ABSTRACT:The pioneering predictor of fluvial bedload transport rate proposed by Meyer-Peter and Müller in 1948 is still extensively used in basic research and engineering applications. A review of the basis for its formulation reveals, however, that an unnecessary bed roughness correction was applied to cases of plane-bed morphodynamic equilibrium. Its inclusion followed a flow resistance parameterization in terms of the Nikuradse roughness height, which has been shown (well after the publication of their work) to be inappropriate for the characterization of

Acoustic cavitation is responsible for both sonochemistry and sonoluminescence. Bubble collapse in liquids results in an enormous concentration of energy from the conversion of the kinetic energy of liquid motion into heating of the contents of the bubble. The high local temperatures and pressures, combined with extraordinarily rapid cooling, provide a unique means for driving chemical reactions under extreme conditions. A diverse set of applications of ultrasound to enhance chemical reactivity has been explored, with important applications in mixed-phase synthesis, materials chemistry, and biomedical uses. For example, the sonochemical decomposition of volatile organometallic precursors in low-volatility solvents produces nanostructured materials in various forms with high catalytic activities. Nanostructured metals, alloys, carbides and sulphides, nanometre colloids, and nanostructured supported catalysts can all be prepared by this general route. Another important application of sonochemistry to materials chemistry has been the preparation of biomaterials, most notably protein microspheres. Such microspheres have a wide range of biomedical applications, including their use as echo contrast agents for sonography, magnetic resonance imaging contrast enhancement, and oxygen or drug delivery.

[1] A common approach for estimating the bed load transport rate in gravel-bed streams is to relate it to deterministic channel-averaged driving parameters and corresponding resistance properties of the bed material. Notwithstanding the proven success of this approach in modeling various morphodynamic scenarios, it does not contain the mechanics necessary to relate the bulk sediment transport rate to the displacement patterns of individual particles. Experiments on entrainment, transport, and deposition of tracer stones in a flume described here were designed to address this issue. Predictors of statistics of bed elevation fluctuations at short timescales, total and elevation-specific particle entrainment rates, particle step lengths, mean and associated probability density function for particle virtual velocity, and thickness of the active layer were developed. The working hypothesis tested in this paper is that the statistics of tracer displacements can be related to channel-averaged hydraulic parameters, and thus linked to macroscopic aspects of bed load transport.

[1] How does a mountain river adjust to accommodate repeated flood hydrographs? Do flood hydrographs cause major cycles of aggradation and degradation of the river bed? Here flume experiments are used to explore this problem. The response of a gravel bed river to repeated floods is modeled in the simplest possible way. The gravel is well sorted, the flume is operated in sediment feed mode, and the gravel feed rate is held constant. The flow discharge, on the other hand, is specified in terms of the repetition of the same hydrograph until mobile bed equilibrium (averaged over the hydrograph) is achieved. The results of the experiments demonstrate a remarkable trade-off. In a short inlet "boundary layer" (transition region) the bed elevation and bed slope fluctuate cyclically with the changing flow discharge, while the gravel transport rate remains nearly equal to the constant feed rate. Downstream of this short reach, however, the bed elevation and bed slope do not fluctuate in response to the hydrograph; all the fluctuation is transferred to the gravel transport rate. These results are verified in terms of onedimensional analytical and numerical modeling. This modeling shows that the trade-off is inevitable as long as the morphologic response time of the reach in question is sufficiently long compared to the duration of a single hydrograph. The implication is that gravel bed rivers tend to adjust to hydrographs so as to minimize the response of the bed and maximize the response of the bed load transport rate to fluctuating flow discharge.Citation: Wong, M., and G. Parker (2006), One-dimensional modeling of bed evolution in a gravel bed river subject to a cycled flood hydrograph,