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1
Content available remote Wavelet Characteristics of Hydrological and Dissolved Oxygen Time Series in a Lowland River
Rajwa-Kuligiewicz A., Bialik R. J., Rowiński P. M.
Acta Geophysica
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2016
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Vol. 64, no. 3
649--669
EN
In this study, we investigated the temporal variability of dissolved oxygen and water temperature in conjunction with water level fluctuations and river discharge in the Narew lowland river reach. For this purpose, high resolution hydrologic and water quality time series have been used. Spectral analyses of time series using continuous wavelet transform scheme have been applied in order to identify characteristic scales, its duration, and localisation in time. The results of wavelet analysis have shown a great number of periodicities in time series at the inter-annual time scale when compared to the classical Fourier analysis. Additionally, wavelet coherence revealed the complex nature of the relationship between dissolved oxygen and hydrological variables dependent on the scale and localisation in time. Hence, the results presented in this paper may provide an alternative representation to a frequency analysis of time series.
2
Content available remote Flow Characteristics over a Gravel Bedform: Kaj River Case Study
Maddahi M. R., Afzalimehr H., Rowiński P. M.
Acta Geophysica
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2016
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Vol. 64, no. 5
1779--1796
EN
The present study deals with the turbulence structure in order to better understand the interaction of bedform and flow characteristics in a gravel-bed river. Data measured above a bedform is used to analyze the importance of coherent structures in turbulent transfer. The Reynolds stress and turbulence intensity in stream-wise direction illustrate significant difference along the bedform, showing a three-layer distribution at the crest and a convex one at the downstream of bedform. Quadrant analysis technique is used to picture momentum exchange above the considered bedform and to find the dominant event in bursting process of the gravel bedform. Quadrant analysis demonstrates that the mechanisms of bedforms generation in sand and gravel-bed rivers are similar and sweep is the dominant event in both rivers.
3
Content available remote Application of one-dimensional model to calculate water velocity distributions over elastic elements simulating Canadian waterweed plants (Elodea Canadensis)
Kubrak E., Kubrak J., Rowiński P.M.
Acta Geophysica
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2013
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Vol. 61, no. 1
194--210
EN
One-dimensional model for vertical profiles of longitudinal velocities in open-channel flows is verified against laboratory data obtained in an open channel with artificial plan ts. Those plants simulate Canadian waterweed which in nature usually fo rms dense stands that reach all the way to the water surface. The model works particularly well for densely spaced plants.
4
Content available remote Scenarios of the spread of a waste heat discharge in a river — Vistula River case study
Kalinowska M.B., Rowiński P.M., Kubrak J., Mirosław-Świątek D.
Acta Geophysica
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2012
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Vol. 60, no. 1
214-231
EN
The problem of two-dimensional mathematical modelling of heated cooling water discharges into running waters is considered in the paper. Two models — one for the evaluation of 2D turbulent velocity field and the other, developed by authors of the study, for 2D heat transport in open-channels — were used in the calculations. Relevant scenarios of the spread of heated water discharged from a designed gas-stem power plant to be constructed at the Vistula River were presented. Environmentally most friendly variant of the discharge of the thermal pollution was selected from among four various variants.
5
Content available remote Influence of a method of evaluation of the curvature of flexible vegetation elements on vertical distributions of flow velocities
Kubrak E., Kubrak J., Rowiński P.M.
Acta Geophysica
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2012
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Vol. 60, no. 4
1098-1119
EN
Methods of computing the deflections of flexible vegetation elements under the dynamic pressure of water were presented in the paper. Two methods, based on Euler–Bernoulli beam theory, were discussed, one designed for small deflections and the other, generalized one, also for larger deflections. The choice of the method for computations of deflections was discussed from the perspective of the computation of flow velocities above flexible vegetation. Computational results were compared with laboratory experiments and it was found that the simplified, computationally less expensive method may be used in many practical situations without deterioration of the results.
6
Content available remote Influence of selected fluorescent dyes on small aquatic organisms
Rowiński P.M., Chrzanowski M.M.
Acta Geophysica
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2011
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Vol. 59, no. 1
91-109
EN
Rhodamine B and Rhodamine WT are fluorescent dyes commonly used as tracers in hydrological investigations. Since introducing intensely red substances into rivers raises understandable doubts of ecological nature, the authors aimed at examining the influence of these dyes on small water fauna using bioindication methods. Quantitative results, calculated with the use of Bliss-Weber probit statistical method, were achieved by means of standardized ecotoxicological tests containing ready-to-hatch resting forms of fairy shrimp (Thamnocephalus platyurus). Qualitative studies included observation of water flea crustacean (Daphnia magna) and horned planorbis snail (Planorbis corneus), both typically present in rivers and representative for temperate climate, as well as guppy fish (Poecilla reticulata), paramecium protozoan (Paramaecium caudatum) and the above-mentioned fairy shrimp. The investigation revealed that both dyes in concentrations used for hydrological purposes are low enough to exert almost no toxic impact on water fauna considered.
7
Content available Shear Stress Statistics in a Compound Channel Flow
Czernuszenko W., Rowiński P. M.
Archives of Hydro-Engineering and Environmental Mechanics
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2008
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Vol. 55, nr 1-2
3-27
EN
The results of comprehensive measurements of three-dimensional turbulent velocities carried out in a laboratory compound channel are presented. Tests were performed in a two-stage channel with a smooth main channel bed consisting of concrete and rough floodplains and sloping banks. Instantaneous velocities were measured with the use of a three-component acoustic Doppler velocimeter. The main aim of the study is the recognition of structure of Reynolds stresses in turbulent open channel flows. Particular attention has been paid to bursting events such as ejections and sweeps. The bursting phenomenon occurs originally near the buffer layer and then shows a coherent or organized flow structure during its convection process. The probability density distributions of the turbulent velocities were measured at different distances from the bed in the main channel and also above the inclined walls. In the main channel, the lateral turbulent velocity is seen to follow the normal Gaussian distribution more closely than the remaining two components. Above the inclined walls, all distributions turned out to have greater skewness. The probability density distributions of correlations between velocity fluctuations were also calculated. These distributions have long tails and sharp peaks and fit the theoretical distributions very well. The structure of instantaneous Reynolds stresses was analyzed by a quadrant technique with an arbitrarily chosen threshold level. It has been shown that the largest contribution to turbulent stresses comes from the second quadrant (ejection) and the fourth quadrant (sweep). The basic temporal characteristics for quadrant events, like the average and maximum time for a zero hole size, have been determined in the study. Calculations of maximum duration times for all events reveal that times are greater for even quadrants than for odd quadrants.
8
Content available Measurements of 3D turbulence structure in a compound channel
Czernuszenko W., Kozioł A., Rowiński P. M.
Archives of Hydro-Engineering and Environmental Mechanics
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2007
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Vol. 54, nr 1
55-73
EN
The paper describes some turbulence measurements carried out in an experimental compound channel with flood plains. The surface of the main channel bed was smooth and made of concrete, whereas the floodplains and sloping banks were covered by cement mortar composed with terrazzo. Instantaneous velocities were measured be means of a three-component acoustic Doppler velocity meter (ADV) manufactured by Sontek Inc. This article presents the results of measurements of primary velocity, the distribution of turbulent intensities, Reynolds stresses, autocorrelation functions, turbulent scales, as well as the energy spectra.
9
Content available remote Truncation errors of selected finite-difference methods for two-dimensional advection-diffusion equation with mixed derivatives
Kalinowska M.B., Rowiński P.M.
Acta Geophysica
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2007
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Vol. 55, no. 1
107-118
EN
The spread of a passive contaminant in an open-channel reach is considered with use of a two-dimensional advection-diffusion equation with the included offdiagonal dispersion coefficients. This paper presents the calculation of truncation errors, namely numerical diffusion and numerical dispersion for various finite difference schemes. The accuracy of the considered finite-difference approximations is analysed by deriving and studying the relevant modified partial differential equation.
10
Content available Properties of a streamwise turbulent flow field in an open two-stage channel
Rowiński P. M., Czernuszenko W., Kozioł A. P., Kubrak J.
Archives of Hydro-Engineering and Environmental Mechanics
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2002
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Vol. 49, nr 2
37-57
EN
The results of the experimental studies, aimed at the recognition of the streamwise turbulent structure in a compound channel, are reported in this paper. Three sets of measurements with electromagnetic liquid velocity meter were used: one in a smooth channel, one with the rough overbank channels and the last one with the modelled high vegetation occurring on floodplains. The analyses included vertical distributions of local mean velocities, depth-averaged mean velocities, bed shear stresses, turbulent intensities, higher order velocity moments, autocorrelation and velocity spectra. Relevant turbulent temporal and spatial scales were evaluated. All the properties were investigated with special emphasis placed on the influence of roughness on them.
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