Non-linear effects on solute transfer between flowing water and a sediment bed

作者：Higashino Makoto; Stefan Heinz G^*

来源：Water Research, 2011, 45(18): 6074-6086.

DOI：10.1016/j.watres.2011.09.004

• Mass transport
• Porewater
• Sediment
• Sediment-water exchange
• Solute
• Stream
• Streambed
• Turbulent flow
• Water quality

A previously developed model of periodic pore water flow in space and time, and associated solute transport in a stream bed of fine sand is extended to coarse sand and fine gravel. The pore water flow immediately below the sediment/water interface becomes intermittently a non-Darcy flow. The periodic pressure and velocity fluctuations considered are induced by near-bed coherent turbulent motions in the stream flow; they penetrate from the sediment/water interface into the sediment pore system and are described by a wave number (x) and a period (T) that are given as functions of the shear velocity (U*) between the flowing water and the sediment bed. The stream bed has a flat surface without bed forms. The flow field in the sediment pore system is described by the continuity equation and a resistance law that includes both viscous (Darcy) and non-linear (inertial) effects. Simulation results show that non-linear (inertial) effects near the sediment/water interface increase flow resistance and reduce mean flow velocities. Compared to pure Darcy flow, non-linear (inertial) effects reduce solute exchange rates between overlying water and the sediment bed but only by a moderate amount (less than 50%). Turbulent coherent flow structures in the stream flow enhance solute transfer in the pore system of a stream bed compared to pure molecular diffusion, but by much less than standing surface waves or bed forms.

• 出版日期2011-11-15