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Results of a numerical simulation investigating the complicated flushing process of an isolated trapped volume of salt water from a bar-blocked estuary are presented. A multiphase model, a part of the commercial code FLUENT 6.2, is applied. The governing equations together with initial and boundary conditions and the numerical scheme are described. The time-dependent salt-wedge position, vertical-density distribution, and proportion of total input kinetic energy converted into potential energy are examined for various incoming flow densimetric Froude number and estuary bed slope. The vertical position and thickness of the interfacial mixed layer between freshwater and salt water as well as the local gradient Richardson number are determined from simulated density profiles and velocity fields. The good agreement between the simulated and measured results indicates that the numerical model can be successfully applied to investigate the complex flushing process involving stratified flow. CE Database subject headings: Flushing; Numerical models; Simulation; Salt water; Estuaries; Stratified flow; Boundaries.

Results from combined laboratory experimental and turbulent numerical modeling studies are presented to investigate the effects of bed roughness (discrete square strips) and slope on the flow over a free overfall in a rectangular channel. A broad range of model parameters such as the bed roughness, channel slope, and incoming upstream Froude number is investigated. The water surface profiles upstream of the brink of the channel, the velocity fields in cavity between two strips, and end depth (water depth at the brink of the channel) are simulated, measured, and discussed for various input conditions. The results show that for a given dimension of bed roughness the relative spacing of roughness (defined as the ratio of the center to center distance to the height of the strip) has a significant effect on the flow. The computational results are in good agreement with the experimental measurements. CE Database subject headings: Stream improvement; Channel design; Geomorphology; Water discharge.