Field and Numerical Investigation of Transport Mechanisms in a Surface Storage Zone

Abstract

In‐stream surface storage zones (SSZs) caused by lateral recirculation areas play a significant role in the transport and fate of contaminants in rivers. Lateral recirculating areas have long residence times that favor nutrient uptake, accumulation of pollutants, and interactions with reactive sediments. In watersheds affected by acid‐mine drainage, SSZs have profound effects on biogeochemical processes, controlling the local concentration and distribution of toxic elements along the channel. Despite the importance of turbulent flow dynamics on these processes, limited work has been carried out to analyze mass transport in natural SSZs with complex geometries. In this investigation we study a SSZ in the Lluta River, located in a high‐altitude environment in northern Chile, by coupling field measurements and 3‐D numerical simulations to understand the transport mechanisms with the main channel. We measure the velocity field using an acoustic Doppler velocimeter (ADV) and large‐scale particle image velocimetry (LSPIV), extracting the bathymetry from digital image processing. Using these data, we perform detached‐eddy simulations (DES) to analyze the mean flow, turbulence statistics, and the dynamics of large‐scale coherent structures. From this detailed description of the turbulent flow, we study the mass exchange and the time evolution of the mean concentration of a passive scalar in the SSZ by testing three upscaled models: a classical linear transport model, a two‐storage formulation, and a fractional transport model. The analysis integrates temporal and spatial scales to provide a new perspective on the turbulent flow in SSZs and their effects on global mass transport in rivers.

Seiches in lateral cavities with simplified planform geometry: Oscillation modes and synchronization with the vortex shedding

“…The natural cavities play a major role in water ecology as they constitute favorable sites for fauna and flora developments. The supply of dissolved and suspended substances to the cavity, such as nutrients, gazes, and pollutants (Sanjou et al, 2018;Sandoval et al, 2019), occurs by mass transfer across the mixing layer at the interface between the cavity and the main stream. Besides, the fluvial and coastal harbors are major infrastructures for navigation and commercial activities, for which continuity of operations is crucial for the economy.…”

Riverine macrophytes control seasonal nutrient uptake via both physical and biological pathways

“…We assumed that the solute exchange rate between mobile and immobile zones (Λ, /s) was first-order, which implies that solute residence times are approximately exponential in the mobile zone. Sandoval et al, 2019). Such a truncated power law is quite flexible in the range of behaviours it can represent, including the compound influences of a hierarchy of exponential zones (e.g.…”

“…Willmann et al, 2008), which have been shown to exist in streams and rivers (e.g. Sandoval et al, 2019). To minimise model degrees of freedom, we fixed the power-law slope (β = 0.75) and allowed V, D, Λ, and τ T to freely vary.…”

Mean residence time of lagoons in shallow vegetated floodplains

“…The flow past a lagoon (deep zone) creates a shear layer at the interface between the flow and the deep zone which is characterized by the highest transport of momentum. In low aspect depth ratios, a main vortex dominates the flow (Jackson et al, 2013; Ouro et al, 2020; Sandoval & Mignot, 2019), while in high aspect depth ratios other secondary rotating structures can be formed. The secondary vortex is reported to increase the residence time of the flow within the deep zone (Jackson et al, 2013).…”