Author(s): Elise Lifschiz; Martin Struck

Linked Author(s): Elise Lifschiz

Keywords: Granulometry; Sediment management; Waterways; River-bed armouring; Bed load nourishment

Abstract: The Rhine is Germany’s most important inland waterway and has been subject to substantial anthropogenic modifications along most of its length, influencing the river’s morphological and sedimentary regime. This contribution focuses on the free-flowing section of the German Upper Rhine, starting downstream of Iffezheim barrage in south-western Germany. Since the completion of the barrage in 1977, natural sediment supply from upstream is blocked. The resulting sediment deficit downstream is compensated by continuous bed load nourishment practices, with the overall aim to sustain river bed elevation along the free-flowing section of the Upper Rhine. This section is characterized by sets of groynes and connections to cut-off meanders, the latter resulting from former rectification measures. These and other characteristics affect the local hydraulics of the river and thus have the potential to cause changes in bed elevation and grain size distribution. To ensure safe shipping conditions, and to be able to prevent adverse developments, permanent monitoring of the system parameters is required. One of these parameters is river-bed granulometry, which can hint at morphological issues and sediment transport processes. To assess the state of the granulometric composition of the river bed, the German Federal Waterways Engineering and Research Institute (BAW), in cooperation with the Federal Waterways and Shipping Administration (WSV), conducted a spatially high-resolution sediment sampling campaign in 2019, as a continuation to the long-standing sampling tradition in this section. The campaign was carried out between Iffezheim and Mainz (~159 km), using a diving bell ship to collect a total of 840 samples from two defined depths of 102 cross sections, with an average spacing of less than two kilometres. In this contribution, the results of this campaign are presented. By means of specific examples it is shown, how knowledge about major spatial and temporal changes in granulometric composition provides insights into the combined effects of current bed load nourishment practices and local waterway particularities.

DOI: https://doi.org/10.3850/IAHR-39WC2521711920221470

Year: 2022