Flume

About: Flume is a research topic. Over the lifetime, 3565 publications have been published within this topic receiving 68254 citations.

Flume observations on flow dynamics in Zostera marina (eelgrass) beds

Abstract: Flow dynamics in Zostera marina L. (eelgrass) were studied in a large seawater flume. Velocity and turbulence intensity profiles were measured at 3 free-stream flow velocities (5. 10 and 20 cm S-'), at 5 shoot densities (1200, 1000,800, 600 and 400 shoots rne2), and at 5 along-stream positions relative to the leading edge of the eelgrass bed (10 cm upstream of the bed; 25, 50, 75 and 100 cm downstream of the leading edge of the bed). All the profiles (75) above the canopy or over bare sand fitted a log-profile relationship. At all densities and ambient velocities tested, mean velocity increased above the canopy, while within the bed water speed dropped distinctly below the canopy-water interface. Depending on shoot density, water speed was from 2 to 10 times lower under the canopy than upstream of the seagrass bed. Shear velocities (U%) above the canopy were 2 to 11 times greater than outside the bed at equivalent height, and Increased significantly with distance into the meadow. No significant differences among dens~ties were observed. Turbulence intensity showed a dramatic increase in all the profiles at the canopy-water interface, a significant increase with distance into the bed, but showed no significant differences between densities. Fluid flux within the bed decreased significantly with distance into the meadow, but exhibited no significant dependence on density. Downstream, vertically integrated fluid flux at 100 cm into the bed ranged between 14.7 and 40.6 O/O of upstream values. The least flux reduction occurred at the highest velocity (20 cm S-'). Trends in shear velocity and turbulence intensity show clearly that within the bed one can distinguish 2 dynamically different environments. The 'canopy-water interface' habitat 1s characterized by high shear stress and high turbulence intensity; the 'below-canopy' habitat is characterized by low shear stress and a reduction of turbulence intensity.

Hydrodynamic processes affecting benthic recruitment1

Abstract: Recruitment of animals into initially dcfaunated sites containing simulated stalks of a marsh grass was studied on an intertidal sandflat Laboratory flume experiments were used to predict the effects of these structures on near-bed flow, the sediment size-frequency composition, and the patterns and rates of benthic recruitment The effects of simulated stalks on both rates of fluid transport near the bed and boundary shear stress change profoundly with their numerical density Patterns of sedimentation in the field and patterns and rates of rccruitment of several taxa depended strongly on the presence and numerical density of these structures, in agreement with a priori predictions assuming passive (ie purely hydrodynamic) dispersal Hydrodynamic (or other physical) effects of manipulation are important and form an additional, but infrequently posed, null hypothesis against which biological effects such as substrate selection, competition, predation, or disturbance should be tested

Is the critical Shields stress for incipient sediment motion dependent on channel‐bed slope?

Abstract: Data from laboratory flumes and natural streams show that the critical Shields stress for initial sediment motion increases with channel slope, which indicates that particles of the same size are more stable on steeper slopes. This observation is contrary to standard models that predict reduced stability with increasing slope due to the added downstream gravitational force. Processes that might explain this discrepancy are explored using a simple force-balance model, including increased drag from channel walls and bed morphology, variable friction angles, grain emergence, flow aeration, and changes to the local flow velocity and turbulent fluctuations. Surprisingly, increased drag due to changes in bed morphology does not appear to be the cause of the slope dependency because both the magnitude and trend of the critical Shields stress are similar for flume experiments and natural streams, and significant variations in bed morphology in flumes is unlikely. Instead, grain emergence and changes in local flow velocity and turbulent fluctuations seem to be responsible for the slope dependency due to the coincident increase in the ratio of bed-roughness scale to flow depth (i.e., relative roughness). A model for the local velocity within the grain-roughness layer is proposed based on a 1-D eddy viscosity with wake mixing. In addition, the magnitude of near-bed turbulent fluctuations is shown to depend on the depth-averaged flow velocity and the relative roughness. Extension of the model to mixed grain sizes indicates that the coarser fraction becomes increasingly difficult to transport on steeper slopes.

Transportation of Suspended Sediment by Water

Abstract: Measurements of the sediment and velocity distributions in a laboratory flume were made for various values of rate of flow, slope of channel, and size and amount of suspended load. The experimental...

Sediment transport and bed morphology at river channel confluences

Abstract: River channel confluences form important morphological elements of every river system, being points at which rapid changes in flow, sediment discharge and hydraulic geometry must be accommodated. This article presents results of a quantitative investigation of sediment transport at channel confluences accomplished through both scaled laboratory flume simulation and complementary monitoring of a natural channel confluence. Bed morphology at channel confluences is characterized by three distinct elements: avalanche faces at the mouth of each confluent channel, a deep central scour and a bar within the separation zone formed at the downstream junction corner. These elements are controlled predominantly by the confluence angle and the ratio of discharges between the tributary and mainstream channels. As confluence angle and discharge ratio increase, the sediment contributions from the confluent channels are progressively segregated in their paths through the junction, with sediment being transported around rather than through the centre of the confluence. This segregation of sediment loads is accompanied by the retreat of the main channel avalanche face from the confluence, an increase in the scour depth, a change in the orientation of the scour and an increase in the size of the separation zone bar. Field measurements closely replicate the flume simulation. A model of sediment transport and bed morphology links these features to the fluid dynamics of these sites. An understanding of confluence dynamics is important not only in considerations of channel morphology and design criteria but must form the basis for the interpretation of confluence sediments in the ancient record.