Surficial sediment erodibility from time-series measurements of suspended sediment concentrations: development and validation

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.

Seasonal, Spring‐Neap, and Tidal Variation in Cohesive Sediment Transport Parameters in Estuarine Shallows

“…Data were filtered to include the accelerating portions of flood and ebb only, to ignore periods when deposition occurred (Maa & Kim, ; Mathew & Winterwerp, ), and we removed τ bcw during tidal periods when wave energy grew large, u br >0.05 m/s, to remove the immediate effect of wave‐enhanced resuspension. We computed m and τ crit (with 95% confidence intervals) for 7‐day periods overlapping at 2‐day intervals throughout the deployment.…”

“…Fine sediment erosion occurs when shear stresses from currents and waves suspend particles at the sediment-water interface into the water column. While several formulas have been developed to predict erosion rate (Grabowski et al, 2011), a simplified form (equation 2), known as Type II erosion, applies well when erosion magnitude does not vary with eroded sediment depth (e.g., Mathew & Winterwerp, 2017;Sanford & Maa, 2001).…”

Dynamics and kinematics of an estuarine network

“…Tides within the estuarine network are largely semidiurnal, with a mean range of 1.5 m (Mathew & Winterwerp, 2017). Tidal velocity and water level are 90 degrees out of phase within Newark Bay (Chant et al, 2011).…”

Why and How Do We Study Sediment Transport? Focus on Coastal Zones and Ongoing Methods

“…While classical instrumentation is improving as well (see, e.g., [295] for bedload measurements), more accurate formulations are proposed to account for various mechanisms such as, for example, recently: the bedload grain size distribution [121]; the alternative approach, referred to as the "entrainment flux method" for quantifying the erosion properties of surficial sediments [173]; the integration of multiple classes in 3D models [296]; or new probabilistic formulations for bedload [297]. New types of models are developed, tested and evaluated on simple configurations to improve knowledge of basic mechanisms at a fine scale, e.g., direct numerical simulation of bedform evolution and/or sediment transport [298,299], emerging methods of smoothed particle hydrodynamics for fluid-flow interaction [194].…”

“…Resuspension of the fluff layer is another kind of hydrosedimentary process over mixed sediment which needs to be better known and quantified [172,173].…”