A random walk approach for investigating near- and far-field transport phenomena in rivers with groin fields

Abstract

Dead-water-zones in rivers formed by groin fields strongly influence the dispersive mass transport of dissolved pollutants. The cause for this influence is the exchange process between groin fields and main stream. With the help of laboratory experiments the most important parameters, such as storage time, velocity distribution and distribution of the diffusivity have been investigated. A transport model using a Lagrangian- Particle-Tracking-Method (LPTM) has been developed, to transfer the locally obtained experimental results for a single dead-water-zone into the global parameters of a one-dimensional far field model that comprises the action of many dead water zones. It is shown that in the presence of large dead water zones at the river banks, an equilibrium between longitudinal dispersion and transverse diffusion can be reached if the morphologic conditions do not change. The simulations result in a cross sectional averaged concentration distribution that converges asymptotically to a Gaussian distribution over the longitudinal coordinate. Due to the presence of dead water zones the distribution of tracer material becomes inhomogeneous in transverse direction.