The significance of channel-flow processes for the coupling of runoff-generation with dissolved and particulate transport - an analysis based on artificial flood waves in two meso-scale middle-mountain catchments

The hydrological and hydrochemical responses of a catchment to a precipitation pulse always consists of two groups of sub-processes. The one group of processes comprises the spatial-temporal dynamics of source activation and of the transport pathways of the water in the catchment, while the other group describes the processes in the open channel and in the branched drainage network. The superposition of the two process groups in the course of natural flood events creates complex patterns of interacting processes that make it difficult to interpret the measured signals at gauging stations and to analyze the generation of the flood and the fluvatile transport of contaminants. If one wants to model the hydrochemical responses to a precipitation pulse in order to provide a basis for environmental management, one has to extract the relevant processes and must consider the two process groups separately. The Research Group "Channel-flow processes" of the University of Trier in cooperation with the Stadtwerke (municipal utility) Trier studied this phenomenon in two meso-scale middle-mountain catchments (35 and 239 km super(2)) in the region of Trier by generating artificial flood waves. It could be shown in both these water-courses that the wave, the water column, and the transported suspended matter become increasingly decoupled along the flow path. The separation of wave and water column is due to the kinematic wave effect, that was thus proven to occur even in small catchments. While the concentration changes of dissolved substances within the water column are essentially controlled by longitudinal dispersion, suspended solids experience a complete exchange of material in the wave already on short flow distances, what is finally also controlled by the kine-matic effect. In catchments, where channel-flow processes can be explained largely by the dynamics of mass transfer, it is accordingly not possible to consider runoff, dissolved and particulate matter as parallel phenomena regarding their origin and synthesis. Moreover, in these cases the assumptions made in the mixing models do not apply, so that these approaches to describe runoff generation and dissolved and particulate transport need to be reviewed.