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Turbulence measurements over a smooth wall in unsteady open-channel flows were conducted accurately by the simultaneous use of a two-component LDA system and water-wave gauges. The “ general ” log-law distributions, in which the von Karman constant is a universal one of χ=0.41 but the integration constant A is a function of main-flow conditions, were obeyed well in the wall region for both the rising and falling stages of flood. On the other hand, the log-wake law was reasonably applied to the outer region including the depth-varying zone. The Coles' wake parameter Π increased for the rising stage, whereas it decreased for the falling stage. The turbulence is stronger for the rising stage than for the falling stage, except for very near the free surface. These unsteady characteristics in open-channel flows with variation of the water surface are quite different from those in closed duct flows. Of particular significance is the findings counterclockwise loops of velocity and turbulence against the varying depth in unsteady open-channel flows.

Fundamental structures of turbulence in two-dimensional (2-D) and further three-dimensional (3-D) open-channel flows have recently been almost clarified theoretically and experimentally through accurate experimental data which were obtained using a laser-Doppler anemometer system in laboratory flumes ; this detailed knowledge is now available in an IAHR monograph written by Nezu & Nakagawa (1992). Many of these experiments have, however, been conducted at moderate Reynolds numbers, say Re 記号 10⁴. Therefore, it is not yet clear whether such laboratory data of open-channel turbulence can be applied to river turbulence at high Reynolds numbers. In this study, velocity measurements of the Biwako-Sosui River (Re = 8 × 10⁵) in Kyoto and the Aichi Irrigation Channel (Re = 6 × 10⁵) in Nagoya have been conducted, using three-component electromagnetic flow meters. It was first found that multi-cellular secondary currents and free-surface secondary currents were evident in actual rivers. The features of such secondary currents in rivers were in a good agreement with those in laboratory flumes. Key Words : turbulence-driven secondary currents ; river turbulence ; field measurements ; velocity-dip phenomenon ; effects of aspect ratio.

In this paper, we describe a numerical model that is called “the crevice method” using a triangular mesh difference to simulate tidal currents in an island basin with a large area of beach ; the land boundaries move with the shift of the tide, and with geometrically complex boundaries. This model is based on shallow water momentum and continuity equations. For simulating variational boundaries, crevices which are artificially imagined are erected all over the shallows where the bed elevations are not lower than the lowest tidal level and where the water depth in the crevices changes with the ascent and descent of the tidal levels. For simulating a flow field within geometrically complex island boundaries, especially in flow circumstances near the islands, the triangular mesh difference is adopted in this model. The second derivative of u, ν and ζ with respect to time and the semi-implicit scheme are used in the triangular mesh difference for the purpose of increasing stability and accuracy, Practical calculation of tidal currents shows that this model has the advantages of better stability, higher accuracy, shorter calculation time, and it saves computer memory. The calculated results coincide reasonably with the measured ones.

The hydrodynamic response of the turbulent flow in a compound rectangular open channel to the flood plain depth, roughness, and symmetry and to the channel Reynolds number was demonstrated. The flow in the four basic asymmetric channels measured by Tominaga and Nezu (1991) was numerically simulated, as well as other channel configurations including symmetric channels. Turbulence was modeled by the energy dissipation model, combined with the algebraic stress model suggested by Naot and Rodi (1982). The three-dimensional flow with secondary currents in compound open channels was solved numerically using the parabolic pressure correction algorithm of Patankar and Spalding (1972). The examples suggest data bases for the estimation of friction factors, and for the mass exchange rate between the flood plain interior and its threshold. A possible explanation for the multi-cellular structure in wide open channels is also given.

In order to explain the bed-load transport process by water flow, stochasticmodel is one of the useful methods which can describe the behavior of individualparticle of alluvial system.Most of the studies of bed-load thansport process by stochastic model has beencarried out only for the steady-uniform flow. But, the effect of flow unsteadiness onbed-load transport process should be considered in some real alluvial systems. Inthis study, stochastic model of the bed load transport process in unsteady butuniform flow characterized by oscillation-current coexitsing flow is proposed. Andthen, applicability of the present model is investigated by experimental results ofbed load behavior. Agreement of computed result with experiment is fairly good, and thus the unsteady uniform alluvial system can be described with the aid of thepresent model.

In order to explain the bed-load transport process by water flow, stochasticmodel is one of the useful methods which can describe the behavior of individualparticle of alluvial system.Most of the studies of bed-load thansport process by stochastic model has beencarried out only for the steady-uniform flow. But, the effect of flow unsteadiness onbed-load transport process should be considered in some real alluvial systems. Inthis study, stochastic model of the bed load transport process in unsteady butuniform flow characterized by oscillation-current coexitsing flow is proposed. Andthen, applicability of the present model is investigated by experimental results ofbed load behavior. Agreement of computed result with experiment is fairly good, and thus the unsteady uniform alluvial system can be described with the aid of thepresent model.