Convective transport within stable river sediments

Abstract

Local pressure variations of the order of 100–1000 N/m 2 can be observed between the upstream and downstream faces of the typically triangular‐shaped dunelike sediment structures that form at the sediment‐water interface of rivers. Laboratory experiments were conducted examining the influence of this localized pressure variation on contaminant transport processes within the sediment. Numerical modeling of the in‐bed flow via boundary element methods was also undertaken in order to predict convective transport under typical field conditions. The laboratory experiments and numerical simulation of the in‐bed flow in several rivers verified that the pressure distribution observed on the sediment surface and the resulting interstitial fluid convection can control transport of chemically inert, nonsorbed contaminants in stable sediments. In‐bed Peclet numbers were of the order of 100–1000, indicating the negligible influence of diffusion under the conditions examined.