Quantifying microplastic particle transport and retention in an experimental flume environment

<p>Rivers and streams are the dominant transport vectors for microplastic (MP) input into marine environments. During transport, complex physicochemical interactions between particles, water and river sediments influence particle mobility and retention. The specific transport mechanisms of MP in fluvial systems are not yet fully understood, and the main reason lies in the limitation in reliable data derived from experimental analysis.</p><p>In our subproject of the ‘CRC 1357 Microplastics’, we investigate the hydrodynamic mechanisms that control the transport and retention behavior of MP in open channel flows and streambed sediments. In an experimental flume environment, we create realistic hydrodynamic and hyporheic flow conditions by using various porous media (e.g. glass beads or sand) and bedform structures (e.g. riffle-pool sequences, ripples and dunes), modelled from real stream systems.</p><p>The method developed here can quantitatively analyze the transport of pore-scale particles (1-40 µm) based on fluorometric techniques. Particle velocity distributions and particle transport are measured using Particle-Image-Velocimetry and Laser-Doppler-Velocimetry. With our setup, we can quantitatively investigate time-resolved MP transport and retention through the aqueous and solid phase in a flume scale experiment.</p>

Influence of baffles on upstream passage of brook trout and brown trout in an experimental box culvert

There is much to learn about improving baffle designs to increase successful fish passage through culverts. A fish’s motivation to attempt entry into the culvert is essential. Upon entry, successful passage will largely depend on the physiological ability of the fish to navigate the entire culvert length. In this study, the motivation of brook trout (Salvelinus fontinalis (Mitchill, 1814)) and brown trout (Salmo trutta Linnaeus, 1758) to attempt ascent of an experimental flume, which mimics a roadway culvert left bare (smooth) or fitted with either spoiler or weir baffles, is assessed. Performance, measured as maximum distance of ascent within the flume, is also quantified. The bare flume was the most motivating for brook trout, and the weirs were most motivating for brown trout. As a rule, brown trout showed less motivation to stage attempts than brook trout, except within the weir baffle treatments. Performance was greatest in the weirs for smaller trout and in the spoiler baffles for larger trout. Our findings suggest that baffle form influences passage rates at road crossings in ways previously unknown and further stresses the importance of considering fish motivation and performance together when assessing the efficacy of baffle forms.

Minimizing Scour of Contraction Stepped Spillways

The scour downstream spillways can endanger the stability of the dams. Hence, determining the scour depth downstream of spillways was vital importance which scours holes formed around and near the foundations of spillways can endanger the stability of dams and may lead to their failure. So, this paper, investigate the scour downstream contraction stepped spillways. The experimental flume used 16.2 m length, 66 cm width and 65 cm depth. The used number of stepped spillways was 4 Sep, contraction ratio was 60% from flume width and the opening area in breaker 10% from the breaker area on all sides putting in down of breakers. The breaker used above the stepped spillway with different shapes of openings as rectangle, triangle and trapezoidal and different numbers by 2, 4, 6 and 8 of beakers. The divergent angle changes by 45º, 30º, 15ºand 10º. The results were showed that the best numbers of openings is 4openings with rectangle shape because it reduces the scour by 54.51%. In finally to improve this scour by divergent angle lead to the best angle is 10º can minimize the scour is 65.38%.

Morphological development of river widenings with variable sediment supply

River widening is a common restoration approach to mitigate the adverse effects of past stream alterations on infrastructure and the riparian ecosystem by stabilizing the river bed and enhancing habitat heterogeneity. In this study, two river widening approaches, excavated and dynamic, are described for the case of moderately steep gravel-bed rivers in the Alpine foothills, with a focus on dynamic river widening. As most channelized rivers exhibit ongoing degradation due to the lack of sediment supply and efforts to restore sediment transport are increasing, the consideration of the response of river widenings to variable sediment supply is important. For this purpose, insights from regime theory are applied to river widening and several experimental flume and field studies on channel response to variable sediment supply are reviewed. Dynamic river widenings are expected to be morphologically active in weakly degraded rivers with sufficient sediment supply, while they may not be an appropriate restoration approach for highly degraded rivers due to persistent impairment of morphological activity.

Development and Tests of a 3D Fish-Tracking Videometry System for an Experimental Flume

To design effective and efficient fish passage facilities at hydropower plants, the knowledge of swim behaviour of fish is essential. Therefore, living wild fish were investigated at different fish guidance structures in an experimental flume in a test section of 11 m length and 2.5 m width at water depths of about 0.6 m. Besides analysis of time data and manual recordings of the fish behaviour, video recordings of the fish movements can allow more detailed analysis of fish behaviour in different hydraulic situations. Thus, a videometry system was installed consisting of eleven synchronous cameras with overlapping views lined-up under dry conditions outside the flume. A 3D tracking algorithm was developed and implemented to analyse the video data. Core of the code is a motion-based multiple object tracking method, in which several objects can be tracked in 2D pixel-frame coordinates at the same time. After undistorting and stereo-calibrating the cameras, the 2D tracks are transferred to a 3D metric-space according to their epipolar geometry. Within this paper video data from a single experimental run of 15 min with three fishes with lengths of 100–150 mm are analysed exemplarily. The path-time diagram gives a distinct ‘big picture’ of the fish movement, which helps to identify preferred and disliked regions. However, due to imperfect actual camera setup, a 3D view in the near field of the cameras and an automated separation of individual tracks in a group of fish remains challenging.