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Proposed hydropower dams at more than 350 sites throughout the Amazon require strategic evaluation of trade-offs between the numerous ecosystem services provided by Earth’s largest and most biodiverse river basin. These services are spatially variable, hence collective impacts of newly built dams depend strongly on their configuration. We use multiobjective optimization to identify portfolios of sites that simultaneously minimize impacts on river flow, river connectivity, sediment transport, fish diversity, and greenhouse gas emissions while achieving energy production goals. We find that uncoordinated, dam-by-dam hydropower expansion has resulted in forgone ecosystem service benefits. Minimizing further damage from hydropower development requires considering diverse environmental impacts across the entire basin, as well as cooperation among Amazonian nations. Our findings offer a transferable model for the evaluation of hydropower expansion in transboundary basins.

Integrated approaches are needed to understand and respond to changes in tropical mountain ecosystems and communities brought about by receding glaciers and changes in land use.

This contribution presents MStaT, a wavelet-based open-source software developed to provide a detailed characterization of large meandering river morphodynamics. MStaT integrates three independent modules: (i) meandering morphometrics module; (ii) migration module; and (iii) confluence module. MStaT delivers a short and medium-term framework to analyze the river centerline and valley-meandering channel interrelationship at low computational cost. It provides quantitative information on the spatial distribution of the arc-wavelength, migration rates, cutoffs events, and tributary channels influences. Data are presented through a user-friendly graphical user interface that makes the output interpretation easier, and that is freely available to the communities of river morphodynamics scientists and engineers.

The rivers in the Peruvian Amazon basin are the veins that feed the largest rainforest on the planet. They connect habitats and ecosystems and are considered a source of high biodiversity. Since be...

Amazonian rivers are highly interconnected and dynamic systems. Their behavior depends, to a large extent, on their geomorphology, being classified in 1) meandering rivers (MR), characterized by hi...

Introduction: Coastal wetlands are currently threatened by human drivers, such as agriculture, infrastructure development, and urban sprawl. Pressures on these ecosystems disturb their morphology and biogeochemical cycles, resulting in the degradation of ecosystem services. However, little has been done to understand the wetland response to identify proper conservation strategies. Along the Peruvian coast, wetlands present a diversity of landscapes that face similar threats and pressures; however, the ecosystem response in each one may be different. Objective: This study aims to assess the environmental impacts on ecosystem services based on the understanding of geomorphic features and the status of the Eten coastal wetland (Peru). Methods: The methodology combines the application of open-source GIS tools and the collection of field data to characterize the geomorphic settings and to analyze the changes in environmental parameters. Then, the main threats and pressures on the Eten wetland are defined and related to impacts on ecosystem services using a cause-effect model. Results: Overall, the results indicated that the river plays a vital role in defining the wetland landscape and functions. The biological diversity of aquatic habitats is disturbed by hydraulic structures and agricultural activities. Current land use affects supporting and regulation services, such as water regulation.

The Peruvian Andes are a hotspot of vulnerabilities to impacts in water resources due to the propensity for water stress, the highly unpredictable weather, the sensitivity of glaciers, and the socio-economic vulnerability of its population. In this context, we selected the Vilcanota-Urubamba catchment in Southern Peru for addressing these challenges aiming at our objectives within a particular hydrological high-mountain context in the tropical Andes: a) Develop a fully-distributed, physically-based glacier surface energy balance model that allows for a realistic representation of glacier dynamics in glacier melt projections; b) Design and implement a glacio-hydrological monitoring and data collection approach to quantify non-glacial contributions to water resources and the impact of catchments interventions; c) Mapping of human water use at high spatiotemporal resolution and determining current and future levels of water (in)security; and d) Integrate last objectives in a glacier - water security assessment model and evaluate the tool's capacity to support locally embedded climate change adaptation strategies. The RAHU project intends to transform the scientific understanding of the impact of glacier shrinkage on water security and, at the same time, to connect to and inform policy practices in Peru. It follows a "source to tap" paradigm, in which is planned to deliver a comprehensive and fully integrated water resources vulnerability assessment framework for glacier-fed basins, comprising state-of-the-art glaciology, hydrology, water demand characterisation, and water security assessment. It includes glacio-hydrological and water resources monitoring campaigns, to complement existing monitoring efforts of our project partners and collaborators, and new remotely sensed data sets. Those campaigns will be implemented using the principles and tools of participatory monitoring and knowledge co-creation that our team has pioneered in the tropical Andes. The datasets produced by this approach, combined with existing monitoring implemented by our team and collaborators, will allow us to build an integrated water supply-demand-vulnerability assessment model for glacierized basins, and to use this to evaluate adaptation strategies at the local scale. This research is part of the multidisciplinary collaboration between British and Peruvian scientists (Newton Fund, Newton-Paulet).

This paper 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 subaerially and inundated during flood stage. Detailed data on the topography of the outer banks were obtained subaerially using terrestrial LiDAR during low flow conditions and subaqueously using multibeam echo sounding (MBES) during near-bankfull conditions. The contributions of various length scales of topographic irregularity to roughness for subaerial conditions were evaluated for different elevation contours on the bank faces using Hilbert-Huang Transform (HHT) spectral analysis. Statistical characteristics for discrete areas on the bank faces were determined by calculating the root-mean-square of normal distances from a TIN surface. Results of the HHT analysis show that the characteristics of roughness along bank faces composed primarily of non-cohesive sediment, and eroding into cropland, vary with bank elevation and exhibit a dominant range of roughness length scales (~15-50 m). On the other hand, bank faces composed predominantly of cohesive material and carved into a forested floodplain have relatively uniform topographic roughness characteristics over the vertical extent of the bank face and do not exhibit a dominant roughness length scale or range of length scales. Additionally, comparison between local surface roughness for subaerial versus subaqueous conditions shows that roughness decreases considerably when the banks are submerged, most likely because of the removal of vegetation and eradication of small-scale erosional features in non-cohesive bank materials by flow along the bank face. Thus, roughness appears to be linked to the hydraulic conditions affecting the bank, at least relative to conditions that develop when banks are exposed subaerially.

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 characteristics. Three-dimensional velocities were measured during two different events – a near-bankfull flow and an overbank event. Detailed data on channel bathymetry and bedform geometry were obtained during a near-bankfull event. Flow structure within the loops is characterized by strong topographic steering by the point bar, by the development of helical motion associated with flow curvature, and by acceleration of flow where bedrock is exposed along the outer bank. Near-bank velocities during the overbank event are less than those for the near-bankfull flow, highlighting the strong influence of the point bar on redistribution of mass and momentum of the flow at sub-bankfull stages. Multiple outer bank pools are evident within the elongate meander loop with low outer bank roughness, but are not present in the loop with high outer bank roughness, which may reflect the influence of abundant large woody debris on near-bank velocity characteristics. The positions of pools within both loops can be linked to spatial variations in planform curvature. The findings indicate that flow structure and bed morphology in these large elongate loops is similar to that in small elongate loops, but differs somewhat from flow structure and bed morphology reported for experimental elongate loops. This article is protected by copyright. All rights reserved.

One-dimensional (1D) models of open-channel flow are efficient for simulating in-channel hydrodynamics over long reaches and time periods, but cannot accurately simulate overbank flows that require two-dimensional (2D) models. The derivation and discussion of the behaviour of the coupling terms for horizontal and vertical coupling of the governing equations of 1D and 2D flow are presented here for the first time. Transfer terms for mass and momentum are introduced. Also, for the first time, the quantification of these transfer terms for the case of an experimental meandering channel with overbank flow is presented. For both coupling methods and relatively high overbank flow depth, the advective momentum transfer exceeded the diffusive momentum transfer. The diffusive momentum transfer has similar magnitude between both coupling approaches. The advective momentum transfer was one order of magnitude higher for the horizontal-coupling approach than for the vertical-coupling approach.

The upper reach of the Amazon River has a very dynamic morphology, with the highest rates of migration observed in the entire Amazon River. It has an anabranching channel pattern which alternates between a condition of single channel and anabranching structures; in particular, the anabranching structure near Iquitos City shows an interesting channel behavior. Its channels migrate at different rates, where there are processes of narrowing and widening, and also collision and development of new channels. The temporal evolution of the Iquitos anabranching structure is described during the period from 1985 to 2014. The study is carried out by using satellite images to track the migration patterns, which are contrasted to the underlying geological units in the valley. Bathymetry of the structure and several velocity transects were obtained during a field campaign prior to the 2012 historic flood event. This information allowed for numerical modeling in order to compute the hydrodynamic flow field that complements the temporal analysis, aiming to understand the planform migration patterns after the 2012 flood event. It is observed that the geological units play an important role in modulating the migration rates and planform development of the channels. The channels in the structure are in contention to be the main channel, which become the secondary channel after migration. This causes the channels to experience a rise in bed elevation and narrowing of the channel itself; if this trend continues for several more years, these channels will detach from the Iquitos anabranching structure, thus forming paleo-channels. This geomorphic process is important for horizontal and vertical soil heterogeneity along the floodplain. In general, the analysis shows a complex interaction between the underlying geological units, flow structure, morphology of the bed and planform migration. Copyright © 2016 John Wiley & Sons, Ltd.

Spatial heterogeneity in the erosion-resistance properties of the channel banks and floodplains associated with sediment characteristics, vegetation, or bedrock can have a substantial influence on the morphodynamics of meandering rivers, resulting in highly variable rates of bank erosion and complex patterns of planform evolution. Although past studies have examined the spatial variability in bank erodibility within small rivers, this aspect of the erosion-resistance properties for large rivers remains poorly understood. Furthermore, with the exception of recent numerical modeling that incorporates stochastic variability of floodplain erosional resistance, most models of meandering river dynamics have assumed uniform erodibility of the bank and floodplain materials. The present paper investigates the lateral and vertical heterogeneity in bank material properties and riparian vegetation within two elongate meander loops on a large mixed bedrock-alluvial river using several geotechnical field and laboratory methods. Additionally, the bank stability and toe-erosion numerical model (BSTEM) and repeat terrestrial LiDAR surveys are used to evaluate the capacity of the bank material properties to modify the rates and mechanisms of bank retreat. Results show that the textural properties of the bank materials, soil cohesion, and critical shear stress necessary for sediment entrainment differ substantially between the two bends and are also highly variable within each bend — laterally and vertically. Trees growing along the banks increase the resistance to erosion by contributing to the shear strength of the bank materials and are capable of increasing bank stability along a large river. Locally outcropping bedrock also influences bank erodibility in both bends. The results of this study demonstrate that spatial variability in the erosion-resistance properties of the channel banks is an important factor contributing to spatial variability in the rates and mechanisms of bank erosion determined from short-term studies of bank retreat and long-term analysis of changes in channel planform.

Meandering channels develop different geometry patterns alongthe floodplain during its evolution. These natural processes lead todeveloping lateral and longitudinal migration, describing a sort of sweptthat affect the human activities. As the equilibrium geometry of naturalchannels depends on: the flow and sediment discharge, geologicalconditions of valley, soil properties, and vegetation among others, thepreliminary characterization is not easy. Due to this, several engineering and scientific problems require an appropriate description ofmorphological processes. The dynamic characterization like thequantification of wavelength, amplitude, sinuosity, and curvature usingMedium Temporal Scheme (MTS) is using widely. Unlike the traditionalscheme that only uses short or long-term schemes, MTS includes relevantmorphological events (e.g., cutoff). In addition this, the satellite images has increased and achieves a high spatial resolution, even more when studying large basins. This paper presents and validates a MATLAB®-based toolbox called Meander Statistics Toolbox (MStaT) to perform thedynamic characterization of several meandering channels using the MTS.To run MStaT only need the centerline (CL), and the average width ofchannel as input parameters. To maximize the toolbox, MStaT incorporatesthe Wavelet Analysis (WA) to decompose the signal (CL) and obtains thepower spectrum. Finally, two studies cases (synthetic and natural channels) will be presented to validate MStaT. Fil: Dominguez Ruben, Lucas Gerardo. Universidad Nacional del Litoral. Facultad de Ingeniería y Ciencias Hídricas. Departamento de Hidráulica; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Gutierrez, Ronald. Universidad de Ingeniería y Tecnologia; Perú Fil: Ponte, Yoch. Universidad de Ingeniería y Tecnologia; Perú Fil: Abad, Jorge D.. Universidad de Ingeniería y Tecnologia; Perú Fil: Carrera, Oscar. Universidad de Ingeniería y Tecnologia; Perú

We present a study to relate the sinuosity of the main channel and its effect on the dynamics of the secondary channels of anabranching structures. For this purpose, two locations of the Peruvian Amazon River were selected: (1) a site with a medium to high-sinuosity main channel (MS site: Muyuy, Peru) and (2) a site with a low-sinuosity main channel (LS site: at the triple boundary between Brazil, Colombia, and Peru). The main channels for both the MS and LS anabranching structures have freedom to migrate in the lateral direction, while at least one of their secondary channels is adjacent to the geological valley. For MS and LS sites, temporal analysis of planform evolution was carried out using 30 years of satellite imagery from which metrics such as width, sinuosity, and annual maximum migration rates of main and secondary channels were calculated. Additionally, detailed hydrodynamic and bed morphology field measurements were carried out, and a two-dimensional shallow water numerical model was developed. For a medium to high-sinuosity main channel anabranching structure, the secondary channels present a dominant mechanism for reworking the floodplain, while for the low-sinuosity anabranching structure, the main channel planform dynamics is dominant. Flow velocities along the main and secondary channels for low, transition, and high-flow discharges describe that for MS (LS) site, the velocities are much higher along the secondary (main) channels.

Experimental sediment transport and river morphologic studies in laboratory flumes can use two sediment-supply methods: an imposed feed at the upstream end, or a recirculation of sediment f...

Improvements in horizontal drilling and hydrofracturing have revolutionized the energy landscape by allowing the development of so-called “unconventional” gas resources. The Marcellus play in the northeastern U.S.A. documents how fast this technology developed: the number of unconventional Marcellus wells in Pennsylvania (PA) increased from 8 in 2005 to ~ 7234 today. Publicly available databases in PA show only rare evidence of contamination of surface and groundwaters. This could document that incidents that impact PA waters have been relatively rare and that contaminants were quickly diluted. However, firm conclusions are hampered by i) the lack of information about location and timing of incidents; ii) the tendency to not release water quality data related to specific incidents due to liability or confidentiality agreements; iii) the sparseness of sample and sensor data for the analytes of interest; iv) the presence of pre-existing water impairments that make it difficult to determine potential impacts from shale-gas activity; and v) the fact that sensors can malfunction or drift. Although the monitoring data available to assess contamination events in PA are limited, the state manages an online database of violations. Overall, one fifth of gas wells drilled were given at least one non-administrative notice of violation (NOV) from the PA regulator. Through March 2013, 3.4% of gas wells were issued NOVs for well construction issues and 0.24% of gas wells received NOVs related to methane migration into groundwater. Between 2008 and 2012, 161 of the ~ 1000 complaints received by the state described contamination that implicated oil or gas activity: natural gas was reported for 56% and brine salt components for 14% of the properties. Six percent of the properties were impacted by sediments, turbidity, and/or drill cuttings. Most of the sites of groundwater contamination with methane and/or salt components were in previously glaciated northern PA where fracture flow sometimes allows long distance fluid transport. No cases of subsurface transport of fracking or flowback fluids into water supplies were documented. If Marcellus-related flowback/production waters did enter surface or groundwaters, the most likely contaminants to be detected would be Na, Ca, and Cl, but those elements are already common in natural waters. The most Marcellus-specific “fingerprint” elements are Sr, Ba, and Br. For example, variable Br concentrations measured in southwestern PA streams were attributed to permitted release of wastewaters from unconventional shale gas wells into PA streams through municipal or industrial wastewater treatment plants before 2011. Discharge has now been discontinued except for brines from a few plants still permitted to discharge conventional oil/gas brines after treatment. Overall, drinking water supply problems determined by the regulator to implicate oil/gas activities peaked in frequency in 2010 while spill rates increased through 2012. Although many minor violations and temporary problems have been reported, the picture that emerges from PA is that the fast shale-gas start may have led to relatively few environmental incidents of significant impact compared to wells drilled; however, the impacts remain difficult to assess due to the lack of transparent and accessible data.

The continuous wavelet transform is applied to the analysis of curvature signals from both synthetic meanders and 52 realizations from 16 natural meanders ranging from class B to class G (Brice classification), thus providing information on the spatial distribution of their arc-wavelength spectrum, and therefore, representing an objective characterization of meanders. Past research has studied the meander dynamics by using the centerline (short-term frame) and the valley centerline (long-term frame). The present study introduces a medium term frame, termed the mean center (MC), which is defined as the medium term coherent wave being present in the meander planimetry for a period that is strongly governed by the occurrence of cutoff events; although in the absence of them, it is present for ∼10 to ∼30 years. The MC is obtained by using a methodology that combines the capabilities of the principal component analysis and the discrete wavelet transforms. The application of wavelet cross correlation shows that peaks in the centerline curvature are strongly correlated with those of the MC suggesting that (1) a linear relationship between them may be associated to bank processes and, (2) in all other cases, a higher nonlinear relationship may be induced by autogenic hydrodynamic processes. In freely meandering rivers, compound bends, multiple loops, and cutoff events are associated to peaks in the MC local curvature. We define the planform amplitudes as the orthogonal distance of the centerline from mean center. Planform amplitudes (orthogonal distance of the centerline from mean center) are normally distributed and ranges from 2 to 20 river mean widths.

Meander migration and planform evolution depend on the resistance to erosion of the floodplain materials. To date, research to quantify meandering river adjustment has largely focused on resistance to erosion properties that vary horizontally. This paper evaluates the combined effect of horizontal and vertical floodplain material heterogeneity on meander migration by simulating fluvial erosion and cantilever and planar bank mass failure processes responsible for bank retreat. The impact of stream bank failures on meander migration is conceptualized in our RVR Meander model through a bank armoring factor associated with the dynamics of slump blocks produced by cantilever and planar failures. Simulation periods smaller than the time to cutoff are considered, such that all planform complexity is caused by bank erosion processes and floodplain heterogeneity and not by cutoff dynamics. Cantilever failure continuously affects meander migration, because it is primarily controlled by the fluvial erosion at the bank toe. Hence, it impacts migration rates and meander shapes through the horizontal and vertical distribution of erodibility of floodplain materials. Planar failures are more episodic. However, in floodplain areas characterized by less cohesive materials, they can affect meander evolution in a sustained way and produce preferential migration patterns. Model results show that besides the hydrodynamics, bed morphology and horizontal floodplain heterogeneity, floodplain stratigraphy can significantly affect meander evolution, both in terms of migration rates and planform shapes. Specifically, downstream meander migration can either increase or decrease with respect to the case of a homogeneous floodplain; lateral migration generally decreases as result of bank protection due to slump blocks; and the effect on bend skewness depends on the location and volumes of failed bank material caused by cantilever and planar failures along the bends, with possible achievement of downstream bend skewness under certain conditions.

[1] Fluvial channels present bed forms such as dunes and ripples that alter instantaneous hydrodynamics parameters such as flow velocities, water surface profiles, bed shear stresses, and Reynolds stresses and create turbulent coherent structures that are significantly different from those presented in flat bed conditions. It is known that LES-based models are more suitable than RANS models to reproduce the complex hydrodynamics around bed forms. Herein, a LES model is applied to describe the mean and turbulent flow structure under superimposed bed forms. Three cases were simulated: RUN I (train of ripples), RUN II (superimposed bed forms), and RUN III (amalgamated bed forms). The LES modeling was performed using a free surface condition to allow the model to develop undulations and boils on the water surface caused by effect of the bed forms. Some important conclusions from this study are: the division of high and low shear stresses on the stoss side of the dune, the progression of the flow field topology from RUN I and RUN III, and the type of turbulent coherent structures found in each stage. The region of high shear stresses was related to turbulence production, in which the streamwise velocity fluctuations (where strips structures are related to streaks) were associated to the modification of the bed morphology. The turbulence Horseshoes Vortices (THV) were more frequent in RUN I than in the other two cases (where streamwise rolls were more frequent). Finally, the frequency of the bursting events increased from RUN I to RUN II and decreased from RUN II to RUN III. Implications of detailed hydrodynamics into bed forms processes are also presented and discussed.

[1] There is no standard nomenclature and procedure to systematically identify the scale and magnitude of bed forms such as bars, dunes, and ripples that are commonly present in many sedimentary environments. This paper proposes a standardization of the nomenclature and symbolic representation of bed forms and details the combined application of robust spline filters and continuous wavelet transforms to discriminate these morphodynamic features, allowing the quantitative recognition of bed form hierarchies. Herein the proposed methodology for bed form discrimination is first applied to synthetic bed form profiles, which are sampled at a Nyquist ratio interval of 2.5–50 and a signal-to-noise ratio interval of 1–20 and subsequently applied to a detailed 3-D bed topography from the Rio Parana, Argentina, which exhibits large-scale dunes with superimposed, smaller bed forms. After discriminating the synthetic bed form signals into three-bed form hierarchies that represent bars, dunes, and ripples, the accuracy of the methodology is quantified by estimating the reproducibility, the cross correlation, and the standard deviation ratio of the actual and retrieved signals. For the case of the field measurements, the proposed method is used to discriminate small and large dunes and subsequently obtain and statistically analyze the common morphological descriptors such as wavelength, slope, and amplitude of both stoss and lee sides of these different size bed forms. Analysis of the synthetic signals demonstrates that the Morlet wavelet function is the most efficient in retrieving smaller periodicities such as ripples and smaller dunes and that the proposed methodology effectively discriminates waves of different periods for Nyquist ratios higher than 25 and signal-to-noise ratios higher than 5. The analysis of bed forms in the Rio Parana reveals that, in most cases, a Gamma probability distribution, with a positive skewness, best describes the dimensionless wavelength and amplitude for both the lee and stoss sides of large dunes. For the case of smaller superimposed dunes, the dimensionless wavelength shows a discrete behavior that is governed by the sampling frequency of the data, and the dimensionless amplitude better fits the Gamma probability distribution, again with a positive skewness. This paper thus provides a robust methodology for systematically identifying the scales and magnitudes of bed forms in a range of environments.

The flow characteristics around two partially buried objects, a short cylinder (SC) and a truncated cone (TC) were examined experimentally and numerically. Experiments were conducted in a large tilting flume with vertical walls made of acrylic plastic and steel floor covered by a 24-m long sand pit. For each experiment, the object was placed on a flat sandy bed, the flume was filled to a water depth of 41 cm, and a steady unidirectional current was established at high Reynolds numbers while sinking of the object was tracked over time. Velocity records were taken with an acoustic Doppler velocimeter (ADV) probe at the final stage of burial and scour hole evolution. The flow structure around each object was further investigated using a model that solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with a κ-e turbulence closure model, and results were compared to the experimental measurements. Measurements and numerical simulations allowed identification of regions of high and low vel...

River meander planforms can be described based on wavelet analysis, but an objective method to identify the main characteristics of a meander planform over all spatial scales is yet to be found. Here we show how a set of simple metrics representing meander shape can be retrieved from a continuous wavelet transform of a planform geometry. We construct a synoptic multiple looping tree to establish the meander structure, revealing the embedding of dominant meander scales in larger-scale loops. The method can be applied beyond the case of rivers to unravel the meandering structure of lava flows, turbidity currents, tidal channels, rivulets, supraglacial streams, and extraterrestrial flows.

The rate of migration, calculated by numerical models of river meandering, is commonly based on a method that relates the rate of migration to near-bank excess velocity multiplied by a dimensionless coefficient. Notwithstanding its simplicity, since the early 1980s this method has provided important insight into the long-term evolution of meander planforms through theoretical exercises. Its use in practice has not been as successful, because the complexity of the physical processes responsible for bank retreat, the heterogeneity in floodplain soils, and the presence of vegetation, make the calibration of the dimensionless coefficient rather challenging. This paper presents a new approach that calculates rates of meander migration using physically-based streambank erosion formulations. The University of Illinois RVR Meander model, which simulates meandering-river flow and bed morphodynamics, is integrated with algorithms for streambank erosion of the US Department of Agriculture channel evolution computer model CONCEPTS. The performance of the proposed approach is compared to that of the more simple classic method through the application to several test cases for idealized and natural planform geometry. The advantages and limitations of the approach are discussed, focusing on simulated planform pattern, the impact of soil spatial heterogeneity, the relative importance of the different processes controlling bank erosion (hydraulic erosion, cantilever, and planar failure), the requirements for obtaining stable migration patterns (centerline filtering and interpolation of bank physical properties), and the capability of predicting the planform evolution of natural rivers over engineering time scales (i.e., 50 to 100 years). The applications show that the improved physically-based method of bank retreat is required to capture the complex long-term migration patterns of natural channels, which cannot be merely predicted from hydrodynamics only.

Meandering channels is a vast research field, spanning a broad variety of time and space scales, environmental domains, and conceptual and methodological approaches. This paper serves as an introduction to this special issue of Geomorphology “Meandering Channels”, which addresses the need for sustained scientific dialogue on the dynamics of meandering channels. In an effort to place this issue in the broad context of this rapidly changing and advancing research field, we begin by discussing the motivation behind this issue. Then, we continue by summarizing the main novel research contributions of each paper. Finally, we conclude by proposing five major research directions that directly develop from the ensemble of the scientific contributions to this special issue. These research directions emphasize the critical importance of the coupling of near-bank geomorphic and flow processes; the characterization of co-evolution of meandering rivers and their floodplains; the need to improve linkages between meandering rivers research and river management and restoration; the potential of expanding laboratory-based research; and the integration of holistic and reductionist approaches.

The flow of deep-sea turbidity currents in meandering channels has been of considerable recent interest. Here we focus on the secondary flow associated with a subaqueous bottom current in a meandering channel. For simplicity, a saline bottom current may be used as a surrogate for a turbidity current driven by a dilute suspension of fine-grained sediment that does not easily settle out. In the case of open channel flow, i.e. rivers, the classical Rozovskiian paradigm is often invoked to explain secondary flow in meandering channels. This paradigm indicates that the near-bottom secondary flow in a bend is directed inward, i.e. toward the inner bank. It has recently been suggested based on experimental and theoretical considerations, however, that this pattern is reversed in the case of subaqueous bottom flows in meandering channels, so that the near-bottom secondary flow is directed outward (reversed secondary flow), towards the outer bank. Experimental results presented here, on the other hand, indicate near-bottom secondary flows that have the same direction as observed in a river (normal secondary flow). The implication is an apparent contradiction between experimental results. We use theory, experiments and reconstructions of case studies from fieldscale flows to resolve this apparent contradiction based on the densimetric Froude number of the flow. We find three ranges of densimetric Froude number, such that a) in an upper regime, secondary flow is reversed, b) in a middle regime, it is normal and c) in a lower regime, it is reversed. We apply our results at field scale to previous studies on channel-forming turbidity currents in the Amazon submarine canyon-fan system (Amazon Channel) and the Monterey canyon and a saline underflow in the Black Sea flowing from the Bosphorus. Our analysis indicates that secondary flow should be normal throughout most of the Amazon submarine fan reach, lower-regime reversed in the case of the Black Sea underflow, and upperregime reversed in the case of the Monterey canyon. The theoretical analysis predicts both normal and reversed regimes in the Amazon submarine canyon reach.

Many models of river meander migration rely upon a simple formalism, whereby the eroding bank is cut back at a rate that is dictated by the flow, and the depositing bank then migrates passively in response, so as to maintain a constant bankfull channel width. Here a new model is presented, in which separate relations are developed for the migration of the eroding bank and the depositing bank. It is assumed that the eroding bank consists of a layer of fine-grained sediment that is cohesive and/or densely riddled with roots, underlain by a purely noncohesive layer of sand and/or gravel. Following erosion of the noncohesive layer, the cohesive layer fails in the form of slump blocks, which armor the noncohesive layer and thereby moderate the erosion rate. If the slump block material breaks down or is fluvially entrained, the protection it provides for the noncohesive layer diminishes and bank erosion is renewed. Renewed bank erosion, however, rejuvenates slump block armoring. At the depositing bank, it is assumed that all the sediment delivered to the edge of vegetation due to the transverse component of sediment transport is captured by encroaching vegetation, which is not removed by successive floods. Separate equations describing the migration of the eroding and depositing banks are tied to a standard morphodynamic formulation for the evolution of the flow and bed in the central region of the channel. In this model, the river evolves toward maintenance of roughly constant bankfull width as it migrates only to the extent that the eroding bank and depositing bank ‘talk’ to each other via the medium of the morphodynamics of the channel center region. The model allows for both (a) migration for which erosion widens the channel, forcing deposition at the opposite bank, and (b) migration for which deposition narrows the channel forcing erosion at the opposite bank. Copyright © 2010 John Wiley & Sons, Ltd.

A modeling framework that combines both two-dimensional (2D) and one-dimensional (1D) numerical models for the evaluation of organic-matter transport across the bed-water interface is presented. Emphasis is placed on capturing oxygen demand in the water column associated with the resuspension of organic sediments from the bottom. The proposed numerical approach solves the hydrodynamics coupled with sediment transport and water quality dynamics and represents a substantial improvement to the state of the art of water quality modeling methodologies available in the literature. A biochemical oxygen demand (BOD)–dissolved oxygen (DO) water quality module is incorporated into the 2D depth-averaged numerical model STREMR-HySedWq. The model is applied to the South Fork of the South Branch of the Chicago River, known as Bubbly Creek, with the goal of modeling combined sewer overflow (CSO) events and their impact on DO levels in the short-term (hours or days). Given the intermittent nature of this kind of events, ...

The wavelet transform (WT) has been successfully implemented in many fields such as signal and image processing, communication theory, optics, numerical analysis, and fluid mechanics. However, the application of WT to describe bedform morphology in coastal areas, oceans, and rivers is rare. The present study demonstrates the capability of WT analysis to fully represent the space–frequency characteristics of signals describing bed topography generated in marine and river environments. In this study WT is used to examine the morphological characteristics of bedforms generated in two separate laboratory facilities: a wave tank and a meandering channel. In the wave tank a set of ripples superimposed upon large wave ripples were generated; while in the meandering channel, 2D and 3D migrating ripples and dunes were observed. The WT proved to be a useful tool in detecting the complex variability of the generated bedform structures. The size distribution of the bottom features such as ripples, large wave ripples and sandbars were first examined along a 2D bed profile. Later analysis studied the variability of features in the transverse direction by using the power Hovmoller. Experiments in the wave tank were conducted for a mobility number of ψ=(10, 28), and a Reynolds wave number of Rew=(17,500, 83,500) which correspond to waves alone (WA) and to combined flow (CF) scenarios, respectively. Experiments in the meandering channel were conducted under a morphological regime that produced mainly migrating sandbars.

Streambank erosion is an important management issue, particularly for meandering rivers. Recently, bendway weirs have become popular control measures for bank erosion along small meandering streams in the agricultural Midwest. Although these structures have successfully mitigated bank erosion in some cases, there is evidence that the weirs do not always perform as anticipated. Scientific understanding of how bendway weirs influence flow dynamics, streambank erosion, and aquatic habitat is limited. Current design criteria are based primarily on expert judgment rather than a formalized technical design procedure. At field-scale studies, the present paper represents a first step toward an integrated geomorphological and engineering evaluation of the performance of bendway weirs in rivers. To accomplish this initial phase, three-dimensional (3D) velocity data were collected on Sugar Creek at Brookside Farm, Ill., and 3D numerical simulations for low-flow conditions were performed to validate the computational...

A 2D depth-averaged hydrodynamic, sediment transport and bed morphology model named STREMR HySeD is presented. The depth-averaged sediment transport equations are derived from the 3D dilute, multiphase, flow equations and are incorporated into the hydrodynamic model STREMR. The hydrodynamic model includes a two-equation turbulence model and a correction for the mean flow due to secondary flows. The suspended sediment load can be subdivided into different size classes using the continuum (two-fluid) approach; however, only one bed sediment size is used herein. The validation of the model is presented by comparing the suspended sediment transport module against experimental measurements and analytical solutions for the case of equilibrium sediment-laden in a transition from a rigid bed to a porous bed where re-suspension of sediment is prevented. On the other hand, the bed-load sediment transport and bed evolution numerical results are compared against bed equilibrium experimental results for the case of a meander bend. A sensitivity analysis based on the correction for secondary flow on the mean flow including the effect of secondary flow on bed shear stresses direction as well as the downward acceleration effect due to gravity on transverse bed slopes is performed and discussed. In general, acceptable agreement is found when comparing the numerical results obtained with STREMR HySeD against experimental measurements and analytical solutions.

Acoustic Doppler current profilers (ADCPs) are commonly used to measure streamflow and water velocities in rivers and streams. This paper presents laboratory, field, and numerical model evidence of errors in ADCP measurements caused by flow disturbance. A state-of-the-art three-dimensional computational fluid dynamic model is validated with and used to complement field and laboratory observations of flow disturbance and its effect on measured velocities. Results show that near the instrument, flow velocities measured by the ADCP are neither the undisturbed stream velocity nor the velocity of the flow field around the ADCP. The velocities measured by the ADCP are biased low due to the downward flow near the upstream face of the ADCP and upward recovering flow in the path of downstream transducer, which violate the flow homogeneity assumption used to transform beam velocities into Cartesian velocity components. The magnitude of the bias is dependent on the deployment configuration, the diameter of the instrument, and the approach velocity, and was observed to range from more than 25% at 5 cm from the transducers to less than 1% at about 50 cm from the transducers for the scenarios simulated.

RVR Meander was developed as a toolbox for modeling restoration and naturalization processes in rivers. This model includes Windows-based and Geographical Information System-based programs for analyzing and modeling planform migration of streams. In the past, several rivers have been channelized causing environmental and ecological problems. Restoration techniques evolve as natural solutions to channelization, therefore, the prediction of planform migration in rivers is indispensable for economic and social reasons such as development of urban areas close to rivers, prevention of damages to infrastructure, reduction of agricultural land losses, and for the maintenance of biological diversity in rivers. Abad and Garcia [2004, Conceptual and mathematical model for evolution of meandering rivers in naturalization processes. On CD-ROM of Proceedings of Joint Conference on Water Resources Engineering and Water Resources Planning and Management, ASCE, June 27-July 1, Salt Lake City, Utah, 10pp.] presented a conceptual and mathematical model for evolution of meandering rivers that can be used in restoration and naturalization processes. In this work, the description of RVR Meander is based on the computational characteristics and applicability rather than presenting its theoretical basis. RVR Meander is an object oriented user-friendly model for restoration purposes. Two modules are included: statistical analysis and planform migration of rivers. This model has been successfully tested on Microsoft Windows NT 4.0/2000/XP and on ArcMap 8.1/8.2/8.3.

River dynamics involve complex, incompletely understood interactions among flow, sed- iment transport and channel form. The capacity to predict these interactions is essential for a variety of river management problems, including channel migration, width adjustment and habitat develop- ment. To address this need, high-resolution numerical models increasingly are being used by river engineers, fluvial geomorphologists and river biologists to explore the complexity of river dynamics and to predict fluvial behavior. This paper presents numerical simulations through a natural meader- ing river using two different models: a depth-averaged numerical code with secondary flow correction and a fully 3-D, state-of-the-art, Computational-Fluid-Dynamics (CFD) code. Models predictions are compared to high-quality 3-D velocity data collected in a highly sinuous reach of the Embarras River in Central Illinois, showing a successful simulation of the main flow features. Implications for sediment transport, planform development and habitat structure throughout the reach are analyzed, demonstrating the potential use of the models as a tool for river management.

Fossil fuel power generation technologies offer a number of alternatives, which involve different fuel supply, production, power generation, and pollution control devices with varied environmental impacts. The holistic approach to examining these impacts through Life Cycle Assessment (LCA) can help decision makers to quantify the many emissions trade-offs inherent in any change to the fuel supply and power production systems and ensure that a change in fuel or fuel sourcing does not result in increases of other environmental and health impacts. Besides endpoint emissions exiting from a smokestack in natural gas-fueled power generation, air toxics such as formaldehyde, benzene and xylenes are also generated through the supply chain from compressor engines, oil/condensate tanks, as well as intermittent sources such as well drilling and fracturing engines, well completions, gas processing, and also fugitive emissions from production and transmission. These emissions sources differ in quantity, species, spatially and in overall risk to the surrounding population. People exposed to air toxics at sufficient concentrations and durations may have an increased risk of developing cancer or experiencing other serious health effects. The purpose of this paper is to identify the appropriate air toxics emission factors for natural gas production and utilize a LCA approach to quantify the "cradle-to-gate" air toxics emissions in terms of one (1) kWh of electricity generated.

An in-house fully three-dimensional general-purpose finite element model is applied to solve the hydrodynamic structure in a periodic Kinoshita-generated meandering channel. The numerical model solves the incompressible Reynolds-averaged Navier–Stokes equations for mass and momentum, while solving the k − e equations for turbulence. The free surface is described by the rigid-lid approximation (using measured water surface data) for flat (smooth-bed) and self-formed (rough-bed) conditions. The model results are compared against experimental measurements in the ‘Kinoshita channel’, where three-dimensional flow velocities and turbulence parameters were measured. This validation was carried out for the upstream-valley meander bend orientation under smooth (flat bed) conditions. After validation, several simulations were carried out to predict the hydrodynamics in conditions where either it was not possible to perform measurements (e.g. applicability of the laboratory acoustic instruments) and to extrapolate the model to other planform configurations. For the flat smooth-bed case, a symmetric (no skewness) planform configuration was modeled and compared to the upstream-skewed case. For the self-formed rough-bed case, prediction of the hydrodynamics during the progression of bedforms was performed. It appears that the presence of bedforms on a bend has the following effects: (i) the natural secondary flow of the bend is disrupted by the presence of the bedforms, thus depending on the location of the dune, secondary flows might differ completely from the traditional orientation; (ii) an increment on both the bed and bank shear stresses is induced, having as much as 50% more fluvial erosion, and thus a potential increment on the migration rate of the bend. Implications on sediment transport and bend morphodynamics are also discussed in the paper. Copyright © 2013 John Wiley & Sons, Ltd.