Ricardo N. Szupiany

Multi-frequency acoustics for suspended sediment studies: an application in the Parana River

A method of using two acoustic Doppler current profilers operating at different frequencies and employed at the same measuring vertical to sample a profile of suspended sediment concentration has been previously applied in the Parana River (Argentina) but has not been validated by direct sediment samples. The present work fills this gap by reporting new field data and comparing them with acoustically inferred sediment concentrations. The agreement between directly measured sediment concentrations and grain sizes with corresponding estimates from an employed backscatter model was found to be good (squared correlation coefficients are 0.9 and 0.8, and mean deviations are 14 and 6%, respectively). The interrelations between flow velocity and suspended sediment concentration at fixed locations and in a moving mode along a river cross-section have been also investigated. Observed events of bed sediment re-suspension were found to be highly correlated with fluctuations of the vertical flow velocity, with a 100–150s quasi-periodicity. The size of re-suspension plumes was increasing from the channel thalweg to the low-submerged bar areas.

Estimation of Concentration and Load of Suspended Bed Sediment in a Large River by Means of Acoustic Doppler Technology

Fil: Latosinski, Francisco Guillermo. Universidad Nacional del Litoral. Facultad de Ingenieria y Ciencias Hidricas. Departamento de Hidraulica; Argentina. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe; Argentina

The role of discharge variability in determining alluvial stratigraphy

We illustrate the potential for using physics-based modeling to link alluvial stratigraphy to large river morphology and dynamics. Model simulations, validated using ground penetrating radar data from the Rio Parana, Argentina, demonstrate a strong relationship between bar-scale set thickness and channel depth, which applies across a wide range of river patterns and bar types. We show that hydrologic regime, indexed by discharge variability and flood duration, exerts a first-order influence on morphodynamics and hence bar set thickness, and that planform morphology alone may be a misleading variable for interpreting deposits. Indeed, our results illustrate that rivers evolving under contrasting hydrologic regimes may have very similar morphology, yet be characterized by marked differences in stratigraphy. This realization represents an important limitation on the application of established theory that links river topography to alluvial deposits, and highlights the need to obtain field evidence of discharge variability when developing paleoenvironmental reconstructions. Model simulations demonstrate the potential for deriving such evidence using metrics of paleocurrent variance.

Parana River morphodynamics in the context of climate change

ABSTRACT This paper presents an analysis of the sediment dynamics that takes place at different scales within the Middle and the Lower Parana River in the La Plata Basin. The aim of this study is to provide a multi-disciplinary and multi-scale approach for the prediction of river future morphology in the context of climate change, the intended use of which is the prognosis of river morphodynamics’ long-term impact on manmade structures and activities over or near the river. The study is based on three levels of mathematical modelling, with the output of wider-scale models providing the input conditions for more specific ones. Climate models give the input ensemble, i.e. future precipitation and temperature over La Plata Basin. The semi-distributed macroscale variable infiltration capacity hydrological model simulates the flow discharge time series that are applied to an own-developed 1D morphodynamic model. The 1D model simulates future rate of sediment transport and corresponding bed-level changes at watershed scale and provides the boundary conditions for a 2D model. Therefore, streamflow divagations at channel scale are simulated by means of the MIKE21C code developed by the Danish Hydraulic Institute. The analysis indicates a rather low sensitivity of the Parana River bed profile, i.e. 1D morphology, to the increase predicted in flow discharge, whereas the streamflow appreciably divagates. In particular, surpassing an upper bound in the most frequent discharge appears effective in driving the actual bifurcated morphology into a meandering-multithread configuration.

Flow structure at a confluence: experimental data and the bluff body analogy

ABSTRACT An experimental characterization of the hydrodynamics of a mixing interface at an open channel confluence is presented. In the laboratory experiments, both a confluence and a cylinder set-up were studied in order to validate the bluff body analogy, which has been proposed to characterize the mixing interface. The experimental characterization included flow visualization and the computation of the mean flow field, time scales of the coherent structures, and turbulent kinetic energy. The comparison among the two configurations confirms the validity of the analogy as similar features were found for the mean flow field and time scales of the coherent structures. However, differences in the length of the stagnation zone, the flow velocity deficit, and the turbulence intensity were observed. These differences should be taken into account when the bluff body analogy is used to characterize the confluence hydrodynamics and to quantify the mixing at the confluence interface.

Hydrodynamics and sediment transport in an estuary with an abrupt depth step

ABSTRACT The hydrodynamic patterns resulting from the combination of tide flow, riverine discharge and bathymetry and their effects on water circulation and sediment transport are studied to assess the impact of geomorphic changes in the Quequén Grande River estuary (Buenos Aires, Argentina). A depth step located at about 2 km from the sea, created by dredging to provide favourable navigational conditions in the harbour, induces different flow patterns in the deeper and shallow estuarine parts, creating an attractive system to study. The main purpose of this paper is to report key physical features of this water system and the results of detailed longitudinal and transverse measurements of velocity and backscatter intensity. The data reveal the selective settling of suspended sediments in the harbour and a net loss of sediments to the sea. The effects of local severe storms that cause an intense tidal intrusion and mixing as well as a stronger ebb flow and seiches are also described.

Linking hydro‐morphology with invertebrate ecology in diverse morphological units of a large river‐floodplain system

Fil: Blettler, Martin Cesar Maria. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Conicet - Santa Fe. Instituto Nacional de Limnologia. Universidad Nacional del Litoral. Instituto Nacional de Limnologia; Argentina