Entrainment, transport and deposition of sediment by saline gravity currents

Zordan, Jessica; Juez, Carmelo; Schleiss, Anton; Franca, Mário J.

doi:10.1016/j.advwatres.2018.02.017

Cited by 43 publications

(36 citation statements)

References 57 publications

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“…and the current height, h(t), that is identified here by the position at which the streamwise velocity is equal to zero, as in Zordan et al (2018a). H is thus defined as…”

Section: The Shape Of the Currentmentioning

confidence: 99%

“…Ambient fluid is entrained due to shear and buoyancy instabilities at the upper interface (Cantero et al, 2008), resulting in the dilution of the underlying current and modification of the density profile that characterizes a gravity current under stable density stratification (Turner, 1973). If the gravity current travels above an erodible bed, entrainment of material from the bottom can take place, which is conveyed with the current and sometimes redeposited at large distances from the original position (Zordan et al, 2018a). High shear stress associated with intense ejection and burst events influences erosion and bed load transport (Niño and Garcia, 1996;Cantero et al, 2008;Zordan et al, 2018a).…”

Section: Introductionmentioning

confidence: 99%

“…If the gravity current travels above an erodible bed, entrainment of material from the bottom can take place, which is conveyed with the current and sometimes redeposited at large distances from the original position (Zordan et al, 2018a). High shear stress associated with intense ejection and burst events influences erosion and bed load transport (Niño and Garcia, 1996;Cantero et al, 2008;Zordan et al, 2018a). For example, in the shallow shelf region of the lake it is frequently observed that cold water, which is relatively denser than that in open waters, starts to descend down the slope as a cold gravity current (Fer et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

“…Previous studies mainly focused separately on either low slopes or large slopes, missing the analysis of the transition that is tested here thanks to a specific experimental setup that allows for a wider range of configurations. Finally, we use a parameter previously defined in Zordan et al (2018a) for the evaluation of the bottom erosion capacity as a surrogate to evaluate the influence of each different trigger condition on the erosion capacity of the currents. Britter and Linden (1980) reproduced gravity currents down a slope with no breaks and found a critical angle, which is typically less than a degree, over which buoyancy force is large enough to counteract the bottom friction, producing a steady flow.…”

Section: Introductionmentioning

confidence: 99%

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Potential erosion capacity of gravity currents created by changing initial conditions

2019

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Abstract. We investigate to what extent the initial conditions (in terms of buoyancy and geometry) of saline gravity currents flowing over a horizontal bottom influence their runout and entrainment capacity. In particular, to what extent the effect of the introduction of an inclined channel reach, just upstream from the lock gate, influences the hydrodynamics of gravity currents and consequently its potential erosion capacity is still an open question. The investigation presented herein focuses on the unknown effects of an inclined lock on the geometry of the current, on the streamwise velocity, on bed shear stress, and on the mechanisms of entrainment and mass exchange. Gravity currents were reproduced in the laboratory through the lock-exchange technique, and systematic tests were performed with different initial densities, combined with five initial volumes of release on horizontal and sloped locks. The inclination of the upstream reach of the channel (the lock) was varied from 0 % to 16 %, while the lock length was reduced by up to 1∕4 of the initial reference case. We observed that the shape of the current is modified due to the enhanced entrainment of ambient water, which is the region of the current in which this happens most. A counterintuitive relation between slope and mean streamwise velocity was found, supporting previous findings that hypothesized that gravity currents flowing down small slopes experience an initial acceleration followed by a deceleration. For the steepest slope tested, two opposite mechanisms of mass exchange are identified and discussed, i.e., the current entrainment of water from the upper surface due to the enhanced friction at the interface and the head feeding by a rear-fed current. The bed shear stress and the corresponding potential erosion capacity are discussed, giving insights into the geomorphological implications of natural gravity currents caused in different topographic settings.

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“…and the current height, h(t), that is identified here by the position at which the streamwise velocity is equal to zero, as in Zordan et al (2018a). H is thus defined as…”

Section: The Shape Of the Currentmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Potential erosion capacity of gravity currents created by changing initial conditions

2019

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“…Nonetheless, boundary shear stress is just one of several impelling forces that result in sediment erosion [30]. Other hydrodynamic quantities, such as turbulent stresses, and turbulent and mean velocities, also govern the mechanisms of sediment entrainment and transport [75].…”

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confidence: 99%

Breaching Flow Slides and the Associated Turbidity Current

Alhaddad

Labeur

Uijttewaal

2020

JMSE

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This paper starts with surveying the state-of-the-art knowledge of breaching flow slides, with an emphasis on the relevant fluid mechanics. The governing physical processes of breaching flow slides are explained. The paper highlights the important roles of the associated turbidity current and the frequent surficial slides in increasing the erosion rate of sediment. It also identifies the weaknesses of the current breaching erosion models. Then, the three-equation model of Parker et al. is utilised to describe the coupled processes of breaching and turbidity currents. For comparison’s sake, the existing breaching erosion models are considered: Breusers, Mastbergen and Van Den Berg, and Van Rhee. The sand erosion rate and hydrodynamics of the current vary substantially between the erosion models. Crucially, these erosion models do not account for the surficial slides, nor have they been validated due to the scarcity of data on the associated turbidity current. This paper motivates further experimental studies, including detailed flow measurements, to develop an advanced erosion model. This will improve the fidelity of numerical simulations.

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Suspended sediment concentration estimation in the Sacramento‐San Joaquin Delta of California using long short‐term memory networks

Kim¹,

He²,

Sandhu³

2022

Hydrological Processes

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Sedimentation is an important aspect of water resources management with many implications. Often, process-based methods are employed to predict and assess the amount of sediment in water, but there are still challenges because the mechanisms that govern sediment transport are not yet fully understood. Furthermore, complex domains make model calibration difficult. Thus, as a complementary tool, a machinelearning model was developed in the present study to emulate an existing processbased model in simulating suspended sediment concentration (SSC). It employs the long short-term memory (LSTM) networks, which are a type of artificial neural networks (ANNs) designed for supervised learning of a sequence of data (e.g., time series). The model was applied to the Sacramento-San Joaquin Delta (the Delta) of California, USA, which is characterized by an interconnected system of sloughs, waterways, and a tidal outlet. The model training was performed with historical records of flow, stage and SSC at various locations within the Delta. The study period was 2010 through 2016, but the training period (i.e., range of observed data used to train the model) was varied to assess the model's sensitivity to the inputs and to determine the optimum model setup. Comparison between the model-estimated SSC and the observation at 12 key locations within the Delta showed that the estimation accuracy of the LSTM model during the study period is comparable or superior to that of the Delta Simulation Model II-General Transport Model (DSM2-GTM), a process-based operational hydrodynamics and water quality model for the Delta. In terms of the ratio of the root-mean-square error to the standard deviation (RSR), LSTM models generally showed higher predictability than DSM2-GTM in all test cases investigated, with the lowest (most desirable) and highest (least desirable) LSTM-based RSR being 0.21 and 1.14, respectively. In comparison, the lowest and highest RSR values with DSM2-GTM were 0.26 and 3.70, respectively. The median LSTM-based RSR of all study locations is around 0.7 while its DSM2-GTM counterpart is about 1.0. LSTM models also yielded remarkably higher (more desirable) Nash-Sutcliffe Efficiency values. Moreover, visual inspection found that LSTM models better captured the timing and magnitude of peaks as well as the temporal variations in the SSC time series. The LSTM model's performance was further analysed with hydro-meteorological data (precipitation and wind speed) incorporated in

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Entrainment, transport and deposition of sediment by saline gravity currents

Cited by 43 publications

References 57 publications

Potential erosion capacity of gravity currents created by changing initial conditions

Potential erosion capacity of gravity currents created by changing initial conditions

Breaching Flow Slides and the Associated Turbidity Current

Suspended sediment concentration estimation in the Sacramento‐San Joaquin Delta of California using long short‐term memory networks

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