DBPapers
DOI: 10.5593/sgem2017/31/S12.023

DETERMINATION OF DISPERSION PARAMETERS IN STREAMS WITH DEAD ZONES

M. Sokac
Monday 11 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7408-04-1 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 31, 183-190 pp, DOI: 10.5593/sgem2017/31/S12.023

ABSTRACT

The dispersion is one of the most important pollution transport phenomena, which is used in numerical water quality models. The dispersion rate is described by the value of the dispersion coefficient in the advection – dispersion equation. The most reliable way of determining the value of the dispersion coefficient is the field tracer experiment. The results of the field experiments are affected by various influences, which occur in the real flow conditions - one of them is the occurrence of transient storage zones (dead zones). Paper describes the field tracer experiments for determination of the coefficient of longitudinal dispersion in streams of lowland type (channels with small slopes and velocities) with expected of dead zones and water vegetation occurrence. Tracer experiments were carried out on three different streams in south Slovakia. The evaluation of field measurements confirmed in all cases the presence of mentioned flow deformation, i.e. river sections and regions with the appearance of small velocities that were formed due to the extensive presence of vegetation in the river. These areas capture part of the transported substance (tracer) and then gradually release the substance and incorporated back into the stream, creating a significant distortion of the tracer concentration time course. Strong influence of these impacts raises the question of the adequacy using standard analytical solutions, whether for determining the coefficient of longitudinal dispersion or for modelling the dispersion of pollution or other substances carried by the river.

Keywords: hydrodynamic dispersion, longitudinal dispersion coefficient, tracer field experiment, tracer, colouring agent