Hydro-morphological processes through permeable sediment traps at mountain rivers

In alpine regions, villages are often situated near alluvial fans, which are fed by mountain rivers transporting high sediment load during floods. In the past, these mountain rivers on the alluvial fans have often been channelized near urbanized areas, where the bed and banks were lined with large sawed granite or gneiss blocks laid into concrete layer. Some of these channels have still a mobile bed, which is fixed with transversal sills against erosion. These channels have a high discharge and sediment transport capacity as long as no sediment deposits occur. The latter may be triggered by constrictions as they occur at bridges or by backwater effect when the channel enters the main river in the plain. In order to avoid sediment deposits in the channel, which can create dangerous overtopping with catastrophic consequences in the nearby urbanized areas, sediment traps have been installed upstream of the alluvial fans with the purpose to retain bed load during such critical floods. Practical experience with most of these sediment traps have shown that they retain already sediments for quite low and not yet dangerous floods. Thus, for such conditions the morphology of the river downstream becomes impoverished since traveling bed load creating gravel bars during frequent floods is missing. Furthermore, it has been observed in many cases that unwanted flushing of sediment traps occurred during the flood where they should safely retain sediments. In his research, Dr. Sebastian Schwindt developed a new concept of sediment traps, which are permeable for bed load transport up to floods which are frequent and not yet dangerous for the downstream reach, but which retain safely sediment for hazardous floods. With systematic laboratory experiments, it could be revealed that a guiding channel implemented across the deposition area upstream of the barrier, having a combination of mechanical and hydraulic control structures, provides a reliably working concept for permeable sediment traps. Combined mechanical-hydraulic control is achieved by an appropriate orifice or slot in the barrier, which is equipped with an especially designed bar screen in front of it. Smaller bed load-laden discharges, which correspond to the bank-full discharge of the guiding channel, can pass unhindered through such combined barriers. For higher discharges, the hydraulic control at the orifice or slot provokes a backwater, which reduces flow velocities in the upstream guiding channel, causing of the channel banks followed by bedload deposition. The latter, especially in the presence of large boulders, lead to a mechanical blocking of the bar screen which can then prevent unwanted sediment flushing with increasing filling of the deposition area. As a basis for the new sediment trap concept, Dr. Schwindt could give design recommendations about the required bottom clearance of the bar screen and the spacing between the vertical bars, as well as the size of the orifice or slot in the barrier and the function of the guiding channel capacity

Air concentration distribution in deflector-jets

As an alternative to ski jumps, deflectors can be implemented on spillways to generate free jets. They guide, up to a certain limit, the jet to an achieved location onto the plunge pool surface, and furthermore enhance the process of jet disintegration. The present research addresses the following aspects, derived from physical model tests: (1) length and shape of the jet black-water core and further characteristic air concentration contour lines, (2) streamwise development of average and minimum sectional air concentrations, as well as jet thickness, and (3) sectional air concentration profiles along the jet. It is shown that all mentioned parameters depend only on the relative blackwater core length, being a function of the approach flow characteristics, the deflector geometry and the chute slope

An interdisciplinary model chain quantifies the footprint of global change on reservoir sedimentation

Global change alters hydro-climatic conditions, affects land use, and contributes to more frequent droughts and floods. Large artificial reservoirs may effectively alleviate hydro-climatic extremes, but their storage capacities are threatened by sedimentation processes, which in turn are exacerbated by land use change. Envisioning strategies for sustainable reservoir management requires interdisciplinary model chains to emulate key processes driving sedimentation under global change scenarios. Therefore, we introduce a model chain for the long-term prediction of complex three-dimensional (3d) reservoir sedimentation considering concurrent catchment, hydro-climatic, and land-use conditions. Applied to a mountainous Mediterranean catchment, the model chain predicts increased sediment production and decreased discharge for high and medium emission pathways. Increased winter precipitation, accompanied by a transition from snowfall to rainfall, is projected to aggravate reduced summer precipitation, emphasizing a growing need for reservoirs. Additionally, higher winter precipitation proliferates sediment production and reservoir sedimentation. Land use change can outweigh the increased reservoir sedimentation originating from hydro-climatic change, which highlights the significance of localized actions to reduce sediment production. Finally, a 3d hydro-morphodynamic model provides insights into interactions between global change and reservoir sedimentation with spatially explicit information on future sedimentation patterns facilitating the implementation of management strategies

Effects of Lateral and Vertical Constrictions on Flow in Rough Steep Channels with Bedload

Two-phase flows occurring at flow constrictions such as bridges or open sediment check dams are complex, especially for steep rivers with bedload transport. Dangerous bedload deposition and backwater effects may occur in steep mountain rivers at bridges. In contrast, sediment deposition is desirable at open check dams combined with sediment traps. For design purposes, the discharge and bedload capacity across these flow constrictions must be known. The energy losses, discharge capacity, and bedload transport capacity of vertical and lateral flow constrictions are experimentally studied in a rough, 2% inclined, trapezoidal channel. Both free surface and pressurized flow conditions, as caused by lateral and vertical flow constrictions, respectively, were analyzed because both may occur at bridges and check dams. The experiments demonstrate that the vertical flow constrictions cause a faster increase in the backwater depth, with increasing discharge, than lateral constrictions. The resulting upstream flow conditions can be described by the upstream Froude number, defined as a function of the constriction dimensions (height and width). The bedload transport capacity through the flow constriction decreases with the upstream Froude number. The practical relevance of the findings is illustrated by a design example of flow constrictions at open sediment check dams

Experimental evaluation of the discharge capacity of flow constrictions by check dams in mountain rivers

Open check dams are built to retain bed load in case of major floods and may have filtering, sieving as well as dosing effects on sediment transport. The combination of an upstream reservoir with an open check dam is designated as bed load trap. These structures are crucial elements for flood protection in mountainous regions as the sediment transport capacity of mountain streams is ample, highly unpredictable and therefore an imminent danger for river dwellers. The contemporary design criteria for open check dams are based on theoretical approaches, laboratory experiments or engineering experience. A multitude of different opening types and shapes were studied and built in the past, mostly based on design parameters which are related to grading curves of the river bed. In a series of laboratory experiments, the opening geometry and position is currently optimized in view of sediment transition for frequent floods in order to ensure sediment dynamics downstream. Herein, the results of a first series of experiments are presented, which were dedicated to the evaluation of the discharge capacity of check dam openings, under the influence of bed load transport on a rough river – bed under supercritical flow conditions. Existing experimental and theoretical formulae for purely hydraulic discharges are reviewed and it is found, that the actually applied value for the orifice coefficient μ are too small. These results may also apply for bridges, which serve in some cases intentionally or unintentionally as open check dams

Teildurchgängige Geschiebesammler für sicheren Rückhalt

Geschiebesammler halten oft bei kleineren Hochwassern unnötig Geschiebe zurück. Dadurch wird die öko-morphologische Gewässerkontinuität unterbrochen. Beobachtet werden zudem oft gefährliche, selbsttätige Entleerungen. Durch den Einsatz eines Leitgerinnes im Rückhalteraum von Geschiebesammlern und einem Abschlussbauwerk mit vorgelagertem Grobrechen können die Geschiebedurchgängigkeit bei geringem Abfluss erhöht und der sichere Geschieberückhalt bei Hochwasser verbessert werden

Modelling of plunge pool scour evolution in non-cohesive sediments

Turbulences in liquids caused by jets can be of interest for numerous applications. For one, it concerns flood spillway structures within civil engineering but also is key in any area where turbulent mixing is present. The numerical simulations of jets that impinge into plunge pools are still in an early phase of their development. This paper verifies the accuracy of the Flow-3D software package in regards to simulating 3D scouring processes generated by turbulent water jets impinging on a sediment bed. Scour calculations are performed based on previously examined laboratory experiments. The results of the numerical model compare well with the experimental results in terms of the scour depth and the ridge height which accumulates downstream of the scour hole. The impact angle of the jet is identified as a driving parameter for the establishment of steady state conditions of scour depth and ridge height

Intraosseous access in neonates is feasible and safe – An analysis of a prospective nationwide surveillance study in Germany

BackgroundThis was a prospective surveillance study to investigate reports on the safety and frequency of use of intraosseous (IO) access in neonates.MethodsOver a two-year period, paediatric hospitals in Germany were asked to report all cases of IO access to the nationwide Surveillance Unit for Rare Paediatric Diseases (ESPED). Hospitals reporting a case submitted responses via an anonymised electronic questionnaire, providing details on indication, success rate, system used, location, duration to first successful IO access, complications, alternative access attempts and short-term outcome. We present a subset of data for IO use in infants of less than 28 days.ResultsA total of 161 neonates (145 term and 16 preterm born infants) with 206 IO access attempts were reported. In 146 neonates (91%), IO access was successfully established, and success was achieved with the first attempt in 109 neonates (75%). There was no significant impact of gestational age or provider’s educational level on success rates. In 71 infants with successful IO access (79%), the estimated duration of placement was less than 3 min. The proximal tibia was the predominant site used. A semiautomatic battery-driven device was used in 162 attempts (88%). The most often applied medications via IO access were crystalloid fluid and adrenaline. Potentially severe complications occurred in 9 patients (6%).ConclusionWithin this surveillance study, IO access in neonates was feasible and safe. IO access is an important alternative for vascular access in neonates

A database application framework toward data-driven vertical connectivity analysis of rivers

The description of complex river environments requires interdisciplinary approaches to collect and manage manifold data types and sources. Deriving comprehensive knowledge from complex data sources is challenging and necessitates not only knowledge of environmental science but also statistics and Software engineering. This study introduces a relational database framed in an application called River Analyst for creating and managing river data with open-source standards (Python3 and Django). We conceptualize data models of river environments, which describe sediment characteristics and hydraulics related to hyporheic exchange. River Analyst enabled us to derive novel insights for restoring rivers affected by so-called riverbed clogging, notably, fine sediment infiltration in the hyporheic zone. The database analysis reveals that clogging is not a dominant control process when the fraction of fine sediment exceeds 50%–55%. In conclusion, the new Software holds promise for data-informed advancements in augmenting knowledge to restore ecologically functional hydro-environments