A deep-sea in-situ suspended sediment sampling system

A prototype deep pump filtration system, designed to sample suspended particulate matter in the deep sea, has been developed for use with an in-situ optical nephelometer used to locate zones of high particulate concentration. The filtration system, which has essentially an unlimited depth capability, can sample large volumes of water and is limited only by the concentration of the suspended load and the clogging characteristics of the filter, thereby being ideally suited for use in areas of extremely low particulate concentration. In its present configuration, the unit is capable of collecting as much as 200 mg of suspended sediment per lowering. The system is compact in design and may easily be integrated with any instrument platform, or used independently. In addition, the membrane filtration method utilized provides a convenient means of sample handling during analysis with a minimum of contamination.     

海底沉积物取样的扰动机理研究

海底沉积物取样技术对大洋诸多科学研究来说非常重要,各种研究目标的实现与沉积物样品的质量息息相关.在使用常规管状取样器对松软或轻微固结的沉积物取样时,沉积物样品的扰动总是不可避免的.以机械手持式沉积物取样器为原型机,建立了管状取样器的取样过程模型,分析了沉积物样品的扰动机理;采用球形孔扩张理论获得了沉积物土体受到取样管挤压扩张的理论解;结合太平洋具体沉积物土体物理力学参数,对管状取样器取样造成沉积物扰动的状况给出了一个定量描述,并且提出取样管壁的厚度是减小沉积物扰动的关键参数.     

多频海底声学原位测试系统研制和试用

海底沉积物的声学特性(最重要的是声速和声衰减)以及它们与物理(包括土力学)特性之间的关系是沉积物声学中两个重要的研究项目.介绍了新研制的实时监控多频海底声学原位测试系统.该系统可测量浅表层沉积物的声速.探测频率为8,10,12,15 kHz,可根据实际情况选择发射波形、接收增益和采样长度,采样率为0.5~2.0 MHz,工作水深为300 m.系统具有倾斜传感器、8通道扩充等功能.用该系统在杭州湾测得了四种频率的沉积物原位声速.     

声学悬浮泥沙观测系统的研制和应用

为观测水中悬浮泥沙的浓度剖面、监测水中污染物及研究近岸海区泥沙的迁移和沉积,研制了声学悬浮泥沙观测系统(ASSM).总结了设计时主要技术参数的确定及解决关键技术的方法。应用此系统观测长江口悬浮泥沙,得到典型悬浮泥沙浓度剖面。     

A wave-resolving model for nearshore suspended sediment transport

This paper presents a wave-resolving sediment transport model, which is capable of simulating sediment suspension in the field-scale surf zone. The surf zone hydrodynamics is modeled by the non-hydrostatic model NHWAVE (Ma et al., 2012). The turbulent flow and suspended sediment are simulated in a coupled manner. Three effects of suspended sediment on turbulent flow field are considered: (1) baroclinic forcing effect; (2) turbulence damping effect and (3) bottom boundary layer effect. Through the validation with the laboratory measurements of suspended sediment under nonbreaking skewed waves and surfzone breaking waves, we demonstrate that the model can reasonably predict wave-averaged sediment profiles. The model is then utilized to simulate a rip current field experiment (RCEX) and nearshore suspended sediment transport. The offshore sediment transport by rip currents is captured by the model. The effects of suspended sediment on self-suspension are also investigated. The turbulence damping and bottom boundary layer effects are significant on sediment suspension. The suspended sediment creates a stably stratified water column, damping fluid turbulence and reducing turbulent diffusivity. The suspension of sediment also produces a stably stratified bottom boundary layer. Thus, the drag coefficient and bottom shear stress are reduced, causing less sediment pickup from the bottom. The cross-shore suspended sediment flux is analyzed as well. The mean Eulerian suspended sediment flux is shoreward outside the surf zone, while it is seaward in the surf zone.     

A three-dimensional model of suspended particulate sediment transport

Depth-averaged, one-dimensional and two-dimensional numerical models of bed and suspended particulate sediment transport provide unreliable answers for siltation and erosion quantities in situations dominated by three-dimensional flow patterns, as occur in harbour entrances due to flow separation and wind and density currents. Consequently, a numerical scheme has been developed which solves the complete three-dimensional diffusion-advection equation for suspended sediment concentration and thereby makes possible the study of siltation problems in complex, three-dimensional flows. The model analogue is based on a splitting technique and employs a mixed characteristics and finite difference approach. The accuracy and usefulness of the resulting scheme have been investigated by applying it to a number of hypothetical situations and to a laboratory situation involving the transport and dispersal of lightweight sediment. The results of the various tests show that the proposed approach works well and provides a useful basis for the study of practical problems.     

Response of the suspended sediment transport system to continental shelf dynamics

Surface currents influenced by a wind-driven upwelling event in San Pedro Bay moved total suspended matter (TSM) confined to the inner shelf on 19 April 1978 seaward, so that by 27 April surface TSM had increased over the outer shelf. Near-bottom concentrations of TSM also increased across the shelf during this time. This is explained by sediment resuspended by large surface waves being advected from the inner shelf seaward by the mean flow after this flow had turned from southeasterly to southerly when upwelling ceased on 26 April. These complex shelf dynamics contribute to the off-shelf transport of mud to the slope and deep basins.     

关于定量监测悬浮泥沙浓度方法的回顾和展望

获取近岸水体中悬浮物浓度及相关信息对于理解和管理海洋环境相当重要。历史上对于悬浮物浓度的监测往往通过费时费力的出海观测,而这种观测具有很大的局限性,每次观测只能获取一个站位的信息。为了更快更有效的获得即时悬浮物浓度相关信息,很多新的监测手段及相关科技被开发及应用。各种机载,卫星载遥感设各被用于获得及时,全面的沉积物信息...     

Measurements of coastal suspended sediment concentrations

Three of the methods available for measurement of suspended sediment concentration were chosen and tested in natural conditions. The equipment included sand traps, a radioisotopic probe and a long-action sampler (bathometer).The working conditions of the equipment were studied and the reliability of data obtained was analyzed. Sources of possible errors have been defined together with requirements for the techniques, and optimum technical parameters have been found. Averaging times, necessary with regard to the reliability of data, have also been determined for the measurements. Calibration and cross-calibration of the measuring devices was carried out. Technological requirements, advantages and areas of applicability are discussed for the techniques. Although they require some modifications, the techniques can already be used in measurements of concentration profiles. The data obtained, and partly shown in this paper, shed light on complex phenomena of sediment suspension.     

Development of acoustic suspended sediment monitor

INTRODUCTIONA~q~tityofmudsandSandsbIDughtbyinfluentriverssUSpendin~talseawater.ThemudsandSands,affectedbythetidesandc~ts,areconstantlymoving,tranSportinganddealting,andcancauseseriousinfluencesonharhars,channelsandwaterconservancies,coaStalandOffshae...     

Ebb-tidal jets: A model of suspended sediment and mass transport at tidal inlets

Mass transport by turbulent jets issuing from tidal inlets is investigated through a model that includes lateral mixing and entrainment, bottom friction, bathymetric changes, settling rate of particles (size), possible deposition/erosion at the bottom and ambient currents and concentrations. The bottom frictional jet becomes diluted more slowly than a classical jet. A non-vanishing concentration may result offshore and a maximum may occur in the core. The concentration of a jet on a sloping bottom decreases more rapidly due to increased dilution by entraiment. The effects of bottom friction and bottom slope compete in determining the jet concentration. Deposition to the bottom occurs within the jet mainly on both sides of the centre-line, and at lower rates on the centre-line. Erosion or deposition may occur at the jet core depending on the inlet flow conditions. In the case of erosion at the core, the material extracted is deposited on the margins and the offshore areas. Sorting of the sediments is expected, with coarser materials mainly deposited in the marginal areas, while the finer sediments are more uniformly distributed and jetted further off-shore. The main features of the model are verified through a limited set of observations. The qualitative agreement is enhanced for micro- and meso-tidal inlets that are dominated by tidal hydraulics.     

The suspended sediment balance in Changjiang estuary

Circulation and balance of suspended sediment in Changjiang estuary have been analysed. Strong interaction between different waterways and the fact that they are wide and shallow both contributed to the great spatial and temporal variability in circulation and suspended sediment transport. Using a flux decomposition formula with the relative depth as the vertical coordinate, it was shown that although tidal dispersion was the main dispersion mechanism in the turbidity maximum zone, dispersions due to circulation effects were also important.     

海岸悬沙运移数学模型

根据适合大范围缓变地形情况下,不恒定、非均匀流场中随机波折绕射联合数值模式及波浪作用下的二维浅水环流方程和悬沙扩散方程,建立了波浪、潮流共同作用下二维悬沙数学模型,并将该模型应用于渤海湾北部海域,进行了波、流共同作用下航道疏浚弃土的悬沙扩散、运移及海床演变的数值模拟,为工程单位决策提供科学依据     

Abyssal bedforms and sediment drifts effected by deep-sea flows

The investigation of abyssal bedforms and sediment drifts as a tool for understanding the deep flow characteristics allows us to interprete that a benthic storm is primarily related to sediment distribution, development of longitudinal ripple marks, and concentration of suspended particulate matter. There explicitly exists a strong and periodical bottom flow which is called the benthic storm having a current speed of over 15 cm sec^?1 and duration of more than two days. Hydrodynamic regime has been thought to affect underlying sediment textural natures which can be used to distinguish between bottom currents with different velocities. Therefore, concentration of medium silt mode (0.010–0.017 mm in size) delineates a high-velocity core of the benthic storm in the deep sea bottom. Bottom current measurements in most of the North Pacific Ocean indicate that present bottom current speeds are generally less than 10 cm sec^?1. It appears likely, therefore, that significant erosion is not taking place today. However, at current passages, bases of sea mounts, and other topographic obstructions locally accelerated current flows are recognized to affect bottom configuration. While, it is concluded from bottom echo-characteristics and bottom current measurements that widespread occurrences of echo type 3 (sediment-drift deposit facies) recognized at 22°N and 42°N in the Northwest Pacific are associated with the North Equatorial current and the North Pacific current respectively, and can best be interpreted to be originated from benthic storms, the source of which were come from those surface currents.     

Traction rheological properties of simulative soil for deep-sea sediment

The traction capacity of the mining machine is greatly in?uenced by the traction rheological properties of the deep-sea sediments. The best simulative soil was prepared for substituting the deep-sea sediment based on the deep-sea sediment collected from the Paci?c C-C mining area. Traction rheological properties of the simulative soil were studied by a home-made test apparatus. In order to accurately describe the traction rheological properties and determine traction rheological parameters, the Newtonian dashpot in Maxwell body of Burgers model was replaced by a self-similarity spring-dashpot fractance and a new rheological constitutive model was deduced by fractional derivative theory. The results show the simulative soil has obvious non-attenuate rheological properties. The transient creep and stable creep rate increase with the traction, but they decrease with ground pressure. The fractional derivative Burgers model are better in describing non-attenuate rheological properties of the simulative soil than the classical Burgers model. For the new traction rheological constitutive equation of the simulative soil, the traction rheological parameters can be obtained by ?tting the tested traction creep data with the traction creep constitutive equation. The ground contact length of track and walking velocity of the mining machine predicted by the traction rheological constitutive equation can be used to take full advantages of the maximum traction provided by the soil and safely improve mining effciency.     

Bars formed by horizontal diffusion of suspended sediment

The mechanism responsible for the ubiquitous presence of convex beach profiles and shoreward migration of linear bars is examined using numerical circulation and sediment transport models. The models are validated against laboratory measurements and observed natural beach cross-sections. While not discounting the importance of infragravity and advective horizontal circulation or bed-return flow mechanisms, a robust diffusive process explains the convex profile shape and bar formation. In the presence of concentration gradients across the surf zone, a diffusive sediment flux from high to low concentration results in the transfer of sediment outwards from the breakpoint, both onshore and offshore, and the subsequent formation of a “diffusion bar” and “diffusion profile”. The profiles are characterised by single- and double-convex dome-like shapes, developing during shoreward migration of the bars by the diffusion mechanism. The mechanism explains several phenomena observed on natural beaches, including (i) convex beach profiles; (ii) shoreward migration of the bar with concomitant beach accretion under narrow-band swell; (iii) reduced propensity for bar formation on low-gradient, fine-sand beaches or under wide-band wave spectra (even though multiple bars are common on some low-gradient beaches) and (iv) offshore migration of the bar during periods of increasing wave height. The diffusion mechanism can be dependent on orbital motion alone and, as such, requires no frequency selection or strong correlation between multiple processes for bar formation.     

Nearshore suspended sediment variations,central Surinam coast

Nearshore suspended sediment concentration along the muddy Surinam coast is highly variable; maximum values are many times greater than on other muddy coasts. Water samples taken at four field stations during various stages of the tide range in concentration from 15 to 3,700 mg/l near the surface and from 100 to 30,000 mg/l near the bottom. Highest overall concentrations and greatest variability in concentration occur in water over large banks of fluid mud (thixotropic gel) that extend 2–3 km offshore and 5–10 km along-shore. On both the intertidal and subaqueous portions of these mudbanks highest concentrations are found at low tide. Results provide evidence that an exchange between fluid mud and suspended sediment takes place during each tidal cycle.     

Converting near-bottom OBS measurements into suspended sediment concentrations

 A method of estimating the mass proportion of nonhomogeneous sediment constituents in suspension is presented. This method provides a more accurate conversion of OBS measurements (volts) to suspended sediment concentrations (grams per liter). Given a set of calibration coefficients of end-members, the method allows one to obtain the spatially and temporally varying in situ coefficients that are used in the conversion. Field and/or laboratory experiments are needed to verify the method. Received: 26 April 1996 / Revision received: 23 July 1996