scholarly journals Effects of human alterations on the hydrodynamics and sediment transport in the Sacramento-San Joaquin Delta, California

2015 ◽  
Vol 367 ◽  
pp. 399-406 ◽  
Author(s):  
M. D. Marineau ◽  
S. A. Wright
Keyword(s):  
Nineteenth Century ◽  
Sediment Transport ◽  
Spatial Data ◽  
Shear Velocity ◽  
Previous Literature ◽  
Tidal Marshes ◽  
Water Conveyance

Abstract. The Sacramento-San Joaquin Delta, California, (Delta) has been significantly altered since the mid-nineteenth century. Many existing channels have been widened or deepened and new channels have been created for navigation and water conveyance. Tidal marshes have been drained and leveed to form islands that have subsided, some of which have permanently flooded. To understand how these alterations have affected hydrodynamics and sediment transport in the Delta, we analysed measurements from 27 sites, along with other spatial data, and previous literature. Results show that: (a) the permanent flooding of islands results in an increase in the shear velocity of channels downstream, (b) artificial widening and deepening of channels generally results in a decrease in shear velocity except when the channel is also located downstream of a flooded island, (c) 1.5 Mt/year of sediment was deposited in the Delta (1997–2010), and of this deposited sediment, 0.31 Mt/year (21%) was removed through dredging.

scholarly journals “Clean out of the map”: Knowing and doubting space at India’s high imperial frontiers

2017 ◽  
Vol 55 (1) ◽  
pp. 3-36 ◽  
Author(s):  
Thomas Simpson
Keyword(s):  
Nineteenth Century ◽  
Spatial Data ◽  
Scientific Understanding ◽  
Breaking Point ◽  
British India ◽  
Multiple Agents ◽  
Colonial India ◽  
Embodied Experiences ◽  
Instruments And Techniques ◽  
The Many

During the second half of the nineteenth century, land frontiers became areas of unique significance for surveyors in colonial India. These regions were understood to provide the most stringent tests for the men, instruments, and techniques that collectively constituted spatial data and representations. In many instances, however, the severity of the challenges that India’s frontiers afforded stretched practices in the field and in the survey office beyond breaking point. Far from producing supposedly unequivocal maps, many involved in frontier surveying acknowledged that their work was problematic, partial, and prone to contrary readings. They increasingly came to construe frontiers as spaces that exceeded scientific understanding, and resorted to descriptions that emphasized fantastical and disorienting embodied experiences. Through examining the many crises and multiple agents of frontier mapping in British India, this article argues that colonial surveying and its outputs were less assured and more convoluted than previous histories have acknowledged.

scholarly journals Robustness Analysis of Model Parameters for Sediment Transport Equation Development

2019 ◽  
Vol 12 ◽  
pp. 1-17
Author(s):  
Nadiatul Adilah Ahmad Abdul Ghani ◽  
Junaidah Ariffin ◽  
Duratul Ain Tholibon
Keyword(s):  
Sediment Transport ◽  
Transport Equation ◽  
Polynomial Regression ◽  
Robustness Analysis ◽  
Shear Velocity ◽  
Model Parameters ◽  
Evolutionary Polynomial Regression ◽  
Sediment Transport Equation ◽  
Sediment Data ◽  
Influential Parameters

Robustness analysis of model parameters for sediment transport equation development is carried out using 256 hydraulics and sediment data from twelve Malaysian rivers. The model parameters used in the analyses include parameters in equations by Ackers-White, Brownlie, Engelund-Hansen, Graf, Molinas-Wu, Karim-Kennedy, Yang, Ariffin and Sinnakaudan. Seven parameters in five parameter classes were initially tested. Robustness of the model parameters was measured on the statistical relations through Evolutionary Polynomial Regression (EPR) technique and further examined using the discrepancy ratio of the predicted versus the measured values. Results from analyses suggest  (ratio of shear velocity to flow velocity) and  (ratio of hydraulic radius to mean sediment diameter) to be the most significant and influential parameters for the development of sediment transport equation.

scholarly journals GIS-Based Site Selection for Check Dams in Watersheds: Considering Geomorphometric and Topo-Hydrological Factors

2019 ◽  
Vol 11 (20) ◽  
pp. 5639 ◽  
Author(s):  
Omid Rahmati ◽  
Zahra Kalantari ◽  
Mahmood Samadi ◽  
Evelyn Uuemaai ◽  
Davoud Davoudi Moghaddam ◽  
...  
Keyword(s):  
Sediment Transport ◽  
Spatial Data ◽  
Site Selection ◽  
Drainage Density ◽  
Stream Power ◽  
Topographic Wetness Index ◽  
Stream Network ◽  
Flood Peak ◽  
Check Dams ◽  
The World

Check dams are widely used watershed management measures for reducing flood peak discharge and sediment transport, and increasing lag time and groundwater recharge throughout the world. However, identifying the best suitable sites for check dams within the stream networks of various watersheds remains challenging. This study aimed to develop an open-source software with user-friendly interface for screening the stream network possibilities and identifying and guiding the selection of suitable sites for check dams within watersheds. In this developed site selection software (SSS), multi-criteria decision analysis (MCDA) was integrated into geographic information systems (GIS), which allowed for numerous spatial data of the multiple criteria to be relatively simply and visually processed. Different geomorphometric and topo-hydrological factors were considered and accounted for to enhance the SSS identification of the best locations for check dams. The factors included topographic wetness index (TWI), terrain ruggedness index (TRI), topographic position index (TPI), sediment transport index (STI), stream power index (SPI), slope, drainage density (DD), and stream order (SO). The site identification performance of the SSS was assessed using the receiver operating characteristic (ROC) curve method, with results for the case study example of the Poldokhtar watershed in Iran showing excellent performance and identifying 327 potential sites for efficient check dam construction in this watershed. The SSS tool is not site-specific but is rather general, adaptive, and comprehensive, such that it can and should be further applied and tested across different watersheds and parts of the world.

Bed Load Transport under Complex Flow

2011 ◽  
Vol 255-260 ◽  
pp. 3589-3593
Author(s):  
Chun Rong Liu ◽  
Dao Lin Xu
Keyword(s):  
Sediment Transport ◽  
Time History ◽  
Shear Velocity ◽  
Transport Rate ◽  
Bed Load ◽  
Complex Flow ◽  
Sediment Transport Rate ◽  
Load Transport ◽  
History Of ◽  
Load Sediment

In this paper, the backward-facing step flow and the sediment transport downstream step were studied experimentally. The critical incipient bed shear velocity is obtained by the results of bed shear velocity and sediment incipient probability. It was found that the critical incipient bed shear velocity depends on the flow structures under the complex flow. By using the new critical incipient bed shear obtained in this paper and calculating the Shields parameter based on instantaneous bed shear velocity, the bed load sediment transport rate downstream step was given. The time history of the bed profile downstream step was calculated by bed load sediment transport rate and compared that obtained by the digital images. Good agreement was observed.

Orientation, passive transport, and sediment erosion features of the sea scallop Placopecten magellanicus in the benthic boundary layer

1993 ◽  
Vol 71 (5) ◽  
pp. 953-959 ◽  
Author(s):  
Jonathan Grant ◽  
Craig W. Emerson ◽  
Sandra E. Shumway
Keyword(s):  
Boundary Layer ◽  
Sediment Transport ◽  
Shell Height ◽  
Shear Velocity ◽  
Benthic Boundary Layer ◽  
Passive Transport ◽  
Placopecten Magellanicus ◽  
Shell Size ◽  
Layer Flow ◽  
Sea Scallops

Passive transport and orientation of sea scallops (Placopecten magellanicus; 27–120 mm shell height) were studied in a laboratory flume to assess flow-mediated control of movement and position on the seabed. Additional experiments were conducted to characterize patterns of sediment transport around the scallop shell in relation to recesses occupied by scallops. The critical shear velocity of scallop transport was not correlated with shell height or other size measures, and most scallops were transported with the ventral shell margin facing downstream. Frontal exposure of scallops to the flow as indicated by fineness (shell height/shell depth) was greater in larger scallops, but when pallial gape was included in fineness (shell height/shell depth + gape)), frontal exposure was not correlated with scallop size. This suggests that variation in the drag component of transport was responsible for the lack of correlation between shell morphometry and critical shear velocity. Sediment transport created a horseshoe-shaped trough around the shell and several smaller erosion–deposition features downstream. The dimensions of sediment transport features were dependent on shell allometry, and it is likely that sediment transport contributes to the formation of scallop recesses typically observed in scallop beds. These results indicate that passive transport of sea scallops has a behavioural component related to gape that is independent of shell size. In contrast, scallop orientation and recessing may be explained by physical processes rather than simply by behaviour. Studies of bivalve hydrodynamics require consideration of living animals in addition to shell specimens and must include conditions of benthic boundary layer flow and sediment transport.

Bridging Divides: Verdi's Requiem in Post-Unification Italy

2015 ◽  
Vol 140 (2) ◽  
pp. 313-342
Author(s):  
Francesca Vella
Keyword(s):  
Nineteenth Century ◽  
Sacred Music ◽  
Previous Literature ◽  
Late Nineteenth Century ◽  
Alessandro Manzoni ◽  
Musical Genre ◽  
Political Implications ◽  
Late Nineteenth

ABSTRACTThis article addresses the early Italian reception of Verdi's Messa da Requiem (1874), premièred in Milan on the first anniversary of the death of the novelist Alessandro Manzoni. Previous literature has focused on issues of musical genre and the work's political implications (particularly its connections with Manzoni and with late nineteenth-century Italian revivals of ‘old’ sacred music). The article examines, instead, the curiously pluralistic concerns of contemporary critics, as well as certain aspects of Verdi's vocal writing, with the aim of destabilizing traditional dichotomies such as old/new, sacred/operatic, vocal/instrumental and progress/crisis. It argues for more broad-ranging political resonances of Verdi's work, suggesting that the negotiation of a variety of boundaries both in Verdi's music and in its contemporary discussion made the Requiem dovetail with wider cultural attempts to define Italian identity.

scholarly journals Turbulent and viscous sediment transport – a numerical study

2014 ◽  
Vol 37 ◽  
pp. 73-80 ◽  
Author(s):  
O. Durán ◽  
B. Andreotti ◽  
P. Claudin
Keyword(s):  
Shear Stress ◽  
Sediment Transport ◽  
Numerical Study ◽  
Fluid Velocity ◽  
Density Ratio ◽  
Shear Velocity ◽  
Transport Layer ◽  
Two Phase ◽  
Unit Surface ◽  
The Mean

Abstract. Sediment transport is studied as a function of the grain to fluid density ratio using two phase numerical simulations based on a discrete element method (DEM) for particles coupled to a continuum Reynolds averaged description of hydrodynamics. At a density ratio close to unity (typically under water), sediment transport occurs in a thin layer at the surface of the static bed, and is called bed load. Steady, or "saturated" transport is reached when the fluid borne shear stress at the interface between the mobile grains and the static grains is reduced to its threshold value. The number of grains transported per unit surface therefore scales as the excess shear stress. However, the fluid velocity in the transport layer remains almost undisturbed so that the mean grain velocity scales with the shear velocity u*. At large density ratio (typically in air), the vertical velocities are large enough to make the transport layer wide and dilute. Sediment transport is then called saltation. In this case, particles are able to eject others when they collide with the granular bed. The number of grains transported per unit surface is selected by the balance between erosion and deposition and saturation is reached when one grain is statistically replaced by exactly one grain after a collision, which has the consequence that the mean grain velocity remains independent of u*. The influence of the density ratio is systematically studied to reveal the transition between these two transport regimes. Finally, for the subaqueous case, the grain Reynolds number is lowered to investigate the change from turbulent and viscous transport.

scholarly journals A NUMERICAL MODEL FOR DUNE DYNAMICS

1980 ◽  
Vol 1 (17) ◽  
pp. 95
Author(s):  
J. Sundermann ◽  
H.-J. Vollmers ◽  
W. Puls
Keyword(s):  
Sediment Transport ◽  
Path Length ◽  
Erosion Rate ◽  
Flow Model ◽  
Transport Model ◽  
Shear Velocity ◽  
Mean Flow ◽  
Sediment Transport Model ◽  
The Mean ◽  
Bed Material

A numerical sediment transport model is formulated that serves especially for the simulation of bedform mechanics. The model is based on the idea that sediment transport is determined by the erosion rate and the path length of bed material. Formulas for the erosion rate and the path length are derived from physical considerations and from measurements; they depend mainly on the local values of the shear velocity and the mean flow velocity near the bed. The behaviour of detached sediment is simulated by a Monte Carlo procedure, which is based on the mean flow velocities and the eddy viscosity. All flow properties that are needed for the sediment transport model are computed by a numerical flow model that includes two turbulence equations. Results of the flow model and the sediment transport model are compared with measured data.

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