title: Non-linear effects on solute transfer between flowing water and a sediment bed.
abstract: 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 (χ) 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.
authors: Department of Civil Engineering, Oita National College of Technology, 1666 Maki, Oita 870-0152, Japan. higasino@oita-ct.ac.jp
authors: Makoto
authors: M
authors: Higashino
authors: Heinz G
authors: HG
authors: Stefan
mesh_terms: D019015:Geologic Sediments / Q000737:chemistry*; D008956:Models, Chemical; D017711:Nonlinear Dynamics; D010316:Particle Size; D016062:Porosity; D011312:Pressure; D012212:Rheology; D014872:Water Movements