Condition for incision of alluvial fan in an experimental coupled catchment-fan geomorphic system forced by oscillatory precipitation

2020 ◽  
Author(s):  
Stephane Bonnet ◽  
Valeria Zavala Ortiz ◽  
Sébastien Carretier
Keyword(s):  
Extreme Values ◽  
Laser Sheet ◽  
Sediment Concentration ◽  
Alluvial Fan ◽  
Rainfall Rate ◽  
Mountain Range ◽  
Alluvial Fans ◽  
Alluvial Deposits ◽  
The Mean ◽  
The Impact

<p>Alluvial fans are cone-shaped bodies of alluvial deposits accumulated along mountain range fronts at the outlet of catchments. They represent valuable archives of mass transfer in their feeding catchment and can potentially be used to infer the impact of tectonic and climatic variations on erosion and landscapes, because of the influence of these factors on the sediment and water fluxes coming from the upstream catchment. Although a transition from aggradation to incision is observed in many natural alluvial fans, the conditions driving such change remain unclear. We investigate this problem here through a laboratory-scale approach where eroded materials from an uplifting mountain may deposit on a plateau, erosion being driven by the surface runoff of water from an artificial rainfall device. We consider here results from 8 experiments, 700 to 900 minutes-long, performed with the same uplift rate but with different sequences of variations of the rainfall rate (10 to 40 minutes-long) between two extreme values. The topography was digitized every 10 minutes thanks to a high-resolution laser sheet.</p><p>We observe that the mean slope of the alluvial fans is inversely proportional to the mean rainfall rate on the mountain and that the denudation rate of the uplifting landscape varies in phase with the cyclic variations of rainfall. Because catchments are out of equilibrium (denudation equals uplift) during most of the time, the sediment (Qs) and water (Qw) fluxes at their outlet continuously vary with time: Qs varying depending on the balance between erosion and uplift, Qs and Qw varying depending on whether the catchments enlarge or shrink. Depending on these conditions, catchments show a variety of trends of Qs vs Qw for a given value of rainfall, Qs increasing or decreasing with Qw, or being independent of Qw. Then for each catchment, oscillations of rainfall drive alternations between two individual Qs vs Qw trends, the slope of these trends being indicative of the sediment concentration in the mini-rivers at the outlet of catchments that feed alluvial fans.</p><p>From the analyze of our whole dataset, we conclude that incision of alluvial fans occurs when rainfall increases and when it goes with a decrease of the Qs/Qw ratio, i.e. with a decrease of concentration at the outlet of the catchment. This control is modulated by the slope of the fan, incision only occurring for fans above a threshold slope. Then, the decrease in sediment concentration required to initiate the incision is weaker for steeper fans and decreases with increasing fan slope.</p><p>Several studies already demonstrated how a decrease of Qs or an increase of Qw drives incision. We show here that these two parameters are coupled and covariate following the dynamical state of catchments. We also demonstrate that the decrease of the Qs/Qw ratio required for initiating the incision of a fan is lower for steeper fans, that is for fans that develop under more arid condition.</p>

Under what conditions do climatic variations lead to incision of alluvial fans? Insights from coupled catchment-fan system in the lab

2021 ◽  
Author(s):  
Stéphane Bonnet ◽  
Valeria Zavala-Ortiz ◽  
Sébastien Carretier
Keyword(s):  
Extreme Values ◽  
Laser Sheet ◽  
Sediment Concentration ◽  
Precipitation Rate ◽  
Dynamic State ◽  
Alluvial Fans ◽  
Equilibrium Degree ◽  
Artificial Rainfall ◽  
Arid Condition ◽  
Two Parameters

<p>Although a transition from aggradation to incision is observed in many natural alluvial fans and is usually related to variations in climate, the condition driving such change remain unclear. We address this problem here by considering laboratory experiments of coupled catchment-fans systems forced by oscillatory precipitation. In the 8 experiments considered here, eroded materials from an uplifting mountain may deposit on a plateau, erosion being driven by the surface runoff of water from an artificial rainfall device. These experiments, 700 to 900 minutes-long, were performed with the same uplift rate but with different sequences of variations of the rainfall rate (10 to 40 minutes-long) between two extreme values. The topography was digitized every 10 minutes thanks to a high-resolution laser sheet.</p><p>We observe that the sediment (Qs) and water (Qw) fluxes at the outlet of mountain catchments continuously vary with time, not only because of precipitation oscillations but also because of the dynamic state of the landscape. For a given precipitation rate, variations of Qs and Qw depend on whether the catchments enlarge or shrink, with additional variations of Qs depending on the equilibrium degree (steady-state or not). Depending on these conditions, we document a large variety of trends of Qs vs Qw in rivers at catchment outlets, Qs increasing or decreasing with Qw, or being independent of Qw. For a given catchment, oscillations in precipitation rate then drive alternations between two individual Qs vs Qw trends, the slope of these trends being indicative of the sediment concentration in the mini-rivers at the outlet of catchments that feed alluvial fans.</p><p>Our experiments indicate that incision of alluvial fans is controlled by two necessary conditions. First, it occurs when rainfall increases and goes with a decrease of the Qs/Qw ratio, i.e. with a decrease of concentration at the outlet of the catchment. Second, this control is modulated by the slope of the fan, incision only occurring for fans above a threshold slope. Then, the decrease in sediment concentration required to initiate the incision is weak for steeper fans, those that developed under a mean dry climate. A larger drop in concentration is necessary for gentle fans, those that develop under a mean wetter climate.</p><p>Several studies already demonstrated how a decrease of Qs or an increase of Qw drives incision. We show here that these two parameters are also coupled and covariate following the dynamical state of catchments. We also demonstrate that the decrease of the Qs/Qw ratio required for initiating the incision of a fan is lower for steeper fans, that is for fans that develop under more arid condition.</p><p>We conclude that a given amplitude of climate change won’t have the same imprint on landscapes, erosion and transport depending on the mean prevailing climate.</p>

scholarly journals Interactions between channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2019 ◽  
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel-network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may promote or prevent sediment to be moved within the fluvial system, creating different coupling conditions. A prograding alluvial fan, for example, has the potential to disrupt the sedimentary signal propagating downstream through the confluence zone. By analyzing different environmental scenarios, our results indicate the contribution of the two sub-systems to fluvial deposits, both upstream and downstream of the tributary junction, which may be diagnostic of a perturbation affecting the tributary or the main channel only. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which is essential for a correct reconstruction of the climatic or tectonic history of a basin.

A Study of Ecological Water Use Based on the Improved Tennant Method

2010 ◽  
Vol 113-116 ◽  
pp. 1504-1508 ◽  
Author(s):  
Jing Huan Tian ◽  
Ling Yu ◽  
Zhi Hong Zheng
Keyword(s):  
Water Use ◽  
Traditional Method ◽  
Extreme Values ◽  
Mean Value ◽  
Improved Method ◽  
Existing Problems ◽  
Runoff Series ◽  
Tennant Method ◽  
The Mean ◽  
The Impact

To solve the existing problems arose in the Tennant method for estimating ecological water use in river course, a new methodology is proposed to replace the mean value by the median of runoff series in the Tenna nt formula. The motive is to eliminate the impact of some extreme values. Given runoff series of 47 years in Jiaokou reservoir of Zhangxi River, the traditional and the improved method were respectively applied to calculate the ecological water consumption in the river. The results show that the improved Tennant method is more reasonably than the traditional method.

A spectrum of alluvial deposits in the Lower Carboniferous Bonaventure Formation of western Chaleur Bay area, Gaspé and New Brunswick, Canada

1983 ◽  
Vol 20 (7) ◽  
pp. 1098-1110 ◽  
Author(s):  
Brian A. Zaitlin ◽  
Brian R. Rust
Keyword(s):  
New Brunswick ◽  
Alluvial Fan ◽  
Alluvial Fans ◽  
Alluvial Deposits ◽  
Lower Carboniferous ◽  
Bay Area ◽  
Internal Structures ◽  
Sandstone Facies ◽  
Fault Scarps ◽  
Steep Slopes

The Lower Carboniferous Bonaventure Formation of western Chaleur Bay, Gaspé and New Brunswick, is a terrestrial redbed succession with abundant calcretes, deposited in a semi-arid paleoclimate. Facies can be grouped into three associations, conglomeratic, sandstone, and mud-dominated, within two 100–150 m upward-fining megasequences. The megasequences are attributed to alluvial fan progradation due to tectonic rejuvenation.Vertical facies relationships and internal structures indicate that varied alluvial environments are represented. Alluvial fans formed on steep slopes adjacent to fault scarps and are dominated by deposits of the conglomeratic association. Lateral and downslope coalescence of fans into a braid plain is represented by transition from the conglomeratic to the sandstone facies association. Distally, the braid plain is transitional into deposits of the mud-dominated association.Paleocurrents and clast compositions show that sediment in the Gaspé outcrops was derived from the northwest, and that in New Brunswick from the southwest. This indicates that Chaleur Bay is an exhumed Carboniferous paleovalley, with axial drainage to the east.

scholarly journals Event-based runoff and sediment yield dynamics and controls in the sub-humid headwaters of the Blue Nile, Ethiopia

2021 ◽  
Author(s):  
Habtamu Assaye Deffersha ◽  
Jan Nyssen ◽  
Jean Poesen ◽  
Hanibal Lemma ◽  
Derege Meshesha ◽  
...  
Keyword(s):  
Land Use ◽  
Land Management ◽  
Sediment Yield ◽  
Management Practices ◽  
Sediment Concentration ◽  
Rock Fragment ◽  
Grazing Land ◽  
The Mean ◽  
The Impact ◽  
Runoff And Sediment Yield

Land degradation due to soil erosion presents a challenge for sustainable development. We investigated the impact of land use type and land management practices on runoff and sediment yield dynamics in the northwestern highlands of Ethiopia. The study area included 14 zero-order catchments with a surface area ranging from 324 m2 to 1715 m2. V-notch weirs produced from plastic jars were introduced as measuring alternatives that met local constraints. Runoff depth at the weir was registered at 5-min intervals during two rainy seasons in 2018 and 2019. Rainfall was measured using tipping-bucket rain gauges. Runoff samples were collected in 1-L bottles and suspended sediment concentration (SSC) was determined. The mean event runoff coefficient ranged from 3% for forests to 56% for badlands. Similarly, the mean annual sediment yield (SY) was lowest for forests (0.8 Mg ha-1 yr-1) and highest for badlands (43.4 Mg ha-1 yr-1), with significant differences among land use types (14.8 Mg ha-1 yr-1 in cropland, 5.7 Mg ha-1 yr-1 in grazing land, and 2.9 Mg ha-1 yr-1 in plantations). Soil organic matter (SOM) reduced runoff and SY, necessitating the consideration of agronomic and land management practices that enhance SOM. Annual SY decreased exponentially with the rock fragment cover (RFC). In fields where RFC was less than 20%, collecting rock fragments for installing stone bunds resulted in a net increase in SY. Rehabilitating badlands and enhancing SOM content in croplands can substantially reduce catchment SY and, hence considerably contribute to the sustainability of this type of environment.

scholarly journals Sediment load estimation in the Mellegue catchment, Algeria

2016 ◽  
Vol 31 (1) ◽  
pp. 129-137 ◽  
Author(s):  
Kaouther Selmi ◽  
Kamel Khanchoul
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
Sediment Yield ◽  
Agricultural Land ◽  
Water Discharge ◽  
Sediment Concentration ◽  
Sediment Loads ◽  
Recorded Data ◽  
The Mean ◽  
The Impact

AbstractSoil erosion by water and the impact of sediment transport on lakes and streams, can seriously degrade soil and create problems for both agricultural land and water quality. The present study has been carried out to assess suspended sediment yield in Mellegue catchment, northeast of Algeria. Regression analysis was used to establish a relationship between the instantaneous water discharge (Q) and the instantaneous suspended sediment concentration (C) based on all recorded data and seasonal ratings for the period 1970–2003. The regression technique used in this paper involved a division of data into discharge – based classes, the mean concentrations and discharges of which are used to develop power regressions, according to single and season ratings, through log-transformation. Sediment loads estimated by stratified rating curves reduced underestimations to a range from 2 to 4%. The mean annual sediment yield during the 34 years of the study period was 589.23 t·km−2·y−1. Sediment transport is dominated by fall rainstorms accounting for 41% of the annual load. The big supply of sediment during this season confirms the intense geomorphic work by fall storms caused by high intensity rainfall and low vegetation cover.

scholarly journals Interactions between main channels and tributary alluvial fans: channel adjustments and sediment-signal propagation

2020 ◽  
Vol 8 (2) ◽  
pp. 303-322
Author(s):  
Sara Savi ◽  
Stefanie Tofelde ◽  
Andrew D. Wickert ◽  
Aaron Bufe ◽  
Taylor F. Schildgen ◽  
...  
Keyword(s):  
Boundary Conditions ◽  
Signal Propagation ◽  
Main Channel ◽  
Alluvial Fan ◽  
Sediment Supply ◽  
Alluvial Fans ◽  
Fluvial System ◽  
Channel Network ◽  
Fluvial Deposits ◽  
The Impact

Abstract. Climate and tectonics impact water and sediment fluxes to fluvial systems. These boundary conditions set river form and can be recorded by fluvial deposits. Reconstructions of boundary conditions from these deposits, however, is complicated by complex channel–network interactions and associated sediment storage and release through the fluvial system. To address this challenge, we used a physical experiment to study the interplay between a main channel and a tributary under different forcing conditions. In particular, we investigated the impact of a single tributary junction, where sediment supply from the tributary can produce an alluvial fan, on channel geometries and associated sediment-transfer dynamics. We found that the presence of an alluvial fan may either promote or prevent the movement of sediment within the fluvial system, creating different coupling conditions. By analyzing different environmental scenarios, our results reveal the contribution of both the main channel and the tributary to fluvial deposits upstream and downstream from the tributary junction. We summarize all findings in a new conceptual framework that illustrates the possible interactions between tributary alluvial fans and a main channel under different environmental conditions. This framework provides a better understanding of the composition and architecture of fluvial sedimentary deposits found at confluence zones, which can facilitate the reconstruction of the climatic or tectonic history of a basin.

scholarly journals Experimental measurements of flood-induced impact forces on exposed elements

2018 ◽  
Vol 40 ◽  
pp. 05005 ◽  
Author(s):  
Michael Sturm ◽  
Bernhard Gems ◽  
Florian Keller ◽  
Bruno Mazzorana ◽  
Sven Fuchs ◽  
...  
Keyword(s):  
Force Measurement ◽  
Flow Patterns ◽  
Building Envelope ◽  
Alluvial Fan ◽  
Scale Model ◽  
Experimental Measurements ◽  
Alluvial Fans ◽  
Flood Hazards ◽  
Impact Forces ◽  
The Impact

Torrential flood hazards are a major threat for inhabited alluvial fans. They have the potential to relocate large amounts of sediment from the upper catchments to settlement areas on the alluvial fans where typically distributary processes take place. The approaching water-sediment-mixture impacting on building walls are part of a set of damage-generating mechanisms and may cause severe damages to buildings and infrastructure. It is difficult to predict the magnitude and temporal forces on buildings due to the complex flow patterns and sediment deposition processes around obstacles on the floodplain. Our work focuses on experimental measurements of impact forces of flood events on buildings at a 1:30 scale model. It covers the alluvial fan of the Schnannerbach torrent (Austria) with a set of building structures which are equipped with force measurement devices. The measured impact forces are correlated to the approaching flow heights. Influencing factors on the impacts forces such as surrounding buildings on the floodplain and the presence of openings in the building envelope are also analysed. The influence of different hydraulic flow patterns on the impact forces and regression analyses for an estimation of impact forces are presented.

scholarly journals Supernovae in Binary Systems : Production of Run-Away Stars and Pulsars

1982 ◽  
Vol 69 ◽  
pp. 417-443
Author(s):  
Jean-Pierre De Cuyper
Keyword(s):  
Binary Systems ◽  
Extreme Values ◽  
Supernova Explosion ◽  
Keplerian Orbit ◽  
Radio Pulsars ◽  
X Ray ◽  
Ob Stars ◽  
Supernova Shell ◽  
The Mean ◽  
The Impact

AbstractThe effects of an instantaneous asymmetric supernova explosion in an eccentric binary system are analyzed, taking into account the mass loss out of the system, the influence of the impact of the supernova shell on the companion star and the extra “kick” velocity which a collapsed star might receive in an asymmetric supernova explosion. For a random orientat-ion in space of this asymmetric kick velocity, the survival probability and the runaway velocities are derived and their properties discussed for an explosion occurring at a given position in the initial keplerian orbit and the mean and extreme values of these quantities over one orbit are derived. As an example, the outcome of a possible supernova explosion in the ten best known WR+OB binaries is studied and a comparison is made with the observed run-away OB stars, radio pulsars and binary X-ray pulsars.

Asteroid and Comet Impact Speeds upon Mars: Significance for Panspermia and the Supply of Organics

1997 ◽  
Vol 161 ◽  
pp. 197-201 ◽  
Author(s):  
Duncan Steel
Keyword(s):  
Probability Distributions ◽  
Regions Of Interest ◽  
Significant Fraction ◽  
Organic Chemicals ◽  
Impact Speed ◽  
The Mean ◽  
The Impact

AbstractWhilst lithopanspermia depends upon massive impacts occurring at a speed above some limit, the intact delivery of organic chemicals or other volatiles to a planet requires the impact speed to be below some other limit such that a significant fraction of that material escapes destruction. Thus the two opposite ends of the impact speed distributions are the regions of interest in the bioastronomical context, whereas much modelling work on impacts delivers, or makes use of, only the mean speed. Here the probability distributions of impact speeds upon Mars are calculated for (i) the orbital distribution of known asteroids; and (ii) the expected distribution of near-parabolic cometary orbits. It is found that cometary impacts are far more likely to eject rocks from Mars (over 99 percent of the cometary impacts are at speeds above 20 km/sec, but at most 5 percent of the asteroidal impacts); paradoxically, the objects impacting at speeds low enough to make organic/volatile survival possible (the asteroids) are those which are depleted in such species.

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