Author(s): Helmut Habersack; Marcel Liedermann; Michael Tritthart; Marlene Haimann; Andrea Kreisler
Keywords: Bed load transport; Suspended sediment transport; Integrative sediment monitoring method; Numerical modelling; Morphodynamics
Abstract: In this paper, new and innovative methods for bedload and suspended sediment transport monitoring and modelling are described. The development and test of innovative sediment transport monitoring methods at various rivers, ranging from small mountain rivers to the large Danube River showed that only the combination of direct and surrogate techniques – integrative sediment monitoring stations – leads to meaningful, quantitative results. Concerning bedload improved basket samplers, bedload traps and geophones as well as tracers for specific questions allow measuring the temporal and spatial variability in sediment transport. The development of a methodology for tracing artificial pebbles made it possible to track 40 pebble tracers of three different sizes on the Danube over the course of an entire year. Combining the methods it could be determined that e. g. at the Danube bedload already moves at low flow conditions and that bedload transport only increases slightly or even remains constant after reaching bank-full discharge. The tracer study identified size-selective transport – larger sizes were moving less often and over shorter distances than smaller sizes – with a mean transport distance of 3 km per year for the current bed material at Bad Deutsch-Altenburg. In order to determine the temporal and spatial variability of the suspended sediment transport also a combination of direct and indirect methods has been developed. The monitoring methods and their interrelation during the data processing via correction factors are described at the Hainburg Strassenbrucke/Danube measurement site, where a comparison involving different conversion factors was performed. The results of annual and monthly load calculations are presented for the years 2008 and 2009. Recent developments in the simulation of sediment transport and morphodynamics are discussed on the basis of the simulation model iSed, which was developed at the University of Natural Resources and Life Sciences, Vienna. The computer model is coupled with external hydrodynamic models to obtain the flow field as basis for the simulation of sediment transport processes. First, the physical processes that must be captured by a model are described by their underlying equations. Thereafter the general model validation based on data from a laboratory flume with a 180° bend under unsteady flow conditions is shown. The model has also been applied to study a section of the Danube River east of Vienna. The calculated bedload transport rates as well as their spatio-temporal variability showed a very good agreement with measurement data. Moreover the model allowed for the first time a successful simulation of the bed forms present in the Danube as well as their downstream movement. In order to achieve this, non-uniform calculations including grain sorting, as well as detailed field measurement data for the model setup and calibration, constitute essential prerequisites.