Effects of tributary inflow and sediment input on reservoir turbidity current formation and evolution

2021 ◽  
Author(s):  
Yining Sun ◽  
Ji Li ◽  
Zhixian Cao ◽  
Alistair G.L. Borthwick
Keyword(s):  
Yellow River ◽  
Sediment Concentration ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Front Speed ◽  
Sediment Input ◽  
Formation And Evolution ◽  
Maximum Utilization

<p>For reservoirs built on a hyper-concentrated river, tributary inflow and sediment input may affect the formation and evolution of reservoir turbidity current, and accordingly bed morphology. However, the understanding of tributary effects on reservoir turbidity currents has remained poor. Here a series of laboratory-scale reservoir turbidity currents are investigated using a coupled 2D double layer-averaged shallow water hydro-sediment-morphodynamic model. It is shown that the tributary location may lead to distinctive effects on reservoir turbidity current. Clear-water flow from the tributary may cause the stable plunge point to migrate upstream, and reduce its front speed. Sediment-laden inflow from the tributary may increase the discharge, sediment concentration, and front speed of the turbidity current, and also cause the plunge point to migrate downstream when the tributary is located upstream of the plunge point. In contrast, if the tributary is located downstream of the plunge point, sediment-laden flow from the tributary causes the stable plunge point to migrate upstream, and while the tributary effects on discharge, sediment concentration, and front speed of the turbidity current are minor. A case study is presented as of the Guxian Reservoir (under planning) on the middle Yellow River, China. The present finding highlights the significance of tributary inflow and sediment input in the formation and propagation of reservoir turbidity current and also riverbed deformation. Appropriate account of tributary effects is warranted for long-term maintenance of reservoir capacity and maximum utilization of the reservoir.</p>

Three-dimensional numerical simulation of the turbidity current on a flume slope

2020 ◽  
Author(s):  
Ruoyin Zhang ◽  
Baosheng Wu ◽  
Y. Joseph Zhang
Keyword(s):  
Sediment Transport ◽  
Open Channel ◽  
Sediment Concentration ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Concentration Profiles ◽  
Time Step ◽  
Densimetric Froude Number ◽  
Plunge Depth ◽  
Inflow Conditions

<p>Density-driven gravity flows frequently occur in nature, due to density difference between inflowing and ambient water. When a sediment-laden flow reaches the backwater zone of a reservoir, with a greater density than the ambient waters, an underflow can occur along steep bottom slopes. The formation and evolution of an underflow depend on various natural conditions. It is necessary and crucial for reservoir management to understand the dynamics and prediction of the turbidity currents. In addition to field investigation and laboratory experiments, numerical models are gaining popularity for solving open-channel flows and sediment transport processes such as turbidity currents in reservoirs.</p><p>SCHISM (Semi-implicit Cross-scale Hydroscience Integrated System Model) is a 3D seamless cross-scale model grounded on unstructured grids for hydrodynamics and ecosystem dynamics. A general set of governing equations are used for the flow and tracer transport, and a new higher-order implicit advection scheme for transport (TVD<sup>2</sup>) is proposed. A mixed triangular-quadrangular horizontal grid and a highly flexible vertical grid system are developed in the model to faithfully represent complex geometry and topography of environmental flows in open channel cases. SCHISM has found a wide range of cross-scale applications worldwide including general circulation, storm surges, sediment transport and so on. However, the feasibility of simulating turbidity currents caused by sediment-laden flows in a reservoir is rarely validated. In this study, SCHISM is applied to a lab experiment to simulate the turbidity currents on a flume slope to examine how the model predicts the hydraulic characteristics of turbidity currents in a reservoir.</p><p>Model results can describe the process of the turbidity current plunging beneath the free surface with the time step of 0.1s. It is relatively uncommon in previous studies to clearly show the evolution of the velocity and sediment concentration profiles in such a short time step. The simulated velocity and sediment concentration profiles of the turbidity currents match well with the measured profiles at the cross section downstream of the plunge point. The calculated depth-averaged velocity, thickness, and depth-averaged concentration of the turbidity current all agree well with the measured values. The correlation coefficient between the measured and calculated values is 0.92, 0.95, and 0.94, respectively. Also, the densimetric Froude number of the stable plunge point is found to be approximately 0.54 in this study, which is between 0.5 and 0.8 based on previous research. The plunge depth is smaller with higher sediment concentration and smaller discharge of the inflow. Besides, the ratio of plunge depth to inlet depth is proportional to the densimetric Froude number of inflow conditions. This finding can be used to predict the depth and location of the plunge point based on the inflow conditions in a reservoir, which has great practical implications in reservoir management. Our results demonstrated that SCHISM is generally applicable to simulate the turbidity currents in small-scale water environments, and has the potential to be adopted in large-scale open water environments.</p>

scholarly journals Inverse Analysis to Reconstruct Hydraulic Conditions of Non-steady Turbidity Currents: Application to an Ancient Turbidite of the Kiyosumi Formation of the Awa Group, Boso Peninsula, Central Japan

2020 ◽  
Author(s):  
Kento Nakao ◽  
Hajime Naruse ◽  
Shuichi Tokuhashi
Keyword(s):  
Inverse Analysis ◽  
Initial Conditions ◽  
Shallow Water Equation ◽  
Sediment Concentration ◽  
Turbidity Current ◽  
Forward Model ◽  
Turbidity Currents ◽  
Data Sets ◽  
Hydraulic Conditions ◽  
The Individual

Abstract This study proposes a new method of inverse analysis from ancient turbidites to the non-steady turbidity currents with consideration of multiple grain-size classes. The forward model employed in this study is based on the shallow water equation, and the initial condition of flows are assumed to be the lock-exchange type condition. To obtain a solution of the inverse problem, this study employed the genetic algorithm for finding the optimized initial conditions. The present method successfully estimated the true given initial conditions of the turbidity currents from the artificial data sets of deposits created by the calculation of the forward model. The author also applied the method to the turbidite bed in the Kiyosumi Formation. As a result of inverse analysis, the obtained solution fits well to the observed data of the individual turbidite, providing estimates of the flow velocity, the flow thickness and the sediment concentration of the turbidity current. The flow thickness and velocity when the turbidity current reached at the downstream end of the study area were reconstructed to be 334.6 m, 0.98 m/s respectively at the location of the downstream end. Result of our analysis is the first example of reconstructing a reasonable conditions of the turbidity current from an ancient turbidite observed in the field, and the method is expected to be applied in various regions in the future.

scholarly journals The Formation and Evolution of Interorganisational Business Networks in Megaprojects: A Case Study of Chinese Skyscrapers

Complexity ◽  
2020 ◽  
Vol 2020 ◽  
pp. 1-17
Author(s):  
Yujie Lu ◽  
Wei Wei ◽  
Yongkui Li ◽  
Zhilei Wu ◽  
Hao Jin
Keyword(s):  
High Performance ◽  
Large Scale ◽  
Dynamic Network ◽  
Business Networks ◽  
Business Network ◽  
Practical Applications ◽  
Formation And Evolution ◽  
Performance Teams

Megaprojects are implemented by different organisations, such as owners, consultants, and contractors. Gradually, these organisations and their connections can form business networks that influence both the market position of individual organisations and project performance. Previous research on large-scale projects mainly focused on static and homogeneous networks that were constructed by one individual project and/or carried out over one-off collaboration. However, this neglected the consideration of project network diversity, as well as repetitive, dynamic, cross-project coopetition relationship (i.e., collaboration and competition) and long-term business networks formed by key actors. Here, we chose Chinese skyscrapers over 300 meters that were built from 1996 to 2015 as typical megaproject cases and analysed the formation and evolution of megaproject business networks from the perspective of interorganisational coopetition. We identified the key actors involved and empirically studied their dynamic network positions over time. The main contributions of this study are threefold. First, we found that past collaboration experience has direct and dynamic impacts on the formation of megaproject business networks. Second, we identified key actors in the interorganisational business network and unveiled their dynamic positions with clear patterns. Third, we highlighted the temporal-spatial effect on the formation and development of business networks, alongside developments in the megaproject market. The findings of this study also provide practical applications for owners to choose collaboration partners and to build high-performance teams and for suppliers to enter and sustain the business in the megaprojects networks.

scholarly journals Mapping turbidity currents using seismic oceanography

2011 ◽  
Vol 8 (4) ◽  
pp. 1803-1818
Author(s):  
E. A. Vsemirnova ◽  
R. W. Hobbs
Keyword(s):  
Seismic Data ◽  
Sediment Concentration ◽  
Sediment Traps ◽  
Turbidity Current ◽  
Turbidity Currents ◽  
Western Boundary ◽  
Seabed Sediment ◽  
Seismic Oceanography ◽  
Sea Bed ◽  
Oceanographic Data

Abstract. Using a combination of seismic oceanographic and physical oceanographic data acquired across the Faroe-Shetland Channel we present evidence of a turbidity current that transports suspended sediment along the western boundary of the Channel. We focus on reflections observed on seismic data close to the sea-bed on the Faroese side of the Channel below 900m. Forward modelling based on independent physical oceanographic data show that thermohaline structure does not explain these near sea-bed reflections but they are consistent with optical backscatter data, dry matter concentrations from water samples and from seabed sediment traps. Hence we conclude that an impedance contrast in water column caused by turbidity currents is strong enough to be seen in seismic sections and this provides a new way to visualise this type of current and its lateral structure. By inverting the seismic data we estimate a sediment concentration in the turbidity current, present at the time of the survey, of 45 ± 25 mg l−1. We believe this is the first direct observation of a turbidity current using Seismic Oceanography.

Caregivers' Perceptions of Speech-Language Pathologist Talk About Child Language and Literacy Disorders

2020 ◽  
Vol 29 (4) ◽  
pp. 2049-2067
Author(s):  
Karmen L. Porter ◽  
Janna B. Oetting ◽  
Loretta Pecchioni
Keyword(s):  
Language And Literacy ◽  
Collective Case Study ◽  
Study Approach ◽  
School Aged Children ◽  
Speech Language Pathologist ◽  
Therapy Goals ◽  
Semistructured Interviews ◽  
Types Of Information

Purpose This study examined caregiver perceptions of their child's language and literacy disorder as influenced by communications with their speech-language pathologist. Method The participants were 12 caregivers of 10 school-aged children with language and literacy disorders. Employing qualitative methods, a collective case study approach was utilized in which the caregiver(s) of each child represented one case. The data came from semistructured interviews, codes emerged directly from the caregivers' responses during the interviews, and multiple coding passes using ATLAS.ti software were made until themes were evident. These themes were then further validated by conducting clinical file reviews and follow-up interviews with the caregivers. Results Caregivers' comments focused on the types of information received or not received, as well as the clarity of the information. This included information regarding their child's diagnosis, the long-term consequences of their child's disorder, and the connection between language and reading. Although caregivers were adept at describing their child's difficulties and therapy goals/objectives, their comments indicated that they struggled to understand their child's disorder in a way that was meaningful to them and their child. Conclusions The findings showed the value caregivers place on receiving clear and timely diagnostic information, as well as the complexity associated with caregivers' understanding of language and literacy disorders. The findings are discussed in terms of changes that could be made in clinical practice to better support children with language and literacy disorders and their families.

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