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1.
Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China 总被引：2，自引：1，他引：2
The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ～ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud. 相似文献
2.
Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data. 相似文献
3.
Incipient Motion of Sediment Under Currents 总被引：7，自引：3，他引：4
DOU Guoren 《中国海洋工程》2000,14(4):391-406
Summarized in the paper are the author's studies on incipient motion of sediment in recent 40years.In addition to the forces of gravity,drag and lift,the cohesive force and the additional static pres-sure are important for fine particles.The relations between three stages of incipient motion are defined byuse of instantaneous velocity.Formulas for initial velocity and critical shear stress are given and overallverified by the author's and others'experimental data. 相似文献
4.
Tsunamis propagating in the open ocean have associated horizontal particle velocities that do not change with depth — yet the limiting water depth where a tsunami of given characteristics will initiate sediment motion remains unknown. Based upon linear wave theory and a parametrization of the Shields curve, equations are derived and solved, using an iterative scheme, to address the topic of grain movement by tsunami waves as a function of water depth and wave amplitude. The focus is on waves in deep water where tsunami waves behave linearly and on non-cohesive sediment grains. Furthermore, the question is addressed of which grain sizes are picked up on a sloping beach as the wave shoals. According to the results, even the Boxing Day tsunami in 2004 was incapable of moving fine sand in water deeper than 985 m in the Bay of Bengal and 335 m in the Indian and Pacific oceans. The results suggest that tectonic tsunamis of size equal to or smaller than the Boxing Day tsunami cannot initiate motion of deep-water cohesionless sediments that can be correlated on an oceanic basin-wide scale. 相似文献
5.
A comprehensive field study has been undertaken to investigate sediment resuspension dynamics in the Moreton Bay, a large semi-enclosed bay situated in South East Queensland, Australia. An instrumented tripod, which housed three current meters, three OBS sensors and one underwater video camera, was used to collect the field data on tides, currents, waves and suspended sediment concentrations at four sites (Sites 1, 2, 4, and 5) in the bay. Site 1 was located at the main entrance, Site 2 at the central bay in deep water, and Sites 4 and 5 at two small bays in shallow water. The bed sediment was fine sand (d50=0.2 mm) at Site 1, and cohesive sediment at the other three sites. Based on the collected field data, it is found that the dominant driving forces for sediment resuspension are a combination of ocean swell and tidal currents at Site 1, tidal currents at Site 2, and wind-waves at Sites 4 and 5. The critical bed shear stress for cohesive sediment resuspension is determined as 0.079 Pa in unidirectional flow at Site 2, and 0.076 Pa in wave-induced oscillatory flow at Site 5. 相似文献
6.
于2013年11月、2014年1月及3月在青岛市灵山湾海水浴场进行了3次表层沉积物采样,对粒度组分和粒度参数平面分布的变化进行了分析。结果表明,本区沉积物整体有变粗的趋势,细砂组分特别是极细砂和粉砂组分含量下降明显,分选性变好,正偏态及高峰度分布区扩大,粒度参数高值分布区被消除。粒径趋势分析表明,在涨潮流与强盛的冬季风驱动的风浪、沿岸流的综合作用下,研究区沉积物总体呈北东-南西向沿岸输运,运移趋势变化受到波浪、潮流水动力条件与地形相互作用的影响。短期的波能变化足以改变沙滩地貌,从而影响表层沉积物的分布。可为浴场维护提供理论依据。 相似文献
7.
Internal tidal currents are the likely cause of erosional features such as current ripples, sand waves, and truncated bedding horizons on the sediment cap of Horizon Guyot. Current meter data obtained over a 9 month period in 1983–1984 at about 213 m above the guyot show that the tidal currents are anomalously strong for mid-oceanic depths, probably the result of topographically induced generation of internal tidal waves. An analysis of the initiation of motion of the foraminiferal sand by the internal tidal currents indicates that these currents, particularly during the months of March–May, are likely to transport the surficial sediment and generate the observed bedforms. 相似文献
8.
海南岛东南浅海表层沉积物粒度特征及沉积环境 总被引：1，自引：0，他引：1
对海南岛东南浅海377组表层沉积物样品(平均水深112.3 m)开展粒度测定及沉积物类型划分,并运用统计规律及沉积输运趋势分析,探讨了底质沉积物分布格局与物质来源及沉积动力环境关系。结果表明,海南岛东南浅海沉积物类型复杂,共分布13种沉积物类型,粒度组成以粉砂和砂为主,平均粒径均值为5.73Φ,优势粒级为细粉砂级(6~8Φ),分选差。不同海域沉积物粒径差异明显,北部近岸以含砾沉积为主,中部呈NE-SW向的砂质沉积区(水深80~120 m),西南近岸滨海、北中部海域以及东南部海域多为粉砂、黏土沉积。结合地理位置、沉积物源及水动力条件差异,研究区划分为3个沉积区:I区主要以含砾粗颗粒沉积为主,受控于海南岛上径流及强风浪作用,物质来源以万泉河等河流输运及岸线侵蚀物质为主,强动力(高能)沉积环境;II区以砂沉积为主,受到表层流及风浪等共同影响,可能主要是残留滨海沉积混入了海南岛径流及岸线侵蚀、少量珠江流域及外海复杂来源等现代细粒物质的混合沉积,中等动力沉积环境;III区以细粒沉积为主,主要受华南近岸流、风浪作用及南海暖流影响,推测物质来源主要为海南岛河流输入、岸线侵蚀及复杂外海来源细粒物质的加入,弱动力(低能)沉积环境。 相似文献
9.
A previously published wave-averaged version of Bailard's sediment transport formulation, intended for use in a numerical model of shelf sand transport, is compared against available field observations from literature. The objective was to test the performance of the transport relation over the wide range of hydrodynamical conditions that can occur at sea. A modified data analysis method was used to assess the reliability of the field observations. The modification consists of a method to cluster the data into classes to enable statistical analysis. The sediment transport formulation is part of the classification method. The method is in principle also suitable to reduce the size of data sets of non-cohesive sediment transport obtained with modern electronic equipment. The results show that the quality of the published field observations is fair, and that the wave-averaged Bailard formulation performs well for low and medium transport regimes in both currents and waves. For those conditions, it yields a slight overprediction of the transports, and a nearly uniform behaviour as a function of the conditions. The formulation underestimates transport rates for very high flow velocities in absence of waves, which is in agreement with earlier findings. The present version of Bailard's wave averaged sediment transport formulation is suitable for computing the local transport rates of fine to coarse sand on continental shelves in conditions ranging from small currents to moderate currents combined with non-breaking waves. 相似文献
10.
本文通过对黄河三角洲埕岛海域146个表层样的粒度分析,表明该区有5种沉积物类型,以砂质粉砂为主体,呈斑块状分布,极细砂与粗粉砂是沉积物的主要粒级,普遍分选差。运用"粒径趋势"分析的方法,分析探讨了埕岛海域表层沉积物净输运趋势。研究区的沉积物的净输运趋势大致以12 m水深为界,深水区沉积物的净输运趋势向岸,12 m以浅海域的沉积物具有离岸的净输运趋势,说明深水区沉积物受冬季风浪作用向岸运移作用显著,12 m以浅海域的沉积物受夏季风浪作用离岸运移作用显著,沉积物运移的季节变化已成为研究区海域沉积物净运移的主要控制因素。 相似文献
11.
Several important mechanisms for storm-induced entrainment of estuarine cohesive sediments are analyzed using field measurements collected in a moderately energetic estuary, central Long Island Sound, U.S.A. The sediment concentration and hydrographic data were obtained by an array of sensors mounted at 1 m above the bottom. The bottom sediment in the study site composed mostly of silt and silty sand. The study showed that the bottom shear stress, computed using a wave-current interaction model, increased significantly during the episodic wind events. A large resuspension event was triggered by a frontal passage when strong wind-driven currents augmented the tidal currents. The timing of storm waves with respect to the tidal phase also was a critical factor. Based on the changes of suspended sediment concentration, the bottom appeared to respond to the shear stress in two phases: the tidal resuspension and the storm-induced erosion. During each tidal cycle, entrainment was associated with resuspension of high water content, loosely consolidated material. During episodic events, a thin layer of more consolidated bed below the sediment-water interface was eroded by the enhanced bottom stress. 相似文献
12.
Big Jemsa Bay is one of the indentations dissecting the continuity of the Red Sea north-western shoreline. The data was collected
from bathymetric survey, current meters and sediment samples. Analyses have been undertaken of coastal processes, seabed morphology,
grain size characteristics and the effect of current circulation on the distribution of sediment characteristics. The sediment
pattern varies from coarse sand in the southern part to silt and fine sand in the northern part. The central part of the study
area is mainly composed of terrigenous isometric-medium sand facies. The sorting distribution of sediments varies from moderately
well sorted to poorly sort. The significant factors that control the sediment transport process are downslope gravity and
wave-induced currents that are affected by the seafloor configuration and the shoreline orientation. According to the circulation
effect on the sediment transport of the study area where deposition of fine sand and silt was observed in the northern part.
Because sediment transport mitigates the occurrence of pollutant deposition in this part of the bay, we recommend that future
constructions along the bay should be in the southern part. 相似文献
13.
Experiments on silt incipient motion under wave action were carried out.Under wave action,for different wave periods,water depths and bulk densities of silt,the shear stress or height of waves for incipient motion was determined,and a relation between the shear stress and bulk density of silt was established.Results indicate that the critical shear stress depends on the structure of the silt itself,related to the tightness between the grains(or bulk density).Exterior condition is only an external cause of silt incipient motion,and the critical shear stress for the incipient motion is the token of exterior condition. 相似文献
14.
Rong Wang Boris K. Biskaborn Arne Ramisch Jian Ren Yongzhan Zhang Rainer Gersonde Bernhard Diekmann 《Geo-Marine Letters》2016,36(4):259-270
During expedition 202 aboard the RV Sonne in 2009, 39 seafloor surface sediment sites were sampled over a wide sector of the North Pacific and adjoining Bering Sea. The data served to infer land–ocean linkages of terrigenous sediment supply in terms of major sources and modes of sediment transport within an over-regional context. This is based on an integrated approach dealing with grain-size analysis, bulk mineralogy and clay mineralogy in combination with statistical data evaluation (end-member modelling of grain-size data, fuzzy cluster analysis of mineralogical data). The findings on clay mineralogy served to update those of earlier work extracted from the literature. Today, two processes of terrigenous sediment supply prevail in the study area: far-distance aeolian sediment supply to the pelagic North Pacific, and hemipelagic sediment dispersal from nearby land sources via ocean currents along the continental margins and island arcs. Aeolian particles show the finest grain sizes (clay and fine silt), whereas hemipelagic sediments have high abundances of coarse silt. Exposed sites on seamounts and the continental slope are partly swept by strong currents, leading to residual enrichment of fine sand. Four sediment sources can be distinguished on the basis of distinct index minerals revealed by statistical data analysis: dust plumes from central Asia (quartz, illite), altered materials from the volcanic regions of Kamchatka and the Aleutian Arc (smectite), detritus from the Alaskan Cordillera (chlorite, hornblende), and fluvial detritus from far-eastern Siberia and the Alaska mainland (quartz, feldspar, illite). These findings confirm those of former studies but considerably expand the geographic range of this suite of proxies as far south as 39°N in the open North Pacific. The present integrated methodological approach proved useful in identifying the major modern processes of terrigenous sediment supply to the study region. This aspect deserves attention in the selection of sediment core sites for future palaeoenvironmental reconstructions related to aeolian and glacial dynamics, as well as the recognition of palaeo-ocean circulation patterns in general. 相似文献
15.
We present several types of data which show that strong geostrophic bottom currents are present in a broad valley in the deep western Bay of Bengal adjacent to the Indian margin. Sea-floor photographs show well-developed current lineations with scour marks on the northern sides and sediment deposition tails on the southern sides of some objects (such as fecal pellets) suggesting strong southward-flowing bottom currents. A direct current measurement made in the region confirms this inferred flow direction. The nepheloid layer is much stronger in the western Bay of Bengal than in any other region of the northern Indian Ocean and indicates strong turbulence and a high concentration of suspended sediment at or near the sea floor. Additional data which do not provide unequivocal evidence for, but may also be indicative of, the existence of the bottom currents are as follows: the dispersal of the peninsular Indian rivers-derived smectite-rich sediments all along the valley to as far as south of Sri Lanka; a zone of sediment waves (as recorded on 3.5-kHz echograms) parallel to the regional trend of bathymetric contours along the Indian margin; and the frequent occurrence of thin, sharp and uniform layers of fine sand and silt beds rather than thick graded turbidite beds in the cores from the broad valley in the deep western Bay of Bengal. 相似文献
16.
Tide-driven bed load transport is an important portion of the net annual sediment transport rate in many shoreface and shelf environments. However, bed load transport under waves cannot be measured in the field and bed load transport by currents without waves is barely measurable, even in spring tidal conditions. There is, consequently, a strong lack of field data and validated models. The present field site was on the shoreface and inner shelf at 2 to 8.5 km offshore the central Dutch coast (far outside the surfzone), where tidal currents flow parallel to the coast. Bed load transports were carefully measured with a calibrated sampler in spring tidal conditions without waves at a water depth of 13–18 m with fine and medium sands. The near-bed flow was measured over nearly a year and used for integration to annual transport rates. An empirical bed load model was derived, which predicts bed load transports that are a factor of > 5 smaller than predicted by existing models. However, they agree with laboratory data of sand and gravel transport in currents near incipient motion. The damped transport rates may have been caused by cohesion of sediment or turbulence damping due to mud or biological activity. The annual bed load transport rate was calculated using a probability density function (pdf) derived from the near-bed current and orbital velocity data which represented the current and wave climate well when compared to 30 years of data from a nearby wave station. The effect of wave stirring was included in the transport calculations. The net bed load transport rate is a few m2/year. This is much less than predicted in an earlier model study, which is partly due to different bed load models but also due to the difference in velocity pdf. The annual transport rate is very sensitive to the probability of the largest current velocities. 相似文献
17.
波浪作用下大块石稳定性条件的研究,不仅是泥沙运动力学急待发展的内容之一,也是抛石工程合理化设计的重要问题。在收集大量国内外有关研究资料的基础上,分析了在波浪作用下大块石的受力状况,得出当大块石处于失稳临界状态时,其所受失稳应力与其自身有效容重和其当量直径乘积的比值是雷诺数、斯特鲁哈尔数及块石水下休止角的函数。为排除块石形状和块石间相互支撑形式不规则等干扰因素的影响,采用固定钢圈支撑孤立水泥砂球,在波浪槽中进行试验研究。根据试验资料,在斯特鲁哈尔数大于10的条件下,验证了当沙粒雷诺数达到105以后Shields曲线出现跳跃的事实。 相似文献
18.
通过黄河三角洲埕北海域表层沉积物的粒度资料、实测潮流数据以及50 a一遇的波浪要素,分析了埕北海域表层沉积物的分布类型以及粒度参数特征,并计算了表层沉积物的临界起动应力、日平均单宽输沙通量以及波流共同作用下的单宽推移质输沙率。结果表明:研究区表层沉积物主要是粉砂质砂、砂质粉砂、粉砂和泥四种,分选中等偏差,近对称到正偏,中等尖锐到尖锐峰态;对大潮期间埕北海域潮流底应力和表层沉积物的临界起动应力的计算说明潮流在大部分区域具有起动和输运泥沙的作用;秋季潮流作用下的日平均单宽输沙通量均值为372.32 kg/（m·d）,方向为涨潮流向。利用贝克尔（Bijker）和经典的Van Rijn公式计算出的50 a一遇的波流共同作用下单宽推移质日平均净输沙率结果近似相等。 相似文献
19.
20.
利用2014–2017年在台湾海峡西部采集的多波束、单道地震剖面、沉积物粒度样品及海流监测资料,在厦门湾近岸陆架区识别出一系列海底沙波,并对沙波的形态特征、分布规律和沉积物组成特征进行分析,探讨水动力条件及其对沙波发育的影响。结果表明沙波发育区水深一般为10~60 m,地形较平缓开阔,坡度一般为0°~1°;平面上沙波区呈一系列NW-SE向条带状坡地,波脊呈线性或新月形,波脊轴线为SW-NE方向,沙波波长为120~800 m,波高2~12 m,沙波指数较大(>30)。地震剖面显示,波形形态主要分为三类:近对称性沙波、非对称性沙波及叠合沙波。近对称性沙纹的波高较大,沙波指数小;非对称性沙波的波长较长,沙波指数大;稳定沙波经后期水流“改造、激活”形成叠合沙波。砂含量较高,沉积物类型以砂、粉砂质砂及砂质粉砂为主,多为细砂—中砂。厦门湾口外的近岸陆架区水动力较强,流系复杂,总体受浙闽沿岸流、南海表层流和黑潮分支的影响。本区为不正规半日潮,流速为0.3~0.7 m/s,落潮流以S向为主,涨潮流向以NNE向为主,潮流作用对沙波的发育和改造起重要影响。 相似文献