A field-based protocol to approximate variability in critical Shields coarse-bed rivers at the patch scale

In gravel-bed rivers, bedload transport exhibits considerable variability in\ntime and space. Recently, stochastic bedload transport theories have been\ndeveloped to address the mechanisms and effects of bedload transport\nfluctuations. Stochastic models involve parameters such as particle\ndiffusivity, entrainment and deposition rates. The lack of hard information on\nhow these parameters vary with flow conditions is a clear impediment to their\napplication to real-world scenarios. In this paper, we determined the closure\nequations for the above parameters from laboratory experiments. We focused on\nshallow supercritical flow on a sloping mobile bed in straight channels, a\nsetting that was representative of flow conditions in mountain rivers.\nExperiments were run at low sediment transport rates under steady nonuniform\nflow conditions (i.e., the water discharge was kept constant, but bedforms\ndeveloped and migrated upstream, making flow nonuniform). Using image\nprocessing, we reconstructed particle paths to deduce the particle velocity and\nits probability distribution, particle diffusivity, and rates of deposition and\nentrainment. We found that on average, particle acceleration, velocity and\ndeposition rate were responsive to local flow conditions, whereas entrainment\nrate depended strongly on local bed activity. Particle diffusivity varied\nlinearly with the depth-averaged flow velocity. The empirical probability\ndistribution of particle velocity was well approximated by a Gaussian\ndistribution when all particle positions were considered together. In contrast,\nthe particles located in close vicinity to the bed had exponentially\ndistributed velocities. Our experimental results provide closure equations for\nstochastic or deterministic bedload transport models.\n

Based on the interdisciplinary approaches between earth science, engineering, physical geography, ecology and management, this text focuses on the theoretical questions, case-studies, challenges, and constraints taken from river restoration. It is illustrated with reports of new ground-breaking research covering spatial and temporal scales of physical processes in river catchments, coupling catchment and fluvial processes, grain dynamics and fluvial forms and on geo-ecology and restoration in mountain gravel-bed river environments.Each chapter includes discussions and comments providing experience and feedback from the fundamental research. This book covers scales of analysis for gravel-bed rivers, physics and modeling of processes at local and point scales, sediment delivery and storage, eco-geography and eco-hydraulics, and channel management and restoration. Major topics in the field are presented by recognized scientific leaders. Chapters cover theories, practices, and methodologies in river management and restoration. The interdisciplinary approach includes case-studies on new, ground-breaking research.

A general formula for non-cohesive bed load sediment transport

Theoretical, modeling, experimental and monitoring of sediment transport in gravel bed rivers are introduced. The key findings of 27 papers on this theme were published in Earth Surface Processes and Landforms during the past year. Among these, 18 papers were published by attendants of the 8th Gravel Bed River Workshop held in Japan in 2015. This Commentary introduces the main themes associated with these papers including innovations in sediment transport conceptualization and modeling and monitoring, and also three wider themes: the importance of sediment supply; relationships between gravel bed river science and restoration; and the growing recognition of the critical role played by wood in gravel bed rivers. Copyright © 2018 John Wiley & Sons, Ltd.

Interplay of flow and bed morphology caused by pool-riffle sequence formation without upstream sediment supply in gravel-bed rivers

Measuring, observing and pattern recognition of sediment transport in an armoured river using a sampler with attached underwater camera

This article has been developed within the research project Uses and informative preferences in the new media map in Spain: journalism models for mobile devices (Reference: CSO2015-64662-C4-4-R) funded by the Ministry of Economy and Competitiveness (Government of Spain) and co-funded by the ERDF structural fund, as well as it is part of the activi- ties promoted through the International Research Network of Communication Management – XESCOM (Reference: ED341D R2016/019), supported by Conselleria de Cultura, Educacion e Ordenacion Universitaria of Xunta de Galicia. The author Jorge Vazquez-Herrero is a beneficiary of the Faculty Training Program funded by the Ministry of Science, Innovation and Universities (Government of Spain)

The bias in aDcp bottom tracking induced by near-bed particle motion provides a measure of apparent bedload velocity (va ). Previous site specific field and laboratory calibration exercises to relate bedload transport rate (gb ) to va are reviewed. Good linear relations have been obtained, with r2 ranging from 0.30 to 0.91. The calibration relations differ as a function of both bed material and aDcp operating parameters. In general, for a given value of va , higher mass transport is observed in gravel-bed rivers than sand-bed rivers. The influence of bedload grain size is evaluated in detail using a new data set of 144 paired va and gb samples obtained at the braided gravel-bed Rees River, New Zealand. The bed material of the Rees River includes both sand and gravel, with subsurface median (D50) grain size of 7.5 mm, and the D50 of collected bedload samples ranging from 0.2 mm to 13 mm. Relatively poor gb-va correlation was observed for the entire Rees River data set (r2 = 0.29). However, excluding samples with <69% good bottom track data and classifying the remaining samples into subpopulations by bedload grain size (sand, sand with > 10% gravel, gravel with > 10% sand, and gravel) improved gb-va calibration relations (r2 ranging from 0.45 to 0.98). The implications for utilization of such size-dependent gb-va calibration relations in rivers with mixed gravel-sand beds are discussed.

Following construction of a sinuous diversion on an upland gravel-bed river two flood events within three days of each other, with estimated recurrence intervals of between 1·5 and 2·0 years, caused marked geomorphological adjustment to the channel. The floods resulted in bank erosion, point bar formation, scour on the outside of meander bends and particle sorting, but the overall stability of the river diversion, which is to flow adjacent to a new motorway embankment was not affected. Moreover, the channel adjustment brought about beneficial changes in terms of increasing morphological diversity: probably enhancing fish habitat, although spawning gravels placed at the head of riffles in the river diversion were scoured. The extent and nature of the geomorphological changes relate principally to the high stream power and bedload transport capacity of the river. Geomorphological principles, critical stream powers and bedload transport rates can account for the size and redistribution of bed material transport. Other factors accounting for the adjustment include limited vegetation colonization of geotextile-covered river banks and construction of overly narrow and high channel constrictions to promote flow convergence and acceleration at the head of downstream pools. The case study provides lessons for future construction of river diversions on high energy gravel-bed rivers. © 1997 John Wiley & Sons, Ltd.

The event-based bedload yields of a small gravel-bed river (the Esconavette Torrent) have been concomitantly determined by surveying coarse sediment deposition in a trap and by monitoring the active layer of the bed and the displacement of painted tracers. The geometry of the active layer was obtained by means of scour chains and topographic resurveys. The cumulative bedload yield of 4 flow events measured in the trap and by the chain and tracer approach was respectively 174 and 153 m3. The consistency between those two field-based estimates confirms that the deployment of scour chains and tracers in gravel-bed rivers have the potential to provide a robust assessment of bedload transport. This potential theoretically depends on the spatial density of scour chains and the ability of the tracing technique to fit the grain size distribution of the active layer. The results demonstrate that a distance between scour chains that represents 10-15% of the active channel width is sufficient for a rather accurate determination of event bedload transport rate by reconstruction of scour and fill throughout a cross-section.

The present paper aims to put into practice a conceptual framework for gravel-bed river sustainable management previously proposed by Pont et al. [(2009) Conceptual framework and interdisciplinary approach for the sustainable management of gravel-bed rivers: the case of the Drôme River basin (SE France). Aquatic Sciences, 71 (3), 356–370] for the Drôme River Basin (France). It tests the capacity of the functional sector concept (Petts, G.E. and Amoros, C., 1996. Fluvial hydrosystems. Springer) when used to assess the risks of environmental changes. The application of this concept is illustrated by examples focusing on the potential impacts of sediment replenishment on functional sector diversity used as a proxy of habitat diversity, and on trout distribution at a network scale. We used remote sensing and Geographic Information System (GIS) methods to produce original data. A cluster analysis performed on the components of a principal component analysis established a functional sector typology based on channel planform parameters. We calculated an index of present and 1948 functional sector diversity for the entire channel network to highlight past evolutions. A sensitivity analysis was then performed to predict changes in functional sector diversity resulting from defined options of sediment reintroduction through planned forest removal. A similar procedure was developed to evaluate likely changes in brown trout distribution resulting from the impacts of the actions on canopy cover and summer water temperature. The methodological procedure is described, as well as the different assumptions made to move from a theoretical framework to a more practical one. Two examples are used as pilots to evaluate the value of a sensitivity analysis approach based on functional sector types (FSTs) to test management actions aimed at improving aquatic ecology. Limitations and potential improvements are then discussed.

Incipient sediment motion based on turbulent fluctuations

Modelling bedload yield in braided gravel bed rivers

Integrated automatic and continuous bedload monitoring in gravel bed rivers

Three data-driven techniques, namely artificial neural networks, adaptive-network-based fuzzy inference system, and symbolic regression based on genetic programming, are employed for the prediction of bed load transport rates in gravel-bed steep mountainous streams and rivers in Idaho (U.S.A.), and the potential of several input variables is investigated. The input combinations that were tested are based, mainly, on unit stream power, stream power, and shear stress, and exhibited similarly good performance, with respect to the machine learning technique used, accentuating the importance of the regression model. The derived models are robust, generalize very well in unseen data, and generated results superior to those of some of the widely used bed load formulae, without the need to set a threshold for the initiation of motion, and consequently avoid predicting erroneous zero transport rates.