Transport and Mixing at River Confluences

• Applicant: Alexander Sukhodolov, Ph.D.
• Subject Area: Hydrogeology, Hydrology, Limnology, Urban Water Management, Water Chemistry, Integrated Water Resources Management ; Geotechnics, Hydraulic Engineering
• Term: from 2014 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 255884283

River confluences - locations where rivers join one another - are fundamental components of natural drainage networks.Differences in the topography, geology, soils, and land use of watersheds within a drainage network produce differences in conservative properties of river flows and in the materials transported by these flows. These different flows and flow constituents are brought together at confluences, leading to river mixing.Although the fluvial dynamics of confluences have been studied intensively over the past several decades, the role that confluences play in mixing of conservative tracers, suspended sediment, and bed-material sediment has not been examined comprehensively and is still incompletely understood.The proposed research is motivated by this lack of understanding and aims to provide a transformational improvement in knowledge of lateral mixing at and immediately downstream of river confluences through a combination of field experiments designed to evaluate mixing under semi-controlled conditions,field investigations undertaken to assess mixing in the context of hydrological and morphological variability, and three-dimensional numerical modeling based on fundamental physical principles of flow and mass transport.The proposed studies will aim at the direct assessment of mixing and transport processes concomitantly with the controlling factorsin order to better understand the role of streamwise oriented vertical cells and turbulent coherent structures in those processes. The obtained data sets will facilitate development of quantitative theoretical models which will describe formation of those cells and their interactions with the large-scale riverbed morphology including the effect of bed discordance on the streamwise oriented vertical cells. The effects of riverbed roughness and spatial inhomogeneity in pressure distribution will be also explored by carrying out the quantitative assessment of experimental results on confluence dynamics with conventional hydrodynamic models with the outcome that mixing rates will be directly linked to the conventional hydrodynamics characteristics such as turbulent eddy viscosity and bulk flow parameters. The field studies of this research will be performed at the international field research station Tagliamento and on the confluences of rivers Ledra and Oder-Neisse, and Spree. Eddy resolving numerical simulations will expand a range and resolution of the experimental parametric space and will deliver a refined knowledge on the mixing and transport processes which will then be used to expand theory of fluvial processes. The results of the proposed research will have numerous practical outcomes because they will allow better prediction of transport and mixing of pollutants, sediments, and biological substances in fluvial systems.

• DFG Programme: Research Grants