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Bedrock rivers are the keystone to understanding landscape evolution as they control the rate of geomorphic responses to climatic and tectonic signals. Bedrock erosion is driven by channel hydraulics, which are not well understood for complex bedrock river morphologies. Some bedrock rivers exhibit a constriction-pool-widening morphology and associated plunging flow where the core of maximum velocity follows the bed into deep pools. Previous observations suggest that moderate discharges enhance the erosive potential of plunging flows, and that plunging flows are the dominant driver of morphology and downcutting in reaches where they are present. However, there are very few observations of plunging flows in natural environments, so their frequency and cumulative impact on landscape evolution is still unclear. Here we examine Acoustic Doppler Current Profiler and Multibeam Echosounder data collected in the Fraser Canyon of British Columbia, Canada to better understand the general properties and frequency of plunging flows. The entire 375 kms of the Fraser Canyon were analyzed for indicators of plunging flows to estimate their frequency. Results suggest that plunging flows appear to be abundant and are correlated with high shear stresses which are concentrated into deep bedrock pools. When examined using common erosion modelling techniques, observations suggest that reaches with plunging flows are incising at a much faster rate than non-plunging reaches. This work shows that considering reach scale hydraulics is critical for understanding the morphogenesis of large bedrock rivers and the mountainous landscapes that they drain. The abundance of plunging flows in large bedrock rivers suggests the importance of integrating complex flow patterns into bedrock erosion models, informs patterns of bedrock erosion at the reach scale, and begs for further investigation into the distribution of fluid shear stresses in complex bedrock channel morphologies.

An experiment is a programme of observations specially constructed to provide a critical test of theory or generalization about nature. It is designed to acquire firm evidence for or against the effect in question. Accordingly, it must be arranged to control all sources of variability contributing to the phenomena under examination, save those it is intended to study. In the natural environment, this is difficult to achieve. Consequently, classical geomorphology had no established tradition of experimentation. However, in the latter third of the twentieth century, geomorphologists began to explore experimentation as a means to resolve questions that arise in the study of geomorphological processes. In the period 1976–84, an IGU Commission on Field Experiments in Geomorphology formally established an interest in the approach. Although few field studies before the turn of the century achieved experimental status, valuable experience was gained in laboratory experiments, scaled and unscaled, leading to present wide acceptance of experimentation as a means to approach questions about geomorphological processes.

The challenges of polypharmacy and inappropriate prescribing are recognized internationally. This study synthesizes and compares the policies related to these issues introduced in Canada's two most populous provinces - Ontario and Quebec - over the first two decades of the 21st century. Drawing on policy documents and consultations with experts, we found that while medication management to address polypharmacy and inappropriate prescribing has not been an explicit and consistent policy target in either province, some policy changes sought to directly or indirectly impact medication management. These changes include the introduction of primary care teams that include pharmacists, the introduction of a medication review performed by pharmacists (in Ontario), increased emphasis on quality improvement with some attention to potentially inappropriate medications (specifically opioids in Ontario), and investments in information technology to improve communication across providers and move toward electronic prescribing to improve medication safety and appropriateness. Despite growing evidence of the problem of polypharmacy and inappropriate prescribing, there has been limited policy attention targeting these problems directly, and policy changes with potential to improve prescribing and medication management may not have been fully realized. Further research to evaluate the impact of these changes on provider behaviours, and on patient outcomes, warrants attention.

Flume experiments were conducted to understand the role of episodic sediment supply on the threshold of motion, streambed state, and stability in gravel bed channels. We demonstrate the importance of bed surface evolution on grain entrainment and hence channel stability. The grain-size distribution (GSD) of the bed surface coarsened quickly under no feed conditions to develop an armored surface. Armor continued to experience particle exchange but remained intact throughout the experiment, and was relatively insensitive to subsequent sediment supply pulses. Bed surface structures (coarse-grain clusters, stone cells, and imbrication) developed during the experiments and continued to respond dynamically to sediment pulses. Thresholds of motion estimated by various methods increased during the experiment and fluctuated in response to changes in sediment supply, though they were poorly predicted either by surface grain-size changes or by surface structure. This reinforces the idea that the threshold for motion is not constant in poorly sorted gravel-bed streams, and it confirms that the critical Shields number in transport models represents a bed state parameter, not a grain mobility number. Changes are controlled by a variety of factors including sediment supply regime, the degree of bed structuring, and the history of bed evolution. Our results highlight the importance of sediment supply regime as a control on bed surface evolution and the channel stabilizing function played by surface structures. The experiment was conducted in the Mountain Channel Hydraulic Experimental Laboratory at the Department of Geography, The University of British Columbia. AH developed the idea and designed the experiments. Claudia vonFlotow, Maria Elgueta-Astaburuaga and Tobias Müller conducted the experiment. MAH, MS, CF-B, JPLJ, JGV, and MC analysed the data and wrote the paper. The research was funded by NSERC Discovery (to M. Hassan) and Canada Foundation for Innovation (to M. Hassan). Matteo Saletti was supported by a Grant from UBC Dean of Arts Office (to M. Hassan). We thank the journal editor, Luca Solari (the journal associate editor), Paul Grams and two anonymous reviewers for suggestions that significantly improved the presentation. Experimental data can be found at http://doi.org/10.5281/zenodo.1227423; images at http://doi.org/10.5281/zenodo.3558356; digital elevation models at https://zenodo.org/record/1478895#.W-ICWPZFxuk, and in the supporting information.

International audience; There recently has arisen substantial concern for the reproducibility of scientific findings, but the discussion has not significantly impacted Earth science. We consider repetition, replication, and reproducibility in Earth science, using an example from geomorphology. Repetition repeats the program of observations in the same exercise to establish precision of results. Replication is duplication of observations using similar resources but in an independent program. Reproduction is confirmation of scientific principles using different resources in an independent program. We conclude that results will mainly be limited to reproduction-confirmation of principles-and that this is the essential goal for advancing the science. We illustrate these concepts by review of our experiments on the infiltration of fine grains in flowing water into a bed of coarser grains, conducted using glass beads in a laboratory flume.Plain Language Summary Recent years have witnessed a rapid increase in concern for the confidence that can be placed in scientific results. The key to establishing such confidence is reproduction of the result under independent circumstances. The issue has been less discussed in Earth science than in other disciplines. In this commentary we draw attention to the issue using an example from geomorphology involving the infiltration of fine sediments in flowing water into a bed of coarser sediments.

International audience; It is common to use idealised materials to study the dynamics of granular transport in fluid flows, but the impact of this choice upon sediment behaviour has not been extensively explored. To tackle this research gap, two experiments were undertaken to explore the influence of a finer grain input to a channelized coarser granular flow driven by a shallow fluid flow. The first set of runs was undertaken using spherical glass beads, and the second set with natural fluvial sediment. The transport system approximates a narrow slice through the bedload at the bottom of a river. In the runs with natural grains, the infiltration of fine sediment into the bed was similar to the spherical glass beads, but with reduced infiltration capacity. We ascribe this behaviour to irregular and variable pore shapes and sizes in the natural material. The behaviour of the bedload in the natural material runs matched that of the bead runs only when the feed contained a high content of fines. When the feed contained a low content of fines the transport of natural grains was more complex, including the emergence of migrating collections of grains. However, the overall changes in bed and water slope due to the finer grain input were comparable in both sets of experiments. We conclude that artificial, idealised materials qualitatively represent sedimentary phenomena, but that quantitative differences in the outcomes must be expected. (c) 2020 John Wiley & Sons, Ltd.

Introduction: Military sexual trauma (MST) is a serious and pervasive problem among military men and women. Recent findings have linked MST with various negative outcomes including risky, self-destructive, and health-compromising behaviors. Objective: The current review summarizes the existing literature on the association between MST and risky behaviors among military men and women who have served in the U.S. Armed Forces. Method: We systematically searched five electronic databases (PubMed, EMBASE, PSYCINFO, PILOTS, and CINAHL Plus) using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Results: Of the initial 2,021 articles, 47 met the inclusion criteria. Reviewed studies revealed three patterns of findings: (1) largely studied and consistent (i.e., suicidal behaviors, disordered eating), (2) mixed and in need of future research (i.e., alcohol and drug use, smoking), and (3) underexamined (i.e., sexual behaviors, illegal/aggressive behaviors) or completely neglected (e.g., problematic technology use, gambling). Discussion: The current systematic review advances literature by providing strong support for an association between MST and a wide range of risky behaviors. Moreover, it highlights important areas for future research.

Recently, we reported that a major function of histone acetylation at the yeast FLO1 gene was to regulate transcription elongation. Here, we discuss possible mechanisms by which histone acetylation might regulate RNA polymerase II processivity, and comment on the contribution to transcription of chromatin remodelling at gene coding regions and promoters.

Inflammation is the body’s means of defense against harmful stimuli, with the ultimate aim being to restore homeostasis. Controlled acute inflammation transiently activates an immune response and can be beneficial as protection against infection or injury. However, dysregulated inflammatory responses, including chronic inflammation, disrupt the immune system’s ability to maintain homeostatic balance, leading to increased susceptibility to infection, continuous tissue damage, and dysfunction. Aging is a risk factor for chronic inflammation; their coincidence is termed “inflammaging”. Metabolic disorders including obesity, neurodegenerative diseases, and atherosclerosis are often encountered in old age. Therefore, it is important to understand the mechanistic relationship between aging, chronic inflammation, and metabolism. It has been established that the expression of inflammatory mediators is transcriptionally and translationally regulated. In addition, the post-translational modification of the mediators plays a crucial role in the response to inflammatory signaling. Chromatin regulation responds to metabolic status and controls homeostasis. However, chromatin structure is also changed by aging. In this review, we discuss the functional contributions of chromatin regulation to inflammaging.

Within the last two centuries, the Mississippi River basin has been transformed by changes in land use practices, dam construction and training of the rivers for navigation. Here we analyze the contemporary patterns of fluvial sediment yield in the Mississippi River basin using all available data in order to assess the influence of regional land condition on the variation of sediment yield within the basin. We develop regional scale relations between specific sediment yield (yield per unit area) and drainage area to reveal contemporary regional sediment yield patterns and source areas of riverine sediments. Extensive upland erosion before the development of soil conservation practices exported large amounts of sediment to the valleys and floodplains [Trimble, 1981; Belmont et al., 2011]. We show that sediment today is sourced primarily along the river valleys from arable land, and from stream bank and channel erosion, with sediment yields from areas dominated by arable land two orders of magnitude greater than that of grassland dominated areas. Comparison with the “T factor”, a commonly quoted measure of agricultural soil resilience suggests that the latter may not reflect contemporary soil loss from the landscape.

Terrestrial sediment yield – often measured as suspended sediment load in stream channels – commonly scales with drainage area within homogeneous land surface regions. But the effect of drainage area has not usually been recognised in comparative sediment yield analyses, rendering most comparisons of sediment yield from disparate source areas invalid. The procedure to discount scale differences for comparative purposes is presented. Mathematical scaling varies according to landscape condition and provides a physical interpretation of that condition. The results open the way for rational construction of a ‘sediment delivery ratio’.

The vast majority of continental sediment delivered to the world's oceans moves by suspension in rivers. Depth-integrated or point-integrated bottle samplings are the traditional methods used to determine the mean concentration of suspended sediment in rivers. While there has been some investigation of the error associated with depth-integrated sampling, the representativeness of a point-integrated bottle sample has not been addressed in the literature. Here we analyze continuous hour-long measurements of suspended sediment and grain-size fractions collected using a LISST-SL in the sand-bed portion of the Fraser River, British Columbia, to determine an appropriate sampling time. The 2σ uncertainty range of individual 30 s samples varied from ±3% to ±33% about the observed mean, with a systematic increase toward the streambed. Mean concentrations for suspended sediment and grain-size fractions were computed over increasing time periods and compared with a long-duration mean concentration to determine when a sample becomes representative. A cumulative probability distribution was generated from multiple iterations of this process. All suspended sediment load and grain-size fractions bear a low probability of representing the mean concentration over standard bottle sample durations. A probability >90% of representing the mean concentration and grain size of various fractions requires ∼570 s (9.5 min) of sampling. Sampling for a shorter period of 264 s (4.4 min) can yield a sample with 73% probability of representing the mean concentration.

We note the presence in the literature of two different concepts of the term “active layer” in relation to fluvial sediment transport. It has been used to represent the current dynamically active streambed surface, or to represent the depth of event-scale scour and fill. These concepts involve distinct length and time scales. We propose that, when the distinction is important, the concepts be distinguished as either a “dynamical active layer” or an “event active layer.”

Experiments were undertaken to study the nature of granular interaction in running water by examining the influence of fine grain inputs to a coarser sediment bed with a mobile surface. Video recordings of grain sorting by both kinetic sieving and spontaneous percolation are used to diagnose the critical processes controlling the overall bed response. Kinetic sieving takes place in the mobile bed surface, with the finer sediment moving to the bottom of the bedload transport layer at the interface with the underlying quasi-static coarse bed. We show that the behavior at this interface dictates how a channel responds to a fine sediment input. If, by spontaneous percolation, the fine sediment is able to infiltrate into the underlying quasi-static bed, the total transport increases and the channel degrades. However, if the fine sediment input rate exceeds the transport capacity or is geometrically unable to infiltrate into the underlying bed, it forms a quasi-static layer underneath the transport layer that inhibits entrainment from the underlying bed, resulting in aggradation and an increase in bed slope. This article is protected by copyright. All rights reserved.

A horizontally mounted 300 kHz acoustic Doppler current profiler was deployed in Fraser River at Mission, British Columbia, to test its capability to detect size-classified concentration of suspended sediment. Bottle samples in-beam provide a direct calibration of the hADCP signals. We also deployed a 600 kHz vertically mounted ADCP from a boat in combination with bottle samples. Fraser River at Mission is 525 m wide with moderate suspended sediment concentration (up to 350 mg L−1 in our measurements, mostly silt), and a modest sand load only at high flows. We use an entirely empirical approach to calculate the sediment load using ADCPs to test the reliability of acoustic methods when assumptions embedded in the sonar equation about the relation between suspended sediment size and concentration, and acoustic signals are violated. vADCP calibration using matched individual bottle samples and acoustic backscatter departed from the expected theoretical relation. Calibration using depth-averaged sediment concentration and acoustic backscatter more closely matched theoretical expectations, but varied through the season. hADCP calibrations conformed with theoretical expectations and did not exhibit seasonal variation. Silt and sand were successfully discriminated; however, silt dominates the correlations. We found no coherent relation between acoustic attenuation and silt concentration. In-beam results are extended by correlation to estimate mean sediment concentration and total suspended flux in the entire channel: this auxiliary correlation cancels any calibration bias and permits monitoring of size-classified suspended sediment in absence of detailed information of sediment grain-size distribution.

Current understanding of bedform dynamics is largely based on field and laboratory observations of bedforms in steady flow environments. There are relatively few investigations of bedforms in flows dominated by unsteadiness associated with rapidly changing flows or tides. As a consequence, the ability to predict bedform response to variable flow is rudimentary. Using high-resolution multibeam bathymetric data, this study explores the dynamics of a dune field developed by tidally modulated, fluvially dominated flow in the Fraser River Estuary, British Columbia, Canada. The dunes were dominantly low lee angle features characteristic of large, deep river channels. Data were collected over a field ca 1·0 km long and 0·5 km wide through a complete diurnal tidal cycle during the rising limb of the hydrograph immediately prior to peak freshet, yielding the most comprehensive characterization of low-angle dunes ever reported. The data show that bedform height and lee angle slope respond to variable flow by declining as the tide ebbs, then increasing as the tide rises and the flow velocities decrease. Bedform lengths do not appear to respond to the changes in velocity caused by the tides. Changes in the bedform height and lee angle have a counterclockwise hysteresis with mean flow velocity, indicating that changes in the bedform geometry lag changes in the flow. The data reveal that lee angle slope responds directly to suspended sediment concentration, supporting previous speculation that low-angle dune morphology is maintained by erosion of the dune stoss and crest at high flow, and deposition of that material in the dune trough.

Ross Mackay's contributions to periglacial geomorphology are commonly regarded as the fruit of solo inspiration. In fact, his work is an exemplary product of its time. At the outset of his career, geomorphology was entering a radical transformation from interpretive study of landscape history towards quantitative study of landscape-forming processes. Early periglacial geomorphology was concerned mainly with attempting to infer historical environmental conditions on the periphery of the great Pleistocene ice sheets and Mackay's earliest works are historically oriented accounts of regional geography. From 1960, however, his work, following the new perspective, was based on quantitative measurement of landforms and land-forming processes, both in the field and on maps, and application of physical theory to interpret his observations. He focused attention on individual periglacial landforms that had hitherto been only superficially described. Outstanding aspects of Mackay's contributions are his genius for making critical field observations and his ability to use them to test geophysical theory. He was one of a very small number of pioneers who reconstructed periglacial geomorphology. Copyright © 2015 John Wiley & Sons, Ltd.

Temporal dynamics of sediment transport in steep channels using two experiments performed in a steep flume (8%) with natural sediment composed of 12 grain sizes are studied. High-resolution (1 s) time series of sediment transport were measured for individual grain-size classes at the outlet of the flume for different combinations of sediment input rates and flow discharges. Our aim in this paper is to quantify (a) the relation of discharge and sediment transport and (b) the nature and strength of memory in grain-size-dependent transport. None of the simple statistical descriptors of sediment transport (mean, extreme values, and quantiles) display a clear relation with water discharge, in fact a large variability between discharge and sediment transport is observed. Instantaneous transport rates have probability density functions with heavy tails. Bed load bursts have a coarser grain-size distribution than that of the entire experiment. We quantify the strength and nature of memory in sediment transport rates by estimating the Hurst exponent and the autocorrelation coefficient of the time series for different grain sizes. Our results show the presence of the Hurst phenomenon in transport rates, indicating long-term memory which is grain-size dependent. The short-term memory in coarse grain transport increases with temporal aggregation and this reveals the importance of the sampling duration of bed load transport rates in natural streams, especially for large fractions.

Chilliwack River is typical of many Cordilleran valley river systems that have undergone dramatic Holocene degradation of valley fills that built up over the course of Pleistocene glaciation. Downstream controls on base-level, mainly blockage of valleys by glaciers, led to aggradation of significant glaciofluvial and glaciolacustrine valley fills and fan deposits, subsequently incised by fluvial action. Models of such large-scale, long-term degradation present a number of important challenges since the evolution of model parameters, such as the rate of bedload transport and grain size characteristics, are governed by the nature of the deposit. Sediment sampling in the Chilliwack Valley reveals a complex sequence of very coarse to fine textural modes. We present a 1-D numerical morphodynamic model for the river-floodplain system tailored to conditions in the valley. The model is adapted to dynamically adjust channel width to optimize sediment transporting capacity, and to integrate relict valley fill material as the channel incises through valley deposits. Sensitivity to model parameters is studied using four principal criteria: profile concavity, rate of downstream grain-size fining, bed surface sand content, and the timescale to equilibrium. Model results indicate that rates of abrasion and coarsening of the grain size distributions exert the strongest controls on all of the interrelated model performance criteria. While there are a number of difficulties in satisfying all model criteria simultaneously, results indicate that 1-D models of valley-bottom sedimentary systems can provide a suitable framework for integrating results from sediment budget studies and chronologies of sediment evacuation established from dating.

Two empirically consistent explanations exist for the morphology and dynamics of bedrock rivers. The stream power law appears to explain rates of rock incision at large scale (large drainage basins or landscape scale), but appears to be of limited value in predicting reach-scale morphology and dynamics. The underlying reason why stream power is such an effective tool for understanding landscape evolution is because it is an explicit representation of the inverse power relation between slope and area in rivers incising bedrock. This morphometric relation is nearly universal, subject to exogenous contingencies. Independent testing and validation of the stream power incision model is challenging because of the contingencies that exist in almost all landscapes. Mechanistic models of erosion have been tested and validated at small scales, generally below the reach scale, and opportunities exist for independent testing and validation by using them to predict reach-scale morphologies. Predicting larger scale bedrock river morphology requires the assumption that flow, sediment fluxes and bedrock erosion processes that occur at smaller scale are adequately averaged at larger scales, which is not well supported. Reconciling these two scales of explanation is one of the grand challenges of fluvial geomorphology, unless we accept that theory and explanations will be scale-delimited.

Extreme-value statistics has taught us that flood flows can be estimated reasonably well, and that while extreme flows are rare, they are certain to occur. The physical process of flooding is reasonably well understood. However, this knowledge does not extend to steep creeks with potentially highly mobile beds. Most infrastructures on such creeks have been designed for clearwater floods with return periods of up to 200 years. This does not account for hydrogeomorphic processes such as debris floods and debris flows in which parts of, or the entire, channel bed sediments are mobilized and lead to massive erosion of channel bed and banks and debris inundation on terminal alluvial fans. Similarly, the potential for outburst floods – many times larger than normal floods – related to failure of landslide, glacier, moraine, beaver or man-made dams is not systematically included in standard hazard assessments. This paper has the objective of bridging science and practice by highlighting some of the most threaten...

Riprap, consisting of large boulders or concrete blocks, is extensively used to stabilize streambanks and to inhibit lateral erosion of rivers, yet its effect on river morphology and its ecological consequences have been relatively little studied. In this paper, we review the available information, most of it culled from the “grey” literature. We use a simple one-dimensional morphodynamic model as a conceptual tool to illustrate potential morphological effects of riprap placement in a gravel-bed river, which include inhibition of local sediment supply to the channel and consequent channel bed scour and substrate coarsening, and downstream erosion. Riprap placement also tends to sever organic material input from the riparian zone, with loss of shade, wood input, and input of finer organic material. Available information on the consequences for the aquatic ecosystem mainly concerns effects on commercially and recreationally important fishes. The preponderance of studies report unfavorable effects on local numbers, but habitat niches created by openings in riprap can favorably affect invertebrates and some small fishes. There is a need for much more research on both morphological and ecosystem effects of riprap placement.

A survey along the Fraser Canyon in Canada reveals complex flow dynamics involving velocity inversions and upwelling, which suggests ways to improve flow and bedrock incision modelling. Canyons carved into the bedrock in areas of actively uplifting terrain are important for our understanding of the link between tectonics, climate and topography. Fluid flow and sediment transport are processes associated with canyon bedrock incision in models, but to date there are no field observations of the flow structure in bedrock canyons that can be used to test the model components that represent fluid flow. This paper describes a survey along the Fraser Canyon in Canada that provides detailed measurements of flow in a narrow bedrock canyon. The data reveal a more complex flow structure than currently assumed in flow models, implying that a revision in our understanding of bedrock canyon incision is required. Bedrock erosion in rivers sets the pace of landscape evolution, influences the evolution of orogens and determines the size, shape and relief of mountains1,2. A variety of models link fluid flow and sediment transport processes to bedrock incision in canyons. The model components that represent sediment transport processes are increasingly well developed3,4,5. In contrast, the model components being used to represent fluid flow are largely untested because there are no observations of the flow structure in bedrock canyons. Here we present a 524-kilometre, continuous centreline, acoustic Doppler current profiler survey of the Fraser Canyon in western Canada, which includes 42 individual bedrock canyons. Our observations of three-dimensional flow structure reveal that, as water enters the canyons, a high-velocity core follows the bed surface, causing a velocity inversion (high velocities near the bed and low velocities at the surface). The plunging water then upwells along the canyon walls, resulting in counter-rotating, along-stream coherent flow structures that diverge near the bed. The resulting flow structure promotes deep scour in the bedrock channel floor and undercutting of the canyon walls. This provides a mechanism for channel widening and ensures that the base of the walls is swept clear of the debris that is often deposited there, keeping the walls nearly vertical. These observations reveal that the flow structure in bedrock canyons is more complex than assumed in the models presently used. Fluid flow models that capture the essence of the three-dimensional flow field, using simple phenomenological rules that are computationally tractable, are required to capture the dynamic coupling between flow, bedrock erosion and solid-Earth dynamics.