Width control on event scale bedload dynamics in bedrock-confined channels

2021 ◽  
Author(s):  
Kristen Cook ◽  
Jens Turowski ◽  
Niels Hovius
Keyword(s):  
Random Sequence ◽  
Bedload Transport ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Channel Width ◽  
Sediment Grain Size ◽  
Event Scale ◽  
Narrow Channels ◽  
Coarse Sediment ◽  
The Impact

<p>In 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 modeling to address this gap. Observations from two flood events in the Daan River gorge in western Taiwan suggest that coarse sediment evacuation and re-deposition can cause intra-flood changes of up to several meters in channel bed elevation that are distinct from measured before/after bed changes. We hypothesize that this could be related to the abrupt change in width between the 1 km long bedrock gorge and the river upstream and downstream. An analysis of the theoretical relationships between discharge, channel width, and bedload transport capacity shows that for a given slope, narrow channels transport bedload more efficiently than wide ones at low discharges, while 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 modeling 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. Further, the deposition or erosion that takes place within a flood is often not reflected in the before/after changes to the bed, and this disconnect increases with increasing flood size.</p>

scholarly journals Upscaling sediment-flux-dependent fluvial bedrock incision to long timescales

2021 ◽  
Author(s):  
Jens Turowski
Keyword(s):  
Time Scales ◽  
Mechanistic Model ◽  
Bedload Transport ◽  
Sediment Flux ◽  
Channel Width ◽  
Cross Sectional ◽  
Spatial And Temporal Scales ◽  
Long Time ◽  
Free Parameters ◽  
The Impact

<p><span>Fluvial bedrock incision is driven by the impact of moving bedload particles. Mechanistic, sediment-flux-dependent incision models have been proposed, but the stream power incision model (SPIM) is frequently used to model landscape evolution over large spatial and temporal scales. This disconnect between the mechanistic understanding of fluvial bedrock incision on the process scale, and the way it is modelled on long time scales presents one of the current challenges in quantitative geomorphology. Here, a mechanistic model of fluvial bedrock incision that is rooted in current process understanding is explicitly upscaled to long time scales by integrating over the distribution of discharge. The model predicts a channel long profile form equivalent to the one yielded by the SPIM, but explicitly resolves the effects of channel width, cross-sectional shape, bedrock erodibility and discharge variability. The channel long profile chiefly depends on the mechanics of bedload transport, rather than bedrock incision. In addition to the imposed boundary conditions specifying the upstream supply of water and sediment, and the incision rate, the model includes four free parameters, describing the at-a-station hydraulic geometry of channel width, the dependence of bedload transport capacity on channel width, the threshold discharge of bedload motion, and reach-scale cover dynamics. For certain parameter combinations, no solutions exist. However, by adjusting the free parameters, one or several solutions can usually be found. The controls on and the feedbacks between the free parameters have so far been little studied, but may exert important controls on bedrock channel morphology and dynamics. </span></p>

scholarly journals Alluvial cover controlling the width, slope and sinuosity of bedrock channels

2018 ◽  
Vol 6 (1) ◽  
pp. 29-48 ◽  
Author(s):  
Jens Martin Turowski
Keyword(s):  
Bedload Transport ◽  
Rate Of Change ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Channel Width ◽  
Transport Capacity ◽  
Bedrock Channel ◽  
Bed Slope ◽  
The 19Th Century ◽  
Bedrock Channels

Abstract. Bedrock channel slope and width are important parameters for setting bedload transport capacity and for stream-profile inversion to obtain tectonics information. Channel width and slope development are closely related to the problem of bedrock channel sinuosity. It is therefore likely that observations on bedrock channel meandering yields insights into the development of channel width and slope. Active meandering occurs when the bedrock channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments. Here, this idea is taken up by postulating that the rate of change of both width and sinuosity over time is dependent on bed cover only. Based on the physics of erosion by bedload impacts, a scaling argument is developed to link bedrock channel width, slope and sinuosity to sediment supply, discharge and erodibility. This simple model built on sediment-flux-driven bedrock erosion concepts yields the observed scaling relationships of channel width and slope with discharge and erosion rate. Further, it explains why sinuosity evolves to a steady-state value and predicts the observed relations between sinuosity, erodibility and storm frequency, as has been observed for meandering bedrock rivers on Pacific Arc islands.

Outcrop analysis and facies model of an Upper Permian tidally influenced fluvio-deltaic system: Northern Sydney Basin, SE Australia

2019 ◽  
Vol 156 (10) ◽  
pp. 1715-1741 ◽  
Author(s):  
Jake Breckenridge ◽  
Angelos G. Maravelis ◽  
Octavian Catuneanu ◽  
Kevin Ruming ◽  
Erin Holmes ◽  
...  
Keyword(s):  
Source Region ◽  
Depositional Environments ◽  
Sediment Supply ◽  
Upper Permian ◽  
Delta Front ◽  
Sediment Grain Size ◽  
Sequence Stratigraphic ◽  
Delta Plain ◽  
Facies Associations ◽  
The Impact

AbstractAn integrated study of sedimentological, sequence-stratigraphic and palaeodispersal analysis was applied to the Upper-Permian clastic sedimentary succession in the Northern Sydney Basin, Australia. The succession is subdivided into fifteen facies and three facies associations. The facies associations are further subdivided into eight sub-facies associations. The sedimentary evolution involves progradation from delta-front to delta-plain to fluvial depositional environments, with a significant increase in sediment grain size across the unconformable contact that separates the deltaic from the overlying fluvial system. In contrast to the delta front that is wave/storm- and/or river-influenced, the delta plain is significantly affected by tides, with the impact of tidal currents decreasing up-sequence in the delta plain. The general lack of wave-influenced sedimentary structures suggests low wave energy in the delta plain. The abrupt termination of the tidal impact in the fluvial realm relates to the steep topographic gradients and high sediment supply, which accompanied the uplift of the New England Orogen. The sequence-stratigraphic framework includes highstand (deltaic forest and topset) and lowstand (fluvial topset) systems tracts, separated by a subaerial unconformity. In contrast to most of the mud-rich modern counterparts, this is an example of a sand-rich tidally influenced deltaic system, developed adjacent to the source region. This investigation presents a depositional model for tidal successions in regions of tectonic uplift and confinement.

Bedload dynamics in the rapidly changing paraglacial zone of a high alpine catchment

2020 ◽  
Author(s):  
Clemens Hiller ◽  
Kay Helfricht ◽  
Gabriele Schwaizer ◽  
Severin Hohensinner ◽  
Kerstin Wegner ◽  
...  
Keyword(s):  
Bedload Transport ◽  
Sediment Flux ◽  
High Mountain ◽  
Channel Network ◽  
Scientific Debate ◽  
Coarse Sediment ◽  
Sediment Volume ◽  
Mountain Environments ◽  
Fluvial Transport ◽  
Catchment Areas

<p>High mountain environments have been confronted with rising temperatures and geomorphological changes over the past 150 years, with the considerable retreat of glaciers constituting one of the most pronounced impacts in the Alps. Concurrent degradation of permafrost in headwalls exposed from the downwasting ice and in periglacial hillslopes alongside glaciers causes increasing sediment flux onto glacier surfaces. The accumulation of supraglacial debris at the current glacier tongue promotes water-storage in debris-covered ice bodies and is assessed as an important source of sediment in the proglacial zone, since a close connection to the fluvial channel network can be assumed. The evolution of mountain streams, the degree of connectivity and conditional sedimentation-erosion effects significantly determine the dynamics in a generally unstable paraglacial landscape in which retreating glaciers provide high stream discharges while sediment is widely unconsolidated.</p><p>In the recent scientific debate, the anticipated progressive shift from supply-limitation (fluvial transport overcapacity) to transport-limitation (abundance of sediment) in high alpine catchment areas is discussed. Thus, this study intends to contribute by investigating the connection of coarse sediment including supraglacial debris from the proglacial transition zone to downstream fluvial transport. Key aspect is the feedback between increasing debris cover and a shifting runoff regime due to a changing composition of glacier melt, snow melt and heavy rainfall events. In that respect, the focus will be on the dynamics of bedload transport and the proglacial coarse sediment budget.</p><p>This study is part of the Hidden.Ice project and conducts in-depth monitoring of the connectivity, runoff measurements and geomorphological surveys at the LTER site Jamtalferner, Silvretta Range, Austria. Hydraulic modelling of the potential transport capacity supported by bedload trap measurements, the analysis of grain size distribution in the proglacial area and sediment volume changes calculated from UAV-based photogrammetry are aimed at raising knowledge on hydrological and geomorphological dynamics.</p>

scholarly journals Provenance of Bengal Shelf Sediments: 2. Petrology and Geochemistry of Sand

Minerals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 642 ◽  
Author(s):  
Eduardo Garzanti ◽  
Giovanni Vezzoli ◽  
Sergio Andò ◽  
Mara Limonta ◽  
Laura Borromeo ◽  
...  
Keyword(s):  
Equatorial Indian Ocean ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Estuarine Sediments ◽  
Heavy Minerals ◽  
Geochemical Data ◽  
Nd Isotope ◽  
Shelf Sediments ◽  
Compositional Variability ◽  
The Impact

The Bangladesh lowlands are traversed by the largest sediment flux on the planet. Detritus generated mostly in Himalayan highlands and conveyed through the Ganga–Brahmaputra rivers and Meghna estuary reaches the Bay of Bengal, where it forms a composite deltaic system. This study integrates the vast existing database on Ganga–Brahmaputra sediments of all grain sizes from clay to sand with new petrographic, mineralogical, and geochemical data on estuarine and shallow-marine sands. A large spectrum of compositional signatures was used to: (i) assess the relative supply of the Ganga and Brahmaputra rivers to estuarine and shelfal sediments; (ii) define the compositional variability of estuarine sediments and the impact exerted by hydraulic sorting and climate-related chemical weathering on provenance signals; (iii) define the compositional variability of shelf sediments and the potential hydrodynamic segregation of fast-settling heavy minerals in coastal environments and of slow-settling platy micas on low-energy outer-shelf floors; (iv) consider the potential additional mud supply from the western subaerial part of the delta formerly built by the Ganga River; and (v) draw a preliminary mineralogical comparison between fluvio-deltaic sediments and turbidites of the Bengal–Nicobar deep-sea fan, thus tracing sediment dispersal across the huge sedimentary system extending from Tibet to the equatorial Indian Ocean. All investigated mineralogical and geochemical parameters, as well as Sr and Nd isotope ratios and clay–mineral assemblages, showed a clear prevalence in sediment supply from the Brahmaputra (60–70%) over the Ganga (30–40%). Heavy-mineral suites and Sr and Nd isotope fingerprints of Bengal shelf sediments are nearly identical to those of the Brahmaputra River and Meghna estuary, also because the Brahmaputra carries almost twice as many Ca-plagioclase grains and heavy minerals including epidote than the Ganga, and these minerals control the large majority of the Sr and Nd budgets. The experience gained in modern settings can be directly extrapolated only to the recent past, because sediments older than the late Pleistocene and buried more than a few hundred meters begin to lose less durable ferromagnesian minerals by selective chemical dissolution, which makes quantitative estimates progressively less robust in more deeply buried older strata.

Investigating the impact of low-head dams on sediment transport dynamics in gravel-cobble streams

2020 ◽  
Author(s):  
Colm M. Casserly ◽  
John J. O'Sullivan ◽  
Michael Bruen ◽  
Jonathan N. Turner ◽  
Craig Bullock ◽  
...  
Keyword(s):  
Suspended Sediment ◽  
Empirical Studies ◽  
Fish Passage ◽  
Sediment Flux ◽  
Local Source ◽  
Tracer Transport ◽  
Event Scale ◽  
Downstream Reach ◽  
Low Head ◽  
The Impact

<p>Sediment connectivity, though typically viewed as subsidiary to concerns surrounding fish passage, serves an important role in a functioning riverine ecosystem, with both substrate stability and particle size distribution acting as key determinants of benthic community structure and spawning habitat. However, despite more than a decade of pressure to restore stream continuity under the Water Framework Directive (WFD), there have been very few empirical studies on the impact that low-head dams (i.e. weirs) have on bed and suspended sediment conveyance, and little progress in the development of replicable quantitative methodologies for doing so. In this study we explore these knowledge gaps through field investigations of three gravel-cobble streams in southeast Ireland using RFID technology to investigate bedload connectivity, and integrated high-resolution monitoring of turbidity and discrete suspended sediment sampling to establish above dam vs, below dam patterns of suspended sediment conveyance.</p><p>Suspended sediment inputs and outputs over a range of flow conditions (above baseflow) reveal elevated sediment flux at the downstream station (below dam) compared to that coming into the reach (above dam). These observations are indicative of a local source of sediment between monitor­ing stations. Here we suggest that as sediment inputs became exhausted before peak discharge, the structure’s impounded zone (typically considered a depositional area) becomes the dominant source of sediment to the downstream reach. We argue that if sediment trapped behind the structure is available for transportation during high flow events, the system must be trapping sediment under lower flows, which is consistent with field observations.</p><p>Results for bedload connectivity and tracer transport over low-head dams demonstrate that particles exceeding the reach D<sub>90</sub> can be carried through and over these structures, which is consistent with what has been reported from the US. This observation suggests that both structures may have reached a state of ‘transient storage’ as hypothesized by other authors. However, RFID tracer data when reinterpreted as fractional transport rates using a workflow based on existing empirical relations, indicate patterns consistent with supply-limited conditions downstream, demonstrating conflicting lines of evidence between the event-scale tracer movement and long-term sediment regime. Utilizing our empirical data and additional observations collected from a stationary RFID antenna mounted on a weir crest, we expand on existing models and mechanisms to show how a system may continue to exhibit supply-limited conditions downstream without the need for a net attenuation of sediment to occur indefinitely.</p><p>These results indicate that low-head dams may continue to alter the hydrosedimentary processes of fluvial systems long after dam construction and any hypothetical storage capacity has been reached. Though the impact low-head dams have on sediment disconnectivity to the downstream reach is likely to be variable and relatively localized, we hypothesize that the magnitude of any supply-limitation experienced downstream is predominantly a function of both dam height and the structure’s propensity to become drowned out under high flows.</p>

scholarly journals Alluvial cover controlling the width, slope and sinuosity of bedrock channels

2017 ◽  
Author(s):  
Jens Martin Turowski
Keyword(s):  
Theoretical Explanation ◽  
Rate Of Change ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Channel Width ◽  
Bedrock Channel ◽  
The Pacific ◽  
Storm Frequency ◽  
Bed Slope ◽  
Bedrock Channels

Abstract. The problem of bedrock channel meandering is closely related to the problems of channel width and slope. Active meandering occurs when the channel walls are eroded, which also drives channel widening. Further, for a given drop in elevation, the more sinuous a channel is, the lower is its channel bed slope in comparison to a straight channel. It can thus be expected that studies of bedrock channel meandering give insights into width and slope adjustment and vice versa. The mechanisms by which bedrock channels actively meander have been debated since the beginning of modern geomorphic research in the 19th century, but a final consensus has not been reached. Remote sensing studies of the Pacific Arc islands show that regional channel sinuosity scales with storm frequency and inversely with the erodibility of the substrate. However, no mechanisms are known that effectively reduce sinuosity and keep it at a constant value, and a coherent theoretical explanation for the field observations is lacking. It has long been argued that whether a bedrock channel meanders actively or not is determined by the availability of sediment relative to transport capacity, a notion that has also been demonstrated in laboratory experiments. Here, this idea is taken up by postulating that the rate of change of both width and sinuosity over time is dependent on bed cover only. Based on the physics of erosion by bedload impacts, a scaling argument is developed to link bedrock channel width, slope and sinuosity to sediment supply, discharge and erodibility. It is shown that this simple model built on sediment-flux driven bedrock erosion yields the observed scaling relationships of channel width and slope with discharge and erosion rate, can explain why sinuosity evolves to a steady state value and predict the observed relations between sinuosity, erodibility and storm frequency.

scholarly journals Determining the dynamics of coarse bedload transport using passive indirect monitoring: time-dependent variability at event to inter-annual scales

2018 ◽  
Vol 40 ◽  
pp. 05014
Author(s):  
Peter W. Downs ◽  
Philip J. Soar
Keyword(s):  
Bedload Transport ◽  
Sediment Supply ◽  
Peak Efficiency ◽  
Catchment Scale ◽  
Event Scale ◽  
Sustainable Solutions ◽  
Passive Sensors ◽  
Seismic Impact ◽  
Annual Scale ◽  
Variable Water

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

scholarly journals Did the Construction of the Bhumibol Dam Cause a Dramatic Reduction in Sediment Supply to the Chao Phraya River?

Water ◽  
2021 ◽  
Vol 13 (3) ◽  
pp. 386
Author(s):  
Matharit Namsai ◽  
Warit Charoenlerkthawin ◽  
Supakorn Sirapojanakul ◽  
William C. Burnett ◽  
Butsawan Bidorn
Keyword(s):  
Saltwater Intrusion ◽  
River System ◽  
Sediment Supply ◽  
Sediment Flux ◽  
Hydroelectric Power ◽  
Chao Phraya River ◽  
The Impact ◽  
Total Sediment ◽  
Hydroelectric Power Generation

The Bhumibol Dam on Ping River, Thailand, was constructed in 1964 to provide water for irrigation, hydroelectric power generation, flood mitigation, fisheries, and saltwater intrusion control to the Great Chao Phraya River basin. Many studies, carried out near the basin outlet, have suggested that the dam impounds significant sediment, resulting in shoreline retreat of the Chao Phraya Delta. In this study, the impact of damming on the sediment regime is analyzed through the sediment variation along the Ping River. The results show that the Ping River drains a mountainous region, with sediment mainly transported in suspension in the upper and middle reaches. By contrast, sediment is mostly transported as bedload in the lower basin. Variation of long-term total sediment flux data suggests that, while the Bhumibol Dam does effectively trap sediment, there was only a 5% reduction in sediment supply to the Chao Phraya River system because of sediment additions downstream.

Childbirth and Posttraumatic Stress Responses

2006 ◽  
Vol 22 (4) ◽  
pp. 259-267 ◽  
Author(s):  
Eelco Olde ◽  
Rolf J. Kleber ◽  
Onno van der Hart ◽  
Victor J.M. Pop
Keyword(s):  
Posttraumatic Stress Disorder ◽  
Posttraumatic Stress ◽  
Stress Responses ◽  
Rating Scales ◽  
Rating Scale ◽  
Stress Disorder ◽  
Traumatic Experience ◽  
Event Scale ◽  
Self Rating ◽  
The Impact

Childbirth has been identified as a possible traumatic experience, leading to traumatic stress responses and even to the development of posttraumatic stress disorder (PTSD). The current study investigated the psychometric properties of the Dutch version of the Impact of Event Scale-Revised (IES-R) in a group of women who recently gave birth (N = 435). In addition, a comparison was made between the original IES and the IES-R. The scale showed high internal consistency (α = 0.88). Using confirmatory factor analysis no support was found for a three-factor structure of an intrusion, an avoidance, and a hyperarousal factor. Goodness of fit was only reasonable, even after fitting one intrusion item on the hyperarousal scale. The IES-R correlated significantly with scores on depression and anxiety self-rating scales, as well as with scores on a self-rating scale of posttraumatic stress disorder. Although the IES-R can be used for studying posttraumatic stress reactions in women who recently gave birth, the original IES proved to be a better instrument compared to the IES-R. It is concluded that adding the hyperarousal scale to the IES-R did not make the scale stronger.

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