scholarly journals Sediment load determines the shape of rivers

2021 ◽  
Vol 118 (49) ◽  
pp. e2111215118
Author(s):  
Predrag Popović ◽  
Olivier Devauchelle ◽  
Anaïs Abramian ◽  
Eric Lajeunesse
Keyword(s):  
Sediment Load ◽  
Sediment Flux ◽  
Sediment Discharge ◽  
Physically Based Model ◽  
Water And Sediment ◽  
Physically Based ◽  
Discharge Regime ◽  
Flux Profile ◽  
Large Discharge ◽  
Total Sediment

Understanding how rivers adjust to the sediment load they carry is critical to predicting the evolution of landscapes. Presently, however, no physically based model reliably captures the dependence of basic river properties, such as its shape or slope, on the discharge of sediment, even in the simple case of laboratory rivers. Here, we show how the balance between fluid stress and gravity acting on the sediment grains, along with cross-stream diffusion of sediment, determines the shape and sediment flux profile of laminar laboratory rivers that carry sediment as bedload. Using this model, which reliably reproduces the experiments without any tuning, we confirm the hypothesis, originally proposed by Parker [G. Parker, J. Fluid Mech. 89, 127–146 (1978)], that rivers are restricted to exist close to the threshold of sediment motion (within about 20%). This limit is set by the fluid–sediment interaction and is independent of the water and sediment load carried by the river. Thus, as the total sediment discharge increases, the intensity of sediment flux (sediment discharge per unit width) in a river saturates, and the river can transport more sediment only by widening. In this large discharge regime, the cross-stream diffusion of momentum in the flow permits sediment transport. Conversely, in the weak transport regime, the transported sediment concentrates around the river center without significantly altering the river shape. If this theory holds for natural rivers, the aspect ratio of a river could become a proxy for sediment discharge—a quantity notoriously difficult to measure in the field.

scholarly journals Seasonal logging, process response, and geomorphic work

2013 ◽  
Vol 1 (1) ◽  
pp. 311-335 ◽  
Author(s):  
C. H. Mohr ◽  
A. Zimmermann ◽  
O. Korup ◽  
A. Iroumé ◽  
T. Francke ◽  
...  
Keyword(s):  
Quantile Regression ◽  
Overland Flow ◽  
Timber Harvest ◽  
Dry Season ◽  
Sediment Flux ◽  
Slope Instability ◽  
High Temporal Resolution ◽  
Sediment Discharge ◽  
Dimensional Parameter ◽  
Water And Sediment

Abstract. Deforestation is a prominent anthropogenic cause of erosive overland flow and slope instability, boosting rates of soil erosion and concomitant sediment flux. Conventional methods of gauging or estimating post-logging sediment flux focus on annual timescales, but potentially overlook important geomorphic responses on shorter time scales immediately following timber harvest. Sediments fluxes are commonly estimated from linear regression of intermittent measurements of water and sediment discharge using sediment rating curves (SRCs). However, these often unsatisfactorily reproduce non-linear effects such as discharge-load hystereses. We resolve such important dynamics from non-parametric Quantile Regression Forests (QRF) of high-frequency (3 min) measurements of stream discharge and sediment concentrations in similar-sized (~ 0.1 km2) forested Chilean catchments that were logged during either the rainy or the dry season. The method of QRF builds on the Random Forest (RF) algorithm, and combines quantile regression with repeated random sub-sampling of both cases and predictors. The algorithm belongs to the family of decision-tree classifiers, which allow quantifying relevant predictors in high-dimensional parameter space. We find that, where no logging occurred, ~ 80% of the total sediment load was transported during rare but high magnitude runoff events during only 5% of the monitoring period. The variability of sediment flux of these rare events spans four orders of magnitude. In particular dry-season logging dampened the role of these rare, extreme sediment-transport events by increasing load efficiency during more moderate events. We show that QRFs outperforms traditional SRCs in terms of accurately simulating short-term dynamics of sediment flux, and conclude that QRF may reliably support forest management recommendations by providing robust simulations of post-logging response of water and sediment discharge at high temporal resolution.

scholarly journals Sedimentation in the Three Gorges Dam and its impact on the sediment flux from the Changjiang (Yangtze River), China

2009 ◽  
Vol 6 (4) ◽  
pp. 5177-5204 ◽  
Author(s):  
B. Q. Hu ◽  
Z. S. Yang ◽  
H. J. Wang ◽  
X. X. Sun ◽  
N. S. Bi
Keyword(s):  
Sediment Load ◽  
Sediment Flux ◽  
Trapping Efficiency ◽  
Three Gorges Dam ◽  
Three Gorges ◽  
Sediment Discharge ◽  
The Three Gorges ◽  
Coastal Sea ◽  
The Mean ◽  
The Three Gorges Dam

Abstract. After the operation of the Three Gorges Dam (TGD) in 2003, the mean annual sediment load at Yichang station, 44 km downstream of the TGD, decreased drastically by 84% of that in the pre-TGD period (1986–2002). Annually, about 162 million tons (Mt) sediment was trapped by the TGD in 2003–2007, of which 92% was deposited within the region from Cuntan to TGD site; the remaining 8% deposited in the upstream of Cuntan owing to the effect of the extended backwater region of TGD. The theoretical trapping efficiency of the cascade reservoir on the lower Jinshajiang was calculated and its impact on the Changjiang sediment in the coming decades discussed. The results show that the cascade reservoir will trap up to 91% of the sediment discharge coming from the Jinshajiang tributary, and then the sediment discharge from the Changjiang to the sea will continuously decrease to less than 90 Mt/yr in the coming decades. In the presence of low sediment discharge, profound impacts on the morphology of estuary, delta and coastal sea are expected.

SEDIMENT LOAD CALCULATION WITHIN A RURAL BASIN BY USING A PHYSICALLY-BASED MODEL (ARCSWAT)

2019 ◽  
Author(s):  
MIGUEL ANGEL BRIBIESCA RODRIGUEZ ◽  
JORGE IVAN JUAREZ DEHESA ◽  
FERNANDO J GONZALEZ VILLARREAL ◽  
GABRIELA GUTIÉRREZ AVIÑA
Keyword(s):  
Sediment Load ◽  
Physically Based Model ◽  
Load Calculation ◽  
Physically Based

scholarly journals Attenuation of solar radiation in Arctic snow: field observations and modelling

2000 ◽  
Vol 31 ◽  
pp. 364-368 ◽  
Author(s):  
S. Gerland ◽  
G. E. Liston ◽  
J.-G. winther ◽  
J. B. Ørbæk ◽  
B.V. Ivanov
Keyword(s):  
Grain Size ◽  
Solar Radiation ◽  
Solar Spectrum ◽  
Physically Based Model ◽  
Snow Properties ◽  
Radiation Properties ◽  
Physically Based ◽  
Flux Profile ◽  
Absorption And Reflection Coefficients ◽  
Radiation Measurements

AbstractSolar radiation was measured above and in the snowpack on Svalbard using a spectroradiometer and a quantum meter measuring average photosynthetically active radiation (PAR). In order to specify the effect of melting on the snow’s radiation properties, all measurements were performed before and during the melt season in May and June 1997 and 1998. Along with the radiation measurements, physical and structural snow properties were logged in snow pits. A physically based model was used to simulate the penetration of radiation into the snow The model formulation accounts for the spectrally dependent interactions between the radiation and snow grains, and requires inputs of the incoming solar radiation spectrum and the vertical snow density and grain-size. The vertical radiation-flux profile was computed using a two-stream radiation approximation where the absorption and reflection coefficients are related to the surface albedo, solar spectrum, grain-size and number of grains per unit volume. In general, snow before the onset of melt attenuates solar radiation more than coarser-grained snow that has been exposed to melting conditions. Quantum-meter measurements of PAR before and during melt can be explained by model outputs using both constant and variable extinction coefficients. Spectroradiometer measurements at fixed depth levels showed, in addition, that impurities in the snow reduce its transparency and therefore have the opposite effect to aging.

scholarly journals Sedimentation in the Three Gorges Dam and the future trend of Changjiang (Yangtze River) sediment flux to the sea

2009 ◽  
Vol 13 (11) ◽  
pp. 2253-2264 ◽  
Author(s):  
◽  
◽  
◽  
◽  
◽  
...  
Keyword(s):  
Yangtze River ◽  
Sediment Deposition ◽  
Sediment Flux ◽  
Trapping Efficiency ◽  
Three Gorges Dam ◽  
Three Gorges ◽  
Sediment Discharge ◽  
The Three Gorges ◽  
Total Sediment ◽  
The Three Gorges Dam

Abstract. The Three Gorges Dam (TGD) on the upper Changjiang (Yangtze River), China, disrupts the continuity of Changjiang sediment delivery to downstream and coastal areas. In this study, which was based on 54 years of annual water and sediment data from the mainstream and major tributaries of Changjiang, sediment deposition induced by the TGD in 2003–2008 was quantified. Furthermore, we determined the theoretical trapping efficiency of the cascade reservoir upstream of the TGD. Its impact on Changjiang sediment flux in the coming decades is discussed. Results show that about 172 million tons (Mt) of sediment was trapped annually by the TGD in 2003–2008, with an averaged trapping efficiency of 75%. Most of the total sediment deposition, as induced by the TGD (88%), accumulated within the region between the TGD site and Cuntan. However, significant siltation (12% of the total sediment deposition) also occurred upstream of Cuntan as a consequence of the upstream extended backwater region of the TGD. Additionally, the Changjiang sediment flux entered a third downward step in 2001, prior to operation of the TGD. This mainly resulted from sediment reduction in the Jinshajiang tributary since the late 1990s. As the cascade reservoir is put into full operation, it could potentially trap 91% of the Jinshajiang sediment discharge and, therefore, the Jinshajiang sediment discharge would most likely further decrease to 14 Mt/yr in the coming decades. Consequently, the Changjiang sediment flux to the sea is expected to continuously decrease to below 90 Mt/yr in the near future, or only 18% of the amount observed in the 1950s. In the presence of low sediment discharge, profound impacts on the morphology of estuary, delta and coastal waters are expected.

scholarly journals A new approach to mapping landslide hazards: a probabilistic integration of empirical and physically based models in the North Cascades of Washington, USA

2019 ◽  
Vol 19 (11) ◽  
pp. 2477-2495
Author(s):  
Ronda Strauch ◽  
Erkan Istanbulluoglu ◽  
Jon Riedel
Keyword(s):  
Statistical Approach ◽  
Joint Probability ◽  
North Cascades ◽  
Physically Based Model ◽  
New Approach ◽  
The North ◽  
Debris Avalanches ◽  
Landslide Hazards ◽  
Infinite Slope Stability Model ◽  
Physically Based

Abstract. We developed a new approach for mapping landslide hazards by combining probabilities of landslide impacts derived from a data-driven statistical approach and a physically based model of shallow landsliding. Our statistical approach integrates the influence of seven site attributes (SAs) on observed landslides using a frequency ratio (FR) method. Influential attributes and resulting susceptibility maps depend on the observations of landslides considered: all types of landslides, debris avalanches only, or source areas of debris avalanches. These observational datasets reflect the detection of different landslide processes or components, which relate to different landslide-inducing factors. For each landslide dataset, a stability index (SI) is calculated as a multiplicative result of the frequency ratios for all attributes and is mapped across our study domain in the North Cascades National Park Complex (NOCA), Washington, USA. A continuous function is developed to relate local SI values to landslide probability based on a ratio of landslide and non-landslide grid cells. The empirical model probability derived from the debris avalanche source area dataset is combined probabilistically with a previously developed physically based probabilistic model. A two-dimensional binning method employs empirical and physically based probabilities as indices and calculates a joint probability of landsliding at the intersections of probability bins. A ratio of the joint probability and the physically based model bin probability is used as a weight to adjust the original physically based probability at each grid cell given empirical evidence. The resulting integrated probability of landslide initiation hazard includes mechanisms not captured by the infinite-slope stability model alone. Improvements in distinguishing potentially unstable areas with the proposed integrated model are statistically quantified. We provide multiple landslide hazard maps that land managers can use for planning and decision-making, as well as for educating the public about hazards from landslides in this remote high-relief terrain.

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