Lagrangian Observations and Modeling of Turbulence Along a Tidally Influenced River

Abstract

Turbulence has a pronounced effect on many aspects (erosion, deposition, vertical mixing, and flocculation) of sediment transport in estuaries and coastal waters, and many coastal management projects rely on the ability to accurately predict the dispersal and settling of such particles, which are mainly governed by the settling velocity. For cohesive sediments, flocculation (i.e., the aggregation of particles) adds substantial complexity to modeling by altering the size, composition and hence settling velocity of particles over time. Flocculation has been shown to be largely affected by turbulent shear, among other factors (e.g., Kumar et al., 2010;Manning & Dyer, 1999;Winterwerp, 1998). Therefore, robust numerical model predictions of the structure of turbulence within the water column are required as a first step for modeling of flocculation and cohesive sediment transport.Turbulence can be described over multiple lengthscales in riverine environments: horizontally (width of the river channel), vertically (depth of the channel) and over the Kolmogorov microscale λ K , that is, the smallest turbulent eddies (Yokosi, 1967). Studies on flows within riverine environments have shown the importance of meander bends, and particularly the effects of their curvature and amplitude (e.g.

Predicting near-term, out-of-sample fish passage, guidance, and movement across diverse river environments by cognitively relating momentary behavioral decisions to multiscale memories of past hydrodynamic experiences

“…A "passive" particle that is neutrally buoyant and massless will follow the water flowline and provides a means to conceptualize and mathematically determine the contribution of physical water flow to an entity's movement (displacement) in a river. The movement of a simulated passive particle, however, depends inherently on the accuracy and spatiotemporal resolution of the available water flow data (Déjeans et al, 2022). Therefore, determining an entity's volitional movement behavior (which equals the measured total movement minus what a passive particle would do) depends also on the accuracy and spatiotemporal resolution of the available water flow data.…”

Measurement of Near-Surface Current Shear Using a Lagrangian Platform and Its Implication on Microplastic Dispersion

“…This approach aids in studying the immediate effects of wind-induced surface currents on a localized scale. Lagrangian drifters have been utilized to deduce surface currents [24,25], and Lagrangian observational platforms fitted with ADCPs have been employed to probe turbulence measurements [26,27]. A wave glider equipped with an ADCP has also demonstrated its proficiency as a platform for profiling near-surface currents.…”