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Turbulence measurements over a smooth wall in unsteady depth-varying open-channel flows were conducted by the simultaneous use of a two-component laser Doppler anemometer (LDA) and a water-wave gauge. In the present study, velocity measurements in the viscous sublayer of highly unsteady flow have been first conducted to evaluate the friction velocity independently of the log-law. The von Karman constant [Kappa] was calculated using this friction velocity. It was proven then that the value of [Kappa] was really a constant of 0.41 even in unsteady open-channel flows. Next, statistical structures of mean velocity and turbulence characteristics were investigated across the whole flow from the near-wall region up to the free surface. In particular, turbulence measurements near the depth-varying water-surface zone of flood flow were conducted successfully for the first time with the LDA; such measurements have been impossible with conventional velocity instruments such as hot-film anemometers. Mean velocity profiles and turbulence characteristics were revealed in both the rising and the falling stages of the flood period.

The hydrodynamic response of turbulent flow in a compound wide rectangular open channel with a vegetated domain at the channel bank, in a channel corner and in a floodplain, to the vegetation density and diameter is discussed. To this end a phenomenological model was imbedded in an algebraic stress model with the vegetation modeled as an internal resistance that exerts drag force, produces energy of turbulence, and interferes with its anisotropy and length scale. Simple suggestions for some modeling problems associated with the presence of wide vegetated domains are used to yield the three-dimensional flow. Vorticity sources relaxation was implemented to smooth periodic behavior, and dissipation correction was introduced as a coordinate-invariant damping. With these, the results represent fully developed flow.

The nature of secondary currents in curved rivers was defined. The velocity vector is composed of cross-stream and long-stream flow patterns. Accurate velocity data can be determined through a correct orientation of the meter. Cross-streams flow patterns are sensitive to alignment variations of the meter, which, however, is not the case with long-stream currents. A suggested technique for stream field measurements is to adjust the meter so that the value of the positive and negative streams is equal to zero.

A study was conducted on the hydrodynamic behavior of a compound rectangular open channel and flow in such a channel. Three configurations were used in studying the influence of the channel's shape on flow patterns, namely, flow along a 270-degree corner, flow along a threshold of deep flood plain, and flow through shallow flood plain. Open surface dynamics were also analyzed. Results revealed that reasonable solutions for the longitudinal vortex pair were still obtained by the stress model despite the presence of a unique coherence structure in the 270-degree corner at the flood-plain threshold. Hossain and Rodi's proposed extrapolated dissipation length concept was also proven.

Basic knowledge of turbulent structures in open-channel flows are now available from accurate experimental data that were obtained using a laser Doppler anemometer in laboratory flumes. Many of these experiments have, however, been conducted at moderate Reynolds numbers. 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 in Kyoto and the Aichi Irrigation Channel in Nagoya have been conducted by making use of three-component electromagnetic flow meters. Multicellular secondary currents were evident in a wide river, whereas large-scale free-surface secondary currents associated with velocity-dip phenomena were generated in a narrow river. The features of such secondary currents in rivers could be explained by theory of turbulence, and also they coincided well with the laboratory experiments and numerical calculations.

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 is demonstrated. The flow in the four basic asymmetric channels measured by Tominaga and Nezu in 1991 is numerically simulated, as well as other channel configurations, including symmetric channels. Turbulence is modeled by the energy-dissipation model, combined with the algebraic stress model suggested by Naot and Rodi in 1982. The three-dimensional flow is solved using the parabolic pressure correction algorithm of Patankar and Spalding. The examples suggest estimations for the friction factors, and the mass exchange rate between the flood plain interior and its threshold.

Unstable patterns are identified in the results of numerical simulations of two cases of partly vegetated open channels, at the free unobstructed flow side of the shear layer that separates the unobstructed channel from the vegetated zones. A time-dependent pattern was identified in a rectangular open channel compound with a vegetated bank, and cellular structure was found in a wide rectangular open channel spanning over a vegetated thin layer at the channel bed. Distinction between three modes of algebraic stress models: a prompt algebraic stress model, a delayed algebraic stress model, and an algebraic stress model with longitudinal vorticity sources relaxation, and the modeling of time-dependent turbulence is made, and discussed in the present context.