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Start Over Creator Velísková, Yvetta

2. An approximate method for 1-D simulation of pollution transport in streams with dead zones

Creator:
Sokáč, Marek, Velísková, Yvetta, and Gualtieri, Carlo
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
environmental hydraulics, river pollution, hydrodynamic dispersion, longitudinal dispersion, and dead zones
Language:
Slovak
Description:
Analytical solutions describing the 1D substance transport in streams have many limitations and factors, which determine their accuracy. One of the very important factors is the presence of the transient storage (dead zones), that deform the concentration distribution of the transported substance. For better adaptation to such real conditions, a simple 1D approximation method is presented in this paper. The proposed approximate method is based on the asymmetric probability distribution (Gumbel’s distribution) and was verified on three streams in southern Slovakia. Tracer experiments on these streams confirmed the presence of dead zones to various extents, depending mainly on the vegetation extent in each stream. Statistical evaluation confirms that the proposed method approximates the measured concentrations significantly better than methods based upon the Gaussian distribution. The results achieved by this novel method are also comparable with the solution of the 1D advection-diffusion equation (ADE), whereas the proposed method is faster and easier to apply and thus suitable for iterative (inverse) tasks.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

3. CFD simulation of flow behind overflooded obstacle

Creator:
Velísková, Yvetta, Chára, Zdeněk, Schügerl, Radoslav, and Dulovičová, Renáta
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
velocity profile, computational fluid dynamics (CFD), free surface flow, bridge, ADV, laboratory flume, numerical simulation, and RANS models
Language:
Slovak
Description:
This paper deals with studying of two topics – measuring of velocity profile deformation behind a over-flooded construction and modelling of this velocity profile deformation by computational fluid dynamics (CFD). Numerical simulations with an unsteady RANS models - Standard k-ε, Realizable k-ε, Standard k-ω and Reynolds stress models (ANSYS Fluent v.18) and experimental measurements in a laboratory flume (using ADV) were performed. Results of both approaches showed and affirmed presence of velocity profile deformation behind the obstacle, but some discrepancies between the measured and simulated values were also observed. With increasing distance from the obstacle, the differences between the simulation and the measured data increase and the results of the numerical models are no longer usable.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

4. Change of Žitný Ostrov channel network aggradation state

Creator:
Dulovičová, Renáta and Velísková, Yvetta
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
Rye Island, bed silts, channel network, field measurement, Žitný Ostrov, dnové nánosy, kanálová sieť, and terénne merania
Language:
Slovak
Description:
The channel network at this region was built up for drainage and also to provide irrigation water. The water level in the whole channel network system affect groundwater level and viceverse. From the view of mutual interaction between channel network and groundwater it has been necessary to assess impact of channel network silting on this interaction. The measurements of thickness of silts along three main channels were carried out in 1993. Then in 2004 there were done measurements in selected profiles along three channels: Aszód, Gabčíkovo-Topoľníky and Komárňanský channel. The paper shows changes in measured thickness and volume of silt in particular channels. It was shown the channel silting up has not been changed significantly during the monitored period. This fact is documented by graphical presentation of silt thicknesses of channels. The differences between silt top and channel bottom levels are presented. and Obsahom príspevku je hodnotenie zmien stavu kanálovej siete Žitného Ostrova z hľadiska zanesenia kanálov dnovými nánosmi v období rokov 1993 až 2004. Kanálová sieť bola vybudovaná v tomto regióne v priebehu 19. storočia jednak na čiastočné odvodnenie územia a zároveň na zabezpečenie závlah. Hladina vody v kanáloch ovplyvňuje výšku hladiny podzemnej vody v ich okolí a naopak. Z hľadiska procesu vzájomnej interakcie kanálovej siete s okolitou podzemnou vodou je nevyhnutné venovať pozornosť vplyvu zanášania kanálov dnovými nánosmi, keďže tieto môžu v značnej miere tento proces ovplyvňovať. V roku 1993 boli merané zanesenia kanálovej siete ŽO na vopred stanovených priečnych profiloch niektorých hlavných kanálov. V priebehu rokov 2004 boli vykonané kontrolné merania zanesenia vo vybraných profiloch kanálov Aszód, Gabčíkovo-Topoľníky a Komárňanského kanála. Tieto kontrolné merania sa robili vždy v úseku na začiatku, v strede a na konci jednotlivých kanálov, pretože sa uvažovalo s predpokladom lineárnych zmien hrúbok nánosov pozdĺž kanálov. Grafickými prílohami príspevok dokumentuje skutočnosť, že v priebehu sledovaného obdobia nedošlo k podstatným zmenám zanesenia kanálovej siete. Keďže pre účely príspevku sú dôležité hrúbky nánosov (teda rozdiely medzi dnom kanála a vrchom nánosovej vrstvy), bolo postačujúce, aby kontrolné merania boli robené od hladiny a neboli vztiahnuté na nadmorské výšky.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

5. Comparison of two concepts for assessment of sediment transport in small agricultural catchments

Creator:
Hlavčová, Kamila, Kohnová, Silvia, Velísková, Yvetta, Studvová, Zuzana, Sočuvka, Valentin, and Ivan, Peter
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
soil erosion, reservoir storage volume, sediment, bathymetry, and Svacenicky Creek
Language:
Slovak
Description:
The erosion, transport and deposition of sediments in small valley reservoirs represent a significant impact on their operations, mainly with regard to reducing the volume of their accumulation. The aim of this study is a comparison and uncertainty analysis of two modelling concepts for assessment of soil loss and sediment transport in a small agricultural catchment, with an emphasis on estimating the off-site effects of soil erosion resulted in sedimentation of a small water reservoir. The small water reservoir (polder) of Svacenicky Creek which was built in 2012, is a part of the flood protection measures in Turá Lúka and is located in the western part of Slovakia, close to the town of Myjava. The town of Myjava in recent years has been threatened by frequent floods, which have caused heavy material losses and significantly limited the quality of life of the local residents. To estimate the amount of soil loss and sediments transported from the basin, we applied two modelling concepts based on the USLE/SDR and WaTEM/SEDEM erosion models and validated the results with the actual bathymetry of the polder. The measurements were provided by a modern Autonomous Underwater Vehicle (AUV) hydrographic instrument. From the sediment data measured and the original geodetic survey of the terrain conducted at the time of the construction of the polder, we calculated changes in the storage volume of the polder during its four years of operation. The results show that in the given area, there has been a gradual clogging of the bottom of the polder caused by water erosion. We estimate that within the four years of the acceptance run, 10,494 m3 of bottom sediments on the Svacenicky Creek polder have accumulated. It therefore follows that repeated surveying of the sedimentation is very important for the management of the water reservoir.
Rights:
http://creativecommons.org/publicdomain/mark/1.0/ and policy:public

6. Influence of surface water level fluctuation and riverbed sediment deposits on groundwater regime

Creator:
Koczka Bara, Márta, Velísková, Yvetta, Dulovičová, Renáta, and Schügerl, Radoslav
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
surface water - groundwater interaction, groundwater flow modelling, and infiltration/drainage resistance of rivers
Language:
Slovak
Description:
The spatial and temporal patterns of surface water (SW) - groundwater (GW) exchange are significantly affected by riverbed silting, clogging or erosion processes, by altering the thickness and hydraulic conductivity of riverbed sediments. The duration of SW-GW exchange is controlled by the drainage and infiltration resistance of river bottom sediments (e.g. Andrássy et al., 2012). Generally, these two parameters primarily depend on the hydraulic conductivity and on the thickness of clogged layer. In this study the flow processes between GW and SW were modeled by model TRIWACO for different infiltration resistance and drainage resistance of riverbed sediments. The model area is situated on the Rye Island, which is a lowland area with very low slope. In this area a channel network was built up, where the flow conditions are controlled by water-gates. Because of the low slope and the system of water gates built on the channels, the riverbeds are influenced by intensive clogging processes. First, the applicability of model TRIWACO in the study area was tested by modelling the response of GW on SW level fluctuation. It was simulated, how the regulation of water level and flow direction in the channels influence the GW level, especially in extreme hydrological conditions (drought/flood), and if the GW flow direction and GW level change as it was expected. Next, the influence of channel network silting up on GW-SW interaction was modeled. The thickness of riverbed sediments was measured and their hydraulic conductivity from disturbed sediment samples was evaluated. The assessed hydraulic conductivity was used to calculate the infiltration resistance and the drainage resistance of riverbed sediments in the study area. Then, the GW level and flow direction was simulated for different infiltration resistance and drainage resistance of sediments.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

8. Stanovenie koeficienta priečnej disperzie na hornom úseku rieky Hron

Creator:
Velísková, Yvetta
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
transverse dispersion, surface waters, field measurements, numerical simulation, priečna disperzia, povrchové toky, terénne merania, and numerická simulácia
Language:
Slovak
Description:
The paper deals with the method of transverse dispersion coefficient statement from field measurement and with a way of correction of their values through the mathematical modelling. A constant steady source of tracer was used by the method of the computation of transverse dispersion coefficient from the field measurements and the method can be applied in wide and shallow rivers. It is based on the work of Demetracopoulos and Stefan (1983). The transverse dispersion coefficients were determined by this method at about 4 km long part of the Hron River. There was found out that the applied method gives overestimated results of transverse dispersion coefficients, so they had to be corrected by application of 2-dimensional numerical model of dispersion MODI with which there were simulated the results of field measurements. The summary of result values of these coefficients are in Tab. 1. and Príspevok opisuje spôsob stanovenia koeficientov priečnej disperzie a korekciu ich hodnoty za pomoci matematického modelu MODI, vychádzajúc z terénnych meraní. Pri terénnych meraniach bola aplikovaná metóda stanovenia priečneho disperzného koeficienta publikovaná Demetracopoulosom a Stefanom (1983). Táto metóda využíva konštantný zdroj stopovacej látky a je aplikovateľná pre široké plytké korytá. Na jej základe boli stanovené hodnoty priečnych disperzných koeficientov na cca 4 km dlhom úseku rieky Hron medzi zaústením toku Istebník a mostom v Banskej Bystrici-Šalkovej. Metóda Demetracopoulosa a Stefana (1983) však dáva vo všeobecnosti nadhodnotené výsledky priečnych disperzných koeficientov, preto hodnoty týchto koeficientov boli na základe simulácie výsledkov terénnych meraní modelom MODI následne korigované. Výsledky sú zhrnuté v tab. 1.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

9. Suspended particulate matter concentrations retrieved from self-calibrated multispectral satellite imagery

Creator:
Onderka, Milan, Rodný, Marek, and Velísková, Yvetta
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
self-calibration, suspended sediments, SPM, saturation, optimization, samokalibrácia, suspendované sedimenty, saturácia, and optimalizácia
Language:
Slovak
Description:
Inland waters are known to be laden with high levels of suspended particulate matter (SPM). Remotely sensed data have been shown to provide a true synoptic view of SPM over vast areas. However, as to date, there is no universal technique that would be capable of retrieving SPM concentrations without a complete reliance on time-consuming and costly ground measurements or a priori knowledge of inherent optical properties of water-borne constituents. The goal of this paper is to present a novel approach making use of the synergy found between the reflectance in the visual domain (~ 400-700 nm) with the near-infrared portion of the spectrum (~ 700-900 nm). The paper begins with a brief discourse of how the shape and spectral dependence of reflectance is determined by high concentrations of SPM. A modeled example is presented to mimic real-world conditions in fluvial systems, with specific absorption and scattering coefficients of the virtual optically active constituents taken from the literature. Using an optical model, we show that in the visual spectral domain (~ 400-700 nm) the water-leaving radiance responds to increasing SPM (0-100 g m-3) in a non-linear manner. Contrarily to the visual spectra, reflectance in the near infrared domain (~ 700-900 nm) appears to be almost linearly related to a broad range of SPM concentrations. To reduce the number of parameters, the reflectance function (optical model) was approximated with a previously experimentally verified exponential equation (Schiebe et al., 1992: Remote sensing of suspended sediments: the Lake Chicot, Arkansas project, Int. J. Remote Sensing, 13, 8, 1487-1509). The SPM term in Schiebe’s equation was expressed as a linear function of top-of-atmosphere reflectance. This made it possible to calibrate the reflectance in the visual domain by reflectance values from the near-IR portion of the spectrum. The possibility to retrieve SPM concentrations from only remote sensing data without any auxiliary ground mea-surements is tested on a Landsat ETM + scene acquired over a reservoir with moderately turbid water with SPM concentrations between 15-70 g m-3. The retrieved concentrations (on average) differ from in-situ measurement by ~ 10.5 g m-3. and Cieľom príspevku je prezentovať alternatívne spracovanie satelitných snímok na odhad koncentrácie suspendovaných sedimentov vo vodných útvaroch. Prvá časť článku sa venuje teórii a fyzikálnej podstate reflektancie a vplyvu prirodzene sa vyskytujúcich opticky aktívnych prvkov vo vode (suspendované sedimenty, pigmenty a rozpustené látky) na reflektanciu snímanú prostriedkami diaľkového prieskumu Zeme. Na modelovom príklade sme ukázali, že so zvyšovaním koncentrácie suspendovaných látok dochádza k saturácii signálu reflektancie.V druhej časti príspevku sme opísali spôsob využitia nelineárnosti vzťahu medzi reflektanciu vo viditeľnej časti (~ 400-700), a kvázi-linearitov v infračervenej časti (~ 700-900 nm) elektromegnetického spektra a koncentrácie suspendovaných sedimentov. Optimalizáciou tohto nelineárneho vzťahu sme odhadli koncentrácie suspendovaných sedimentov pre zdrž Hrušov pri Bratislave s RMSE 10.5 g m-3.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

10. The risk of the soil salinization of the eastern part of Žitný ostrov

Creator:
Kováčová, Viera and Velísková, Yvetta
Format:
bez média and svazek
Type:
model:article and TEXT
Subject:
salinization, alkalization, total dissolved solids (TDS), sodium adsorption ratio (SAR), electrical conductivity (EC), exchangeable sodium percentage (ESP), salinizácia, alkalizácia, celkové rozpustené látky (TDS), sodíkový adsorpčný pomer (SAR), elektrická vodivosť (EC), and výmenné sodíkové percento (ESP)
Language:
Slovak
Description:
Salinization is an increasing enviromental problem in ecosystems. The assessment of total dissolved solids (TDS), pH, electrical conductivity (EC), exchangeable sodium percentage (ESP), alkalinity and the concentrations of main ions makes possible to identify salinization and alkalization degree. The saltaffected soils occur in the south part and south-east part of Žitný ostrov, where the dry and mild summer climate, evaporation soil water regime and mineralized groundwater create conditions for development of the saline and alkaline soils. Five localities with highly-mineralized groundwater were monitored to evaluate salinity and alkality in the period 1989-2006. At the bottom horizons in localities 1 - 5 evaporative residues (salt content) reached value 0.1 - 0.2 %. In 2006 dry evaporative residues (salt content) was higher than 0.2 %, EC was higher than 250 mS m-1 at the bottom horizons in localities 1, 2, 4. The mentioned data allow us to state that salinization and alkalization of soils is developing, it starts from the bottom of soil horizons through middle part of the soil profile up to the top horizons. This phenomenon was observed in all investigated soils in different stages of development. and Salinizácia v ekosystémoch je stále významnejší enviromentálny problém. Stanovenie celkového množstva rozpustených látok (TDS), elektrickej vodivosti (EC), sodíkového adsorpčného pomeru (SAR) a obsahu výmenného sodíka (ESP) umožňuje identifikáciu kritického potenciálu salinizácie a degradácie pôdy. Záujmové územie bolo vymedzené vo východnej časti Žitného ostrova, kde suché a horúce klimatické podmienky spolu s vysokomineralizovanými podzemnými vodami sú príčinou translokácie solí do pôdneho profilu. Bolo monitorovaných 5 lokalít v období 1989 - 2006. Namerané údaje poukazujú na vzrastajúci obsah solí, ktorý v r. 2006 dosiahol 0,1 - 0,2 % v celom pôdnom profile vo všetkých monitorovaných lokalitách, hodnoty EC 200 - 400 mS m-1 v spodných horizontoch vytvárajú podmienky pre rozvoj zasolených pôd.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public