Turbulence in Rivers

The study of turbulence has always been a challenge for scientists working on geophysical flows. Turbulent flows are common in nature and have an important role in geophysical disciplines such as river morphology, landscape modeling, atmospheric dynamics and ocean currents. At present, new measurement and observation techniques suitable for fieldwork can be combined with laboratory and theoretical work to advance the understanding of river processes. Nevertheless, despite more than a century of attempts to correctly formalize turbulent flows, much still remains to be done by researchers and engineers working in hydraulics and fluid mechanics. In this contribution we introduce a general framework for the analysis of river turbulence. We revisit some findings and theoretical frameworks and provide a critical analysis of where the study of turbulence is important and how to include detailed information of this in the analysis of fluvial processes. We also provide a perspective of some general aspects that are essential for researchers/ practitioners addressing the subject for the first time. Furthermore, we show some results of interest to scientists and engineers working on river flows

Expériences d'écoulements dans un lit composé dont les plaines d'inondations s'élargissent

The paper presents an experimental investigation of the flow in a compound channel with symmetrically enlarging floodplains. These results complement previous work on symmetrically narrowing floodplains. Both these data enable a better understanding of the mass and momentum transfer occuring in non-prismatic compound channels, without facing the complexity of a fully meandering geometry. The new experiments show that, in this diverging geometry: (1) the flow expends on the floodplains with a significant shift in the downstream direction, with the discharge on the floodplains significantly lower than their conveyance capacity in a prismatic compound channel with the same cross-section; (2) the lateral distribution of velocities presents a large gradient from the interface between subsections to the floodplain lateral bank; and (3) in some large discharge cases, the flow behaves like a jet, with the maximum velocity filament oscillating from one main-channel bank side to the other, and recirculation zones developing on the floodplains

Pre-study of the hydraulic works for the Seine-Scheldt-East Project

peer reviewe

Méthode de calcul des écoulements non-uniformes en lit composé (i.e. après débordement)

This paper focuses on numerical modelling of non-uniform flows in prismatic and non-prismatic compound channels. A new 1D computation methodology is presented which is called Independent Subsections Method (ISM). While conventional 1D models solve the momentum or energy equation on the overall cross-section area, the ISM treats the flow dynamics in the main channel and the floodplains separately. It solves an ordinary differential equations system which calculates the water level and mean velocity in the floodplains and the main channel, simultaneously. This method accounts explicitly for lateral mass exchanges, interfacial shear stress and associated momentum transfer between subsections. ISM simulations of water level and subsection velocities are in agreement with experimental data for four different geometries: straight compound channel; slightly narrowing floodplains; abrupt floodplain contraction; and skewed floodplain boundaries