Morphodynamic equilibrium of lowland river systems during autoretreat

Geology ◽  
2020 ◽  
Vol 48 (11) ◽  
pp. 1062-1066 ◽  
Author(s):  
Chenliang Wu ◽  
Jeffrey A. Nittrouer ◽  
Tetsuji Muto ◽  
Kensuke Naito ◽  
Gary Parker
Keyword(s):  
Dynamic Equilibrium ◽  
Sediment Supply ◽  
Hydrodynamic Condition ◽  
Lowland River ◽  
River Systems ◽  
Fluvial Systems ◽  
Natural Systems ◽  
Base Level ◽  
Dynamic Equilibrium State ◽  
Sustained Rate

Abstract Lowland river systems (with channel slopes of 10−5 to 10−4) inevitably shift away (retreat upstream) from the receiving basin under a sustained rate of base-level rise, even if the system can maintain a period of advance at the onset of rise. This autogenic pattern of transition from progradation to retrogradation through steady base-level rise and sediment supply is termed “autoretreat.” Using a morphodynamic model of autoretreat, this study explored the varying channel hydrodynamics of lowland fluvial systems and associated stratigraphic record under sustained base-level rise and constant sediment supply. Results from the numerical simulations show that a fluvial system will reach a state of dynamic equilibrium during autoretreat where both the backwater length and the morphodynamic adjustment of the downdip channel profile become steady. Moreover, when this dynamic equilibrium state is realized, simulated systems display a persistent twofold downstream deepening of flow depth across the backwater zone, a pattern that is also present in many natural systems. In general, backwater effects play a key role in the morphodynamics of a lowland fluvial-deltaic system during autoretreat, and this hydrodynamic condition is therefore critical for predicting river responses to sea-level change.

scholarly journals Alluvial channel response to environmental perturbations: fill-terrace formation and sediment-signal disruption

2019 ◽  
Vol 7 (2) ◽  
pp. 609-631 ◽  
Author(s):  
Stefanie Tofelde ◽  
Sara Savi ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen
Keyword(s):  
Water Discharge ◽  
Sediment Supply ◽  
Fluvial Systems ◽  
Fluvial Terraces ◽  
Base Level ◽  
Environmental Perturbations ◽  
Alluvial Channel ◽  
Channel Slope ◽  
Lag Times ◽  
Sediment Export

Abstract. The sensitivity of fluvial systems to tectonic and climatic boundary conditions allows us to use the geomorphic and stratigraphic records as quantitative archives of past climatic and tectonic conditions. Thus, fluvial terraces that form on alluvial fans and floodplains as well as the rate of sediment export to oceanic and continental basins are commonly used to reconstruct paleoenvironments. However, we currently lack a systematic and quantitative understanding of the transient evolution of fluvial systems and their associated sediment storage and release in response to changes in base level, water input, and sediment input. Such knowledge is necessary to quantify past environmental change from terrace records or sedimentary deposits and to disentangle the multiple possible causes for terrace formation and sediment deposition. Here, we use a set of seven physical experiments to explore terrace formation and sediment export from a single, braided channel that is perturbed by changes in upstream water discharge or sediment supply, or through downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace cutting, and (3) the transient response of sediment export from the basin. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, thus preserving the initial channel slope on terrace surfaces, and it also produces a transient increase in sediment export from the system. In contrast, a decreased upstream sediment-supply rate may result in longer lag times before terrace cutting, leading to terrace slopes that differ from the initial channel slope, and also lagged responses in sediment export. Finally, downstream base-level fall triggers the upstream propagation of a diffuse knickzone, forming terraces with upstream-decreasing ages. The slope of terraces triggered by base-level fall mimics that of the newly adjusted active channel, whereas slopes of terraces triggered by a decrease in upstream sediment discharge or an increase in upstream water discharge are steeper compared to the new equilibrium channel. By combining fill-terrace records with constraints on sediment export, we can distinguish among environmental perturbations that would otherwise remain unresolved when using just one of these records.

Sediment slugs: large-scale fluctuations in fluvial sediment transport rates and storage volumes

1995 ◽  
Vol 19 (4) ◽  
pp. 500-519 ◽  
Author(s):  
A.P. Nicholas ◽  
P.J. Ashworth ◽  
M.J. Kirkby ◽  
M.G. Macklin ◽  
T. Murray
Keyword(s):  
Sediment Transport ◽  
Sediment Supply ◽  
Fluvial Systems ◽  
Event Scale ◽  
Fluvial Sediment ◽  
Sediment Routing ◽  
Basin Scale ◽  
Wide Range ◽  
And Storage ◽  
Fluvial Sediment Transport

Variations in fluvial sediment transport rates and storage volumes have been described previously as sediment waves or pulses. These features have been identified over a wide range of temporal and spatial scales and have been categorized using existing bedform classifications. Here we describe the factors controlling the generation and propagation of what we term sediment slugs. These can be defined as bodies of clastic material associated with disequilibrium conditions in fluvial systems over time periods above the event scale. Slugs range in magnitude from unit bars (Smith, 1974) up to sedimentary features generated by basin-scale sediment supply disturbances (Trimble, 1981). At lower slug magnitudes, perturbations in sediment transport are generated by local riverbank and/or bed erosion. Larger-scale features result from the occurrence of rare high- magnitude geomorphic events, and the impacts on water and sediment production of tectonics, glaciation, climate change and anthropogenic influences. Simple sediment routing functions are presented which may be used to describe the propagation of sediment slugs in fluvial systems. Attention is drawn to components of the fluvial system where future research is urgently required to improve our quantitative understanding of drainage-basin sediment dynamics.

scholarly journals Supplemental Material: Morphodynamic equilibrium of lowland river systems during autoretreat

2020 ◽  
Author(s):  
Chenliang Wu ◽  
et al.
Keyword(s):  
Numerical Model ◽  
Lowland River ◽  
River Systems ◽  
Model Code ◽  
Morphodynamic Equilibrium

Additional details on the numerical model, code availability, and data from natural examples.<br>

scholarly journals Efficacy of bedrock erosion by subglacial water flow

2015 ◽  
Vol 3 (3) ◽  
pp. 849-908 ◽  
Author(s):  
F. Beaud ◽  
G. E. Flowers ◽  
J. G. Venditti
Keyword(s):  
Water Flow ◽  
Water Pressure ◽  
Water Discharge ◽  
Sediment Supply ◽  
Fluvial Systems ◽  
Glacial Meltwater ◽  
Erosion Rates ◽  
Subglacial Environment ◽  
Basin Scale ◽  
Bedrock Erosion

Abstract. Bedrock erosion by sediment-bearing subglacial water remains little-studied, however the process is thought to contribute to bedrock erosion rates in glaciated landscapes and is implicated in the excavation of tunnel valleys and the incision of inner gorges. We adapt physics-based models of fluvial abrasion to the subglacial environment, assembling the first model designed to quantify bedrock erosion caused by transient subglacial water flow. The subglacial drainage model consists of a one-dimensional network of cavities dynamically coupled to one or several Röthlisberger channels (R-channels). The bedrock erosion model is based on the tools and cover effect, whereby particles entrained by the flow impact exposed bedrock. We explore the dependency of glacial meltwater erosion on the structure and magnitude of water input to the system, the ice geometry and the sediment supply. We find that erosion is not a function of water discharge alone, but also depends on channel size, water pressure and on sediment supply, as in fluvial systems. Modelled glacial meltwater erosion rates are one to two orders of magnitude lower than the expected rates of total glacial erosion required to produce the sediment supply rates we impose, suggesting that glacial meltwater erosion is negligible at the basin scale. Nevertheless, due to the extreme localization of glacial meltwater erosion (at the base of R-channels), this process can carve bedrock (Nye) channels. In fact, our simulations suggest that the incision of bedrock channels several centimetres deep and a few meters wide can occur in a single year. Modelled incision rates indicate that subglacial water flow can gradually carve a tunnel valley and enhance the relief or even initiate the carving of an inner gorge.

scholarly journals MODELLING LANDSCAPE MORPHODYNAMICS BY TERRESTRIAL PHOTOGRAMMETRY: AN APPLICATION TO BEACH AND FLUVIAL SYSTEMS

2016 ◽  
Vol XLI-B8 ◽  
pp. 1175-1182 ◽  
Author(s):  
E. Sánchez-García ◽  
A. Balaguer-Beser ◽  
R. Taborda ◽  
J. E. Pardo-Pascual
Keyword(s):  
Morphological Changes ◽  
Spatial Scales ◽  
Cost Effective ◽  
Point Clouds ◽  
Field Work ◽  
Fluvial Systems ◽  
Natural Systems ◽  
3D Point Clouds ◽  
Pilot Channel ◽  
Terrestrial Photogrammetry

Beach and fluvial systems are highly dynamic environments, being constantly modified by the action of different natural and anthropic phenomena. To understand their behaviour and to support a sustainable management of these fragile environments, it is very important to have access to cost-effective tools. These methods should be supported on cutting-edge technologies that allow monitoring the dynamics of the natural systems with high periodicity and repeatability at different temporal and spatial scales instead the tedious and expensive field-work that has been carried out up to date. The work herein presented analyses the potential of terrestrial photogrammetry to describe beach morphology. Data processing and generation of high resolution 3D point clouds and derived DEMs is supported by the commercial Agisoft PhotoScan. Model validation is done by comparison of the differences in the elevation among the photogrammetric point cloud and the GPS data along different beach profiles. Results obtained denote the potential that the photogrammetry 3D modelling has to monitor morphological changes and natural events getting differences between 6 and 25 cm. Furthermore, the usefulness of these techniques to control the layout of a fluvial system is tested by the performance of some modeling essays in a hydraulic pilot channel.

Investigating the Response of Tectonic Loading in the Himalayas on the Peripheral Forebulge through Drainage Network Analysis

2021 ◽  
Author(s):  
Parv Kasana ◽  
Vimal Singh ◽  
Rahul Devrani
Keyword(s):  
Dynamic Equilibrium ◽  
Ganga River ◽  
Indian Plate ◽  
River Networks ◽  
Drainage Network ◽  
River Systems ◽  
Himalayan Orogeny ◽  
Narmada River ◽  
Indian Lithosphere ◽  
Tectonic Loading

&lt;p&gt;Drainage divide migration is a conspicuous natural process through which a landscape evolves. In response to a forced climatic and tectonic disturbance, susceptible river networks transfer the transient signals to the entire river basin, which results in an incision or aggradation. The Himalayan orogeny and subduction of the Indian plate have resulted in an upward flexure in the Indian lithosphere known as a peripheral forebulge. A forebulge can flexurally uplift and migrate following the variation in tectonic load. The emergence of the central Indian plateau is a consequence of the upwarping of the Indian lithosphere (Bilham et al. 2003).&amp;#160; In this work, we are trying to assess the drainage network dynamics between the Narmada and Ganga river systems, which drain the uplifted central Indian plateau. We have calculated the Chi(&amp;#967;) metrics, steepness index (Ksn), knickpoints for the channels in the study area. We have generated Topographic swath profiles to analyze the topographic variations on the plateau. It has been observed from the results that the rivers in the study area lack dynamic equilibrium, and river capturing is an evident response to the perturbations. Our analysis shows that the Narmada River tributaries are gaining drainage area and aggressing Northwards by capturing adjacent Ganga river tributaries. The field observations show a variation in the surface slope and presence of knickpoints (waterfalls) along the &quot;aggressor&quot; drainages. We propose a model to show a correlation between the tectonic loading of Himalayas, movement of forebulge, and its feedback to the river systems present on the forebulge.&lt;/p&gt;

Imprint of landscape dynamics in the luminescence signal of fluvial sediments (Rangitikei River, NZ)

2021 ◽  
Author(s):  
Anne Guyez ◽  
Stephane Bonnet ◽  
Tony Reimann ◽  
Sébastien Carretier ◽  
Jakob Wallinga
Keyword(s):  
Light Exposure ◽  
Experimental Testing ◽  
Landscape Dynamics ◽  
Sediment Supply ◽  
Fluvial Sediments ◽  
Fluvial Systems ◽  
The Earth ◽  
New Information ◽  
Landscape Response ◽  
Minimum Age

&lt;p&gt;Enlightenment of sediments pathways and storage patterns within river systems is critical to apprehend sediment transfer at the Earth&amp;#8217;s surface and landscape response to tectonics and climate. Because direct tracing methods (painted, fluorescent or magnetic sediments) are of limited use in terms of their analytical resolution in time and space, alternative physico-chemical methods suitable for larger spatial-temporal scales have been developed (e.g. cosmogenic isotope, detrital thermochronology, isotopic geochemistry, etc). The study of the natural luminescence of sediment particles is emerging for this purpose and seems promising for providing new information complementary to existing methods. This method is based on the quartz/feldspar grains ability to store energy while buried below the Earth&amp;#8217;s surface and to emit lumen with light exposure. Some recent studies have used this property to solve geomorphological questions regarding particle fluxes in soil or fluvial systems (Reimann et al., 2017; Sawakuchi et al., 2018) and to quantify rock exhumation (e.g. Herman et al., 2010). Here, we present an experimental testing of an innovative single-grain luminescence-based approach on feldspars. Focusing alongstream the Rangitikei River (RR), New Zealand, we carried out analysis on both modern sediment and Holocene terraces deposits.&lt;/p&gt;&lt;p&gt;We based our analysis on two complementarians proxies, the paleodose estimated using the bootstrapped minimum age model (Cunningham and Wallinga, 2012) and the percentage of grains eroded from bedrock and re-deposited in the river without signal resetting, i.e. saturated grains. We document changes in the luminescence signature of fluvial sediments while the RR evolves in response to uplift and climate change; from a late Pleistocene-early Holocene braided system to a Holocene incising canyon that subsequently widen. &amp;#160;This allows us to appraise temporal changes in the alongstream contribution of canyon flanks landsides to sediment supply to the river. Overall, we show that distinct landscape dynamics gives distinct luminescence signatures.&lt;/p&gt;

scholarly journals Geosystems‘ Pathways to the Future of Sustainability

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Mihai Voda ◽  
Shadrack Kithiia ◽  
Edward Jackiewicz ◽  
Qingyun Du ◽  
Constantin Adrian Sarpe
Keyword(s):  
Dynamic Equilibrium ◽  
Objective Assessment ◽  
Google Earth ◽  
Integrative Approach ◽  
Positioning Systems ◽  
Technological Advances ◽  
Identification Evaluation ◽  
Global Positioning ◽  
Dynamic Equilibrium State ◽  
Societal Changes

Abstract The world’s future development depends on effective human-computer linkages. From local to global, the virtual illustrations of a geographical place have to emphasize in an integrative approach peoples‘ key position in the Geosystem. Human values and social networks are now empowered by the unlimited creativity of smartphone applications. Our Geosystem grounded theory envisions that the sustainable management of natural resources is a lifelong learning environment where the poor communities have access to the new technological advances. This paper will attempt to show the effectiveness of Geomedia techniques in the Geosystems identification, evaluation, and valorization processes for the benefit of local inhabitants. This present research methodology uses smartphone apps, Google Earth environmental datasets, Global Positioning Systems, and WebGIS for a geographical investigation and objective assessment of regions throughout the world. The results demonstrate that self-sustainable Geosystems will always be capable to regulate, control and assess progress towards their dynamic equilibrium state, continuously adapting to environmental and societal changes.

scholarly journals Limiting the development of riparian vegetation in the Isère River: A physical modelling study

2018 ◽  
Vol 40 ◽  
pp. 02015
Author(s):  
Nicolas Claude ◽  
Clément Leroux ◽  
Marion Duclercq ◽  
Pablo Tassi ◽  
Kamal El Kadi Abderrezzak
Keyword(s):  
Plant Development ◽  
Dynamic Equilibrium ◽  
Initial Conditions ◽  
Physical Modelling ◽  
Sand Mixture ◽  
Dynamic Equilibrium State ◽  
Actual Configuration ◽  
Vegetation Encroachment ◽  
Movable Bed ◽  
Riparian Plant

Physical modelling experiments are conducted to investigate if a modification of the Isère River (French Alps) hydrology by changing dams management is able to foster riverbed morphodynamic and, thus limiting riparian plant development. The experimental setup is a 1:35 scale, undistorted movable bed designed to ensure the Froude number similarity and initial conditions for sediment particle motion. The physical model is 35 m long, 2.6 m wide, with a sand mixture composed of three grain size classes. Two runs with different flow and bed load conditions are simulated. Preliminary results show an intense riverbed activity when the system reaches a dynamic equilibrium state. Under these conditions, bar mobility is strong enough to limit vegetation encroachment only when water discharges are higher than the discharge of a 5-years flood during more than 10 days. These results indicate that the hydrological characteristics of the Isère River and the actual configuration of the hydropower structures could be not able to release annually the flow conditions needed to control riparian plant development.

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