Martin Glas

The Danube so colourful: a potpourri of plastic litter outnumbers fish larvae in Europe's second largest river.

Previous studies on plastic pollution of aquatic ecosystems focused on the worlds oceans. Large rivers as major pathways for land-based plastic litter, has received less attention so far. Here we report on plastic quantities in the Austrian Danube. A two year survey (2010, 2012) using stationary driftnets detected mean plastic abundance (n = 17,349; mean ± S.D: 316.8 ± 4664.6 items per 1000 m−3) and mass (4.8 ± 24.2 g per 1000 m−3) in the river to be higher than those of drifting larval fish (n = 24,049; 275.3 ± 745.0 individuals. 1000 m−3 and 3.2 ± 8.6 g 1000 m−3). Industrial raw material (pellets, flakes and spherules) accounted for substantial parts (79.4%) of the plastic debris. The plastic input via the Danube into the Black Sea was estimated to 4.2 t per day.

Accuracy and comparison of standard k-ϵ with two variants of k-ω turbulence models in fluvial applications

ABSTRACT Racetrack flumes are established experimental settings in ecohydraulics and sediment studies. Their experimental results are often coupled with numerical simulations. The two-equation turbulence closures of the Reynolds-Averaged Navier-Stokes equations are applied widely in such engineering applications. They are preferred for their ease of use and low computational costs compared with more sophisticated turbulence models involving large-scale fluvial simulations. Here, three variants of two-equation models, i.e. the standard k-ϵ model and two variants of k-ω models, were applied to tackle mean flow and turbulence in a racetrack flume and a river reach. Regarding model performances, we found an overall reasonable agreement between simulated and measured mean velocity values. Nonetheless, the simulated turbulent kinetic energy exhibited discrepancies to the measured values. The computational costs of all investigated model variants are comparable. Therefore, there is no significant preference among models. The findings confirm the application of these model approaches for mean flow-related investigations (e.g. habitat modeling) but suggest exercising caution for applications sensitive to turbulent processes.

Hydrodynamic and morphodynamic sensitivity of a river’s main channel to groyne geometry

ABSTRACT As is widely known, the groyne layout affects the three-dimensional flow situation and sediment budget in groyne fields. Lack of knowledge exists concerning the evolution of hydrodynamics and morphodynamics in the main channel of rivers due to distinct groyne layouts. Accordingly, the sensitivity of the stream flow and the river bed in the fairway to groyne geometry were investigated with the help of a three-dimensional hydrodynamic model and a sediment transport model by considering eight variants and seven discharges in a straight reach of the River Danube. The variation of crest elevation and length indicated highest sensitivity, especially at modelled discharges for which the largest geometrical changes due to the modification of the groyne layout were implemented. Within a curved reach larger effects for length variation and smaller ones for the variation of crest elevation were found. These findings can be incorporated into future research and planning of groyne layouts.