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
The local scour around bridge piers influences their stabilities and plays a key role in the bridge failures. The estimation of the maximum possible scour depth around bridge piers is an important step in the design of the bridge pier foundations. In this study, the temporal evolution of local scour depths as well as the equilibrium scour depths were analyzed.
The experiments were carried out in a rectangular flume by using uniform sediment with median diameter of 3.5 mm and geometric standard deviation of 1.4. The diameters of the tested circular bridge piers were 40 mm, 80 mm, 150 mm and 200 mm. The flow and scour depths were determined by ultrasonic sensors. The experiments were realized in clear water conditions with various constant flow rates.
The experimental findings were compared with those calculated from some empirical equations existing in the literature. A new empirical relation involving the flow intensity, the relative water depth and the dimensionless time is also introduced. The advantage of this proposed relation is that the only parameter requiring the calculation is the critical velocity, other parameters being known geometric and hydraulic parameters. The performance of this relation was tested by using experimental data available in the literature, and a satisfactory compatibility was revealed between the experimental and numerical results.