Channel Network Morphodynamics in the Lower Paraná Delta

Abstract

The La Plata Basin is the second largest drainage basin in South America. The Paraná River, the basin’s main river, discharges into the Río de la Plata estuary in Argentina. In the Lower Paraná Delta, near the deltaic front, a complex system of mostly natural and some man-made channels redistribute a part of the river flow. Like the river and the estuary, the channel network has been subject to sediment deposition, limiting the navigability needed for the small-scale transport of goods, leading to hindrance to tourism and other economic activities in the Lower Delta. Compared to the river system on the large scale, not much is known about the characteristics and the morphodynamic behaviour of the channel network. The objective of this research is to set a first step in providing insight on the relevant processes and human activities that influence morphology changes in the Lower Delta channel network.

Making use of existing data, a literature study and data obtained during several field surveys, various hypotheses were formulated. Hypotheses included the potential influence of land use change in the catchment and climate change related trends in precipitation patterns, climatic variability associated with El Niño Southern Oscillation, the effect of artificially deepening one of the two main branches of the Paraná River and the excavation of artificial channels in the Lower Delta in the early twentieth century. The effects of said processes and human activities are tested with a scenario-based hydrodynamic modelling study, making use of Delft3D Flexible Mesh with sediment transport and morphology modules.

Our analysis provided various insights in the behaviour of the Lower Delta channel network, and the influence of human activities and natural processes on this behaviour. A notable finding is that artificial deepening of the Paraná de Las Palmas by dredging its thalweg since 1990 has lead to a significant reduction in river flow entering channels supplied by the river branch and increased sedimentation rates in these channels. In addition, insight was gained on the spatial distribution of depositional and erosive patterns instigated by discharge and sediment input changes.

This research has provided a first, global insight into the relevant processes governing channel morphodynamics. Some of the findings can serve as input for future dredging strategies, as results imply that the current strategy has lead to limitations to the navigability of an intensively navigated part of the channel network. Furthermore, the outcome of this research can serve as a starting point for research on one of the specific topics covered by the hypotheses, including but not limited to the influence of storm surges, the effect of a potential spatial heterogeneity in soil composition and the influence of tidal divides on morphological features in the channel network.