Steep Channel Research Articles

Sediment sources, spatiotemporal variability and rates of fluvial bedload transport in glacier-connected steep mountain valleys in western Norway (Erdalen and Bødalen drainage basins)

Contemporary fluvial bedload transport rates are still very difficult to measure and, as a result of this, in many sites only quantitative data on suspended and solute transport are included in sediment budget studies carried out for defined drainage basin systems. The presented analysis of fluvial bedload dynamics in different defined subsystems of the glacier-connected Erdalen (79.5km2) and Bødalen (60.1km2) drainage basins in the steep fjord landscape of western Norway provides insights into (i) detectable relevant sediment sources, (ii) instream channel storage of bedload material, (iii) spatiotemporal variability and controls of bedload transport rates and bedload yields, and (iv) the absolute and relative importance of fluvial bedload transport within the sedimentary budgets of these steep cold climate mountain valleys. Rockfalls, snow avalanches, stream channel bank erosion, and fluvial transfers through small tributaries draining slope systems are relevant sediment sources for fluvial bedload transport in the main stream channels, whereas the main outlet glaciers in both drainage basins are not of importance as all bedload material delivered directly from these outlet glaciers is trapped within proglacial lakes. Narrow valleys within both drainage basin systems are characterized by a higher intensity of slope-channel coupling and display higher rates of sediment supply from slopes into the main stream channels than wider valleys. Snow avalanches are the most important sediment source in Erdalen, whereas fluvial transfers through small tributaries followed by snow avalanches are most important in Bødalen. Longer term, instream channel storage is not of great importance in the steep Bødalen drainage basin but currently plays an important role within the Erdalen drainage basin, which is characterized by a stepped longitudinal main valley bottom profile favoring deposition of bedload material within less steep main channel reaches. The mean annual bedload yields (2010–2013) are 2.4tkm−2y−1 for the entire Erdalen and 13.3tkm−2y−1 for the entire Bødalen drainage basin, which are comparably low values for steep and partly glacierized drainage basin systems. Because of supply-limited conditions, the intensity of fluvial bedload transport is generally much more related to the availability of sediments than to channel discharge. Fluvial bedload transport accounts for about one-third of the total fluvial transport and accordingly plays an important role within the sedimentary budgets of both drainage basin systems.

Patterns of bedload entrainment and transport in forested headwater streams of the Columbia Mountains, Canada

AbstractWe monitor bedload transport and water discharge at six stations in two forested headwater streams of the Columbia Mountains, Canada. The nested monitoring network is designed to examine the effects of channel bed texture, and the influence of alluvial (i.e. step pools and riffle pools) and semialluvial morphologies (i.e. boulder cascades and forced step pools) on bedload entrainment and transport. Results indicate that dynamics of bedload entrainment are influenced by differences in flow resistance attributable to morphology. Scaled fractional analysis shows that in reaches with high form resistance most bedload transport occurs in partial mobility fashion relative to the available bed material, while calibers finer than 16 mm attain full mobility during bankfull flows. Equal mobility transport for a wider range of grain sizes is achieved in reaches exhibiting reduced form resistance. Our findings confirm that the Shields value for mobilization of the median surface grain size depends on channel gradient and relative submergence; however, we also find that these relations vary considerably for cobble and gravel bed channels due to proportionality between dimensionless shear stress and grain size. Exponents of bedload rating curves across sites correlate most with the D90s of the mobile bed, however, where grain effects are controlled (i.e. along individual streams), differences in form resistance across morphologies exert a primary control on bedload transport dynamics. Application of empirical formulae developed for use in steep alpine channels present variable success in predicting transport rates in forested snowmelt streams. Formulae that explicitly account for reductions in mobile bed area and high morphological resistance associated with woody debris provide the best approximation to observed empirical data. Copyright © 2014 John Wiley & Sons, Ltd.

Numerical simulation of the fluvial processes in the channels by sediment mining

This study aims to experimentally and numerically investigate the fluvial processes of channels disturbed through sand or gravel mining. A two-dimensional numerical model is applied to simulate flume experiments. A moving boundary-fitted coordinate system is used to describe the channel changes. As a numerical scheme, the cubic interpolated pseudoparticle method is used to calculate the flow field and bed changes, which introduces little numerical diffusion. The numerical model is verified with experimental data. The inflow sediment from the upstream is trapped into a pit and the sediment deposit wedge migrated to the downstream with a steep submerged angle of repose. The numerical and experimental results show that the sediment deposit wedge in the pit migrates to the downstream under the condition of steady state. The adjustment time within the disturbed channels increases as the dimension of the pit is increased. The sediment mining pit migrates with speed in the steep channel. Moreover, the numerical experiments show that the migration speed is proportional to the sediment inflow. And the disturbed channels by the sediment mining are affected by the sediment inflow conditions of the upstream and adjusted to the new state of equilibrium.

Bed load fluctuations in a steep channel

AbstractBed load transport rate fluctuations have been observed over time in steep rivers and flumes with wide grain size distributions even under constant sediment feeding and water discharge. The observed bed load transport rate pulses are periodic and a consequence of grain sorting. Moreover, the presence of large, relatively immobile boulders, such as erratic stones, which are often present in mountain streams, has an impact on flow conditions. The detailed analysis of a 13 h laboratory experiment is presented in this paper. Boulders were randomly placed in a flume with a steep slope (6.7%), and water and sediment were constantly supplied to the flume. Along with the sediment transport and bulk mean flow velocity, the boulder protrusion, boulder surface, and number of hydraulic jumps, which are indicators of the channel morphology, were measured regularly during the experiment. Periodic bed load transport rate pulses are clearly visible in the data collected during this long‐duration experiment, along with correlated fluctuations in the flow velocity and bed morphology. The links among the bulk velocity, the time evolution of the morphology variables, and the bed load transport rate are analyzed via correlational analysis, showing that the fluctuations are strongly related. A phase analysis of all observed variables is performed, and the average shapes of the time cycles of the fluctuations are shown. Observations indicate that the detected periodic fluctuations correspond to different bed states. Furthermore, the grain size distribution through the channel, which varies in time and space, clearly influences these bed load transport rate pulses. Finally, known bed load transport rate formulae are tested, showing that only the application of a drag shear stress allows a correct estimation of the time fluctuations.

Inner structure of anchor ice and ice dams in steep channels

Dynamic ice growth (composed primarily of anchor ice and ice dams) is the dominant process in steep (slope>0.3%) channels during winter. The ice growth (in all its manifestations) regulates water levels, flow resistance, bathymetry, flow rate, water quality and fish habitat. Empirical models of the processes are available but in order to develop more physically-based models, more knowledge about the nature of ice in these channels is required. This paper presents original data from two channels of the Montmorency River watershed known for their intense anchor ice and ice dam development activity. The data include time-lapse photographs, underwater photographs, water level records, and water and air temperatures collected during winter 2012–2013. Moreover, anchor ice and ice dam samples were analyzed with thin sections and using computed axial tomography (CAT) scan technology. This study aims at understanding the development processes of both anchor ice accumulations and ice dams by investigating their crystal types and sizes, their growth mechanisms, patterns, and orientation, and their porosity.Two main types of ice crystals were observed: columnar ice crystals and fixed-frazil ice crystals. Relatively large columnar ice crystals grew upwards (away from the bed) perpendicularly to the local flow surface and were only observed in ice dam samples. Fixed-frazil crystals originated from the deposition and/or interception of drifting frazil particles that became “fixed” to the bed and to existing ice accumulations. The data suggest that in-situ growth of fixed-frazil ice crystals was the dominant process (accounted for the most ice development) for both anchor ice and ice dams. Fixed-frazil ice consists of a bonded mass of interlocking plate shaped crystals demonstrating a preference to be perpendicular to the bed and water surfaces. The mass displays some variability in porosity (mean value 41%). When analyzed using CAT scan slices, the interlocking plates appear as a tree-like or dendritic structure. The average size of resulting crystal segments and the maximum size of individual whole crystals within fixed-frazil ice structures were significantly more important for ice dam samples than for anchor ice samples.

Experimental evidence for fluvial bedrock incision by suspended and bedload sediment

Fluvial bedrock incision sets the pace of landscape evolution and can be dominated by abrasion from impacting particles. Existing bedrock incision models diverge on the ability of sediment to erode within the suspension regime, leading to competing predictions of lowland river erosion rates, knickpoint formation and evolution, and the transient response of orogens to external forcing. We present controlled abrasion mill experiments designed to test fluvial incision models in the bedload and suspension regimes by varying sediment size while holding fixed hydraulics, sediment load, and substrate strength. Measurable erosion occurred within the suspension regime, and erosion rates agree with a mechanistic incision theory for erosion by mixed suspended and bedload sediment. Our experimental results indicate that suspension-regime erosion can dominate channel incision during large floods and in steep channels, with significant implications for the pace of landscape evolution.

Multiple failure styles related to shallow gas and fluid venting, upper slope Canadian Beaufort Sea, northern Canada

The continental slope of the Canadian Beaufort Sea presents an exceptional opportunity to study the relationship between the fluid venting and the formation of mass-transport deposits. The continental shelf was emergent and partially ice-free during the last glaciation and is underlain by widespread permafrost. Water-column backscatter has shown the locations of more than 40 active gas vents along seaward margin of the subsea permafrost at the shelf break and upper slope. New multibeam bathymetry and subbottom profiler data show shallow potentially late Holocene failures and mass-transport deposits on the upper slope. Upslope from a prominent headscarp, undulating seabed with apparent growth faults overlies an acoustically incoherent to stratified horizon at 50 m sub-bottom interpreted as a decollement surface over which progressive creep has occurred. Similar creep is present in places on the upper slope and in places seems to have evolved into small translational slides, involving more compacted sediment buried > 25 m, or into muddy debris flows where sediments buried < 25 m have failed. Much of the slope failed during a regional retrogressive event, the Ikit slump, likely initiated on steep channel walls on the lower slope. Characteristic ridge and trough morphology resulting from retrogressive spreading or rotational slumping are preserved on gradients < 2° on the upper slope, but appear to have been completely evacuated on gradients of 3° on the mid slope, where muddy debris-flow deposits are found. Correlations between radiocarbon dated cores and sub-bottom profiles show that the retrogressive failure occurred in the last 1000 years. This study implies that Holocene shelf break and upper slope stability in the Beaufort Sea are strongly linked to the dynamics of the permafrost and the presence of weak, gas-rich sediments. It demonstrates that creep deformation evolves into either muddy debris flows or translational slides, dependent on sediment strength. • Water column backscatter shows active gas vents near the subsea permafrost limit. • Creep with growth faults occurs over a gas-charged decollement zone. • Creep evolves to translational slides where thick, debris flows were thin. • A major < 1 ka retrogressive slump is the largest failure in the area.

Incipient sediment motion across the river to debris-flow transition

Sediment transport in mountain channels controls the evolution of mountainous terrain in response to climate and tectonics and presents major hazards to life and infrastructure worldwide. Despite its importance, we lack data on when sediment moves in steep channels and whether movement occurs by rivers or debris flows. We address this knowledge gap using laboratory experiments on initial sediment motion that cross the river to debris-flow sediment-transport transition. Results show that initial sediment motion by river processes requires heightened dimensionless bed shear stress (or critical Shields stress) with increasing channel-bed slope by as much as fivefold the conventional criterion established for lowland rivers. Beyond a threshold slope of ∼22°, the channel bed fails, initiating a debris flow prior to any fluvial transport, and the critical Shields stress within the debris-flow regime decreases with increasing channel-bed slope. Combining theories for both fluvial and debris-flow incipient transport results in a new phase space for sediment stability, with implications for predicting fluvial sediment transport rates, mitigating debris-flow hazards, and modeling channel form and landscape evolution.

Scaling relationships between bed load volumes, transport distances, and stream power in steep mountain channels

Bed load transport during storm events is both an agent of geomorphic change and a significant natural hazard in mountain regions. Thus, predicting bed load transport is a central challenge in fluvial geomorphology and natural hazard risk assessment. Bed load transport during storm events depends on the width and depth of bed scour, as well as the transport distances of individual sediment grains. We traced individual gravels in two steep mountain streams, the Erlenbach (Switzerland) and Rio Cordon (Italy), using magnetic and radio frequency identification tags, and measured their bed load transport rates using calibrated geophone bed load sensors in the Erlenbach and a bed load trap in the Rio Cordon. Tracer transport distances and bed load volumes exhibited approximate power law scaling with both the peak stream power and the cumulative stream energy of individual hydrologic events. Bed load volumes scaled much more steeply with peak stream power and cumulative stream energy than tracer transport distances did, and bed load volumes scaled as roughly the third power of transport distances. These observations imply that large bed load transport events become large primarily by scouring the bed deeper and wider, and only secondarily by transporting the mobilized sediment farther. Using the sediment continuity equation, we can estimate the mean effective thickness of the actively transported layer, averaged over the entire channel width and the duration of individual flow events. This active layer thickness also followed approximate power law scaling with peak streampower and cumulative stream energy and ranged up to 0.57min the Erlenbach, broadly consistent with independent measurements.

Particle velocity and concentration profiles in bedload experiments on a steep slope

ABSTRACTDepth profiles of particle streamwise velocity, concentration and bedload sediment transport rate were measured in a turbulent and supercritical water flow. One‐size 6 mm diameter spherical glass beads were transported at equilibrium in a two‐dimensional 10% steep channel with a mobile bed. Flows were filmed from the side by a high‐speed camera. Particle tracking algorithms made it possible to determine the position, velocity and trajectory of a very large number of particles. Approximately half of the sediment transport rate was composed by rolling grains, and the other half by saltation. This revealed a complex structure, with several concentration and flux peaks due to rolling, and one peak due to saltation. With an increase of the sediment transport rate, the depth structure remained the same at the water/granular interface, with peak value increases but with no shift in elevations. The saltation region expanded towards higher elevations with an increase of the particle velocity commensurate to the water velocity. The proportion of the sediment transport rate in saltation did not vary significantly. The particle streamwise velocity profiles exhibited three segments: an exponential decay in the bed, a linear increase where rolling and saltation co‐existed, and above this, a logarithmic‐like shape due to saltating particles. These results are comparable to profiles measured and modelled in dry granular free surface flows and in more intense bedload such as sheet flows. Copyright © 2014 John Wiley &amp; Sons, Ltd.

Dynamics of dense gravity currents and mixing in an up-sloping and converging vee-shaped channel

Detailed velocity and density measurements are used to investigate dense water dynamics in an inclined, silled channel of triangular cross-section with varying side slope α and adverse bed slope φ. For the steeper channel configuration considered (φ=3.6°), the dense-water bottom current is shown to be frictionally-controlled, with an internal flow structure characterized by a sharp pycnocline and decreasing isopycnal separation in the along-channel direction. For the milder up-sloping channel (φ=1.7°), the dense water outflow is shown to be hydraulically-controlled as the channel sill section is approached, with internal flow dynamics characterized by increasing isopycnal separation in the along-channel direction. Analysis of the gradient Richardson number Rig of the flow confirms that hydraulically-controlled flows dilute the active bottom water due to interfacial mixing. A gradually-varying internal flow model and a two-layer hydraulic modelling approach are shown, respectively, to represent adequately the outflow behaviour for these two bed slope conditions.

Instream Woody Debris and Riparian Forest Characteristics in the Sabine River, Texas

We examined instream large woody debris (LWD) dynamics on the Sabine River, TX. All wood >10 cm in diameter and >2 m long was measured on four river meanders (meander wavelengths) below the dam on Toledo Bend Reservoir. We determined LWD species, degree of decay, bank orientation, jam association, and stage contact. We also measured riparian vegetation characteristics on each meander. LWD volumes were significantly greater at the site immediately below Toledo Bend Dam, due to the relatively steeper channel gradient and higher rates of channel erosion. Based on mass balance estimates, between 11 and 21% of total annual recruitment came from upstream fluvial transport, and the remainder resulted from bank erosion and tree mortality. We estimated average LWD residence time to be 12–14 years. The lower Sabine River is transport-limited for sediment, and the same is true for LWD. Based on these measurements, it is unlikely that Toledo Bend Reservoir is having a significant impact on LWD dynamics at the measurement reaches due to lacustrine wood storage. Of greater concern in the study system are riparian forest degradation and invasive species spread, which may dramatically affect future LWD loadings and residence times, and thus, riverine biota.

The Effect of Road Crossing on River Morphology and Riverine Aquatic Life: A Case Study in Kunur River Basin, West Bengal

Road crossings play important role in land transport system, but improper designed stream crossing may alter the form and function of stream geomorphology, floodplain ecosystem, habitat and movement of aquatic organisms. The objective of this paper is to explain the local level impact of a road crossing on channel morphology and aquatic lives of the Kunur River, based on geomorphic survey and stream classification. This study shows a comparison between upstream and downstream reaches of Kunur River where the State Highway-14 crossed the river over a bridge. There are changing fluvio-geomorphic indicators like mean and maximum bankfull channel depth, cross-section area, flow velocity, entrenchment ratio, channel bed gradient, water level and depth, braided index (BI), pool-riffle sequence, area and shape of bars, and others taken into consideration. Results are temporally increases of BI and expansions of bars. In the downstream, river channel is deeply incised by massive bed degradation and highly entrenched with high flow velocity and steep channel bed gradient, low entrenchment ratio (&lt;2.2), low width-depth ratio (11.26) and increasing inter pool-riffle distance. Present study reveals that bank failure is a common phenomenon here with deep scours and making unsuitable environment for fish habitat. Alternatively, it has appeared to be greater deposition of fine sediment in the upstream reaches with high braiding index, area of bars. High entrenchment ratio (&gt;2.2) and width-depth ratio (&gt;35) also indicates well developed floodplain ecosystem here.Key Words: Anthropogenic feature; channel morphology; bed degradation; bank failure; fine sediment

Assessing fish distribution and threats to fish biodiversity in the Yangtze River Basin, China

The Yangtze River (6,380 km long) is the longest river in Asia and the third-longest one in the world. Its river basin (a complex riverine–lacustrine network) is especially rich in fish fauna, representing high species richness and endemism, and therefore is a globally significant area for preserving fish biodiversity (Dudgeon 2000; Park et al. 2003). However, during the past several decades, loss of fish biodiversity in the Yangtze River Basin has been accelerated by a series of direct and indirect effects of human activities and environmental changes, e.g., disappearance, shrinkage, and fragmentation of habitats for fish spawning, feeding and migration, overfishing, water pollution, and invasion of exotic species (Zeng 1990; Xie and Chen 1999). Despite numerous publications on ichthyological research in the Yangtze River Basin since the 1950s, synthesis and analysis or assessment of fish distribution patterns and quantification of major threats to fishes are still limited, which in turn limits formulation of biodiversity conservation strategies. In this study, we collected and synthesized the scattered data from relevant literature, with the purposes of (1) assessing large-scale distribution and endemic species composition of Yangtze fishes, (2) ranking the contribution of major threats as well as intrinsic factors to fish endangerment, and (3) providing recommendations for fish conservation in the basin. The Yangtze River Basin consists of five defined areas (Fig. 1). The riverhead is located on the Tibetan Plateau, where the mean elevation is over 4,500 m (Zeng 1990). The upper reach extends upstream from Yichang (in Hubei Province), with a length of more than 4,300 km and a drainage basin area of 100 9 10 km. The Yangtze flows primarily across mountainous regions with steep channel slopes of 10–40 9 10 (Chen et al. 2001). The famous Three Gorges Dam is located in the upper mainstream. The middle reach lies between Yichang and Hukou (in Jiangxi Province), with a length of about 950 km and a drainage area of 68 9 10 km. Low relief topography with channel slopes of 2–3 9 10 and meandering platforms are characteristics of this region. Here, the river connects with shallow lakes of various sizes and numerous tributaries and forms an endemic Chinese compound ecosystem of inland water. The lower reach extends from Hukou downward to the mouth of the river, with a length of 930 km and a drainage area of 12 9 10 km. This segment of the river wanders among plains and hills with lower channel slopes of 0.5–1.0 9 10. Several large interior lakes, such as Lake Caohu and Lake Taihu in association with many tributaries, drain into the reach (Chen et al. 2001). The river empties into the East China Sea at the estuary, which is characterized by three bifurcations and four outlets into the sea and a complicated temporal and spatial salinity distribution (Mao et al. 2001). Fish taxonomy and distribution in the five defined basin areas were compiled from scattered published fish surveys since the 1950s. To ensure data quality and authenticity, faunal compositions derived from extensive surveying and/ or long-term monitoring were adopted. The used literatures include Chu (1955), Anonymous (1976, 1980), Yang (1987), Zeng (1990), Wu and Wu (1992), Ding (1994), Chen (1998), Chu et al. (1999), Yue (2000), Ni and Zhu (2005), Zhuang et al. (2006), and Wu and Zhong (2008). Endemic species were defined according to their distribution being limited to the Yangtze River Basin. Patterns of distribution range of the fishes were indicated by the S. Ye (&) Z. Li T. Zhang J. Liu S. Xie State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan 430072, P. R. China e-mail: yeshw@ihb.ac.cn

The hydro-cryologic continuum of a steep watershed at freezeup

• Freezeup is a very dynamic period of the year. • Ice dams store and release substantial volumes of water in the drainage system . • Stage and discharge variations can be associated with specific weather conditions. • Ice processes in small channels significantly affect the discharge of larger channels. • Monitoring simple parameters can improve our discharge estimations at freezeup. Ice processes that occur in steep (gravel bed) channels are completely different from those occurring in mild-gradient rivers. As such, the impact of ice on water level and discharge in steep streams is different than what is usually found documented for large channels. Whereas in large mild rivers, the development of a surface ice cover generates a nominal increase in stage in the order of 30%, in steep channels, the formation of series of ice dams caused the water level to rise by up to 500%. The increase in stage caused a maximum estimated ice-induced discharge depression of 50%. The ice-dam stage may represent the highest level of the year whereas the freezeup discharge may temporarily drop to its annual minimum. Ice formations significantly alter local channel hydraulic conditions (bed elevations, cross-sectional area, riffle-pool sequences, etc.) and both stage and discharge vary drastically in a short time. ‘Dynamic’ ice processes (particularly the formation of ice dams) in steep channels depend on morphology and are driven by heat fluxes into and out of the system. Based on the authors observations of many steep channels over many winters, the inter-relationships (synchronicity) between air temperature fall (and rise), ice dam formation (and breaching), water level rise (and drop) and discharge depletion (and increase) are documented here. This paper presents air and water temperatures, water stages, discharges, and ice processes taking place on an hourly basis in four channels of increasing Strahler order. The data and hydro-crologic continuum analyses presented significantly improve our understanding and hence our ability to interpret freezeup water level signals. The paper also discusses how hydrographers may use this understanding and additional data to provide better estimates of discharge in steep channels at freezeup.

Slope Correction for Calculation of Bedload Sediment Transport Rates in Steep Channels

AbstractClassical theories developed for investigating bedload sediment transport are applicable largely for channel beds of a gentle slope. Examples are the well-known Shields diagram for the evaluation of the critical condition for initial sediment motion and the classical bedload transport formulas derived with deterministic or probabilistic approaches. How to apply the existing bedload formulas for steep channels remains challenging. In this study, a simple procedure is proposed for correcting slope effects so that the existing bedload formulas can be extended for steep channels. To verify the proposed correction factor, two representative bedload formulas are modified and checked against published data of sediment transport rates that were significantly affected by steep slopes.

Bedload dynamics and associated snowmelt influence in mountainous and semiarid alluvial rivers

The influence of snowmelt in semiarid alluvial rivers is determined by the river bed configuration and erosion processes. Moreover, the large amount of available sediment in the floodplains of these rivers limits traditional bedload sampling methodologies and suggests the use of large control volumes and long-term studies to understand erosive dynamics. In this study, bedload monitoring in a large control volume (0.2hm3) from 2004 to 2010 was used to study erosive processes of the Guadalfeo River, a semiarid alluvial river in southeastern Spain with high mountain influences and a hydrological regime conditioned by snow dynamics. The methodological approach to testing the performance of different transport models included characterization of the forcing agents (precipitation and snowmelt events), hydraulic configuration of the river, determination of the river bed material (surface and substrate), and one-off measurements for particular events. The results indicate a sediment volume–effective runoff relationship that is consistent with the existence of steep channels with a flashy runoff regime, although the existence of an armored layer derived from snowmelt events greatly controls the transport dynamics, with equivalent fractions of cobble–gravel and sand in the measured bedload. This apparent predominance of near-equal mobility was confirmed by the calibrated hiding function exponent (x≈0.94–0.97). The thresholds for entrainment and transport efficiency are similar to those observed for mountain rivers that exhibit torrential flow, although notable differences can be observed in the dynamics of the processes. The strong performance of the original Meyer-Peter and Müller model (with c=8) is shown to estimate the total transported volume associated with intense events when the variability of d50 is included in the analysis. However, this model does not sufficiently capture transport because of moderate events (rain or snowmelt) and thus underestimates bedload on medium and long timescales. The calibrated model of Parker–Klingeman adequately represents erosive dynamics, with τr50⁎ values between 0.03 and 0.041 for moderate and intense events, respectively, and a flow threshold of 14.2m3s−1 that separates these two situations. Nevertheless, these models based on hiding functions present greater dispersion if the variability of diameters related to cobbles and pebbles is considered. For such cases, the Wilcock and Crowe model performed better for both intense and moderate events. The latter is important in the study area, where snowmelt pulses occasionally exceed the critical flow and break the surface layer with significant sediment contributions. These processes differentiate the transport dynamics from other studies and are distinctive characteristics that are more closely related to mountainous influences in semiarid environments where pulses of intense snowmelt are common. Despite its limitations, the proposed methodology, based on a large check-dam, has proven to be adequate and representative for assessment of erosion processes.

Green-wavelength terrestrial laser scanning of mountain channel

Abstract. It is crucial to understand and predict how the water and sediment flow in mountain channels for better disaster risk management. Detailed and quantitative measurement of channel and stream-bed structure is in great demand. In this paper, the utility of greenwavelength TLS for measurement of submerged stream-bed is preliminary examined in a steep mountain channel. The ability of through water measurement is evaluated in terms of water depth and flow velocity. Automated extraction of submerged objects is also tested. The results of comparison of water depth derived by TLS and survey displayed significant correlation between them, presenting good performance of green-wavelength TLS for measurement of submerged stream-bed. The analysis using a Generalized Liner Model (GLM) indicated that each of water depth and flow velocity alone does not affect the accuracy of TLS measurement, however, the interaction between water depth and flow velocity may have an influence. The attempt to automatically extract the dimension of submerged objects was partially successful, achieving maximum error of +0.8 cm for two objects.

Tectonic controls upon Kaveri River drainage, cratonic Peninsular India: Inferences from longitudinal profiles, morphotectonic indices, hanging valleys and fluvial records

The Indian Peninsula is generally considered as a tectonically stable region, where ancient rocks, rivers and land surfaces predominate. In some parts of this ancient landscape, however, the role of tectonic landsculpting is strongly indicated by the presence of youthful topography and historical seismic activity. The present study is primarily focused on the middle domain of the Kaveri River, which displays such youthful features. The tectonic controls on this cratonic river were evaluated on the basis of the investigations of the longitudinal profiles, morphotectonic indices of active tectonics, and fluvial records. The presence of steep channel gradients, prominent knickpoints, hanging valleys, narrow bedrock gorges, and channel-in-channel morphology imply rapid erosion rates in the middle domain of the basin in response to active deformation, particularly in the reach defined by two major active faults — the Kollegal–Sivasamudram Fault and the Mekedatu Fault. Further, considering the remarkably low modern and long-term denudation rates and OSL ages of the alluvial deposits (30–40ka), the tectonically-driven rejuvenation does not appear to be geologically recent as postulated by earlier workers.

Quantifying steep channel freezeup processes

Abstract Freezeup processes in steep channels are particularly dynamic and generate important water level, water temperature, and discharge variations. This work presents unique field data quantifying steep channel ice processes during the freezeup period. Water temperature variability and ice dam buildup and breaching rates measured in the Montmorency watershed, Quebec, Canada are reported. The conditions leading to the development and melting of ice dams are discussed. The rate at which water is stored in the drainage system at different channel Strahler orders and the consequent freezeup flooding rates and discharge depressions are estimated. A major contribution of this paper is the formulation and application of an original heat budget model designed to specifically address the particularities of steep channel heat fluxes. The modeled net heat flux is compared with measured water temperature and with the timing of ice dam buildup and breaching events for a second order channel. This work can be of interest for cold region hydraulic and transportation engineers who are responsible for the safe design of bridges and culverts, for cold region hydrologists, for hydroelectric producers and for water intake operators in need of evaluating and forecasting low freezeup discharge conditions. Freshwater and riparian zone biologists can also refer to this work to evaluate the conditions that affect the fauna and flora at freezeup and public emergency services can use this work to quantify the risk of freezeup flooding along steep channels.