Abstract
Numerical models of fine sediment transport depend on different approaches to parameterize the erosion properties of surficial sediment strata. These properties, namely the critical shear stress for erosion and the erosion rate coefficient, are crucial for reproducing the short-term and long-term sediment dynamics of the system. Methods to parameterize these properties involve either specialized laboratory measurements on sediment samples or optimization by model calibration. Based on observations of regular patterns in the variation of suspended sediment concentrations (SSC) over the tidal cycle in a small, narrow estuary, an alternate approach, referred to as the entrainment flux method, for quantifying the erosion properties of surficial bed strata is formulated and applied. The results of this method are shown to be analogous to the erosion data used to formulate the standard linear erosion formulation developed by various authors. The erosion properties inferred from the entrainment flux method are also compared to direct measurements of erodibility on sediment samples from the same site using the Gust microcosm apparatus. The favorable comparison of the two approaches suggests that the entrainment flux method can be used to infer and quantify the erodibility of surficial sediment strata in similar small and narrow estuaries. This method has certain advantages, chiefly its ease of implementation and the fact that it uses SSC time series which would typically be expected to be available for the study of or for model application at a given site. Guidelines for selecting the appropriate dataset for the application of the method are also presented.
Highlights
Fine sediment transport in aquatic systems is a subject of considerable study and interest from environmental and commercial perspectives
1 Moffatt & Nichol, 529 5th Ave, New York, NY 10017, USA 2 Delft University of Technology, Delft, The Netherlands 3 Department of Civil Engineering and Geosciences, Delft University of Technology, PO Box 5048, 2600 GA Delft, The Netherlands 4 Deltares, Delft, The Netherlands has certain advantages, its ease of implementation and the fact that it uses suspended sediment concentrations (SSC) time series which would typically be expected to be available for the study of or for model application at a given site
In the case of stations 5 and 9, the critical shear stress reaches 0.4 Pa at depths
Summary
Fine sediment (generally defined as clays and silts with particle diameters less than 63 μm) transport in aquatic systems is a subject of considerable study and interest from environmental and commercial perspectives. The transport processes for fine sediments involve advection and dispersion in the water column and the bed-water exchange processes of erosion and deposition. The former bed-water exchange process represents the mobilization of sediments from the bed followed by entrainment into the water column, and the latter process represents the settling of suspended sediment through the water column followed by deposition onto the bed surface. This paper focuses on the erosion dynamics of fine sediments. Erosion of fine sediments in the natural environment occurs under the action of shear stresses imposed at the bed-water interface by waves and currents. Erosion can be distinguished into four different modes, roughly in increasing order with respect to the magnitude of shear stress responsible and the resulting erosion rate: floc erosion, surface erosion, mass erosion, and liquefaction
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