Application of tracers for transport investigations in unregulated rivers

The proper understanding and mathematical description of transport processes mechanism in unregulated rivers is unsatisfactory up to now. More of previous experience have based on solutions of dispersion model for straight channel approximation. Such approach does not take into account the riverbed morphology which is suspected to play a significant role for pollution transport in unregulated rivers. One of the most important phenomena accompanied stream flow in meandering rivers are generating dead or stagnant flow volumes. The factors described that phenomena have been introduced to the one-dimensional dispersion model. Such approach seems to be very promising, but should be checked in field conditions. The first our results coming from Wkra River - 1998 experiment did not give definite answer if this model is valid or not, because of relative low dead volume (about 10%) at chosen experimental river course. That was the reason for looking for river with more complex morphology. We have chosen the upper Narew, the low-land strongly meandered river in the East-Poland region. At 16 km section the five measuring profiles have been located and characterized by hydrometric and hydraulic measurements. The Br-82 has been used as a test tracer of transverse mixing process. The results of that test help the decision of proper localization of the first measuring profile which should be localized wider than the transverse mixing distance (between tracer injection cross-section and first measuring profile). It is the fundamental criteria should be fulfilled for one-dimensional dispersion. The Rhodamine WT has been selected as a fluorescent tracer for main experiment. The time and spatial distribution of the tracer concentration have been measured in all selected cross-sections of the Narew river by means of Turner fluorometers. The dead volume one-dimensional dispersion model with mass exchange between flow and dead zones has been successfully validated on the base of obtained experimental results