Abstract Advances in hydroclimate change predictions in rivers include regional estimates of changes in annual flow volumes and storm peakedness. Such nuanced projections are used here to estimate relative changes in annual coarse sediment load and grain size in transport using a novel modification to magnitude–frequency analysis, the method routinely used to estimate bed material yield. The approach employs highly discretised annual flow distributions obtained from gauging station records, with data split by season, that are transformed to simulate projected multipliers on flow volumes and peak flow magnitudes over the existing flow regime. Initial testing is reported for three steepland catchments in south and west Scotland (drainage areas of 2.1–37.5 km 2 ) to reveal the impact of increases in winter flow volumes, compensatory decreases in summer flow volumes and increases in winter and summer peak flow magnitudes. Using Recking's transport function with projected hydroclimate changes suggests annual bedload yield potential increases by 27%–127%, varying inversely with drainage area. Increasing winter rainfall volume by 20%–30% over baseline increases yields by 15%–28%, whereas increasing winter peakedness by 40%–50% only increases yields by 2%–16% because of shorter flow durations. Increasing flow peakedness by 50% also increases the potential maximum grain size transported by 6%–14%, again inversely with catchment area. Monte Carlo‐based sensitivity tests on ±10% changes in input variables singly and ±20% in combination illustrate the approach to be robust to parameter variability (or error), with an average signal‐to‐noise ratio across the test sites exceeding 5:1 for the ±20% sensitivity tests. Hindcasting suggests that sediment yields 60 years ago may have only been 50%–65% of current totals. The model (MFACC, Magnitude–Frequency Analysis for Climate Change) provides a rapid screening tool for estimating ‘first order’ fluvial geomorphology risks attributable to changes in hydroclimate that could be subsequently combined with estimates of sediment supply changes and mediation by channel morphology adjustment.

Improvements in simulating and communicating the evolutionary trajectory of river morphology in response to environmental forcing over multi-decadal timeframes would foreshadow the development of "foresight competency" in river management, whereby resource managers could strategically plan toward the most preferred of several plausible futures. Of the six steps in foresight competency, visioning, which involves translating scientific forecasts into a format useable by resource managers via a user-friendly and interactive decision support tool that supports transparent decision-making, is the least well developed. The approach requires converting forecasting model outputs into metrics of channel evolution that highlight transitions either within or between channel morphology states. Here, seven process-based state transition metrics are proposed covering channel planform, morphological stability, corridor belt width, floodplain connectivity, bank erosion rate, bedform habitat diversity, and ecohydraulic diversity. To aid decision support, the metrics are converted into graphical indicators that are intuitive for management use and assembled into several prototype dashboard-style graphical user interfaces designed to facilitate interactivity. A proof-of-concept illustration is provided and priorities in development toward a fully operational decision support tool are discussed. Such developments are critical in ensuring the practical relevance of geomorphology.

Riparian zones in drylands provide important refugia for plants but depend on groundwater and thus are subject to local temporal and spatial variability in abiotic controls. In lieu of costly field-based sampling, we used readily available data to establish site-scale interannual relationships among riparian plant health and the abiotic factors that control their water balance for a historically persistent wetland adjoining the Santa Clara River in southern California, USA. Non-linear generalized additive model (GAM) analysis of plant health, represented using the normalized difference vegetation index (NDVI), confirmed robust relationships among plant health and various geomorphological and hydrological factors over multi-decadal timeframes, including years since last high-flow event, intra-year groundwater elevation changes and magnitude of 2-year cumulative surface water inflows. Geomorphic controls are related to years with high flows that cause extensive scour and deposition that re-set riparian plant communities. Relationships with dry-season groundwater declines reflect direct plant access to sub-surface moisture. Hydrological dependence via cumulative inflow magnitude indicates the dependency of groundwater elevations on sufficient winter recharge to prevent precipitous groundwater decline. GAMs-based inflection point analysis of surface water inflows versus groundwater elevations confirmed that the cumulative magnitude of multi-year inflows is critical in avoiding catastrophic groundwater declines and that large flood events drive groundwater recovery. We show that abiotic controls on plant health can be derived from readily available data and that non-linear analysis better represents the complexity of these scalar controls. Our analysis has relevance for ecosystem management of human-altered rivers and climate change adaptation.

This paper provides the editorial to accompany a Special Issue of Earth Surface Processes and Landforms produced to honour the memory of Professor Ken Gregory, a key figure in late 20th‐ and early 21st‐century geography and geomorphology. It provides an overview of Ken Gregory's career in research, teaching, and university administration, and elaborates on his key research contributions and legacy across geography and geomorphology. Ten interrelated research themes are identified where Ken made particular impacts: (1) river catchment processes and process–form relationships; (2) wood in rivers; (3) anthropogenic impacts on rivers and catchments; (4) approaches to river management that better respect natural processes; (5) public perceptions of rivers; (6) quantitative palaeohydrology; (7) chronology of river floods and deposits; (8) key physical geography/geomorphology concepts and their metrics; (9) the nature of the discipline of physical geography; and (10) concepts in physical geography teaching. These themes provide a framework to introduce the papers in this Special Issue. Through his publications, leadership style, personality, and positive influence on the many people with whom he interacted, Ken Gregory has left a legacy that will continue to inspire present and future generations of geographers and geomorphologists.

The fact that bedload transport is an inherently time‐variant and location‐sensitive fluvial process was revealed by systematic sampling, nine decades ago. Subsequent stream‐wide measurements, that frequently incorporated lengthy collection periods, as well as the adoption of standardized sampling procedures, averaged out some temporal and spatial variability. However, continuous, highly resolved, long‐period records of transport activity generated by active and passive bedload monitoring on diverse rivers have recently brought this variability into sharp focus. A defining characteristic of these ‘big data’ is that there are many possible bedload transport rates for each discharge and a wide range of discharges associated with each transport rate. Crucially, this incoherent scatter, which is generated by the various factors that affect bedload transport, can no longer be viewed as ‘noise’ that can be averaged out. We demonstrate that, even for small datasets, different methods of reporting and analysing bedload transport records provide different perspectives on the bedload transport rate–flow relation. The inclusion/exclusion of zero values, present in all data that capture the intermittent nature of bedload transport, also affects the relation. To unlock the potential of big data and facilitate the development of bedload transport–flow relations from field measurements, it is essential to employ modes of analysis that are robust to outliers and do not assume that associations between the independent and dependent variables are the same at all levels.

High-elevation alluvial river environments are little studied by geomorphologists despite their sensitivity to disturbance and their critical role as the landform supporting montane meadow ecosystems. Here, we establish the fundamental fluvial functioning and legacy factors inherent to the upper Tuolumne River in Tuolumne Meadows (elevation 2620 m asl), Yosemite National Park, USA. Evidence was drawn from structured field reconnaissance, morphological surveys, and sediment analysis; integrated with LiDAR monitoring and assess-ments of flood frequency, flood inundation, and sediment transport potential. Results indicate a sinuous single-thread channel in dynamic equilibrium with fluvial processes but with reduced rates of meander activity over the past century. Geomorphic processes are dominated by the influence of snowmelt discharge, partly because at-mospheric river events rarely influence this high elevation. Process intensity is thus directly related to snowpack depth with monitored bank erosion rates substantially higher following the deep snowpack of 2016-17. Diurnal cycling of flow means that bedload-transport potential scales very well with total annual discharge volume. The legacy of human activity is unique here, with perturbations caused primarily by early-to-mid twentieth century infrastructure development rather than typical patterns of watershed development. Pre-eminent was 1930s instream aggregate extraction for road improvements. In conjunction with naturally very low rates of sediment supply, the resulting pit is still only one-quarter full and could disconnect downstream sediment supplies for several centuries more. The gravel pit appears to explain incision of the upper channel reach and reduced rates of lateral activity farther downstream. Future impacts will be dominated by climate change, including the potential increased influence of atmospheric river events, reduced snowpack depth, and tradeoffs in sediment production and connectivity as headwater glaciers recede. The upper Tuolumne River and its meadow typify the unusual, but not singular, geomorphology of high-elevation alluvial rivers, whose high ecological and social values justify greater attention.

Many lowland fluvial systems are suspected to possess a morphological legacy from a long history of channel modifications as a consequence of limited energy and sediment supply to facilitate recovery. We explore the extent of such modifications using a regionally extensive dataset of physical habitat surveys compiled by non‐specialist surveyors. Representative photographs for each surveyed site were used to quality check channel width, depth and bed grain size information derived from Modular River Physical (MoRPh) surveys. Following checking, 1659 surveys were retained for analysis from alluvial sites, almost entirely in England. The photographs were also inspected for evidence of clear ‘overdeepening’ that would preclude frequent overtopping of the lower bank top. Results indicated that almost one‐third of the sites were overdeepened, that width‐to‐depth ratios defined using the active bed width showed stronger discrimination of overdeepening than bankfull width, that highly statistically significant identification of overdeepened channels was possible in channels up to 10 m wide and with only minimal differences attributable to channel bed materials. Stepwise regression analysis estimated relationships between channel width‐to‐depth ratios and channel size for overdeepened and non‐overdeepened channels. We demonstrate that large data sets collected by numerous non‐specialist surveyors can, with careful filtering, generate statistically robust results of geomorphological value over areas larger than is otherwise practicable. Furthermore, we reveal a notable legacy of overdeepening in the analysed lowland rivers, which presents a significant ‘hydromorphological’ management challenge.

Understanding how river bedload responds to climate and land use changes and water resource management initiatives is critical in developing sustainable approaches to river management. Passive monitoring techniques permit investigation of interannual dependencies in bedload transport in high resolution, including sediment supply factors. Here, seismic impact plate records are processed using a probabilistic model BedLoad from Impact Plates model to derive a 5‐year bedload data set at 5‐min intervals for the lower River Avon, Devon, UK. For water years that range from very dry to very wet, annual coarse bedload yields are estimated to vary through two orders of magnitude with wide prediction intervals. The most effective discharge occurs consistently at about one‐third of bankfull flow, morphologically at “subbarfull” stage, the result of hysteretic trends and falling limb transport in this non‐threshold channel. A two‐phase sediment rating curve is revealed with a variable supply related “bulge” during in‐bank flows, giving way to a near‐linear trend during overbank flows. The supply related component is predicted well using a sensitivity style metric that combines the cumulative duration of competent flows with the magnitude‐duration product of near‐threshold flows, defining a field‐scale exemplar of “stress history.” Further, the relative proportion of supply related coarse bedload yield relates strongly to the relative wetness of the previous year. High resolution, multiyear data reveal that controls on bedload dynamics are unique to a site's hydrogeoclimatic context and position in the river basin. Passive monitoring holds promise for generating “type sites” of bedload behavior critical for use in improving aquatic biodiversity and the sustainability of river management.

Evidence for the proposed Anthropocene epoch in fluvial geomorphology hinges on the influence of human activities relative to natural forcing. However, research on cause-effect understanding in river channel evolution has rarely focused on the cumulative impact of multiple drivers for change, limiting insights. Systematic review of 25 recent studies professing to explain reach-scale channel responses to cumulative impacts of human activities and natural forcing over the recent past (ca. 1880-2005) reveals some consistencies in spatio-temporal response across various catchment sizes (median 3000 km(2)) in mostly industrialized nations. Common drivers for change include changing flood and flow regimes, dam construction, changing land uses and forest cover, bank protection and instream aggregate mining. Recent channel evolution has predominantly involved narrowing, incision and terrace development, reduced bed sediment storage, lower activity rates and simplified channel geometries. Rates of channel change frequently peaked 1955-1990, providing some support for the Anthropocene 'Great Acceleration'. Evidence here suggests that many river systems are now in morphologically-novel configurations, coinciding temporally with dramatic recent declines in global freshwater aquatic biodiversity. Sustainable approaches to freshwater management must acknowledge these configurations, placing emphasis on process based approaches to river ecosystem health in which sediment cascades are reconceived to reflect altered longitudinal and lateral connectivity. However, the reviewed studies are driven largely by expert judgment, depicting cause-effect associations through summary conceptual models based on spatial proximity and temporal synchronicity, providing insufficient scientific proof for the Anthropocene based on the 'overwhelming' impact of human factors. More conclusive cause-effect statements will require hypothetic-deductive approaches, explicit functional criteria and best-practice environmental model building. Geomorphologists should now move beyond the 'phase of discovery' and develop rigorous proofs for cause-effect relationships of cumulative impact; this may be enhanced by developing an avowedly 'Anthropocene' perspective in which rivers are viewed critically as socio-biophysical systems co-evolving with human activity. (C) 2019 Elsevier B.V. All rights reserved.

The utility of sediment budget analysis is explored in revealing spatio-temporal changes in the sediment dynamics and morphological responses of a fluvial system subject to significant human impacts during the recent Anthropocene. Sediment budgets require a data-intensive approach to represent spatially-differentiated impacts adequately and are subject to numerous estimation uncertainties. Here, field and topographic surveys, historical data, numerical modelling and a representative-area extrapolation method are integrated to construct a distributed, process-based sediment budget that addresses historical legacy factors for the highly regulated Lagunitas Creek (213 km(2)), California, USA, for the period 1983-2008. Independent corroboration methods and error propagation analysis produce an uncertainty assessment unique to a catchment of this size. Current sediment yields of similar to 20 000t a(-1) +/- 6000 t a(-1) equate to unit rates of similar to 300 t km(-2) a(-1) +/- 90 t km(-2) a(-1) over the effective sediment contributing area of 64 km(2). This is comparable with yields associated with early Euro-American settlement in the catchment, despite loss of sediment supply upstream of the two large dams. It occurs because similar to 57% of the sediment is now derived from incision-related channel erosion. Further, the highly efficient routing of channel-derived sediments in these incised channels suggests an efflux of 84% of contemporary sediment production, contrasting with the efflux of approximate to 10-30% reported for unregulated agricultural catchments. The results highlight that sediment budgets for regulated rivers must accommodate channel morphological responses to avoid significantly misrepresenting catchment yields, and that volumetric precision in sediment budgets may best be improved by repeat, spatially dense, channel cross-section surveys. Human activities have impacted every aspect of the sediment dynamics of Lagunitas Creek (production, storage, transfer, rates of movement through storage), confirming that, while distributed sediment budgets are data demanding and subject to numerous error sources, the approach can provide valuable insights into Anthropocene fluvial geomorphology. Copyright (C) 2017 John Wiley & Sons, Ltd.

The dynamics of coarse bedload transport in rivers is governed by multiple hierarchical factors including catchment-scale controls on sediment production, annually variable hydroclimatic driving of segment-scale sediment supply, and reach-scale factors related to the interaction of hydraulic forces with channel morphology. Exploring hydroclimatic drivers can beneficially utilise passive sensors to record coarse bedload transport over extended time periods and in previously unattainable resolution. For the River Avon (Devon, UK), five-minute coarse bedload frequency data collected using seismic impact plates inherently records the instantaneous variability of bedload transport intensity, patterns of event-scale hysteresis and selective path transport, and the influence of inter-event supply variations. Converting a four-year record of impacts into loads via a probabilistic, data-driven model illustrates the combined influence of hydroclimate and sedimentology on bedload at the inter-annual scale. Despite highly variable water years, the results indicate that 'bar-building flows' consistently achieve the peak efficiency for coarse bedload transport whereas bankfull flows are relatively ineffective. Further, annual sediment rating curves combine both supply and transport limiting phases. Sediment transport forecasting is thus sensitive to both flow year type and antecedent controls on sediment supply, with implications for advancing sustainable solutions in river management.

The Anthropocene is proposed as a new interval of geological time in which human influence on Earth and its geological record dominates over natural processes. A major challenge in demarcating the Anthropocene is that the balance between human‐influenced and natural processes varies over spatial and temporal scales owing to the inherent variability of both human activities (as associated with culture and modes of development) and natural drivers (e.g. tectonic activity and sea level variation). Against this backdrop, we consider how geomorphology might contribute towards the Anthropocene debate by focusing on human impact on aeolian, fluvial, cryospheric and coastal process domains, and how evidence of this impact is preserved in landforms and sedimentary records. We also consider the evidence for an explicitly anthropogenic geomorphology that includes artificial slopes and other human‐created landforms. This provides the basis for discussing the theoretical and practical contributions that geomorphology can make to defining an Anthropocene stratigraphy. It is clear that the relevance of the Anthropocene concept varies considerably amongst different branches of geomorphology, depending on the history of human actions in different process domains. For example, evidence of human dominance is more widespread in fluvial and coastal records than in aeolian and cryospheric records, so geomorphologically the Anthropocene would inevitably comprise a highly diachronous lower boundary. Even to identify this lower boundary, research would need to focus on the disambiguation of human effects on geomorphological and sedimentological signatures. This would require robust data, derived from a combination of modelling and new empirical work rather than an arbitrary ‘war of possible boundaries' associated with convenient, but disputed, ‘golden’ spikes. Rather than being drawn into stratigraphical debates, the primary concern of geomorphology should be with the investigation of processes and landform development, so providing the underpinning science for the study of this time of critical geological transition. Copyright © 2016 John Wiley & Sons, Ltd.

A data-driven, uncertainty-bound estimation technique for bedload transport rates is developed based on passive sensing devices. The model converts sediment samples to a mass in transit for each instantaneous discharge according to impacts detected and a Monte Carlo simulation of the load determined at random from the particle size distribution. Using impact count data autogenically produces a supply-limited, location-specific and high-resolution time-series of bedload rates, while the probabilistic approach inherently accommodates the stochastic nature of bedload transport. Application to the River Avon (Devon, U.K.) provides cross-sectional bedload rate estimates within the bounds of experimental data and calibrated to observed field behaviour. This new procedure offers an alternative ‘class’ of bedload estimation to existing approaches and has the potential for wide-ranging applications in river management and restoration, while contributing to the integration of ‘big data’ into a progressive agenda for hydrogeomorphology research.

Indirect, passive approaches for monitoring coarse bedload transport could allow cheaper, safer, higher-resolution, longer-term data that revolutionises bedload understanding and informs river management. Here, insights provided by seismic impact plates in a downstream reach of a flashy gravel-bed river (River Avon, Devon, UK) are explored in the context of plate performance. Monitoring of a centrally-situated plate (IP1) during an extremely wet 12-month period demonstrated that impacts were related to discharge as a measure of transport potential (R-2=0.38) but that factors other than transport limitations are important. Analysis of discrete flow events revealed consistent rising-limb and falling-limb impact spikes biased toward the latter for larger events. Such patterns may result from disruption of the upstream armour layer (rising limb) and supply enhancements related to both upstream mass bank failures and/or flood routing of non-local sediment sources (falling limb). Installation of additional impact plates indicated that plate IP1 was indeed dominantly related to instantaneous discharge, that a three-plate lateral array somewhat better explained impact variability (R-2=0.49), and that the bedload track shifts laterally with discharge. Aggregating event-total IP1 impacts against volumetric discharge further increases explanation as intra-event and stochastic bedload factors are subsumed but left 26% unexplained variance related to the unsampled bedload mass, inter-event supply differences, and attributes of plate performance. Annualising the data created an impact-based 'effective discharge' for this extremely wet year that was closer to morphological bar-full in magnitude than bankfull, but the preceding results imply this outcome is related as much to supply limitations as transport limitations. Overall, passive approaches offer a liberating prospect for bedload monitoring, capable of producing insights only achievable through high resolution, extended time periods. Such results could potentially inform threshold conditions and geomorphological effectiveness of flows for future river management strategies. Copyright (c) 2015 John Wiley & Sons, Ltd.

Geomorphologists intent on modelling fluvial geomorphological processes and the dynamics of resulting river systems therefore have a significant challenge in integrating various influences over relevant time frames. This chapter focuses on model types with an avowedly catchment-scale potential for application. There are various approaches available to represent the transport laws implicit to landscape evolution models and in the reduced complexity modelling approach, the accuracy of process representation is forsaken to permit pseudo-realistic change in fluvial landforms over geomorphological time-scales. The different approaches to catchment processes modeling includes: conceptual model, problem-centred interpretative model, data-driven empirical model and numerical model. The chapter also considers tools for developing a catchment process model focusing on issues of representation and accuracy. Finally, it outlines the prospects for future model developments. Improved knowledge of geomorphological processes and transfer functions will give the component parts of catchment models increasingly more process accuracy.