The Experts below are selected from a list of 318 Experts worldwide ranked by ideXlab platform
Jack Lewis - One of the best experts on this subject based on the ideXlab platform.
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Turbidity controlled suspended sediment sampling for runoff event load estimation
Water Resources Research, 1996Co-Authors: Jack LewisAbstract:For estimating suspended sediment concentration (SSC) in rivers, Turbidity is generally a much better predictor than water discharge. Although it is now possible to collect continuous Turbidity data even at remote sites, sediment sampling and load estimation are still conventionally based on discharge. With frequent calibration the relation of Turbidity to SSC could be used to estimate suspended loads more efficiently. In the proposed system a programmable data logger signals a pumping sampler to collect SSC specimens at specific Turbidity thresholds. Sampling of dense field records of SSC and Turbidity is simulated to investigate the feasibility and efficiency of Turbidity-controlled sampling for estimating sediment loads during runoff events. Measurements of SSC and Turbidity were collected at 10-min intervals from five storm events in a small mountainous watershed that exports predominantly fine sediment. In the simulations, samples containing a mean of 4 to 11 specimens, depending on storm magnitude, were selected from each storm's record, and event loads were estimated by predicting SSC from regressions on Turbidity. Using simple linear regression, the five loads were estimated with root mean square errors between 1.9 and 7.7%, compared to errors of 8.8 to 23.2% for sediment rating curve estimates based on the same samples. An estimator for the variance of the load estimate is imprecise for small sample sizes and sensitive to violations in regression model assumptions. The sampling method has potential for estimating the load of any water quality constituent that has a better correlate, measurable in situ, than discharge.
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Turbidity-controlled suspended sediment sampling
1996Co-Authors: Jack Lewis, Rand EadsAbstract:For estimating suspended sediment concentration (SSC) in rivers, Turbidity is generally a much better predictor than water discharge. Turbidity is an optical measure of the cloudiness of water caused by light scattering from suspended particles, organics, and dissolved constituents. Although it is now possible to collect continuous Turbidity data even at remote sites, sediment sampling and load estimation are still conventionally based on water discharge. With frequent calibration, the relation of Turbidity to SSC can be used to estimate suspended loads more effi
Christopher J Gippel - One of the best experts on this subject based on the ideXlab platform.
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potential of Turbidity monitoring for measuring the transport of suspended solids in streams
Hydrological Processes, 1995Co-Authors: Christopher J GippelAbstract:Investigating the transport of suspended solids by water sampling usually leads to an underestimation of loads and an unrealistically high sampling frequency is required to properly characterize temporal trends. An alternative method is to use in situ optical turbidimeters to estimate the suspended solids concentration; however, the relationship between Turbidity and suspended solids concentration is potentially confounded by variations in particle size, particle composition and water colour. Field measurements, and laboratory measurements using the type of natural material suspended in streamwater, were made to quantify the influences of these factors on nephelometric Turbidity (Hach 2100A) and attenuance Turbidity (Partech 7000 3RP MKII). The attenuance Turbidity was approximately 2.5 times higher than nephelometric Turbidity. The Turbidity instruments were most sensitive to dispersions with a median diameter of 1.2-1.4γm. Particle size variation can cause the Turbidity to vary by a factor of four for the same concentration of suspended solids. However, the numerous close correlations between Turbidity and suspended solids concentration reported previously suggests that either the particle size variations are not usually great, or that particle size variations are often associated with variations in suspended solids concentration. For the same concentration and particle size, organic particles gave attenuance Turbidity values two to three times higher than mineral particles. However, shortterm temporal variations from purely organic to purely mineral particle loads are rare in nature, so variations in the percentage of organic matter in the paniculate load will not confound Turbidity to this extent. Coloured dissolved organic matter is unlikely to alter the Turbidity reading by more than 10%. An adequate relationship between Turbidity measured in the field and suspended solids concentration should be expected in most situations. Some variance can be tolerated because a continuous estimate of suspended solids concentration overcomes the problem of infrequent sampling, which is the greatest source of error in the estimation of stream sediment loads.
Ruey Fang Yu - One of the best experts on this subject based on the ideXlab platform.
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a study on the removal of organic substances from low Turbidity and low alkalinity water with metal polysilicate coagulants
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2008Co-Authors: Wen Po Cheng, Chun Chang Li, Ruey Fang YuAbstract:The coagulants of poly-aluminum-chloride (PAC), poly-aluminum-silicate-chloride (PASiC) and poly-aluminum-ferric-silicate-chloride (PAFSiC) were prepared in this study to evaluate their coagulation efficiencies and mechanisms in synthetic low-Turbidity and low-alkalinity water containing organic matter. The experimental results show that PASiC and PAFSiC could remove the kaolin Turbidity of the synthetic water with or without salicylic acid present. On the other hand, when the synthetic water contained both kaolin and humic acid in low Turbidity and alkalinity, PAC would remove the Turbidity but charge reversal of the colloidal particles would occur easily. Also, effective coagulation was limited to a very narrow dosage range. Conversely, the dosage range for the effective coagulation of both PASiC and PAFSiC was wider, although a higher dosage was required to remove the Turbidity of wastewater. Therefore, the effective removal of Turbidity was not only related to the kind of coagulant, but also to the types of organic matter. The coagulants PASiC and PAFSiC, particularly, proved themselves to be superior to the PAC in the treatment of low-Turbidity water.
Britta Schaffelke - One of the best experts on this subject based on the ideXlab platform.
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intra annual variation in Turbidity in response to terrestrial runoff on near shore coral reefs of the great barrier reef
Estuarine Coastal and Shelf Science, 2013Co-Authors: Katharina Fabricius, Glenn Death, Craig Humphrey, Irena Zagorskis, Britta SchaffelkeAbstract:Seawater Turbidity is a fundamental driver of the ecology of coastal marine systems, and is widely used as indicator for environmental reporting. However, the time scales and processes leading to changes in Turbidity in tropical coastal waters remain poorly understood. This study investigates the main determinants of inshore Turbidity in four inshore regions along ∼1000 km of the Australian Great Barrier Reef, based on ∼3 years of almost continuous in situ Turbidity logger data on 14 reefs. Generalized additive mixed models were used to predict spatial and temporal variation in weekly mean Turbidity based on variation in resuspension and runoff conditions. At any given wave height, wave period and tidal range, Turbidity was significantly affected by river flow and rainfall. Averaged across all reefs, Turbidity was 13% lower (range: 5–37%) in weeks with low compared with high rainfall and river flows. Additionally, Turbidity was on average 43% lower 250 days into the dry season than at the start of the dry season on reefs with long-term mean Turbidity >1.1 NTU. The data suggest the time scale of winnowing or consolidation of newly imported materials in this zone is months to years. In contrast, Turbidity returned to low levels within weeks after river flows and rainfall on reefs with long-term mean Turbidity of <1.1 NTU. Turbidity was also up to 10-fold higher on reefs near compared to away from river mouths, suggesting inter-annual accumulation of fine resuspendible sediments. The study suggests that a reduction in the river loads of fine sediments and nutrients through improved land management should lead to measurably improved inshore water clarity in the most turbid parts of the GBR.
G. Shanmugam - One of the best experts on this subject based on the ideXlab platform.
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Submarine fans: A critical retrospective (1950–2015)
Journal of Palaeogeography, 2016Co-Authors: G. ShanmugamAbstract:When we look back the contributions on submarine fans during the past 65 years (1950–2015), the empirical data on 21 modern submarine fans and 10 ancient deep-water systems, published by the results of the First COMFAN (Committee on FANs) Meeting (Bouma et al., 1985a), have remained the single most significant compilation of data on submarine fans. The 1970s were the “heyday” of submarine fan models. In the 21st century, the general focus has shifted from submarine fans to submarine mass movements, internal waves and tides, and contourites. The purpose of this review is to illustrate the complexity of issues surrounding the origin and classification of submarine fans. The principal elements of submarine fans, composed of canyons, channels, and lobes, are discussed using nine modern case studies from the Mediterranean Sea, the Equatorial Atlantic, the Gulf of Mexico, the North Pacific, the NE Indian Ocean (Bay of Bengal), and the East Sea (Korea). The Annot Sandstone (Eocene–Oligocene), exposed at Peira-Cava area, SE France, which served as the type locality for the “Bouma Sequence”, was reexamined. The field details are documented in questioning the validity of the model, which was the basis for the turbidite-fan link. The 29 fan-related models that are of conceptual significance, developed during the period 1970–2015, are discussed using modern and ancient systems. They are: (1) the classic submarine fan model with attached lobes, (2) the detached-lobe model, (3) the channel-levee complex without lobes, (4) the delta-fed ramp model, (5) the gully-lobe model, (6) the suprafan lobe model, (7) the depositional lobe model, (8) the fan lobe model, (9) the ponded lobe model, (10) the nine models based on grain size and sediment source, (11) the four fan models based on tectonic settings, (12) the Jackfork debrite model, (13) the basin-floor fan model, (14) supercritical and subcritical fans, and (15) the three types of fan reservoirs. Each model is unique, and the long-standing belief that submarine fans are composed of turbidites, in particular, of gravelly and sandy high-density turbidites, is a myth. This is because there are no empirical data to validate the existence of gravelly and sandy high-density Turbidity currents in the modern marine environments. Also, there are no experimental documentation of true Turbidity currents that can transport gravels and coarse sands in turbulent suspension. Mass-transport processes, which include slides, slumps, and debris flows (but not Turbidity currenrs), are the most viable mechanisms for transporting gravels and sands into the deep sea. The prevailing notion that submarine fans develop during periods of sea-level lowstands is also a myth. The geologic reality is that frequent short-term events that last for only a few minutes to several hours or days (e.g., earthquakes, meteorite impacts, tsunamis, tropical cyclones, etc.) are more important in controlling deposition of deep-water sands than sporadic long-term events that last for thousands to millions of years (e.g., lowstand systems tract). Submarine fans are still in a stage of muddled turbidite paradigm because the concept of high-density Turbidity currents is incommensurable.
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50 years of the turbidite paradigm 1950s 1990s deep water processes and facies models a critical perspective
Marine and Petroleum Geology, 2000Co-Authors: G. ShanmugamAbstract:Abstract Under the prevailing turbidite paradigm, the term turbidite (i.e., deposits of Turbidity currents with Newtonian rheology and turbulent state) is used very loosely and is commonly applied to deposits of debris flows with plastic rheology and laminar state. For example, because high-density Turbidity currents are defined on the basis of three different concepts (i.e., flow density, grain size, and driving force), there are no consistent criteria for recognition of their deposits. As a result, deep-water massive sands of debris-flow origin are routinely misinterpreted as high-density turbidites. The concept of waxing flow as a type of Turbidity current is problematic because waxing flows are defined on the basis of velocity, not on fluid rheology and flow state. The waxing-flow concept allows inversely graded sands to be misinterpreted as turbidites. Perhaps, the most problematic issue is the use of alluvial channel traction bed forms observed in flume experiments as the analog for the five divisions of the Bouma Sequence (i.e., classic turbidites deposited from suspension). This is because flume experiments were conducted under equilibrium flow conditions, whereas natural Turbidity currents deposit sediment under disequilibrium waning flow conditions. This and other problems of deep-water processes and facies models are addressed in this paper from the authors personal perspective. Classification of sediment-gravity flows into Newtonian flows (e.g., Turbidity currents) and plastic flows (e.g., debris flows), based on fluid rheology and flow state, is a meaningful and practical approach. Although popular deep-water facies models are based on transport mechanisms, there are no standard criteria in the depositional record to reliably interpret transport mechanisms. According to existing turbidite-facies models, an ideal turbidite bed, which has normal grading, with gravel- to mud-size particles should contain a total of 16 divisions. However, no one has ever documented a complete turbidite bed with 16 divisions in modern or ancient deposits. Recognition of units deposited by deep-water bottom currents (also referred to as contour currents) is difficult. Traction structures are good indicators of bottom-current reworking, but distinguishing deposits of bottom currents from deposits of overbanking Turbidity currents is difficult even though it has important implications for developing depositional models for hydrocarbon exploration and production. I consider sandy debris flows to be the dominant process responsible for transporting and depositing sands in the deep sea. Experiments on sandy debris flows suggest that low clay content (as little as 1%) is sufficient to provide the strength necessary for sandy debris flows. Deposits of experimental sandy debris flows are characterized by massive sand, sharp upper contacts, floating clasts, inverse grading, normal grading with clasts, and water-escape structures. As a counterpart to turbidite-dominated fan models suited for basinal settings, a slope model is proposed that is a debris-flow dominated setting with both non-channelized and channelized systems. Contrary to popular belief, deposits of sandy debris flows can be thick, areally extensive, clean (i.e., mud poor), and excellent reservoirs. High-frequency flows tend to develop amalgamated debris-flow deposits with lateral connectivity and sheet-like geometry. Submarine-fan models with turbidite channels and lobes have controlled our thinking for nearly 35 years, but I consider that these models are obsolete. The suprafan lobe concept was influential in both sedimentologic and sequence-stratigraphic circles because it provided a basis for constructing a general fan model and for linking mounded seismic facies with sheet-like turbidite sandstones. However, this concept recently was abandoned by its proponent, which has left the popular sequence-stratigraphic fan models with a shaky foundation. A paradigm shift is in order in the 21st century. This shift should involve the realization that thick deep-water massive sands are deposits of debris flows, not high-density turbidites. However, there are no standard vertical facies models that can be applied universally for either turbidites, contourites, or sandy debris flows. Science is a journey, whereas facies models terminate that journey and become the final destination.
