Gravity-driven open-channel flows carrying coarse sediment over an erodible granular deposit are studied. Results of laboratory experiments with artificial sediments in a rectangular tilting flume are described and analyzed. Besides integral quantities such as flow rate of mixture, transport concentration of sediment and hydraulic gradient, the experiments include measurements of the one-dimensional velocity distribution across the flow. A vertical profile of the longitudinal component of local velocity is measured across the vertical axis of symmetry of a flume cross section using three independent measuring methods. Due to strong flow stratification, the velocity profile covers regions of very different local concentrations of sediment from virtually zero concentration to the maximum concentration of bed packing. The layered character of the flow results in a velocity distribution which tends to be different in the transport layer above the bed and in the sediment-free region between the top of the transport layer and the water surface. Velocity profiles and integral flow quantities are analyzed with the aim of evaluating the layered structure of the flow and identifying interfaces in the flow with a developed transport layer above the upper plane bed.
Intense transport of sediment is studied in flows of steep slopes. Transport- and friction formulae suitable for flows at high shear stress above eroded bed are discussed. The formulae are further incorporated to a proposed simple model for open-channel flow with gradually varied transport of sediment. Two variants of the formulae are used alternatively in the model. Tilting-flume experiments are described that provided steady-flow data suitable for a validation of the formulae and unsteady-sediment-transport data for a validation of the designed model of gradually varied transport. A comparison of experimental results with formulae predictions and model simulations shows a very reasonable agreement for both variants of the transport and friction formulae. and Obsahuje seznam literatury a znaků
In the paper, authors are concerned with a hydraulic behaviour of bridges at high water stages and especially with the so far almost unregarded case when bridge roadway is overflowing. There are mentioned their own solutions for the estimation of the backwater by the bridge besides assessment of the applicability of some used relations. These new solutions were derived on the basis of research on the physical model at hydraulic laboratory of the Faculty of Civil Engineering of the Czech Technical University in Prague in 2001 and 2002. and Studie se zabývá hydraulickým chováním mostů při vysokých vodních stavech a zejména dosud téměř opomíjeným případem, kdy dochází k přelévání mostovky. Vedle posouzení aplikovatelnosti některých používaných vztahů jsou zde také uvedena vlastní řešení pro stanovení vzdutí mostem. Tato nová řešení byla odvozena na základě výzkumu na fyzikálním modelu prováděného v letech 2001 a 2002 v hydraulické laboratoři Fakulty stavební ČVUT v Praze.
The paper describes results of validation of authors' recently proposed formulae for sediment transport and bed friction in the upper plane bed regime using laboratory experiments in a pressurized pipe. Flows of mixture of water and fine to medium ballotini (d50 = 0.18 mm) were observed in a rectangular pipe (51 x 51 mm) with a deposit at the bottom of the pipe. A comparison of test results with transport-formula predictions shows a satisfactory match confirming a good prediction ability of the proposed transport formula at high bed shear. A prediction ability of the friction formulae appears to be less convincing but still reasonable. A joint use of the formulae for transport and friction predicts the delivered concentration of transported sediment within the accuracy range of ± 40 per cent for flows in which transported sediments strongly affect the bed friction, i.e. for flows with delivered concentration of sediment higher than say 3 per cent.
The paper deals with a calculation of discharge flowing above an entirely submerged bridge deck. Authors submit an analysis of the solution based on a weir equation and own results too. The results are issuing form laboratory experiments carried out in a hydraulic laboratory of the Faculty of Civil Engineering of CTU in Prague. and Článek se zabývá problematikou výpočtu průtoku vody nad přelévanou konstrukcí mostovky. Autoři předkládají rozbor výpočtu tohoto průtoku založeného na aplikaci rovnice přepadu a prezentují výsledky vycházející z vlastního fyzikálního výzkumu uskutečněného ve vodohospodářské laboratoři Fakulty stavební ČVUT v Praze.