Backscattered intensity profiles from horizontal Acoustic Doppler Current Profilers

River engineeringInnovative field and laboratory instrumentatio

An estimation of gravel mobility over an alpine river gravel bar (Arc en Maurienne, France) using PIT-tag tracers

River morphodynamics and sediment transportRiver morphology and morphodynamic

Contrasted sediment processes and morphological adjustments in three successive cutoff meanders of the Danube Delta

Since the 1980s intensive anthropogenic disturbances have affected the channel of the St. George branch, the southern distributary of the Danube River. The meander cutoff programme since 1984–1988 induced different hydrosedimentary impacts on the local distribution of river flow velocities, discharge, and sediment fluxes between the former meanders and the man-made canals (Ichim and Radoane, 1986; Popa, 1997; Panin, 2003). This paper selects three large cutoff meander reaches of the St. George branch (the Mahmudia, Dunavăţ de Sus, and Dunavăţ de Josmeanders noted here asM1,M2, andM3, respectively) as an example to analyse the human impact in the Danube River delta. The diversion of the flow induces strong modifications by acceleration of the fluxes through the artificial canals combined with dramatically enhanced deposition in the former meander where it was observed in two cases (M1 and M3) with slight modifications in M2. An exceptional flood that occurred in April 2006 offered a good opportunity for scanning different cross sections of the meander systems. Bathymetry, flow velocity, suspended-load concentration, and liquid and solid discharge data were acquired throughout several cross sections of both natural channels and artificial canals of the three cutoffs, using acoustic Doppler current profiler (ADCP) technology, in order to investigate the distribution of the flowand sediment and its impact on the hydrosedimentary processes in each channelized reach and adjacent former meander. Therefore, the results obtained during the 2006 flood were referred to a long-term evolution (1970–2006), analysed by GIS techniques

Multi-solitary waves for the nonlinear Klein-Gordon equation

International audienceWe consider the nonlinear Klein-Gordon equation in $\R^d$. We call multi-solitary waves a solution behaving at large time as a sum of boosted standing waves. Our main result is the existence of such multi-solitary waves, provided the composing boosted standing waves are stable. It is obtained by solving the equation backward in time around a sequence of approximate multi-solitary waves and showing convergence to a solution with the desired property. The main ingredients of the proof are finite speed of propagation, variational characterizations of the profiles, modulation theory and energy estimates

Application de la méthode LSPIV pour la mesure de champs de vitesse et de débits de crue sur modèle réduit et en rivière

International audienceLSPIV technique enables the measurement of surface flow velocities using image sequence analysis. EDF and Irstea partnership made possible the development of Fudaa‑LSPIV freeware by DeltaCAD Company. Two software applications at flume and field scales are detailed: (i) bed shear stresses were calculated owing to LSPIV velocities, water depth and bathymetry for a physical model of the Old Rhine; (ii) the software was used to optimize the calculation parameters of LSPIV flood discharge measurement stations in Mediterranean rivers.La technique LSPIV (Large Scale Particle Image Velocimetry) permet de mesurer les vitesses de surface d'un écoulement par analyse de séquence d'images. Pour faciliter l'application opérationnelle de la méthode, un logiciel, Fudaa-LSPIV, a été développé par la société DeltaCAD dans le cadre d'une collaboration entre EDF et Irstea. Deux applications en laboratoire et en rivière sont présentées : (i) couplée avec des mesures de hauteur d'eau et de bathymétries, la LSPIV a permis d'estimer des paramètres de Shields sur le modèle physique à fond mobile du Vieux-Rhin ; (ii) le logiciel a été utilisé pour procéder à des analyses de sensibilité pour paramétrer ainsi au mieux les stations LSPIV de mesure de débit en crue de rivières cévenoles

Mesure acoustique des sédiments en suspension dans les rivières : impact potentiel des micro-bulles d'air?

Underwater Acoustics Conference and Exhibition 2017, Skiathos, GRC, 03-/09/2017 - 08/09/2017International audienceFollowing the success of Acoustic Doppler Current Profiler (ADCP) technology for measuring river discharge, there has been a growing interest in the last decade in extracting information on river suspended sediment fluxes from acoustic backscatter data. Despite the efforts to find a relationship between suspended sediment concentration (SSC) and backscatter, an inversion technique applicable to vertical river backscatter profiles is still missing. The theoretical and empirical bases of such techniques have been originally developed for ocean bottom suspended sediment monitoring. As a first step in our attempt to adapt these models to rivers, we measured the acoustic response of a usual glass beads suspension in a tank. Unsurprisingly, the acoustic model agrees quite well with the measurements as soon as the effect of air micro-bubbles is limited. As a second step, we deployed an acoustic backscatter profiler in the Rhône River (France) in very clear water conditions (SSC < 10 mg/l). The recorded acoustic intensities were stronger than expected at low frequency, suggesting that other scatters may contribute to the recorded echo. Typical river sediment suspensions are expected to produce weak backscatter signal, especially at common ADCP frequencies, due to small particle sizes (Rayleigh regime) and relatively low concentrations. In such conditions, the impact of air micro-bubbles - generally neglected at the bottom of the ocean - could be relevant in rivers. This preliminary work calls for further investigation to assess the potential impact of nonsediment scatterers on acoustic backscatter when trying to measure SSC with sonar technologies in rivers

Configuration mixing in 188^{188}Pb : band structure and electromagnetic properties

In the present paper, we carry out a detailed analysis of the presence and mixing of various families of collective bands in $^{188}$Pb. Making use of the interacting boson model, we construct a particular intermediate basis that can be associated with the unperturbed bands used in more phenomenological studies. We use the E2 decay to construct a set of collective bands and discuss in detail the B(E2)-values. We also perform an analysis of these theoretical results (Q, B(E2)) to deduce an intrinsic quadrupole moment and the associated quadrupole deformation parameter, using an axially deformed rotor model.Comment: submitted to pr

On the stability of standing waves of Klein-Gordon equations in a semiclassical regime

We investigate the orbital stability and instability of standing waves for two classes of Klein-Gordon equations in the semi-classical regime.Comment: 9 page

Morphodynamics of the exit of a cutoff meander: experimental findings from field and laboratory studies

The morphological evolution of the entrances and exits of abandoned river channels governs their hydrological connectivity. The study focusses on flow and sediment dynamics in the exit of a cut-off meander where the downstream entrance is still connected to the main channel, but the upstream entrance is closed. Two similar field and laboratory cases were investigated using innovative velocimetry techniques (acoustic Doppler profiling, image analysis). Laboratory experiments were conducted with a mobile-bed physical model of the Morava river (Slovakia). Field measurements were performed in the exit of the Port-Galland cut-off meander, Ain river (France). Both cases yielded consistent and complementary results from which a generic scheme for flow patterns and morphological evolution was derived. A simple analogy with flows in rectangular side cavities was used to explain the recirculating flow patterns which developed in the exit. A decelerating inflow deposits bedload in the downstream part of the cavity, while the upstream part is eroded by an accelerating outflow, leading to the retreat of the upstream bank. In the field, strong secondary currents were observed, especially in the inflow, which may enhance the scouring of the downstream corner of the cavity. Also, fine sediment deposits constituted a silt layer in a transitional zone, located between the mouth of the abandoned channel and the oxbow-lake within the cut-off meander. Attempts at morphological prediction should consider not only the flow and sediment conditions in the cavity, but also the dynamics of the main channel