Functional Relationships between Critical Erosion Thresholds of Fine Reservoir Sediments and Their Sedimentological Characteristics

Abstract

This study investigated multivariate relationships between critical erosion thresholds of reservoir sediments and their physicochemical and biological characteristics to unravel the effect of sedimentological parameters on fine sediment erosion. We collected 22 sediment cores from the deposits of two reservoirs located in southern Germany, Grosser Brombachsee (GBS), and Schwarzenbachtalsperre (SBT). An erosion flume and an advanced photogrammetric method were used to quantify critical erosion thresholds for a succession of vertical layers over sediment depth. The functional relationships between the critical erosion thresholds and a collection of sediment parameters including bulk density, sediment composition, percentiles, cation exchange capacity, organic content, extracellular polymeric substances (EPS proteins and carbohydrates), and chlorophyll-a were examined. The clay-dominated sediments of the GBS with comparatively low total organic carbon and sand content were, on average, 10 times more stable than the sandy sediments of the SBT. Consequently, for the clay-dominated sediments, strong positive correlations were found between the erosion thresholds and clay content. In contrast, the sandy sediment layers experienced strong positive correlations with the sand content and percentiles. The bulk density was mainly positively correlated, and the total organic carbon content was mainly negatively correlated, with the erosion thresholds. Furthermore, EPS and chlorophyll-a were not good indicators for the erosion thresholds, suggesting an ambiguous influence of biology. Generally, the strength of the relations decreased for sediment layers deeper than 10 cm. Overall, our results underline the need to investigate the influence of sediment characteristics on fine sediment erodibility from varying natural environments.