Sándor Baranya

Acoustic mapping velocimetry

Knowledge of sediment dynamics in rivers is of great importance for various practical purposes. Despite its high relevance in riverine environment processes, the monitoring of sediment rates remains a major and challenging task for both suspended and bed load estimation. While the measurement of suspended load is currently an active area of testing with nonintrusive technologies (optical and acoustic), bed load measurement does not mark a similar progress. This paper describes an innovative combination of measurement techniques and analysis protocols that establishes the proof-of-concept for a promising technique, labeled herein Acoustic Mapping Velocimetry (AMV). The technique estimates bed load rates in rivers developing bed forms using a nonintrusive measurements approach. The raw information for AMV is collected with acoustic multibeam technology that in turn provides maps of the bathymetry over longitudinal swaths. As long as the acoustic maps can be acquired relatively quickly and the repetition rate for the mapping is commensurate with the movement of the bed forms, successive acoustic maps capture the progression of the bed form movement. Two-dimensional velocity maps associated with the bed form migration are obtained by implementing algorithms typically used in particle image velocimetry to acoustic maps converted in gray-level images. Furthermore, use of the obtained acoustic and velocity maps in conjunction with analytical formulations (e.g., Exner equation) enables estimation of multidirectional bed load rates over the whole imaged area. This paper presents a validation study of the AMV technique using a set of laboratory experiments.

Estimation of Suspended Sediment Concentrations with Adcp in Danube River

Abstract An estimation procedure for suspended sediment concentrations based on the intensity of backscattered sound of acoustic Doppler current profilers (ADCP) is introduced in this paper. Based on detailed moving and fixed boat ADCP measurements with concurrent sediment sampling, we have successfully calibrated the estimation method for a reach of River Danube in Hungary, characterized by significant suspended sediment transport. The effect of measurement uncertainty and various data filtering on sediment load determination is also analyzed and quantified. Some of the physical model parameters describing the propagation of sound in water are estimated based on known empirical formulas, while other parameters are derived from measured. Regression analysis is used to obtain a relationship between the intensity of backscattered sound and sediment concentrations. The empirical relationship has been then used to estimate the suspended sediment concentrations from the ADCP data collected in fixed and moving boat measurement operation mode, along verticals and path-lines, respectively. We show that while some measurement uncertainty is inherent to the acoustic Doppler principle, it is further enhanced by the complexity of the near-bottom sediment-laden flow. This uncertainty has then a significant effect on the local sediment load estimation. In turn, reasonable smoothing of raw velocity and backscatter intensity data shows insignificant impact on cross-sectional sediment load estimation.

Three-dimensional RANS modeling of flow around circular piers using nested grids

Abstract The paper introduces a three-dimensional numerical model that solves the Reynolds Averaged Navier-Stokes (RANS) equations on a curvilinear grid system using a novel nested grid approach. The main benefit of the model is the possibility to model locally complex hydraulic features in large rivers like the flow field at hydraulic structures. The entire study domain in such a case can be discretized with a coarser resolution, whereas a much finer resolution can be applied to a defined zone of the obstructions, where a detailed description of the flow field is needed. The model is tested on a laboratory experiment carried out at the Georgia Institute of Technology, where the flow field around a single and two double circular cylinders in a flatbed flume was studied. Simulated flow velocity, turbulent kinetic energy and bed shear stress distributions are in good agreement with measurements. However, deviations downstream of the piers indicate the limitation of the steady state description of the flow in the unstable wake zone. Nevertheless, the nested grid approach presented herein is a promising step towards the modeling of the local scouring phenomenon due to the relatively low computational demand.

A Shear Reynolds Number Based Method to Assess the Locally Dominant Sediment Transport Modes in Large Rivers with Complex Morphodynamics

The aim of this study is to introduce a method which can suggest if sand or gravel 11 dominated bed load transport presents in rivers with mixed-size bed material. As a conventional 12 way, the Shields-Parker diagram could be used for such purposes, however, the method has certain 13 applicability limits, due to the fact that it is based on uniform bed material and provides information 14 rather on river-scale, instead of reach or local scale. When dealing with large rivers with spatially 15 complex hydrodynamics and morphodynamics the bed load transport modes can also indicate 16 spatially strong variation even locally, which calls for a more suitable approach to estimate the 17 locally unique behavior of the sediment transport. Here, we suggest that the decision criteria utilizes 18 the shear Reynolds number (Re*), which can be estimated based on the local characteristic bed grain 19 size (e.g. d50) and local bed shear stress ( ). The method was verified against field and laboratory 20 measurement data, both performed at non-uniform bed material compositions. The comparative 21 assessment of the results by the novel method and the one suggested by the Shields-Parker diagram 22 highlights that the Shields-Parker diagram might be applied with care due to its high uncertainty 23 when the hydro-morphological conditions are complex. In contrast, the results show that the shear 24 Reynolds number based method is expected to predict the sand or gravel transport domination with 25 a <5% uncertainty. The introduced results can greatly contribute to the improvement of numerical 26 sediment transport modeling as well as to the field implementation of bed load transport 27 measurements. 28

Habitat mapping of riverine fish by means of hydromorphological tools: Habitat mapping of riverine fish by means of hydromorphological tools

Department of Hydraulic and Water Resources Engineering, Budapest University of Technology and Economics, Budapest, Hungary MTA‐BME Water Management Research Group, Budapest, Hungary MTA Centre for Ecological Research, Danube Research Institute, Budapest, Hungary Duna‐Ipoly National Park Directorate, Budapest, Hungary MTA Centre for Ecological Research, Balaton Limnological Institute, Tihany, Hungary Correspondence Sándor Baranya, Budapest University of Technology and Economics, Department of Hydraulic and Water Resources Engineering, Műegyetem rkp. 3, Budapest 1111, Hungary. Email: baranya.sandor@epito.bme.hu

Complex hydro- and sediment dynamics survey of two critical reaches on the Hungarian part of river Danube

Detailed hydrodynamic survey of two critical river reaches has been performed from hydro- and sediment dynamics points of view, in order to explore the main features, moreover, provide calibration and verification data to related 3D flow and sediment transport modelling. Special attention has been paid to compare moving and fix boat measurement modes for estimating various flow and large-scale bed form features, resulting in recommendations e.g. on the time period needed in stationary mode operation to obtain sufficiently stabilized average velocity profiles and related parameter estimations. As to the study reaches, the first comprises a 5 km long sandy-gravel bed reach of river Danube located in Central-Hungary, presenting problems for navigation. As a conventional remedy, groyne fields have been implemented to make and maintain the reach sufficiently deep, navigable even in low flow periods. As is usually the case, these works resulted in rather complex flow characteristics and related bed topography at places. The second site is another 5 km long reach of river Danube, close to the southern border to Serbia. There the river presents navigational problems similar to the previously mentioned reach, however, having entirely sand bed conditions, abundant in a variety of dunes, especially in the shallower parts. In both study reaches ADCP measurements were done with around 2.5 Hz sampling frequency both in moving boat operation mode providing overall, though locally moderately representative picture, and in fixed boat mode at a considerable number of selected verticals with 10 minutes long measuring time.