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>

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>

Changes in nucleoli and nucleolar fibrillar centres of chromaffin cells in rat adrenal medulla over a 24-hour period: an ultrastructural and stereological analysis

1985 ◽  
Vol 77 (1) ◽  
pp. 255-262
Author(s):  
A. Robaglia ◽  
R. Seite
Keyword(s):  
Adrenal Medulla ◽  
Chromaffin Cells ◽  
Extreme Values ◽  
Sympathetic Neurons ◽  
Cellular Level ◽  
Temporal Organization ◽  
Free Access ◽  
Stereological Analysis ◽  
The Mean ◽  
Two Parameters

A stereological and ultrastructural study was performed on the nucleoli of the adrenal medulla chromaffin cells of rats exposed to a standardized 12 h light/12 h dark cycle with free access to food and water. The animals were killed three at a time, every 4 h during the 24-h span and fixed by intracardiac perfusion. In these reticulated nucleoli, the stereological analysis over a 24-h period showed a variation dependent on the time of killing for the two parameters investigated, the mean nucleolar volume, Vnu, and the mean volume of the fibrillar centres, Vfc(nu). The minimal value occurred at 0300 h (dark span) and the maximal one at 0700 h (at the onset of the light span). Between these two extreme values, Vnu increased 1.8-fold and Vfc(nu) 5.3-fold. These data are compared with a previous description from our laboratory of circadian rhythm in nucleoli of sympathetic neurons of superior cervical ganglion in the same animals. Analogies and differences are pointed out, but apart from these considerations the present study provides a new example of temporal organization at the cellular level in the organelle involved in ribosomal RNA synthesis and ribosome assembly.

Runoff and sheet erosion from tillage trials under artificial rainfall at Harden, New South Wales

Soil Research ◽  
1996 ◽  
Vol 34 (6) ◽  
pp. 863 ◽  
Author(s):  
PIA Kinnell
Keyword(s):  
Cropping System ◽  
Sediment Concentration ◽  
Substantial Effect ◽  
Water Infiltration ◽  
Sowing Time ◽  
Erosion Risk ◽  
Post Harvest ◽  
Tillage Practices ◽  
Artificial Rainfall ◽  
Sheet Erosion

Artificial rainfall was applied to g-m-long plots after the harvest of a canola crop in experiments on a grazed cropping system using a rotation that alternated wheat with lupins and canola. Three tillage treatments were selected for the experiments: one was a direct-drill treatment, while the other two involved the use of a reduced tillage practice during the preparation of the seed bed. Tillage treatment was found to have no substantial effect on runoff and sediment concentration resulting from sheet erosion during the post-harvest period. At sowing time, tillage again had no significant effect on sediment concentration but did have a significant effect on runoff. The roughness produced by the tillage provided a substantial capacity to store water and detached soil particles in surface depressions immediately after cultivation, and the decline in this surface roughness during rainfall was sufficiently small to cause little or no runoff when 1h of 70 mm/h rain was applied to a cultivated surface. The results support indications from SOILOSS, a model that provides local implementation of the Revised Universal Soil Loss Equation (RUSLE), that reduced-till may be as effective as direct-drill at conserving soil at this site. However, since the experiments were restricted to sheet erosion, and no experiments were performed between sowing and harvest or with other crops in the rotation, the results do not provide unconditional support for the SOILOSS result. Despite the result of the experiments reported here, soil erosion risk is likely to be substantially reduced on a field scale through the use of tillage practices which, like the direct-drill treatment, maintain anchored and unanchored crop residue during the fellow and post-sowing periods. Data were also collected in relation to an examination of the ability of the Soil Water Infiltration and Movement (SWIM) model to predict runoff during the post-harvest period. SWIM tended to underpredict runoff but the difference between the observed amount of runoff and that predicted by SWIM was statistically not significant.

scholarly journals Karateristik Distribusi Sedimen Suspensi pada Sungai Alami Menggunakan Persamaan Rouse

2020 ◽  
Vol 21 (1) ◽  
pp. 1
Author(s):  
Rahmat Bangun Giarto ◽  
Bambang Agus Kironoto ◽  
Bambang Yulistiyanto ◽  
Totok Sulistyo
Keyword(s):  
Suspended Sediment Concentration ◽  
Stream Water ◽  
Sediment Concentration ◽  
Suspended Load ◽  
Bed Load ◽  
Sediment Suspension ◽  
Suspension Concentration ◽  
Sediment Transportation ◽  
Measurement Tools ◽  
Two Parameters

Angkutan sedimen suspensi merupakan permasalah yang kerap terjadi pada sungai alami dan dapat mengakibatkan pendangkalan pada sungai. Aliran air yang tercampur dengan sedimen berbutir kasar (bed load) akan lebih cepat mengendap dibandingkan dengan sedimen berbutir halus (suspended load) yang akan terangkut mengikuti aliran sungai. Hal ini dapat mengakibatkan berkurangnya kualitas dan kuantitas dalam pemanfaatan air di sungai. Penelitian dilakukan dengan cara mengukur kecepatan dan konsentrasi sedimen suspensi menggunakan dua parameter yaitu pengukuran arah vertikal dan pengukuran arah transversal. Pengukuran menggunakan metode Point Itegrated Sampling (PIS). Opcon Probe digunakan untuk mengukur konsentrasi sedimen suspensi sedangkan propeller currentmeter digunakan untuk pengukuran kecepatan aliran. Pada saat pelaksanaan pengamatan kedua alat ukur tersebut dimasukkan kedalam air yang mengalir pada tampang melintang di sungai. Konsentrasi sedimen suspensi mengalami peningkatan saat  mendekati dasar sungai dan mengalami penurunan saat mendekati permukaan sungai. Persamaan Rouse dapat digunakan dalam mempredisksi distribusi sedimen suspensi pada tengah sungai, sedangkan untuk arah transversal atau posisi tidak ditengah sungai (0,5B) seperti di tepi sungai profil distribusi konsentrasi sedimen suspensi tidak cukup baik untuk memprediksi distribusi konsentrasi sedimen suspensi  dengan persamaan Rouse. Diperlukan faktor koreksi β untuk memprediksi distribusi konsentrasi sedimen suspensi pada tepi sungai dengan nilai faktor koreksi β > 1.Suspension sediment transportation is the problem which is frequently occurs in the bottom of natural rivers, and it sometimes causes rivers shallowing. The mixing between water and coarse grain sediment or bed load will settle down faster rather than finer grain sediment or suspended load that will be transported further by stream water. Due of those can reduce both quality and quantity of river water. This research was conducted by measurement of sediment suspension concentration using two parameters which are vertical and transversal measurement. Point Integrated Sampling was employed in the measurement processes. Opcon probe was used to measure suspended sediment concentration meanwhile the propeller current meter was used to measure water velocity. In the implementation and observation both of measurement tools was drowned in the flowing water, in position  the cross section of rivers. Closer to the rivers bottom, the sediment suspension concentration is increased in the contrary it is decreased in concentration close to the surface. Rouse equation is able to predict the distribution of sediment suspension in the middle of the river, and when the transversal direction or location is not in the middle of river (0.5B) such as in the river profile side, Rouse equation is not good enough to predict the distribution of sediment suspension concentration. The correction factor (β) is needed in predicting concentration  of sediment suspension in rivers side, where  β > 1.

scholarly journals Impact of Sample Size and Maximum Aggregate Grain on the Representativeness of Concrete Samples

Energies ◽  
2020 ◽  
Vol 13 (13) ◽  
pp. 3358
Author(s):  
Jacek Śliwiński ◽  
Patrycja Duży
Keyword(s):  
Sample Size ◽  
Extreme Values ◽  
Maximum Size ◽  
Minimum Size ◽  
Slight Variation ◽  
Concrete Composition ◽  
Cross Sectional ◽  
Two Parameters ◽  
The Impact ◽  
Composition Changes

One of the basic criteria for the representativeness of composite material samples is the similarity of the quantitative and qualitative composition of the material in the sample to that of the material it represents. The article presents the results of experimental research concerning the impact of the ratio of the minimum size of cubic concrete samples (lmin) to the maximum size of aggregate grain (Dmax). The content of the basic components of concrete, i.e., coarse aggregate, mortar, sand and cement paste, was analysed. The content of these components in the concrete sample was identified by means of analysis of the sample cross-sectional image, and then, compared with the contents resulting from the concrete mixture proportion. Cases where lmin/Dmax was between 2.38 and 12.5 were analysed. The results of the study indicate a moderate correlation between these two parameters. The largest discrepancies between the component contents of the sample and the controlled concrete were usually recorded at the extreme values of the lmin/Dmax ratio. These discrepancies, depending on the component in question, range from approx. −15 to approx. +15%. Acceptable deviations (≤ ±5%) result in the value of this ratio within the estimated range between approximately 5.0 and approximately 10.0. In existing standards, the use of samples that meet the requirement lmin/Dmax ≥ 3.0 or 3.5 is recommended. In light of the presented test results, this requirement is sufficient for the material properties that are not sensitive to slight variation in concrete composition, i.e., compressive and tensile strength. The presented results are useful in the case of sample size selection for the study of concrete properties which are most sensitive to concrete composition changes. These properties include water absorption, permeability to liquids and gases, thermal properties, etc.

scholarly journals POPULATION BOTTLENECKS AND NONEQUILIBRIUM MODELS IN POPULATION GENETICS. III. GENIC HOMOZYGOSITY IN POPULATIONS WHICH EXPERIENCE PERIODIC BOTTLENECKS

Genetics ◽  
1985 ◽  
Vol 111 (3) ◽  
pp. 691-703
Author(s):  
Takeo Maruyama ◽  
Paul A Fuerst
Keyword(s):  
Population Size ◽  
Cycle Length ◽  
Extreme Values ◽  
Gene Diversity ◽  
Population Bottlenecks ◽  
Specific Time ◽  
Large Gene ◽  
Analytical Formulas ◽  
Two Phases ◽  
Two Parameters

ABSTRACT The amount of variability in a population that experiences repeated restrictions in population size has been calculated. The restrictions in size occur cyclically with a fixed cycle length. Analytical formulas for describing the gene identity at any specific time in the expanded and restricted phases of the cycle, and for the average and second moment of the gene identity, have been derived. It is shown that the level of genetic diversity depends critically on the two parameters that account for the population size, mutation rate and the time of duration for each of the two phases in the cycle. If one or both of these composite parameters are small, the gene diversity will be much reduced, and population gene diversity will then be predictable from knowledge of the harmonic mean population size over the entire cycle. If these parameters take on intermediate values, diversity changes constantly during the cycle, fluctuating steadily from a high to a low value and back again. If these parameters are large, gene diversity will fluctuate rapidly between extreme values and will stay at the extremes for long periods of time.

scholarly journals Climatology of Three-Dimensional Eliassen–Palm Wave Activity Fluxes in the Northern Hemisphere Stratosphere from 1981 to 2020

Climate ◽  
2021 ◽  
Vol 9 (8) ◽  
pp. 124
Author(s):  
Indrė Gečaitė
Keyword(s):  
Northern Hemisphere ◽  
Extreme Values ◽  
Time Lag ◽  
Three Dimensional ◽  
Reanalysis Data ◽  
Wave Activity ◽  
Initial State ◽  
Eddy Heat Flux ◽  
Key Factor ◽  
Two Parameters

Based on the Modern-Era Retrospective Analysis for Research and Applications version 2 (MERRA-2) reanalysis data from 1981 to 2020, the climatological features of the vertical components of three-dimensional Eliassen–Palm (EP) wave activity fluxes (WAF) were investigated. The parameter is related to eddy heat flux and is a key indicator of the upward and downward propagation of quasi-stationary planetary-scale waves. Northern Hemisphere data from a 30 km height (or about a 10-hPa level) were used for the analysis. We evaluated the extreme values (daily maxima and minima) of the vertical WAFs, the probability of their recurrences, and their interannual and daily variability observed over the last four decades. The correlation between the upward EP WAF maxima and the 10-hPa stratosphere temperature anomalies were examined. The results show that very close relationships exist between these two parameters with a short time lag, but the initial state of the stratosphere is a key factor in determining the strength of these relationships. Moreover, trends over the last 40 years were evaluated. In this research, we did not find any significant changes in the extreme values of the vertical WAFs. Finally, the dominant spatial patterns of upward and downward extreme WAFs were evaluated. The results show that there are three main regions in the stratosphere where extremely intensive upward and downward WAFs can be observed.

scholarly journals Control of M/Cox-2/s make-to-stock systems

2019 ◽  
Vol 10 (1) ◽  
pp. 26-36
Author(s):  
Özgün Yücel ◽  
Önder Bulut
Keyword(s):  
Dynamic State ◽  
Dynamic Nature ◽  
Two Phase ◽  
State Information ◽  
Parallel Servers ◽  
Processing Times ◽  
Production Policy ◽  
Start Up ◽  
Make To Stock ◽  
Two Parameters

This study considers a make-to-stock production system with multiple identical parallel servers, fixed production start-up costs and lost sales. Processing times are assumed to be two-phase Coxian random variables that allows us to model the systems having rework or remanufacturing operations. First, the dynamic programming formulation is developed and the structure of the optimal production policy is characterized. Due to the highly dynamic nature of the optimal policy, as a second contribution we propose an easy-to-apply production policy. The proposed policy makes use of the dynamic state information and controlled by only two parameters. We test the performance of the proposed policy at several instances and reveal that it is near optimal. We also assess the value of dynamic state information in general by comparing the proposed policy with the well-known static inventory position based policy.

scholarly journals Suspended sediment transport map for disaster mitigation in the upper course of Jangkok River

2021 ◽  
Vol 331 ◽  
pp. 08005
Author(s):  
Yusron Saadi ◽  
IB Giri Putra ◽  
Agus Suroso
Keyword(s):  
Sediment Transport ◽  
Suspended Sediment ◽  
River Flow ◽  
Rapid Change ◽  
Field Measurements ◽  
Sediment Concentration ◽  
Disaster Mitigation ◽  
Suspended Sediment Transport ◽  
Preventive Action ◽  
Two Parameters

Jangkok River, a very important river for irrigation purposes in Lombok Island Indonesia is experiencing a rapid change in the land use of its watershed. The conversion of trees into seasonal crops in the watershed causes a decrease in the carrying capacity of the watershed and reduces its ability to prevent soil erosion. Environmental damages such as erosion and sedimentation along the river are becoming increasingly difficult to control. This paper proposed an idea to identify river conditions based on suspended sediment concentration. A series of field measurements of suspended sediment concentrations and river flow discharges were carried out to obtain the relationship between these two parameters. A resulting watershed map contains information on the rate of suspended sediment transport in the form of a suspended sediment-flow discharge rating curve is designed as a sediment conservation health indicator of the watershed. The map allows the authority to observe the condition of each river order in the upper course of the Jangkok River since the nearby tributaries are most likely to have their pattern of suspended sediment transport rate. The finding from this preliminary study can facilitate the drafting and implementation of the right policy in watershed conservation management planning which leads to preventive action and better preparedness in disaster mitigation.

SMPLNORM : Un modèle simple pour obtenir les probabilités conjointes de deux débits et le niveau qui en dépend

1994 ◽  
Vol 21 (5) ◽  
pp. 883-895 ◽  
Author(s):  
Pierre Bruneau ◽  
Fahim Ashkar ◽  
Bernard Bobée
Keyword(s):  
Marginal Distribution ◽  
Extreme Values ◽  
Joint Probability ◽  
Power Transformation ◽  
Type I ◽  
Marginal Distributions ◽  
Proposed Model ◽  
Bivariate Models ◽  
Valid Estimate ◽  
Two Parameters

Most bivariate models assume the same type of marginal distribution, with two parameters, for two variables (gamma, type I extreme values, and so forth). The disadvantage of these models is that it is often difficult to make adjustments for observed flows. This study shows the application flexibility of a program that calculates the joint probability of two variables, Q1, and Q2, with marginal distributions that have three parameters. The program can also provide the probability of nonexceedence of a third variable, H, mathematically related to the first two variables. Two applications are discussed, in which Q1 and Q2 are the flows of two rivers controlling the variable H, which is a level in both cases. Theoretically, this model could also be applied to other types of variables. The proposed model is based on the hypothesis that a Box–Cox type of power transformation could reduce the marginal distributions of Q1 and Q2 to a normal distribution. One of the main conclusions of the study addresses the importance of taking into account the correlation between Q1 and Q2 to obtain a valid estimate of H. Key words: hydrology, statistics, bivariate models, Box–Cox, flow, water level. [Traduit par la rédaction]

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