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Start Over Language Slovak Rights http://creativecommons.org/licenses/by-nc-sa/4.0/ Type article

33. Turbulence characteristics of flow in an open channel with temporally varying mobile bedforms

Creator:
Hanmaiahgari, Prashanth Reddy, Roussinova, Vesselina, and Balachandar, Ram
Type:
article, model:article, and TEXT
Subject:
turbulence, open channel, bedforms, higher-order moments, PIV, and quadrant analysis
Language:
Slovak
Description:
Turbulence of flow over mobile bedforms in natural open channels is not yet clearly understood. An attempt is made in this paper to determine the effect of naturally formed mobile bedforms on velocities, turbulent intensities and turbulent stresses. Instantaneous velocities are measured using a two-dimensional particle image velocimetry (PIV) to evaluate the turbulence structure of free surface flow over a fixed (immobile) bed, a weakly mobile bed and a temporally varying mobile bed with different stages of bedform development. This paper documents the vertical distribution of velocity, turbulence intensities, Reynolds shear stress and higher-order moments including skewness and turbulent diffusion factors. Analysis of the velocity distributions shows a substantial decrease of velocity near the bed with increasing bedform mobility due to increased friction. A modified logarithmic law with a reduced von Kármán constant and increased velocity shift is proposed for the case of the mobile bedforms. A significant increase in the Reynolds shear stress is observed in the mobile bedforms experiments accompanied by changes over the entire flow depth compared to an immobile bed. The skewness factor distribution was found to be different in the case of the flow over the mobile bedforms. All higher-order turbulence descriptors are found to be significantly affected by the formation of temporally varying and non-equilibrium mobile bedforms. Quadrant analysis indicates that sweep and outward events are found to be dominant in strongly mobile bedforms and govern the bedform mobility.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

34. Using gridded rainfall products in simulating streamflow in a tropical catchment: A case study of the Srepok River Catchment, Vietnam

Creator:
Thi Thom, Vu, Nguyen Khoi, Dao, and Quang, Linh
Type:
article, model:article, and TEXT
Subject:
APHRODITE, CFSR, PERSIANN, TRMM, rainfall, streamflow, and SWAT model
Language:
Slovak
Description:
The precise rainfall estimate with appropriate spatial and temporal resolutions is a key input to distributed hydrological models. However, networks of rain gauges are often sparsely distributed in developing countries. To overcome such limitations, this study used some of the existing gridded rainfall products to simulate streamflow. Four fridded rainfall products, including APHRODITE, CFSR, PERSIANN, and TRMM, were used as input to the SWAT distributed hydrological model in order to simulate streamflow over the Srepok River Catchment in Vietnam. Besides that, the available rain gauges data were also used for comparison. Amongst the four different datasets, the TRMM and APHRODITE data show their best match to rain gauges data in simulating the daily and monthly streamflow with satisfactory precision in the 2000–2006 period. The result indicates that the TRMM and APHRODITE data have potential applications in driving hydrological model and water resources management in data-scarce and ungauged areas in Vietnam.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public

35. Water vapour adsorption on water repellent sandy soils

Creator:
Orfanus, Tomas, Amer, Abdel-Monem Mohamed, Jozefaciuk, Grzegorz, Fulajtar, Emil, and Čelková, Anežka
Type:
article, model:article, and TEXT
Subject:
soil sorptivity, hydrophobization, adsorption isotherm, fractal dimension, and specific surface area
Language:
Slovak
Description:
Soil sorptivity is considered a key parameter describing early stages of water (rain) infiltration into a relatively dry soil and it is related to build-up complexity of the capillary system and soil wettability (contact angles of soil pore walls). During the last decade an increasing water repellency of sandy soils under pine forest and grassland vegetation has been frequently observed at Mlaky II location in SW Slovakia. The dry seasons result in uneven wetting of soil and up to hundredfold decrease in soil sorptivity in these vegetated soil as compared to reference sandy material, which was out of the reach of ambient vegetation and therefore readily wettable. As far as water binding to low moisture soils is governed by adsorption processes, we hypothesized that soil water repellency detected by water drop penetration test and by index of water repellency should also influence the water vapour adsorption parameters (monolayer water content, Wm, specific surface area, A, maximum adsorption water, Wa, maximum hygroscopic water MH, fractal dimension, DS and adsorption energies, Ea) derived from BET model of adsorption isotherms. We found however, that the connection of these parameters to water repellency level is difficult to interpret; nevertheless the centres with higher adsorption energy prevailed evidently in wettable materials. The water repellent forest and grassland soils reached less than 80% of the adsorption energy measured on wettable reference material. To get more conclusive results, which would not be influenced by small but still present variability of field materials, commercially available homogeneous siliceous sand was artificially hydrophobized and studied in the same way, as were the field materials. This extremely water repellent material had two-times lower surface area, very low fractal dimension (close to 2) and substantially lower adsorption energy as compared to the same siliceous sand when not hydrophobized.
Rights:
http://creativecommons.org/licenses/by-nc-sa/4.0/ and policy:public