Laboratory studies of the mechanics of streams flowing over a movable bed of fine sand

[摘要] A laboratory study was made of the characteristics of streams flowing over a loose bed of fine sand in order to determine what factors govern the equilibrium rate of transportation of fine sand in suspensions. Twenty-two experimental runs were performed in a 40-foot tilting flume for various conditions with bed sand of two different sizes (0.10 mm and 0.16 mm). Each run represented a uniform open-channel flow in equilibrium with the sand bed.It was found that more than one equilibrium flow velocity and sediment discharge existed for a given depth, slope, and size of sand because of the extreme variability of channel roughness. At low velocities, the large irregular dunes which formed on the stream bed made the bed friction factor over six times larger than the friction factor for the smooth sand beds obtained at higher flow rates. Thus the transportation rate could not be expressed as a unique function of the bed shear stress, the channel geometry, and properties of the sand as has been supposed in all previous theories for the equilibrium transportation rate of suspended load.By using the mean velocity and the depth (or the water discharge and sediment discharge) as independent variables, and slope as a dependent variable, an orderly qualitative relationship between the pertinent variables was obtained.Because of the importance of the dunes in the mechanics of sediment-laden streams, a special study was made of their characteristics and the mechanisms of their formation and movement. The studies also included some theoretical and experimental investigations of the distribution of velocity and suspended sediment within the flow for runs with a smooth bed.

[发布机构] University:California Institute of Technology;Department:Engineering and Applied Science

[关键词] civil engineering