Turbulent flow and suspended sediment transport in a mobile, sand bed channel with riprap side slopes.

摘要

Located downstream of San Acacia Diversion Dam in central New Mexico, lies the Low Flow Channel test facility from San Acacia Diversion Dam downstream for 16.6 km (10.3 miles). The test facility was designed to evaluate flow and sediment transport in a mobile sand bed channel with riprap side slopes.; The flow and turbulence characteristics, and suspended sediment transport conditions of this type of field channel are not well understood. One goal of this study is to determine the affect the vertical velocity profile, shear velocity, and turbulence intensity has upon suspended sediment transport in this channel over a wide range of flows. A second goal is to develop methods to more accurately estimate suspended sediment transport rates above dunes and riprap side slopes. Specific objectives of this study are to: (1) Provide new experimental data on vertical velocity profiles and turbulent 3-dimensional velocity fluctuations to estimate shear stress, eddy viscosity, shear velocity, time average velocity, anisotropy, mixing length and turbulence intensity, (2) provide experimental data on suspended sediment transport in a mobile sand bed channel with plane and dune bedforms and riprap side slopes, (3) compare the measured sediment transfer functions to the theories of Rouse (1937) and Jobson (1968), and develop sediment transfer functions that better describe suspended sediment transport conditions in the LFC and (4) develop new methods and solutions to the sediment diffusion equation that better describes suspended sediment profiles above dune beds and riprap side slopes.; This research shows that a cable mounted ADV probe provides accurate turbulent velocity fluctuation data for estimating the Reynolds stress, and velocity profiles. Both dune and plane bed conditions were observed during collection making the data a rich source for evaluation. The velocity profiles have an inner logarithmic layer, an outer layer that is described well by logarithmic wake law, a constant velocity layer and a velocity dip layer. The Reynolds shear stress does not consistently follow a linear distribution through the entire depth of flow. The suspended sediment transport for plane bed conditions is shown to follow the Rouse method. Suspended sediment transport for dune bed conditions and above riprap side slopes does not support the Rouse method. The sediment transfer function does not follow the parabolic equation used by Rouse but rather the suspended sediment transfer function increases with depth for the flow above dune beds and riprap side slopes. A new method is developed that was shown to be accurate within -4.45% to 7.64% of measured suspended sediment data above dune beds. The Rouse method is shown to be accurate within -21.7 to -24.29% of the measured data. For suspended sediment above riprap side slopes, the new method is shown to be accurate within -10.7% to 1.96%, while the Rouse method is accurate within -20.42 to -36.06%. The new method clearly improves the estimation of suspended sediment transport.