Comparison of Physical Transport Processes in Noncohesive River Sediments

Abstract

In this paper, the sediment‐side abiotic mechanisms for contaminant transport across the sediment‐water interface of rivers are compared. The transport processes considered include molecular diffusion, colloidal diffusion, pore‐water advection between the stream and its associated aquifer, localized advection due to sediment surface roughness, and sediment movement. A simple model for contaminant transport by active bed‐load transport of noncohesive sediments in triangular dunes is developed and compared to both linearly sorbing and nonsorbing contaminant transport via passive pore‐water processes. The model is limited to homogeneous noncohesive sediment beds and specific flow conditions that lead to steady dune‐migration rates. The results suggest, however, that advection should normally be the dominant mechanism in stable sediments and for nonsorbing contaminants in unstable sediments near the threshold for sediment movement. Sorbing contaminant transport should normally be controlled by the rate of sediment movement.