Validation of a stochastic digital packing algorithm for porosity prediction in fluvial gravel deposits

Porosity as one of the key properties of sediment mixtures is poorly understood. Most of the existing porosity predictors based upon grain size characteristics have been unable to produce satisfying results for fluvial sediment porosity, due to the lack of consideration of other porosity-controlling factors like grain shape and depositional condition. Considering this, a stochastic digital packing algorithm was applied in this work, which provides an innovative way to pack particles of arbitrary shapes and sizes based on digitization of both particles and packing space. The purpose was to test the applicability of this packing algorithm in predicting fluvial sediment porosity by comparing its predictions with outcomes obtained from laboratory measurements. Laboratory samples examined were two natural fluvial sediments from the Rhine River and Kall River (Germany), and commercial glass beads (spheres). All samples were artificially combined into seven grain size distributions: four unimodal distributions and three bimodal distributions. Our study demonstrates that apart from grain size, grain shape also has a clear impact on porosity. The stochastic digital packing algorithm successfully reproduced the measured variations in porosity for the three different particle sources. However, the packing algorithm systematically overpredicted the porosity measured in random dense packing conditions, mainly because the random motion of particles during settling introduced unwanted kinematic sorting and shape effects. The results suggest that the packing algorithm produces loose packing structures, and is useful for trend analysis of packing porosity

Spatial variability in river bed porosity determined by nuclear density gauging: A case study from a French gravel-bed river

Porosity is one of the key properties of fluvial sediments. It is defined as the ratio of pore volume to total volume. In river science, porosity is often assumed to be spatially constant, which might be a gross simplification of reality. Ignoring the spatial variations in porosity can cause errors in morphological, ecological, hydrological, hydrogeological and sedimentological applications. Although detailed information about spatial porosity variations can be obtained from porosity measurements at field sites, such information has never been collected where these variations might be important. In this study, field porosity measurements were carried out to quantify the magnitude of the spatial porosity variation for four different sedimentological environments of a braided river: a confluence, a tributary delta, a braid bar and a secondary channel. A nuclear density gauge was used for the measurement of porosity. The nuclear density gauge proved to be a time‐saving and labour‐saving technique that produces accurate porosity values with a root mean square error of 0.03. The four sedimentological environments showed significant differences in porosity, with mean porosity being lower for confluence and bar than for delta and secondary channel. Semi‐variogram analysis showed the absence of any spatial correlation in porosity for distances beyond 4 m. This shows that distance cannot be used as a parameter for porosity extrapolation in a fluvial system unless the extrapolation distance is less than 4 m. At least eight measurements of porosity are required to obtain a reliable estimate of mean porosity in a sedimentary environment, i.e. with uncertainty <0.03. Although grain size characteristics were found to have a significant impact on porosity, the relationships between these parameters and porosity were not very strong in this study. The unique porosity dataset, presented in this article, provides a valuable source of information for researchers and river managers.Deutsche Forschungsgemeinschaf

Влияние модифицирования бором на изменение состава карбидов хромистых сплавов

River morphodynamics and sediment transportRiver morphology and morphodynamic

Sediment management throughout the Meuse river

The catchment of the Meuse River measures 34,347 km2 and is shared by France, Belgium, the Netherlands, Luxembourg and Germany. The main river is 905 km long and flows from France through Belgium and the Netherlands towards the North Sea. Since the 19th century large engineering works have been carried out to serve navigation, power generation and flood safety. The International Meuse Commission (IMC) was established in 2002 with the signing of the Meuse Treaty (Ghent Convention). The treaty aims at achieving sustainable and integrated water management by addressing transboundary issues such as flood management, water quality and nature and water availability. In this way rules and requirements of the European Water Directive and the Floods Directive are implemented in a coordinated way. Although erosion and sedimentation processes are important for ecology as well as a potential threat for structures and navigation, the directives do not provide clear guidance for sediment management. In this research we made an inventory of sediment related problems in the countries and national sediment management strategies, which until now aim at safeguarding navigation and flood safety through maintenance dredging. However, national sediment research programs started recently including river system aspects and long-term effects of human interference and climate change. France started the program “Know the River” to understand the sediment loads, morphological development and impact of human activity and climate change. In the Netherlands the morphological system is assessed in the “Story of the Meuse”, the “Story of the Sediment” and the Integrated River Management program. In both countries the results will be used for improved management and planning new interventions. The national programs are not coordinated at this stage. This provides a challenge for international cooperation, aiming at understanding of basin wide sediment sources, sinks and fluxes and ultimately recommendations for transboundary sediment management

River Response to Anthropogenic Modification : Channel Steepening and Gravel Front Fading in an Incising River

While most of the world's large rivers are heavily engineered, channel response to engineering measures on decadal to century and several 100 km scales is scarcely documented. We investigate the response of the Lower Rhine River (Germany-Netherlands) to engineering measures, in terms of channel slope and bed surface grain size. Field data show domain-wide incision, primarily associated with extensive channel narrowing. Remarkably, the channel slope has increased in the upstream end, which is uncommon under degradational conditions. We attribute the observed response to two competing mechanisms: bedrock at the upstream boundary increases the channel slope over the upstream part of the alluvial reach to compensate for the reduction of net annual sediment mobility, and extensive channel narrowing reduces the equilibrium slope. Another striking feature is the advance and flattening of the gravel-sand transition, suggesting its gradual fading due to an increasingly reduced slope difference between the gravel and sand reaches.</p

The Successful Return-To-Work Questionnaire for Cancer Survivors (I-RTW_CS):Development, Validity and Reproducibility

Background: Cancer survivors’ perspectives on a successful return to work (RTW) may not be captured in the common measure of RTW, namely time until RTW. Objective: The purpose of this study was therefore to develop an RTW outcome measure that reflects employed cancer survivors’ perspectives, with items that could be influenced by an employer, i.e. the Successful Return-To-Work questionnaire for Cancer Survivors (I-RTW_CS), and to assess its construct validity and reproducibility. Methods: First, three focus groups with cancer survivors (n = 14) were organized to generate issues that may constitute successful RTW. Second, a two-round Delphi study among 108 cancer survivors was conducted to select the most important issues. Construct validity of the I-RTW_CS was assessed using correlations with a single-item measure of successful RTW and the Quality of Working Life Questionnaire for Cancer Survivors (QWLQ-CS; n = 57). Reproducibility (test–retest reliability) was assessed using the intraclass correlation coefficient (ICC; n = 50). Results: Forty-eight issues were generated, of which seven were included: ‘enjoyment in work’; ‘work without affecting health’; ‘confidence of employer without assumptions about work ability’; ‘open communication with employer’; ‘feeling welcome at work’; ‘good work–life balance’; and ‘joint satisfaction with the situation (employer and cancer survivor)’. Correlations with single-item successful RTW and QWLQ-CS were 0.58 and 0.85, respectively. The reproducibility showed an ICC of 0.72. Conclusions: The I-RTW_CS provides an RTW outcome measure that includes cancer survivors’ perspectives and weights its items on an individual basis, allowing a more meaningful evaluation of cancer survivors’ RTW. This study provides preliminary evidence for its construct validity and reproducibility