Changes In Channel Width Research Articles

Modeling on approximation of fluvial landform change impact on morphodynamics at Madhumati River Basin in Bangladesh

This study was carried out to investigate fluvial Landform characteristics and background causes of dynamic changes at Madhumati River Basin and to evaluate the impact of morphodynamics on the hydrology, agriculture systems, and ecosystems services and people livelihoods. To accomplish the research goal, the present study considered to evaluate bank line shifting, course change direction, change of channel patterns, change in channel width, rate of erosion, accretion and sedimentation, fluvial and floodplain landforms transformation, as well as hydrological dynamics. Furthermore, the spatial and temporal scale of morphological change were linked with drivers. For understanding the complex morphological process and response of the river, reliable historical time-series satellite images, and hydrological data were analyzed; as well as taking expert judgment and local knowledge into account. GIS and remote sensing (RS) tools, techniques and models were applied to process, analyze, and extract fluvial parameters from multitemporal Landsat satellite imagery. The results of the study demonstrate that erosion, accretion and historical migrated area significantly increased during the flooding period of 1988 and 1998 and that these hydromorphological hazards badly impacted on flood plain resources, agricultural systems, aquatic, and terrestrial biodiversity. Also, human interference, such as bridge construction and business purpose dredging badly impacted on the hydromorphological characteristics of this river. The results also reveal that Madhumati River had very low sinuosity in the time span 1973–2020. Gradually, the sinuosity value of this river is increasing over time. Sinuosity values of this river ranged between 0.98 (1973) and 1.11 (2020) with an average value 1.04 designating straight to sinuous nature. The scope of this research will suggest possible morphological adjustment for future management strategies of climate change, fluvial disasters, and develop resilience capability to the rural community.

Width control on event‐scale deposition and evacuation of sediment in bedrock‐confined channels

AbstractIn mixed bedrock–alluvial rivers, the response of the system to a flood event can be affected by a number of factors, including coarse sediment availability in the channel, sediment supply from the hillslopes and upstream, flood sequencing and coarse sediment grain size distribution. However, the impact of along‐stream changes in channel width on bedload transport dynamics remains largely unexplored. We combine field data, theory and numerical modelling to address this gap. First, we present observations from the Daan River gorge in western Taiwan, where the river flows through a 1 km long 20–50 m wide bedrock gorge bounded upstream and downstream by wide braidplains. We documented two flood events during which coarse sediment evacuation and redeposition appear to cause changes of up to several metres in channel bed elevation. Motivated by this case study, we examined the relationships between discharge, channel width and bedload transport capacity, and show that for a given slope narrow channels transport bedload more efficiently than wide ones at low discharges, whereas wider channels are more efficient at high discharges. We used the model sedFlow to explore this effect, running a random sequence of floods through a channel with a narrow gorge section bounded upstream and downstream by wider reaches. Channel response to imposed floods is complex, as high and low discharges drive different spatial patterns of erosion and deposition, and the channel may experience both of these regimes during the peak and recession periods of each flood. Our modelling suggests that width differences alone can drive substantial variations in sediment flux and bed response, without the need for variations in sediment supply or mobility. The fluctuations in sediment transport rates that result from width variations can lead to intermittent bed exposure, driving incision in different segments of the channel during different portions of the hydrograph. © 2020 The Authors. Earth Surface Processes and Landforms published by John Wiley & Sons Ltd

Graphene self‐switching diode‐based thermoelectric rectifier

This Letter demonstrates thermoelectric rectification in graphene self-switching diode (GSSD) on SiO2/Si substrate. Nanometre-scale non-linear semiconductor device, called self-switching diode (SSD), has been utilised. Applied bias leads to a change in potential profile and effective channel width of GSSD resulting in diode like I–V characteristics. The excellent electronic properties of graphene potentially make it suitable for producing SSD's with high responsivity and low noise equivalent power (NEP). The designed GSSD demonstrates a high Seebeck coefficient (S) of 200 μV/K, voltage detection sensitivity, and NEP of 97.964 V/W and 0.6064 nW/Hz1/2, respectively. Furthermore, the effect of applying backgate voltage on the Seebeck coefficient has also been demonstrated in this work. The GSSD is presented as a potential thermoelectric rectifier, which can convert the thermal energy into useful electrical energy.

Channel width optimized neural networks for liver and vessel segmentation in liver iron quantification

IntroductionMRI T2* relaxometry protocols are often used for Liver Iron Quantification in patients with hemochromatosis. Several methods exist to semi-automatically segment parenchyma and exclude vessels for this calculation. PurposeTo determine if inclusion of multiple echoes inputs to Convolutional Neural Networks (CNN) improves automated liver and vessel segmentation in MRI T2* relaxometry protocols and to determine if the resultant segmentations agree with manual segmentations for liver iron quantification analysis. MethodsMulti echo Gradient Recalled Echo (GRE) MRI sequence for T2* relaxometry was performed for 79 exams on 31 patients with hemochromatosis for iron quantification analysis. 275 axial liver slices were manually segmented as ground truth masks. A batch normalized U-Net with variable input width to incorporate multiple echoes is used for segmentation, using DICE as the accuracy metric. ANOVA is used to evaluate significance of channel width changes in segmentation accuracy. Linear regression is used to model the relationship of channel width on segmentation accuracy. Liver segmentations are applied to relaxometry data to calculate liver T2* yielding liver iron concentration(LIC) derived from literature based calibration curves. Manual and CNN based LIC values are compared with Pearson correlation. Bland altman plots are used to visualize differences between manual and CNN based LIC values. ResultsPerformance metrics are tested on 55 hold out slices. Linear regression indicates that there is a monotonic increase of DICE with increasing channel depth (p = 0.001) with a slope of 3.61e-3. ANOVA indicates a significant increase segmentation accuracy over single channel starting at 3 channels. Incorporation of all channels results in an average DICE of 0.86, an average increase of 0.07 over single channel. The calculated LIC from CNN segmented livers agrees well with manual segmentation (R = 0.998, slope = 0.914, p«0.001), with an average absolute difference 0.27 ± 0.99 mg Fe/g or 1.34 ± 4.3%. ConclusionMore input echoes yields higher model accuracy until the noise floor. Echos beyond the first three echo times in GRE based T2* relaxometry do not contribute significant information for segmentation of liver for LIC calculation. Deep learning models with three channel width allow for generalization of model to protocols of more than three echoes, effectively a universal requirement for relaxometry. Deep learning segmentations achieve a good accuracy compared with manual segmentations with minimal preprocessing. Liver iron values calculated from hand segmented liver and Neural network segmented liver were not statistically different from each other.

Responses and resilience of tallgrass prairie streams to patch‐burn grazing

Abstract Patch‐burn grazing (PBG) can promote terrestrial heterogeneity and biodiversity, but can temporarily increase stream nutrients and ecosystem metabolism, and alter macroinvertebrate assemblages. The impacts of grazing on stream channel morphology and post‐PBG recovery patterns are unclear. We assessed the influence of grazing in PBG managed grassland streams in Missouri, USA, and subsequent recovery when grazing ceased for 2 years. We hypothesized that grazing would degrade water quality, stream biotic integrity and channel morphology, but that riparian fencing would mitigate these effects. We predicted that biological and chemical variables in unfenced streams would return to pre‐PBG levels within 2 years after grazing ceased, but channel morphology would not. Six small headwater streams (two in ungrazed control watersheds, two in PBG watersheds with 10 m fenced riparian zones and two in PBG unfenced) were sampled over 7 years; 2 years before PBG, 3 years during PBG and 2 years post‐PBG. We sampled macroinvertebrates and water chemistry monthly when water was present and surveyed channel morphology at least once each study period. During grazing, unfenced watersheds showed the greatest changes in channel width, depth and area. During the post‐PBG period, one of the two unfenced watersheds showed partial recovery of channel morphology. Although grazing increased concentrations of nutrients and chlorophyll‐a, concentrations returned to pre‐PBG conditions after grazing ceased, indicating recovery. Very fine organic sediments increased in the unfenced watersheds compared to the control during grazing but recovered afterwards. Contributions of Chironomidae to total invertebrate abundance increased in the unfenced watersheds during grazing, and then decreased during the post‐PBG period. Riparian fencing mostly mitigated effects of grazing on the streams. Unfenced streams were resilient to effects of grazing in a PBG managed grassland, with most metrics recovering within 2 years after grazing ceased, except for channel morphology. Synthesis and applications. Grazing in a patch‐burn grazed managed grassland coupled with riparian fencing could be an effective conservation tool for land managers of prairies, with relatively modest influences on stream water quality and biotic integrity. Persistent changes in stream channel morphology and effects of longer periods of grazing deserve further research.

Effect of change of channel width in the downstream of the check dam on controlling sedimentation in Mrica Reservoir

The increasing sedimentation of Mrica reservoir shows that the sedimentation control has not been effective. The sedimentation control has been made include the disposal of sediments that settle in the reservoir by dredging or flushing. However, the results are not optimal. This is caused by the large volume of sediment entering the reservoir each year. The controlling volume of sediment that goes into the reservoir has also been carried out by conducting a watershed conservation program and building a check dam in the upstream Mrica reservoir. However, the existing check dam is still less effective in controlling sediments, especially suspended load sediments, that are transported in the river. Therefore this study was carried out by adopting the sediment trap concept to deposit sediments that escaped from the check dam. This study simulated changes in the width of the downstream channel of the check dam by three variations using HEC-RAS. There was a width of 20%, 40%, and 60% wider than the initial width. The results showed the effect of changing the channel width on volume sediment deposited. Based on the results of the study, the change in width to wider than the initial width could increase the volume of sediment deposits.

Heat transfer model of a particle energy storage‐based moving packed bed heat exchanger

AbstractMoving packed bed particle/supercritical carbon dioxide (SCO2) heat exchanger (MPBE) is a critical equipment to integrate particle thermal energy storage technology with SCO2 power cycle block in the next‐generation concentrated solar power plants. A predictive heat transfer model for designing and evaluation of shell and plate particle/SCO2 moving packed bed heat exchanger is presented, with radiation, pressure drop and SCO2 property variation taking into account. It is found that increasing particle diameter and solids bulk voidage will lower the overall heat transfer coefficient. Change of channel width imposes little effects on the overall heat transfer coefficient, while influences the total heat exchange greatly. MPBE with longer channel length allows smaller overall heat transfer coefficient. Due to approximate linear variation of specific heat and low pressure drop in the nominal boundary operating condition range, ignoring SCO2 Cp variation is valid, and the relative error due to adopting a Cp invariable evaluated at the bulk temperature and constant pressure is less than 1%. Convection resistance generally ranks first in the contribution to thermal resistance, followed by solids‐wall resistance and conduction resistance. Nevertheless, solids‐wall resistance dominates at larger particle diameter (≥550 μm). Radiation is an important contributor to heat transfer behavior, especially at high particle diameter and solids bulk voidage. The relative error caused by neglecting radiation can be up to 23.76%.

Dynamics of ephemeral streams at the foot of degraded catchments in northern Ethiopia

AbstractThe magnitudes of flash floods and their effect on channel width changes were investigated for Hara River in the Raya graben (northern Ethiopia). Precipitation was measured using rain gauges evenly distributed over the study catchment. Event peak discharges were measured with crest‐stage gauges at a reference cross‐section. Changes in channel width were measured at six monitoring sites along a 1.5 km long reach. Decadal channel width change was analyzed over the period 1965–2014. The average rainfall depth of the rainy days was 14.2 ± 9.4 mm whereas the highest was 41.9 mm and the lowest, capable to generate some flow in the river, was only 1.8 mm. The maximum calculated discharge peaked at 408 m3/s whereas the lowest flow was 19.5 m3/s. An average widening of 0.11 ± 0.19 m per flood (for a total of 3.74 m) was measured. The cumulative precipitation and cumulative channel widening suggest that larger and longer lasting rains have substantial influence on channel width change. A marked increase in channel width commonly accompanies 2–3 days of flood duration; it is less marked where there is riparian vegetation on the banks. The long‐term (1965, 1986, 2005, and 2010) measurements indicate that channel width increased rapidly over the last 50 years; nearly 25 m of widening. Generally, channel changes are mainly induced by the duration of floods rather than by their intensity and the data clearly show that ephemeral streams channel dynamics can be triggered also by floods much smaller than bankfull.

Performance study of a novel multi-functional Trombe wall with air purification, photovoltaic, heating and ventilation

A novel multi-functional passive solar wall, i.e., photocatalytic-photovoltaic-Trombe wall (PC-PV-Trombe wall), which can obtain heat, electricity and fresh air simultaneously was proposed firstly. Then a multi-physical fields (velocity, temperature and concentration fields) coupling model was established to study the performance of PC-PV-Trombe wall. The effects of channel height and width on the thermal, electrical and degradation performance of PC-PV-Trombe wall were analyzed. Finally, the performance of PC-PV-Trombe wall, built-in PV-Trombe wall and PC-Trombe wall were compared under different solar radiation intensities and ambient temperatures. The results show that the ventilation volume, thermal efficiency, heat output, electrical efficiency and the clean air delivery rate of PC-PV-Trombe wall present different trends of increase or decrease with the change of channel height and width. As opposed to the effect on the electrical efficiency, the lower ambient temperature has a negative influence on the ventilation volume, thermal performance and air purification performance, especially for the condition of lower solar radiation intensity. PC-PV-Trombe wall can realize the comprehensive utilization for air purification, photovoltaic, heating and ventilation of solar energy and the total efficiency can reach a maximum of 0.67.

Meandering-anabranching river channel change in response to flow-sediment regulation: Data analysis and model validation

Anabranching river has been recognized as an independent river pattern. A variety of investigations have attempted to disclose the formation of anabranching rivers, however, most previous studies mainly focused on the controls of anabranching channels formation. The mechanism of transition among sub-channels with varying flow-sediment regime in anabranching rivers has been poorly understood. In this study, we used multi-source data sets to investigate the changes in river channels and island (Wugui Island, about 7 km2) along the 27-km long Jianli Reach (Tashiyi-Tianziyihao) in the middle Yangtze River. Nine Landsat images (1987, 1990, 1994, 1996, 2000, 2003, 2006, 2010 and 2014) with 30 m spatial resolution were used to map the channel planform dynamics. Obvious changes in channel width and morphology of the island were observed during 1987–2014. The width of the left branch had reduced from 1041 m to 340 m, while the width of the right branch had increased from 632 m to 1531 m. During 1994–1996, the main river channel shifted from the left branch to the right. During the period of 1987–2014, the total width of the compound cross-section increased, and the mean length-width ratio of the island increased from 3.59 to 4.32. The mean annual flow discharge increased about 9%, and mean annual suspended sediment concentration and sediment transport coefficient (the ratio of mean annual suspended sediment concentration to mean annul flow discharge) decreased about 75% and 76% respectively from 1951 to 2009, in response to the operation of Gezhouba Dam and Three Gorges Dam. The meandering-anabranching channel planform adjusted by narrowing the island width and enlarging compound cross-section in response to upstream water-sediment regime. The shift of the main river channel from left branch to the right may resulted from the increase in flow discharge and decrease in sediment transport coefficient since 1980s. The adjustment has been intensified by the changes in the sediment transport rate after 1995. After the main channel was switched from left branch to right branch, the flow-sediment diversion capacity was kept stable with a diversion percentage of 90% in right branch. Due to the persistent influence of the Three Gorges Dam, the right branch will function as the main channel for a long time before the meandering-anabranching system achieves equilibrium. The shift and stability of main channel was closely related with the relative magnitude of flow-sediment partition in each branch. The significance of this study is that we successfully manifested the main channel shift process of anabranching river with the support of direct hydromorphological observation and theoretical verification.

Differential bank migration and the maintenance of channel width in meandering river bends

AbstractComparison of three bare-earth lidar data sets along 30 consecutive river bends on the Trinity River in Texas, USA, shows that differential migration of river banks in a channel bend counterbalances past bank migrations so that a statistically steady-state channel width is maintained. Two difference maps created from lidar flown in 2011, 2015, and 2017 capture this temporal variability in the relative amounts of inner versus outer bank migration. In 20 of the studied river bends, channel narrowing during 2011–2015 was counterbalanced by widening during the second interval, or vice versa. Only four bends recorded significant (>1%) progressive change in channel width during both measurement periods. Each of these four bends recorded progressive channel narrowing that was connected to floodplain complexity associated with past bend cutoffs or tributaries. Subaerial volumes of sediment deposited on inner banks of bends were smaller for 2015–2017 than for 2011–2015, while erosional volumes associated with the outer banks were similar despite 2015–2017 having had almost twice the number of days under flood conditions. Over time, channel width for the river appears roughly constant because differences in outer and inner bank migration at one time are counterbalanced by compensating differences at a later time. For the Trinity River, this compensation happened over time spans as short as 2–3 yr and would lead to the appearance of invariant channel width at the decadal scale. Tighter river bends with relatively smaller radii of curvature have smaller magnitudes of width change compared to broader bends with larger radii of curvature.

Valley-Confinement and River-Tidal Controls on Channel Morphology Along the Fluvial to Marine Transition Zone of the Ðồng Nai River System, Vietnam

Along the fluvial to marine transition zone (FMTZ) of river deltas, the river-tidal dynamics exert a primary control on channel width, sinuosity, and bed elevation; however, other local factors, such as valley confinements, bifurcations, and confluences, can modify the channel morphology. Here, we report a case study of the major channel of the Dong Nai River System (DNRS) that shows complex morphological trends linked to multiple factors. This study is based on the analysis of satellite images and bathymetric maps of the studied channel, together with a digital elevation model of the area and additional climate and hydrology data. Our study shows that channel width, sinuosity, and bed elevation show mutual relationships and complex upstream to downstream trends linked to the river-tidal dynamics and valley confinements, together with more local effects due to bifurcations and confluences. The tidal dynamics is mainly responsible for the seaward-widening and seaward-shallowing trends and the abrupt decrease in channel sinuosity observed in the downstream tract of the channel, whereas the relatively constant channel width and sinuosity in the upstream tract suggest a control of the river dynamics. The studied channel also shows three areas of valley widening or exit, which are characterized by high channel sinuosity, the presence of minor and major bifurcations, and additional changes in channel width and bed elevation, and they are considered important nodes in this system. Valley-related nodes also show different active and inactive features, implying that the degree of activity and importance of these nodes likely varied through time, migrating from upstream to downstream due to the deltaic progradation.

On the mixing of rivers with a difference in density: The case of the Negro/Solimões confluence, Brazil

Confluences are common components of all riverine systems, and characterized by converging streamlines and potential mixing of separate flows. The fluid dynamics of confluences possess a highly complex structure with several common types of flow features observed.An investigation was carried out in both low and relatively high flow conditions at the confluence of the Negro and Solimões Rivers, Brazil, which ranks among the largest river junctions on Earth. During this field research, acoustic Doppler velocity profiling (ADCP) and water quality sampling were applied to investigate hydrodynamics, sediment transport and mixing characteristics at this confluence. It was found that the location and the width of the mixing interface were closely related to changes of the discharge ratio between the tributaries due to both seasonal and annual variations. Second, a timescales analysis was applied to comparatively identify the contribution to mixing at the Negro/Solimões confluence of four processes: difference in (1) velocity and (2) density between the rivers, (3) bed friction, including form drag, and (4) change in channel width. The analysis demonstrated that adjustments of confluence hydrodynamics and morphodynamics can modify the relative importance of each contribution. Immediately downstream of the junction the effects of differences in velocity and density were comparable, while farther downstream the latter was predominant and the role of bed friction was significant. At the end, this study suggests that mixing at the Negro/Solimões confluence can be explained as a combination of the four hydrologic and morphologic processes.

Instrument-free argentometric determination of chloride via trapezoidal distance-based microfluidic paper devices

Chloride (Cl−) is an inorganic anion present in a broad range of samples (e.g. biological, environmental, food, water, etc.), the determination of which is of widespread significance. In this work, we translate the well-established traditional argentometric method (Mohr's precipitation titration) into a small, simple, portable, and low-cost paper-based microfluidic diagnostic device, which provides rapid and quantitative analysis. The developed device enables the determination of chloride sample volumes as small as 5 μL. A distance-based detection method is implemented providing fully instrument-free quantitation. The beneficial effects of channel geometry (variable widths with constant heights) on analytical parameters were investigated. Trapezoidal channels (channel width changes linearly with height) were used to create a gradient of paper surface (titrant) available for the reaction, compared to the typical uniform rectangular channels (constant channel width). The trapezoid with increasing width offered higher sensitivity and lower detection limits (i.e. 0.05 mM vs 0.1 mM from the rectangular channel) for chloride determination across the concentration range of 0.05–25 mM. In addition, the effect of concentration of the deposited reagent on the obtained distance signals was investigated using varying concentrations of titrant (AgNO3), which allowed determination of chloride across a wider dynamic range (up to 200 mM). The utility of the paper devices was demonstrated by determination of chloride in a variety of matrices including body fluids (sweat, serum, and urine) and water samples (drinking, mineral, river water).

Morphodynamics of a Width‐Variable Gravel Bed Stream: New Insights on Pool‐Riffle Formation From Physical Experiments

Field observations, experiments, and numerical simulations suggest that pool‐riffles along gravel bed mountain streams develop due to downstream variations of channel width. Where channels narrow, pools are observed, and at locations of widening, riffles occur. Based on previous work, we hypothesize that the bed profile is coupled to downstream width variations through momentum fluxes imparted to the channel surface, which scale with downstream changes of flow velocity. We address this hypothesis with flume experiments understood through scaling theory. Our experiments produce pool‐riffle like structures across average Shields stresses τ∗ that are a factor 1.5–2 above the threshold mobility condition of the experimental grain size distribution. Local topographic responses are coupled to channel width changes, which drive flows to accelerate or decelerate on average, for narrowing and widening, respectively. We develop theory which explains the topography‐width‐velocity coupling as a ratio of two reinforcing timescales. The first timescale captures the time necessary to do work to the channel bed. The second timescale characterizes the relative time magnitude of momentum transfer from the flowing fluid to the channel bed surface. Riffle‐like structures develop where the work and momentum timescales are relatively large, and pools form where the two timescales are relatively small. We show that this result helps to explain local channel bed slopes along pool‐riffles for five data sets representing experimental, numerical, and natural cases, which span 2 orders of magnitude of reach‐averaged slope. Additional model testing is warranted.

Broadband extraordinary acoustic transmission via hornlike metamaterials

We demonstrate an extraordinary acoustic transmission through a class of hornlike space-coiling metamaterials, in which the gradual change in channel width ensures such a transmission property in a wide frequency band. This phenomenon is explained in terms of the constitutive parameters based on an effective medium approach, and the underlying mechanism stems from the improved impedance matching and effective near-zero density. Numerical simulations based on finite element analysis are used to verify the effectiveness of our designs, and the results show that this class of metamaterials provides an efficient design methodology for broadband extraordinary acoustic transmission.

Fluvial Geomorphology, Root Distribution, and Tensile Strength of the Invasive Giant Reed, Arundo Donax and Its Role on Stream Bank Stability in the Santa Clara River, Southern California

Arundo donax (giant reed) is a large, perennial grass that invades semi-arid riparian systems where it competes with native vegetation and modifies channel geomorphology. For the Santa Clara River, CA, changes in channel width and intensity of braiding over several decades are linked in part to high flow events that remove A. donax. Nevertheless, the area of A. donax at the two study sites increased fivefold over a period of 28 years at one site and fourfold over 15 years at the second site. Effects of A. donax on bank stability are compared to those of a common native riparian tree—Salix laevigata (red willow)—at two sites on the banks and floodplain of the Santa Clara River. There is a significant difference of root density of A. donax compared to S. laevigata and the latter has a higher number of roots per unit area at nearly all depths of the soil profile. Tensile root strength for S. laevigata (for roots of 1–6 mm in diameter) is about five times stronger than for A. donax and adds twice the apparent cohesion to weakly cohesive bank materials than does A. donax (8.6 kPa compared to 3.3 kPa, respectively). Modeling of bank stability for banks of variable height suggests that S. laevigata, as compared to A. donax, increases the factor of safety (FS) by ~60% for banks 1 m high, ~55% for banks 2 m high and ~40% for banks 3 m high. For 3 m high banks, the FS for banks with A. donax is <1. This has geomorphic significance because, in the case of A. donax growing near the water line of alluvial banks, the upper 10–20 cm has a hard, resistant near-surface layer overlying more erodible banks just below the near-surface rhizomal layer. Such banks may be easily undercut during high flow events, resulting in overhanging blocks of soil and A. donax that slump and collapse into the active channel, facilitating lateral bank erosion. Therefore, there is a decrease in the lateral stability of channels if the mixed riparian forest is converted to dominance by A. donax.

The Dynamics of Channel Slope, Width, and Sediment in Actively Eroding Bedrock River Systems

AbstractThe evolution of rivers in eroding landscapes plays a key role in determining landscape relief and modulating climate‐tectonic interactions. A common approach to quantifying river system evolution uses a one‐dimensional, detachment‐limited stream power equation. One potential drawback of this model is that it does not incorporate the effects of changes in channel width or the role of sediment transport dynamics. Here I present a new method for modeling the influence of channel width on river dynamics to explore how variable width and sediment transport impact river profile evolution. With this approach, vertical river erosion can operate based on any number of river erosion models, such as a simple shear stress model (e.g., detachment limited), sediment cover‐shear stress hybrid models, or mechanistic saltation‐abrasion models. I explore the sensitivity of these three models to increases in rock‐uplift rate (i.e., 2, 3, 5, 10, and 20× increase). Generally, the results show that incorporating channel width adjustment or sediment transport dynamics lowers the sensitivity of a river profile to rock‐uplift rate. For the sediment transport‐dependent models, the degree of sensitivity depends on whether the system is limited by bedrock exposure or erosion potential (i.e., detachment potential). The approach produces transient responses that reveal distinct patterns of width and slope, which may provide valuable insight into the limiting physical mechanisms of bedrock erosion in a region. The implications of the work are broad and include the potential to distinguish underlying erosion controls from field observations of width and slope as well as understanding climate‐tectonic interactions.

Numerical optimization of channel to land width ratio for PEM fuel cell

Flow field plays a vital role in proton exchange membrane (PEM) fuel cell where channel geometry being the primary factor. Most of the channel geometry analyses were limited to few number of case studies, whereas in this study total 73 case studies were analyzed for the optimization of channel and land width. A three dimensional isothermal single phase flow mathematical model is developed and further validated with experimental study to optimize the channel and land width through parametric sweep function for a staggering 73 number of case studies. The optimization analyses are carried out for a straight channel geometry considering a fixed operating voltage of 0.4 V and channel depth of 1.0 mm. Due to the large number of case studies, the analyzed performance parameters i.e. current density and pressure drop are easily understandable for the change in different channel and land width. The numerical results predicted that the pressure drop is more dependent on channel width compare to the land width and anode pressure drop is less significant than cathode pressure drop. However, both channel and land width have an equal importance on the cell current density. Considering channel pressure drop and current density, the optimization analyses showed that the channel to land width of 1.0 mm/1.0 mm would be best suitable for PEMFC channel geometry.

Air-photo based change in channel width in the Minnesota River basin: Modes of adjustment and implications for sediment budget

The Minnesota River and major tributaries have experienced large increases in discharge over the past century. Aerial photograph-based measurements of channel width were made for the 1938–2015 period at 16 multibend subreaches by digitizing the area between vegetation lines and dividing by centerline length. Results show considerable increases in width for the main stem (0.62±0.10%/y) and major tributaries (0.31±0.08%/y) but are inconclusive for smaller channels (width<25m). Width change for a 146.5-km reach of the lower Minnesota River between 1938 and 2008 is similar to that from the subreach-scale analysis. Widening was associated with lateral centerline movement and temporal change in at-a-station hydraulic geometry for water surface width, indicating that widening is associated with cross-sectional change and not simply upward movement of the vegetation line. Digital elevation model analysis and regional hydraulic geometry show that the main stem and larger tributaries account for the vast majority (~85%) of bankfull channel volume. High-order channels are thus disproportionately responsible for sediment production through cross section enlargement, although floodplains or off-channel water bodies adjacent to these channels likely represent important sediment sinks. Because channel enlargement can play an important role in sediment production, it should be considered in sediment reduction strategies in the Minnesota River basin and carefully evaluated in other watersheds undergoing long-term increases in discharge.