Two sets of triangular hydrographs were generated in a 12-m-long laboratory flume for two sets of initial bed conditions: intact and water-worked gravel bed. Flowrate ranging from 0.0013 m3 s–1 to 0.0456 m3 s–1, water level ranging from 0.02 m to 0.11 m, and cumulative mass of transported sediment ranging from 4.5 kg to 14.2 kg were measured. Then, bedload transport rate, water surface slope, bed shear stress, and stream power were evaluated. The results indicated the impact of initial bed conditions and flow unsteadiness on bedload transport rate and total sediment yield. Difference in ratio between the amount of supplied sediment and total sediment yield for tests with different initial conditions was observed. Bedload rate, bed shear stress, and stream power demonstrated clock-wise hysteretic relation with flowrate. The study revealed practical aspects of experimental design, performance, and data analysis. Water surface slope evaluation based on spatial water depth data was discussed. It was shown that for certain conditions stream power was more adequate for the analysis of sediment transport dynamics than the bed shear stress. The relations between bedload transport dynamics, and flow and sediment parameters obtained by dimensional and multiple regression analysis were presented.
Acidic herbicide MCPA (4-chloro-2-methylphenoxyacetic acid) is applied to post-emergence control of annual and perennial broad-leaved weeds, mostly in cereals. This study was undertaken with two soils of different properties sampled from two soil horizons to determine the extent of degradation, sorption and desorption of MCPA. These processes are the most important to evaluate the fate of the herbicide in soil and its potential to leach from soil into groundwater. Two soils were used: a calcareous, sandy-loam soil with organic carbon content of 2.486 % (Pararendzina) taken from surface A horizon (the A topsoil) and a calcareous, loamy-sand soil with organic C content of 0.600 % (Fluvisol) sampled from subsurface C horizon (the C subsoil). The extent of degradation, sorption and desorption of MCPA were measured in laboratory batch experiments. Degradation followed first-order kinetics, with the MCPA half-lives of 11 and 24 d for the A topsoil and C subsoil, respectively. Soil organic carbon influenced MCPA degradation. Sorption followed a Freundlich isotherm equation and linear isotherm equation, as well. The distribution coefficient KD was higher in the A topsoil (0.387 l kg-1) than in the C subsoil (0.165 l kg-1), consistent with the higher organic C content of the A soil. The results indicate that MCPA is potentially mobile and might pose a threat to future groundwater quality due to its low sorption, relatively high water solubility and slow degradation in the C subsoil. and MCPA, slabokyslý herbicíd, sa používa postemergentne na ničenie jednoročných a trvalých širokolistých burín, najmä v obilninách. Cieľom tejto práce bolo štúdium degradácie, sorpcie a desorpcie MCPA v dvoch rozdielnych pôdach odobratých z odlišnej hĺbky. Tieto procesy v najväčšej miere ovplyvňujú celkové správanie MCPA v pôdach a determinujú jeho migračný potenciál. Použité pôdy boli: karbonátová, piesčito-hlinitá pôda s obsahom organického uhlíka 2,486 % (pararendzina) odobratá z vrchného A horizontu (pôda A) a karbonátová, hlinito-piesčitá pôda s obsahom organického uhlíka 0,600 % (Fluvizem), so znakmi oglejenia odobratá z C horizontu v hĺbke 2 m (pôda C). Všetky sledované procesy boli realizované v nádobkových experimentoch. Rozklad MCPA vyhovoval rýchlostnej rovnici reakcie prvého poriadku. Rozklad MCPA bol rýchlejší v pôde A so zisteným polčasom rozkladu 11 dní ako v pôde C s polčasom rozkladu 24 dní. Rozklad MCPA súvisel s odlišným obsahom organického uhlíka v týchto dvoch vzorkách pôd. Získané sorpčné izotermy MCPA vyhovovali rovniciam Freundlichovej a lineárnej sorpčnej izotermy. Rozdeľovací koeficient KD MCPA bol vyšší pre pôdu A (0,387 l kg-1) ako pre pôdu C (0,165 l kg-1). Vyššia sorpčná kapacita pôdy A ako pôdy C sa zhodovala s vyšším obsahom organického uhlíka v pôde A. Výsledky tejto práce naznačujú, že MCPA je potenciálne mobilný herbicíd a môže predstavovať veľké riziko pre kvalitu podzemných vôd v dôsledku jeho málo účinnej sorpcie, pomerne vysokej rozpustnosti vo vode a zvýšenej perzistencii v hlbších častiach pôdneho profilu.
Collisional interactions in a sheared granular body are typical for intense bed load transport and they significantly affect behavior of flow carrying bed load grains. Collisional mechanisms are poorly understood and modelling approaches seldom accurately describe reality. One of the used approaches is the kinetic theory of granular flows. It offers constitutive relations for local shear-induced collision-based granular quantities – normal stress, shear stress and fluctuation energy – and relates them with local grain concentration and velocity. Depth distributions of the local granular quantities produced by these constitutive relations have not been sufficiently verified by experiment for the condition of intense bed load transport in open channels and pressurized pipes. In this paper, results from a tilting-flume facility including measured velocity distribution and deduced concentration distribution (approximated as linear profiles) are used to calculate distributions of the collision-based quantities by the constitutive relations and hence to test the ability of the kinetic-theory constitutive relations to predict conditions observed in these collision-dominated flows. This test indicates that the constitutive relations can be successfully applied to model the local collisional transport of solids at positions where the local concentration is not lower than approximately 0.18 and not higher than approximately 0.47.