Mikołaj Karpiński

Bedform characteristics in natural and regulated channels: A comparative field study on the Wilga River, Poland

This paper presents results of a field investigation conducted to examine the bed sediment, riverbed morphology and flow structure over dunes in natural and regulated channels. Field measurements using an acoustic Doppler current profiler (ADCP) have been carried out on two parts of lowland Wilga River in Poland. It is shown that the bedforms with a low angle of lee side develop more frequently than asymmetrical dunes with high lee-side angles, which are mostly associated with the occurrence of local scours and river meanders. Wavenumber analysis of bed elevation confirms the existence of scaling region in the longitudinal wavenumber spectrum, with “−3” scaling exponents for the natural and regulated channels as well. Moreover, the results of flow velocity field are presented in the form of a 2-D streamwise-vertical vector field, showing several similarities to previous laboratory and field investigations conducted on much deeper rivers than the Wilga. The experimental campaign and methods used to obtain the results are also presented briefly. In addition, a short database of fluvial dunes statistics is provided.

Diffusion of bedload particles in open-channel flows: distribution of travel times and second-order statistics of particle trajectories

The motion of bedload particles is diffusive and occurs within at least three scale ranges: local, intermediate and global, each of which with a distinctly different diffusion regime. However, these regimes, extensions of the scale ranges and boundaries between them remain to be better defined and quantified. These issues are explored using a Lagrangian model of saltating grains over the uniform fixed bed. The model combines deterministic particle motion dynamics with stochastic characteristics such as probability distributions of step lengths and resting times. Specifically, it is proposed that a memoryless exponential distribution is an appropriate model for the distribution of rest periods while the probability that a particle stops after a current jump follows a binomial distribution, which is a distribution with lack of memory as well. These distributions are incorporated in the deterministic Lagrangian model of saltating grains and extensive numerical simulations are conducted for the identification of the diffusive behavior of particles at different time scales. Based on the simulations and physical considerations, the local, intermediate, and global scale ranges are quantified and the transitions from one range to another are studied for a spectrum of motion parameters. The obtained results demonstrate that two different time scales should be considered for parameterization of diffusive behavior within intermediate and global scale ranges and for defining the local–intermediate and intermediate–global boundaries. The simulations highlight the importance of the distributions of the step lengths and resting times for the identification of the boundaries (or transition intervals) between the scale ranges.

Application of Lattice Boltzmann Method for Generation of Flow Velocity Field Over River Bed-Forms

In this chapter a Lattice Boltzmann Method (LBM) was presented as a relatively simple tool for generation of flow velocity field over river sand waves. The special attention was paid to the way of discretization of the presented equations. The choice of this method was conditioned by its advantages for modeling of complex geometries. Moreover, the computations with use of this method are easy to parallelize in contrast to the widely used models. The numerical results were compared with the available laboratory data and a reasonable agreement was found among the mean fluid velocity over the stoss, crest and trough of the considered fixed, triangular dune.

Discharge Measurements in Lowland Rivers: Field Comparison Between an Electromagnetic Open Channel Flow Meter (EOCFM) and an Acoustic Doppler Current Profiler (ADCP)

Field tests were carried out on two lowland rivers in Poland, namely Narew and Wilga, both being right tributaries of the Vistula River, in order to compare the results of flow velocity and discharge measurements. Both measurements were completed with the use of an acoustic Doppler current profiler (ADCP RiverSurveyor S5) manufactured by SonTek and an electromagnetic open channel flow meter (model 801) manufactured by Valeport. Narew is one of Europe’s few anastomosing and vegetated rivers. The field measurements were done in the central part of the Narew National Park. By contrast, Wilga is mostly a sandy and meandering river, and the measurements were carried out on the regulated channel that is part of the river. In both cases, field tests in each cross-section were made using both methods. The chapter mostly focuses on the potential errors and differences in the measurements of flow velocity and discharge resulting from: (1) the existence of vegetation on the river bottom; (2) the influence of obstacles such as islands or large fluvial dunes above the measuring cross-section; and (3) the quantity of measuring profiles and measuring execution time for the method using the electromagnetic flow meter. For the latter method a simple but accurate procedure, which is also briefly presented in the chapter, was applied to obtain the flow discharge. It is shown that the differences in the measured values of the flow discharge are from 12 to 35 %, depending on the method of measurement, the nature of the river and flow conditions. The findings of this study may be a suitable tutorial material for education in hydrology, civil engineering and environmental hydraulics.

On the effect of the window size on the assessment of particle diffusion

ABSTRACT In this work the decrease in the number of particles due to decrease in the size of the detection window on particle diffusion is investigated with the use of a numerical model of saltating grains. In order to formulate the problem, the available experimental data of particle diffusion are presented and discussed. Five different detection window sizes are investigated, showing that in both transverse and longitudinal directions the calculated dispersion of the particles noticeably decreases with the decrease in the window size. This highlights the “window” effect on the calculated variance of particle positions. The results indicate that the interpretation of the experimental data may be biased due to the “window” effect leading to potentially false conclusions about the regime of the diffusion of particles.

Dissolved Oxygen in Rivers: Concepts and Measuring Techniques

This chapter presents the basic concepts of methods and techniques used in the measurement of dissolved oxygen in flowing water. Based on field tests carried out on the Narew, Świder and Vistula Rivers, sensor performance was analysed. The results show that the comparability of sensors depends not only on their accuracy, but also on the hydrological conditions under measurement, as well as the duration of measurement and sensor location. For diel measurement, the time delay between the maximum temperature and minimum oxygen concentration is acknowledged and briefly discussed. Moreover, in contrast to other studies, the main attention has been focused on abiotic factors that affect oxygen conditions in rivers. Finally, the key research challenges are highlighted.

Characteristics of Flow Around Aquatic Plants in Natural Conditions: Experimental Setup, Challenges and Difficulties

Measurements of a 3D flow velocity field were conducted in lowland sandy bed river in Poland in two experiments during summer to check reliability of data gathered with the new model of Acoustic Doppler Velocimeter (Vectrino Profiler) in proximity of aquatic plants. For the purpose of this study a platform was built, on which two such velocimeters were mounted. This allowed for simultaneous measurements of flow velocity in front of and behind a single patch of submerged aquatic plants. Despite the promising readings from the first measurements, the results showed unexpected shapes in mean velocity profiles. The second experiment showed good agreement of signals from both devices, but it also revealed major differences in data quality compared with the first experiment. Further analysis showed that only few of all cells from each 35-cells section, which were simultaneously recorded by Vectrino, contained data with good characteristics of signal. The main results of this study showed that use of the Vectrino Profiler in natural conditions requires each time different setup, more densely stacked sections in each profile and constant changes of velocity range during the experiment to achieve best results.

Bed Topography and Discharge Measurements in the Świderskie Islands Nature Reserve, River Vistula, Poland

Field tests were carried out at a section of the River Vistula located within the boundaries of the Świderskie Islands nature reserve in order to analyse bathymetric changes at different discharge values during the period of 2012–2014. The paper shows that the dynamics and transport of sand-waves and sandbanks strongly influence the bathymetry of the riverbed at the selected cross-sections. Moreover, the impact of groynes on the bed topography is briefly discussed. Discharge measurements completed with the use of an acoustic Doppler current profiler (ADCP RiverSurveyor S5, SonTek) are also presented. Results support the values given by the Institute of Meteorology and Water Management (IMGW) at the gauging station in Gusin (461 km from the source) solely for the mean water levels. It is shown that the differences between measured values and values given by IMGW of the flow discharge ranged from 3 to 30 % of measuring values depending on the water level and discharge itself. The findings of this study may provide essential tutorial material for education in hydrology, civil engineering and environmental hydraulics as they emphasize large uncertainties inherent in hydrological modelling resulting from high dynamics of the bedload transport process.