Bruce Lane Rhoads

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• Professor at University of Illinois Urbana-Champaign

Plain Language Summary When two rivers flow into each other they start to mix. Understanding mixing downstream of confluences is important for determining the dispersal of water‐transported materials, including pollutants, within river systems. Past work has focused mainly on mixing at individual confluences, limiting general knowledge of the mixin...

The use of water as a weapon in highly industrialized areas in the Russo-Ukrainian war has resulted in catastrophic economic and environmental damages. We analyze environmental effects caused by the military destruction of the Kakhovka Dam. We link field, remote sensing, and modeling data to demarcate the disaster’s spatial-temporal scales and outl...

Meander chute cutoffs are a common and geomorphically important feature of meandering rivers, exhibiting complex dynamics and distinctive morphologic features. To date, however, the geomorphic processes governing the evolution and formation of these features are poorly understood due to limited knowledge of cutoff hydrodynamics. This paper investig...

Floodplains along low‐gradient, meandering river systems contain diverse hydrogeomorphic features, ranging from isolated depressions to hydrologically‐connected channels. These ephemerally‐flooded features inundate prior to river water overtopping all banks, enhancing river‐floodplain connectivity during moderately high flow stages. Predicting when...

Relatively little is known about the geomorphological characteristics of floodplain secondary channels and the potential for floodplain flows to mobilize bed material within these channels. This study examines the geomorphological characteristics (channel form, material properties, wood jams) and bed‐material mobilization potential of secondary cha...

Floodplains along low-gradient, meandering river systems contain diverse hydrogeomorphic features, ranging from isolated depressions to hydrologically-connected channels. These ephemerally-flooded features inundate prior to river water overtopping all banks, enhancing river-floodplain connectivity during moderately high flow stages. Predicting when...

Stormwater management in urban environments typically involves regulation of release rates of stored water from control structures to mitigate enhanced peak flows that can cause damaging flooding. The extent to which this mitigation influences stream geomorphic stability remains largely unexplored. Moreover, few, if any, studies have examined how i...

The ecology of forested floodplains is intricately linked to river hydrology through the frequency, magnitude, timing and duration of floodplain inundation. Spatial variability in inundation characteristics is influenced by the geomorphic template of a floodplain, both in terms of the topography of floodplain features and connectivity of these feat...

Three primary driving factors are responsible for the lateral flux of streamwise momentum within meander bends: topographic steering of the flow related to changes in channel morphology, rapid changes in channel curvature, and curvature‐driven helical motion. While these factors have been studied previously, their relative contributions to the net...

The extent to which flows mix at confluences is pivotal for determining spatial patterns of water quality and biodiversity. Because mixing processes are complex, predicting rates and characteristic scales of mixing is difficult. Here we introduce a theory for confluence mixing dynamics of shallow flows in which the mixing process is controlled by t...

The spatial patterns of transport‐effective flows at confluences and the relation of these patterns to channel morphology remain poorly understood. This field study uses acoustic Doppler current profiler measurements to explore the spatial structure of different transport‐effective flows at three small stream confluences where measurements of flow...

Environmental regulators use No Net Loss policies to minimize the damaging impacts of development projects on water resources. In this context, regulators prefer standard environmental assessment protocols over ad hoc approaches. This article examines how the St. Louis District of the U.S. Army Corps of Engineers (the Corps) directed the developmen...

The differentiation of human and physical geography is a fundamental distinction in Geography. This commentary examines the past, present, and possible future places of physical geography within Geography, focusing on the situation in the United States. Physical geography played a major role in the establishment of Geography as an academic discipli...

Channelization has changed the form and dynamics of rivers on a global scale. In the midwestern United States, widespread straightening of meandering headwater streams has been undertaken for the purpose of improving land drainage. Few studies have examined in detail how meandering streams respond to straightening, especially over timescales of nea...

This chapter reviews laminar and turbulent flows in the context of flowing waters. It starts with the examinations of balances of forces and introduces the concept of Reynolds averaging for turbulent flows. These are followed by outlines of the basic methods of modeling, which are based on the Boussinesq hypothesis and different assumptions about t...

Despite widespread recognition that confluences are characterized by complex hydrodynamic conditions, few studies have mapped in detail spatial patterns of flow at confluences and variation in these patterns over time. Recent developments in large‐scale particle image velocimetry (LSPIV) have created novel opportunities to explore the spatial and t...

Accurate water temperature forecasting is essential for understanding thermal regimes of rivers in the context of climate change and anthropogenic disturbances, such as dam construction. Machine-learning models proffer an empirically based approach to predicting water temperatures with a high degree of accuracy. This study explores the potential of...

Confluences are important sites for mixing within river networks. Past work has shown that mixing within confluences is highly variable; in some cases flows mix rapidly and in other cases flows remain unmixed far downstream of the confluence. The fluvial processes that govern mixing within confluences remain poorly understood. This study relates pa...

Restoration practices aimed at fish habitat enhancement often include installation of instream structures. However, mixed outcomes have been reported regarding structure effectiveness, while mechanisms underlying success remain unclear. The interactions between fish and flow conditions generated by instream structures and their subsequent impact on...

Mutual adjustment between process and form shapes the morphology of alluvial river channels, including channel banks. The tops of banks define the transition between the channel and adjacent floodplain, which corresponds to the level of incipient flooding. Despite the geomorphological and hydrological importance of this transition, few, if any, stu...

Cambridge Core - Geomorphology and Physical Geography - River Dynamics - by Bruce L. Rhoads

Confluences are locations of complex hydrodynamic conditions within river systems. The effects on hydrodynamics and mixing of temperature‐induced density differences between incoming flows are investigated at a small‐size, concordant bed confluence. To evaluate density effects, results of eddy‐resolving simulations for a densimetric Froude number F...

The flow, sediment and temperature regimes of the Yangtze River have changed greatly due to the construction of the Three Gorges Reservoir (TGR). Although past work has focused mainly on the influence of the TGR on water and sediment regimes, less attention has been given to temperature effects. Water temperature changes have important implications...

Core Ideas IML‐CZO is structured to study system responses through event‐based monitoring. Management legacy has shaped critical zone processes. Management and weather affect landscape heterogeneity and surface–subsurface pathways. In intensively managed landscapes, interactions between surface (tillage) and subsurface (tile drainage) management w...

The Hilbert-Huang transform (HHT) is a method of spectral analysis that is suitable for application to non-stationary and non-linear signals that holds enormous potential for the analysis of turbulent flows in fluvial, aaeolian, and coastal systems. HHT begins with decomposition of the signal into Intrinsic Mode Functions (IMFs) using the Empirical...

Past field studies of confluence dynamics have focused mainly on experimental or small stream confluences and confluences of large rivers. Few studies have explored fluvial processes and forms at confluences of medium-size rivers, especially those where river planform varies from a straight alignment. This study examines changes in flow structure,...

Although past field work at stream confluences has relied on velocity information at specific cross sections to examine flow structure, detailed characterizations of spatial and temporal variations in the hydrodynamics of confluences are lacking. This study uses large-scale particle image velocimetry (LSPIV) obtained from small unmanned aerial syst...

Measuring two-dimensional (2-D) patterns of flow in rivers at high resolution over large areas is challenging using traditional velocity-measurement methods, which provide data at specific locations or cross sections. Large-scale particle image velocimetry (LSPIV) based on imagery obtained from fixed camera platforms can measure flow velocity on th...

Depth-averaged two-dimensional (2D) models are useful tools for understanding river morphodynamics through the computation of hydrodynamics, sediment transport, and an evolving river bed morphology. This paper presents a new parallelized 2D hydrodynamic, sediment transport, and bed morphology model, HydroSedFoam. The model uses the Message Passing...

The damming of rivers has created hotspots for organic carbon sequestration and methane production on a global scale as the reservoirs intercept fluvial suspended and dissolved loads. To better understand how the C-biogeochemistry of a reservoir responds to watershed processes and evolves over time, Lake Decatur, located in the Intensively Managed...

Expansion and intensification of managed landscapes for agriculture have resulted in severe unintended global impacts, including degradation of arable land and eutrophication of receiving water bodies. Modern agricultural practices rely on significant direct and indirect human energy inputs through farm machinery and chemical use, respectively, whi...

Quantifying flow in rivers is fundamental to assessments of water supply, water quality, ecological conditions, hydrological responses to storm events, and geomorphological processes. Image-based surface velocity measurements have shown promise in extending the range of discharge conditions that can be measured in the field. The use of Unmanned Aer...

The flux of fine sediment within agricultural watersheds is an important factor determining the environmental quality of streams and rivers. Despite this importance, the contributions of sediment sources to suspended sediment loads within intensively managed agricultural watersheds remain poorly understood. This study assesses the provenance of fin...

Although past work has noted that contrasts in turbidity often are detectable on remotely sensed images of rivers downstream from confluences, no systematic methodology has been developed for assessing mixing over distance of confluent flows with differing surficial suspended sediment concentrations (SSSC). In contrast to field measurements of mixi...

This article explores the length scales and statistical characteristics of form roughness along the outer banks of two elongate bends on a large meandering river through investigation of topographic variability of the bank face. The analysis also examines how roughness varies over the vertical height of the banks and when the banks are exposed suba...

Few studies have quantified near-bank turbulence at the field-scale in meander bends. As a result, details of the structure of turbulence at the outer bank of bends are poorly understood, despite recognized linkages among turbulence, bank erosion, and channel migration. This study uses high-frequency measurements of flow velocities to analyze the c...

Only a handful of field studies have examined turbulent flow structure at discordant confluences; the dynamics of flow at such confluences have mainly been examined in the laboratory. This paper reports results of a field-based investigation of turbulent flow structure at a discordant river confluence. These results support the hypothesis that flow...

Few studies have examined the three-dimensional flow structure and bed morphology within elongate loops of large meandering channels. The present study focuses on the spatial patterns of three-dimensional flow structure and bed morphology within two elongate meander loops and examines how differences in outer bank roughness influence near-bank flow...

The effects of planform geometry and momentum flux ratio on thermal mixing at a stream confluence with concordant bed morphology are investigated based on numerical simulations that can capture the dynamics of large-scale turbulence. In two simulations, the bathymetry and asymmetrical planform geometry are obtained from field experiments and the mo...

Hydrological regimes strongly influence the biotic diversity of river ecosystems by structuring physical habitat within river channels and on floodplains. Modification of hydrological regimes by dam construction can have important consequences for river ecosystems. This study examines the impacts of the construction of two dams, the Gezhouba Dam an...

Compound meander bends with multiple lobes of maximum curvature are common in actively evolving lowland rivers. Interaction among spatial patterns of mean flow, turbulence, bed morphology, bank failures and channel migration in compound bends is poorly understood. In this paper, acoustic Doppler current profiler (ADCP) measurements of the three-dim...

Large scale particle image velocimetry (LSPIV) has emerged as a valuable tool for measuring surface velocity in a variety of fluvial systems. LSPIV has typically been used in the field to obtain velocity or discharge measurements in relatively simple one-dimensional flow. Detailed two-dimensional or three-dimensional characterization of flow struct...

This special issue honors the contributions of William L. Graf to geomorphology and river science. A hallmark of Will's work over the course of his career has been a focus on the natural and human structuring of river systems. More broadly, Will has been an innovator and leader who has shaped the way in which geomorphologists conduct research. Thro...

Humans have become major geomorphological agents, effecting substantial change in the characteristics of Earth’s physical landscapes. The agricultural Midwest of the United States is a region marked by pronounced human influence at the landscape scale. Humans undoubtedly have strongly influenced critical zone processes, including fluvial processes,...

Confluences are important locations for river mixing within drainage networks, yet few studies have examined in detail the dynamics of mixing within confluences. This study examines the influence of momentum flux ratio, the scale of the flow (cross-sectional area), and density differences between incoming flows on thermal mixing at a small stream c...

Recent field and modeling investigations have examined the fluvial dynamics of confluent meander bends where a straight tributary channel enters a meandering river at the apex of a bend with a 90° junction angle. Past work on confluences with asymmetrical and symmetrical planforms has shown that the angle of tributary entry has a strong influence o...

This study numerically investigates the effects of variations in inflow conditions and planform geometry on large-scale coherent flow structures and bed friction velocities at a stream confluence with natural bathymetry and concordant bed morphology. Several numerical experiments are conducted in which either the Kelvin-Helmholtz mode or the wake m...

Recently, it was observed that migrating bed forms produce temporal and spatial peaks of shear stresses along the outer bank of an experimental meandering channel. These stresses are about 50% larger than the shear stresses exerted by the mean near-bank flow. Because of this increase in bank shear stress the migration rate of the bend may be signif...

Regional change in the variability and magnitude of flooding could be a major consequence of future global climate change. Extreme floods have the capacity to rapidly transform landscapes and expose landscape vulnerabilities through highly variable spatial patterns of inundation, erosion, and deposition. We use the historic activation of the Birds...

Dams are known to create discontinuities in river flow and sediment transport, with ensuing effects on the fluvial geomorphology of dammed systems. While the effects created by large impoundment dams are well documented, less is known about the influence of small run-of-river dams (common across the eastern United States) on river geomorphology. Re...

[1] This paper documents the three-dimensional structure of flow and bed morphology of two developing chute cutoffs on a single meander bend on the lower Wabash River, USA, and relates the flow structure to patterns of morphologic change in the evolving cutoff channels. The upstream end of the cutoff channels is characterized by: (1) a zone of flow...

A recent opinion piece rekindled debate as to whether geography's current interdisciplinary make-up is a historical relic or an actual and potential source of intellectual vitality. Taking the latter position, we argue here for the benefits of sustained integration of physical and critical human geography. For reasons both political and pragmatic,...

The use of acoustic Doppler current profilers (ADCP) for discharge measurements and three-dimensional flow mapping has increased rapidly in recent years and has been primarily driven by advances in acoustic technology and signal processing. Recent research has developed a variety of methods for processing data obtained from a range of ADCP deployme...

Several existing data sets are analyzed empirically to determine the nature of changes in channel characteristics at stream confluences. Classifications of the data indicate that such changes are diverse and do not conform well with predictions based on the hydraulic geometry of synchronous channel-forming flows on major and minor tributaries. Scat...

This paper explores the effect of a partial LWD dam on the spatial pattern of turbulence kinetic energy (TKE) and shear stress within a meander bend of a small stream in East Central Illinois, USA. Field data on three-dimensional velocity components were collected using an acoustic doppler velocimeter (ADV). Results show that upstream of the bend a...

Geomorphic processes typically are viewed as manifestations of mechanical stresses operating on earth materials to produce various forms of strain. This conception is embedded within physics generally and mechanics specifically. Initially, the concept of process was associated with open systems and a time-independent view of process-form adjustment...

The flow and turbulence structure at stream confluences are characterized by the formation of a mixing interface (MI) and, in some cases, of streamwise-oriented vortical (SOV) cells flanking the MI. Depending on the junction angle and planform symmetry, as well as the velocity ratio across the MI, the MI can be in the Kelvin-Helmholtz (KH) mode or...

The dynamic evolution of the planform of meandering rivers often leads to the development of compound loops with multiple lobes of maximum curvature. At present, the interaction among spatial patterns of mean flow, turbulence, bed morphology, bank failures and channel migration in compound loops is poorly understood. In particular, field studies of...

Many drainage ditches in the Midwest have developed a geomorphological configuration characterized by vegetated bars, or benches, on the bottom of the ditch and a stream flowing within a channel inset into these bars or benches. Past work has focused on the sedimentology of the benches and the depositional processes involved in bench development. T...

Flow convergence at stream confluences produces some of the most highly turbulent locations in fluvial systems. The shear layer/mixing interface that develops within the confluence hydrodynamic zone (CHZ) is characterized by complex patterns of three-dimensional flow that varies both spatially and temporally. Although research has been performed on...

Freely meandering rivers typically exhibit complex, continuously evolving patterns of planform geometry involving elongation of the channel path through lateral migration and shorting of this path through bend cutoffs. Despite the importance of cutoffs in shaping the planform geometry of meandering rivers, the fluvial processes operative immediatel...

Freely-meandering natural rivers typically evolve into complex planforms characterized by compound loops or multilobes or into irregular patterns. It is widely acknowledged that spatial heterogeneity in floodplain erodibility should affect the planform evolution of meandering rivers; however, past studies have not systematically explored the import...

In meandering rivers, bend cutoffs have long been recognized as an important mechanism of change in the path of the channel. Meander bend cutoffs can develop by the progressive migration of an elongated bend onto itself, which forms a neck cutoff, or by the erosion of a new channel across the neck of the bend, which is known as a chute cutoff. Rive...

Throughout the Midwestern United States, land owners and managers, mainly farmers, are increasingly considering the possibility of transforming industrial agricultural landscapes that currently are used almost strictly for food production to landscapes that include renewable energy production. Because most land in this region is privately owned and...

Although it is widely acknowledged that spatial heterogeneity in floodplain erosional resistance should affect the planform evolution of meandering rivers, past studies have not systematically explored the importance of this effect. Using a physically-based model of river meandering and stochastically-generated heterogeneous landscapes, we analyze...

River confluences are complex hydrodynamic environments where convergence of incoming flows produces complicated patterns of fluid motion, including the development of large-scale turbulence structures. Accurately simulating confluence hydrodynamics represents a considerable challenge for numerical modeling of river flows. This study uses an eddy-r...

Many channelized streams have straight trapezoidal channels that lack geomorphological structure and physical habitat, such as pools and riffles. This chapter focuses on design and implementation of pool-riffle structures in straight channels through examination of three case studies: one in which pool-riffles have been implemented successfully, on...

The practice of dam removal has received increasing attention as a consequence of maintenance and liability concerns related to the advanced age of many of these structures. Most dams that have been removed thus far are small run-of-river structures. As the number of removals of run-of-river dams increases, it is crucial to understand the effects t...

The Shields number characterizing the threshold of motion for sand is of the order of 0.03. Yet estimates of the Shields numbers of large, low-slope sand-bed rivers at bankfull flow typically fall in the range 1 ~ 3. That is, such rivers, which are many m to 10's of m deep, build their channels so as to maintain Shields numbers that are 30 - 100 ti...

Bend cutoffs are a common mechanism of morphologic change in all scales of meandering rivers worldwide. Cutoffs can develop either by progressive migration of an elongated bend onto itself, forming a neck cutoff, or by erosion of a new channel across the neck of a bend, producing a chute cutoff. In contrast to the slow processes of ``shaving'' of t...

Simultaneous-equation statistical models are an attractive method for directly analyzing interactions among components of geomorphic systems. This study demonstrates that the utility of simultaneous-equation analysis is limited for fluvial systems by inherent multicollinearity among hydrologic and morphologic variables. Although multicollinearity f...

Meandering rivers are intrinsically dynamic geomorphic systems that exhibit progressive change in their planforms as they migrate across their floodplains. Recent research in river meandering has focused on the development of linear mathematical models of meander migration. These models, which are based on momentum and mass conservation principles,...

Previous experimental, field, and modeling studies of confluence dynamics have focused mainly on junctions formed by straight channels. In contrast, natural rivers often meander and tributaries can enter meandering rivers on the outside of bends to form a junction planform known as a confluent meander bend. In this study, field measurements of thre...

Meander cutoffs, which develop when flow cuts across the narrow neck of a bend, are common features along actively migrating meandering rivers. Despite the importance of cutoffs in the dynamics of river meandering and floodplain sedimentation, few, if any, studies have documented in detail the fluvial processes involved in the development of a mean...

Complex meander forms such as compound loops or multi-lobes are common features of natural meandering rivers. Despite a large body of research on river meandering, the development of compound loops is not fully understood. An improved understanding of the development of compound loops is crucial due to the importance of planform migration dynamics...

River meanders are dynamic features that progressively migrate over their floodplains through time. As meanders evolve, complex forms including compound loops, or elongate bends with multiple distinct lobes of maximum curvature, often develop. The relationship between 3-D flow structure, turbulence characteristics, and planform evolution in compoun...

Meandering rivers are among the most dynamic Earth surface systems, exhibiting progressive change in channel location as they migrate across their floodplains over time. Theoretical models of meandering have defined the influence of planform curvature on meandering in the form of a spatial convolution function that expresses migration at any point...

Changes in bed morphology and sedimentology at stream confluences in relation to specific hydrological events have not been documented extensively. Moreover, few, if any, studies have investigated the effect of net hydrological conditions on channel change at a confluence over a period of many years. Repeat cross section surveys and sampling of bed...

Effective watershed-scale environmental management and restoration require a sound understanding of the dynamics of fluvial systems at the watershed-scale and the impact of humans on these dynamics. In Illinois, concern has arisen about the need to implement bank stabilization along meandering rivers, where bank erosion associated with lateral migr...

A Companion to Environmental Geography is the first book to comprehensively and systematically map the research frontier of 'human-environment geography' in an accessible and comprehensive way. Cross-cuts several areas of a discipline which has traditionally been seen as divided; presenting work by human and physical geographers in the same volume....