Author(s): Dennis Oberrecht; Andreas Wurpts
Linked Author(s):
Keywords: No Keywords
Abstract: Fluid mud can have an important impact on the ecological state of estuaries and is found in turbidity zones of many of them (extreme cases e. g. Ems estuary, Gironde estuary, Jiaojiang estuary). Fluid mud is a fluid mixture of clay, silt and organic matter with a complex settling behavior, like flocculation, hindered settling, and consolidation. Observed suspended sediment concentration rates easily exceed the 8-12 g/l threshold, where hindered settling starts to dominate the behavior and reaches values up to several hundreds of grams per liter. Furthermore, fluid mud exhibits non-Newtonian characteristics with rheological properties like thixotropic, shear-thinning, yield stress and time dependent matrix strain behavior. This leads to the formation of distinct fluid mud layers and makes modeling investigations very complex. This is one of the reasons for mainly neglecting fluid mud during modeling studies of such water bodies. The present study shows a new and advanced continuous modeling approach, which implements the aforementioned behavior of fluid mud. The numerical model is validated by long-term measurements of water level elevation and suspended sediment concentrations along the turbidity zone of the Ems estuary (northern Germany). It is shown, that the existing fluid mud layers in the Ems estuary which are of several meters thickness close to a dynamic equilibrium, which then strongly damps the flood dominant sediment transport pattern even at moderate discharge conditions. This has an important overall effect regarding the morphological dynamics of the entire estuary. The results strengthen, that the complex fluid mud behavior must be considered when modeling estuarine environments with fluid mud in order to get a reliable base for estuarine management decisions.
Year: 2018