Laboratory testing of mathematical models for high-concentration fluid mud turbidity currents   总被引：1，自引：0，他引：1  

M.R. Chowdhury 《Ocean Engineering》2011,38(1):256-270

The propagation characteristics of fluid mud turbidity currents were investigated experimentally and theoretically. Parameterizations for propagation phase transition times from slumping to self-similar and self-similar to viscous phases are proposed. Predictive capabilities of different mathematical models that fall into three different modeling approaches (force-balance, box, shallow water) were evaluated for fluid mud turbidity current propagation using our experimental observations. For the slumping and self-similar phases, the box and force-balance models showed superior predictive capabilities than the one-layer shallow water models with deep ambient condition. Fluid mud turbidity currents have a non-Newtonian rheology and their transition and propagation characteristics in the viscous phase differ vastly from the Newtonian currents. We derived and presented a viscous force-balance expression for the propagation of a non-Newtonian power-law fluid current. We then experimentally evaluated the predictive capability of this force-balance and the viscous shallow water model by Di Federico et al. (2006). Both models' predictions are observed to be in notably good agreement with the experimental data. The results of this study are expected to be useful for preliminary swift calculations of the fluid mud turbidity current propagation characteristics as well as in deciding whether more detailed calculations at the expense of complexity are required.  相似文献   

Formation of pockmarks and submarine canyons associated with dissociation of gas hydrates on the Joetsu Knoll,eastern margin of the Sea of Japan     

《Journal of Asian Earth Sciences》2014

This study, based on 3.5 kHz SBP, 3D seismic data and long piston cores obtained during MD179 cruise, elucidated the timing and causes of pockmark and submarine canyon formation on the Joetsu Knoll in the eastern margin of the Sea of Japan. Gas hydrate mounds and pockmarks aligned parallel to the axis on the top of the Joetsu Knoll are associated with gas chimneys, pull-up structures, faults, and multiple bottom-simulating reflectors (BSRs), suggesting that thermogenic gas migrated upward through gas chimneys and faults from deep hydrocarbon sources and reservoirs. Seismic and core data suggest that submarine canyons on the western slope of the Joetsu Knoll were formed by turbidity currents generated by sand and mud ejection from pockmarks on the knoll. The pockmark and canyon formation probably commenced during the sea-level fall, lasting until transgression stages. Subsequently, hydropressure release during the sea level lowering might have instigated dissociation of the gas hydrate around the base of the gas hydrate, leading to generation and migration of large volumes of methane gas to the seafloor. Accumulation of hydrate caps below mounds eventually caused the collapse of the mounds and the formation of large depressions (pockmarks) along with ejection of sand and mud out of the pockmarks, thereby generating turbidity currents. Prolonged pockmark and submarine canyon activities might have persisted until the transgression stage because of time lags from gas hydrate dissociation around the base of the gas hydrate until upward migration to the seafloor. This study revealed the possibility that submarine canyons were formed by pockmark activities. If that process occurred, it would present important implications for reconstructing the long-term history of shallow gas hydrate activity based on submarine canyon development.  相似文献   

The influence of bend amplitude and planform morphology on flow and sedimentation in submarine channels     

Kathryn J. Amos  Jeff Peakall  P. William Bradbury  Mat Roberts  Gareth Keevil  Sanjeev Gupta 《Marine and Petroleum Geology》2010

We present a series of experiments that investigate the morphology of sediment deposits within sinuous submarine channels of different sinuosity (S = 1.14–1.94) and planform (symmetric and asymmetric bends), generated by bedload-dominated turbidity current flows. Flows were generated by releasing dense saline gravity currents over a mobile sediment bed through pre-formed sinuous channels. Flows had a basal-outwards helicity and produced a characteristic bed morphology with point bars downstream of the bend apex at the inside of bends and scour at the outside of bends. An increasing loss of fluid through overspill with increasing channel sinuosity results in a decreasing magnitude of cross-stream velocity downstream, a decreasing amount of erosion and deposition, and decreasing transverse slopes of in-channel deposits. Basal fluid from within the channel is transported over the outer-levee at bends, implying that proximal outer-bend levee deposits will have similar sediment composition to that within the channel. More deposition of coarse material might be expected on levees and in overbank regions close to higher amplitude bends. No simple relationship was observed between superelevation and sinuosity, probably due to changes in the relative influences of downstream velocity and bend curvature on centrifugal force and inertial run-up. In the channel with the tightest initial bend curvature, overspill fluid from Bend 1 re-entered the channel at Bend 2, dominating flow characteristics and disrupting the basal-outwards helicity observed in the other channels. Higher sinuosity channels and those with shallow regional and levee slopes are thus more likely to have a higher proportion of anomalous flow and sedimentation patterns due to the influence of overspill fluid re-entry into the channel. The results of this investigation are combined with published observations to enable the synthesis of a new model for sedimentation in sinuous submarine channels.  相似文献   

Modeling diagnosis of suspended sediment transport in tidal estuarine system     

Wen-Cheng Liu  Chun-Hsien Lee  Chin H. Wu  Nobuaki Kimura 《Environmental Geology》2009,57(7):1661-1673

A three-dimensional, time-dependent hydrodynamic and suspended sediment transport model was performed and applied to the Danshuei River estuarine system and adjacent coastal sea in northern Taiwan. The model was validated with observed time-series salinity in 2001, and with salinity and suspended sediment distributions in 2002. The predicted results quantitatively agreed with the measured data. A local turbidity maximum was found in the bottom water of the Kuan-Du station. The validated model then was conducted with no salinity gradient, no sediment supply from the sediment bed, wind stress, and different freshwater discharges from upstream boundaries to comprehend the influences on suspended sediment dynamics in the Danshuei River estuarine system. The results reveal that concentrations of the turbidity maximum simulated without salinity gradient are higher than those of the turbidity maximum simulated with salinity gradient at the Kuan-Du station. Without bottom resuspension process, the estuarine turbidity maximum zone at the Kuan-Du station vanishes. This suggests that bottom sediment resuspension is a very important sediment source to the formation of estuarine turbidity maximum. The wind stress with northeast and southwest directions may contribute to decrease the suspended sediment concentration. When the freshwater discharges increase at the upstream boundaries, the limits of salt intrusion pushes downriver toward river mouth. Suspended sediment concentrations increase at the upriver reaches in the Danshuei River to Tahan Stream, while decrease at Kuan-Du station.  相似文献   

Transport of suspended solids from a karstic to an alluvial aquifer: the role of the karst/alluvium interface   总被引：1，自引：0，他引：1  

N. Massei  M. Lacroix  H. Q. Wang  B. J. Mahler  J. P. Dupont 《Journal of Hydrology》2002,260(1-4):88-101

This study focuses on the coupled transport of dissolved constituents and particulates, from their infiltration on a karst plateau to their discharge from a karst spring and their arrival at a well in an alluvial plain. Particulate markers were identified and the transport of solids was characterised in situ in porous and karstic media, based on particle size analyses, SEM, and traces. Transport from the sinkhole to the spring appeared to be dominated by flow through karst: particulate transport was apparently conservative between the two sites, and there was little difference in the overall character of the particle size distribution of the particulates infiltrating the sinkhole and of those discharging from the spring. Qualitatively, the mineralogy of the infiltrating and discharging material was similar, although at the spring an autochthonous contribution from the aquifer was noted (chalk particles eroded from the parent rock by weathering). In contrast, transport between the spring and the well appears to be affected by the overlying alluvium: particles in the water from the well, showed evidence of considerable size-sorting. Additionally, SEM images of the well samples showed the presence of particles originating from the overlying alluvial system; these particles were not found in samples from the sinkhole or the spring. The differences between the particulates discharging from the spring and the well indicate that the water pumped from the alluvial plain is coming from the karst aquifer via the very transmissive, complex geologic interface between the underlying chalk formation and the gravel at the base of the overlying alluvial system.  相似文献   

Atmospheric turbidity at athens observatory     

Bas Katsoulis 《Pure and Applied Geophysics》1977,115(3):583-591

Summary In this study, values of the Ångström turbidity coefficient () determined from Solar radiation observations at the National Observatory of Athens over the period 1955–1972 are analysed. Mean daily turbidity lies between 0.020–0.100. Turbidity is higher in summer than in winter. The main factor determining the turbidity is the air mass type. The scavenging by rainfall probably has a considerable effect in determining this distribution. There is some evidence of a trend of increasing turbidity during the period.  相似文献   

Turbidity and suspended solids variations downstream of a regulating reservoir     

D. J. Gilvear  G. E. Petts 《地球表面变化过程与地形》1985,10(4):363-373

A controlled reservoir release from Llyn Celyn to the Afon Tryweryn, Wales, U.K., has been used to study suspended load and turbidity variations. Turbidity was monitored continuously at two sites and 235 suspended solids samples were obtained at these and three additional sites during the passage of the release wave. The results are compared with data for a natural tributary flood event. The reservoir release data relate to sediment source depletion and reflects changing sources along the channel. Close to the dam, fine organic matter dominates the seston which scanning electron microscopy revealed to be predominantly allochthonous organic matter, with algal fragments and inorganic diatom frustules, derived from the periphyton of the channel bed. Coulter Counter analysis showed the seston to be relatively coarse with a median particle-size of 20 μm. Within 3 km of the dam, however, minerogenic particles dominate the sediment load of which more than 90 per cent is finer than 10 μm. This represents the flushing of channel-bed accumulations derived from tributary sources. The relationships between suspended sediment concentration and turbidity during the release are characterized by a marked, anticlockwise hysteresis. This contrasts with the clockwise hysteresis for the tributary flood event, but the different relationships cannot be explained by particle-size variations alone; seston composition also appears to be an important control.  相似文献   

Research Progress and Challenges of Submarine Cyclic Steps     

Dawei Wang  Yue Sun  Shaowen Si  Shiguo Wu 《地球科学进展》1986,35(9):890-901

Cyclic steps structure derived from the supercritical flows is one of the common bedforms， which is commonly found in sedimentary systems such as delta systems， deep-water canyon-channel systems， and carbonate platforms. In this paper， the research progresses of cyclic steps were introduced from the aspects of sedimentary environment， the features of bedforms， sedimentary structure， formation mechanism， and numerical simulation. The Research scale differences associated with the survey techniques or study methods， such as the ship survey and AUV-based multi-beams， sub-bottom profiles， multichannel seismic， the field outcrop， and numerical simulation were discussed. Finally， the breakthrough directions of the cyclic steps research were given. The combining method of ground penetrating radar， multichannel seismic， drilling and well logging were used to accurately detect the location of field outcrop thalweg. Within the area with water depth greater than 500 meters， the blending of multi-data for the cyclic steps research involved the AUV-based and the ship multi-beams， sub-bottom profiles， and multichannel seismic data. With the in situ samples and observation data obtained by human occupied vehicles， three-dimensional numerical simulation was developed to establish a set of dynamic simulation equations suitable for the real cyclic steps. Therefore， the high resolution three dimensional mode of the deep-water cyclic steps could be obtained more accurately.  相似文献   

Response of nephelometric turbidity to hydrodynamic particle size of fine suspended sediment     

《国际泥沙研究》2020,35(5):444-454

Turbidity is used as a surrogate for suspended sediment concentration (SSC), and as a regulatory tool for indicating land use disturbance and environmental protection. Turbidity relates linearly to suspended material, however, can show non-linear responses to particulate organic matter (POM), concomitant with changes in particle size distribution (PSD). In the paper the influence of ultra-fine particulate matter (UFPM) on specific turbidity and its association with POM in suspended sediment are shown for alpine rivers in the Southern Alps of New Zealand. The approach was two-fold: a field-based investigation of the relations between SSC, POM, and turbidity sampled during event flow; and experimental work on hydrodynamic particle size effects on SSC, POM, PSD, and turbidity. Specific turbidity changes over event flow and are sensitive to increasing proportional amounts of sand, UFPM, and POM in suspension. Furthermore, the UFPM is the size fraction (<6 μm) where POM increases. The implications of the current study are that the slopes of turbidity-SSC relations are undesirable in locations that may be dominated by cyclic release of POM or distinct pulses of fine-grained material. At locations where the turbidity-SSC slopes approximate 2, the POM proportion is usually <10% of the total suspended load. However, when turbidity-SSC slopes are <1 this is likely caused by high amounts of side-scatter from UFPM concomitant with higher proportions of POM. Thus, the use of turbidity as a proxy for determining SSC may have serious consequences for the measurement of representative suspended sediment data, particularly in locations where POM may be a significant contributor to overall suspended load.  相似文献   

A Study of Linke Turbidity Factor over Qena / Egypt     

Sayed M. Elshazly 《大气科学进展》1996,13(4):519-532

Data on instantaneous atmospheric Linke turbidity factor TL (m) are reported for clear days at Qena/Egypt in the period from June 1992 to May 1993.TL(m) is determined using the values of irradiance of direct solar radiation (I),which are calculated from global (G) and diffuse (D) - solar radiation measurements.Monthly and seasonally variations of both diurnal and daily average values of TL (m) increases steadily in the direction of sunset in the months from June to December 1992 as well as Summer and Autumn seasons,while it falls generally in this direction for the months from January to March and Winter season.In April and May,TL (m) fluctuates obviously through the day hours,it is also shown that the average values of TL(m) are particularly large during Summer months compared to other months of the year.This behavior of TL(m) is discussed in view of the variations of some weather elements,which affect the content of water vapor and dust particle in the atmosphere of the study region.It seems t be of s  相似文献