution, yet only for point locations. Satellite gravity missions offer a high coverage, yet without the spatial resolution to monitor regional structures. In this study, we compute changes of the local gravitational field induced by hydrological changes through forward modelling. The effect of water change in the linear mass body can be discretized in mass elements. We model them in three different discretizations from highest to lowest level of detail: through tesseroids with time-variable heights, through piecewise line elements with time-variable line density, and through a mass point with time-variable total mass. The aim of this approach is to identify the most suitable approximation for this type of mass body on Earth and in satellite height. For the study area of Baden-Württemberg, Germany, we compute the gravitational effect of the changing Rhine level. We extract the Rhine shape as polygons from OpenStreetMap data and reprocess it to a grid with the spatial resolution 50m x 50m. After simplifications to the Rhine shape, we mutually compare the effects for the three levels of detail. Estimates of typical as well as extreme changes of Rhine level are taken from data of the German Wasserstraßen- und Schifffahrtsverwaltung des Bundes, provided by Bundesanstalt für Gewässerkunde to yield a realistic scenario.