Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China   总被引：2，自引：1，他引：2  

BAI  Yu-chuan 《中国海洋工程》2002,16(4):483-498

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   

ECOMSED模式在杭州湾海域流场模拟中的应用   总被引：13，自引：0，他引：13       下载免费PDF全文

堵盘军  胡克林  孔亚珍  丁平兴 《海洋学报》2007,29(1):7-16

针对杭州湾独特的喇叭型强潮河口湾的特点,基于Blumberg等(1996)的ECOMSED模式,引入动边界技术,建立杭州湾三维动边界的潮流模型.模型以正交曲线坐标下三维非线性水动力方程为基本方程,应用Mellor和Yamada的2.5阶湍流闭合模型计算紊动黏滞系数,嵌入Grant和Madsen的底边界层模型考虑波浪对底部应力的作用,采用干湿网格法模拟潮流漫滩过程;综合考虑径流,风应力,密度流和M₂,S₂,K₁,O₁四个主要分潮和M₄,S₄,MS₄三个浅水分潮的作用,从而提高杭州湾潮流模拟的精度.通过验潮站调和常数和多次海流连续观测资料的验证,表明该文建立的模型可以更好的用于杭州湾流场的预报模拟.  相似文献   

Seasonal and annual variations in the volumetric sediment balance of a macro-tidal salt marsh     

《Marine Geology》2006,225(1-4):103-127

This paper examines the spatial and temporal variability in the volumetric sediment balance of Allen Creek marsh, a macro-tidal salt marsh in the Bay of Fundy. The volumetric balance was determined as the balance of inputs of sediments and organic matter via accretion on the marsh surface and outputs of sedimentary material primarily due to erosion of the marsh margin. Changes in marsh surface elevation were measured at 20 buried plates and 3 modified sediment elevation tables from 1996–2002, and detailed margin surveys were conducted in 1997, 1999 and 2001 using a differential global positioning system. Changes in surface area were calculated using GIS overlay analysis and used in conjunction with accretion and erosion data to derive volumetric estimates of gains and losses of sedimentary material in the marsh system.Currently the volumetric sediment balance at Allen Creek marsh is positive. However the processes of erosion and accretion demonstrate seasonal, annual and spatial variability. Inputs to the system include deposition on the marsh surface from sediment laden waters and from ice rafting of sediments. Sediment is deposited onto the marsh surface year round, even during the winter when vegetation cover is sparse, and the amount of deposition in general is not significantly correlated with the frequency of tidal inundations. Based on the data from 1996 to 2002, the mid and high marsh zones experience mean accretion rates of approximately 1.4 cm year^− 1 whereas accretion rates in the low marsh region are statistically significantly lower (0.8 cm year^− 1). The absolute amount of accretion varies between seasons and from year to year. The main loss to the marsh is through erosion of the marsh margin cliffs which can remove a comparatively large volume of sedimentary material in one mass wasting event and which also decreases the vegetated surface area available for deposition from sediment laden waters. The volume of material removed from the marsh margin almost tripled between 1997 (169 m³) and 2001 (502 m³) following breaching of the side of a tidal creek channel, altering the patterns of margin erosion and deposition in the marsh system. During this time, however, other sheltered areas of the marsh system, such as along the tidal creek banks, showed evidence of new vegetation growth, increasing the amount of vegetated surface area available for deposition.The processes of erosion and deposition on the marsh surface exhibit considerable spatial variability, with different regions of the marsh being more or less sensitive to seasonal variability in the dominant controls influencing sediment deposition and erosion in this system, namely wave activity, vegetation, ice and water depths. A key factor in predicting how a marsh will evolve and respond to a number of different controls, e.g. sea-level rise or reduced sediment supply, is to quantify both accretion of the marsh surface and erosion of the marsh margin, evaluating the marsh system as a volumetric whole. This study demonstrates that a marsh system should be assessed in three dimensions rather than simply as a surface of accumulation. This is particularly important for open coastal marshes exposed to the erosive action of waves.  相似文献   

Bulk particulate organic carbon in the East China Sea: Tidal influence and bottom transport   总被引：4，自引：0，他引：4  

Zhuo Yi Zhu  Jing Zhang  Ying Wu 《Progress in Oceanography》2006,69(1):37-60

Five oceanographic surveys were carried out in the East China Sea (ECS) and Yellow Sea from 1999 to 2003. In all, seven different sections were surveyed, but one section (the PN section) was observed on every cruise. Two time-series stations were also surveyed, one located at the Changjiang River mouth, the other over the continental shelf in the PN section.We identified biogeochemical characteristics for waters close to the Changjiang Estuary and in the Kuroshio waters (KW), respectively. Resuspension is a strong feature near bottom over the ECS continental shelf, with suspended matter values 13 times higher than that for the surface. A model of particulate organic carbon (POC) dynamics based on a rectangle equation reveals that POC concentration close to the Changjiang Estuary varies with a semidiurnal period of ∼13 h, coinciding with the tidal period. The upper limit for POC residence times in the seasons we covered over the shelf are estimated to be on the order of weeks and generally increase seaward from near the Changjiang Estuary to the KW. Short POC residence times suggest that POC in the ECS is rapidly exported from euphotic waters.A nepheloid layer, observed as elevated suspended matter in near the bottom of the water column, is important in particle transfer over the shelf, especially in winter when the residual current flows mainly eastward. Cross-shelf transport of POC via the nepheloid layer is estimated to be 0.22 × 10¹² g yr⁻¹. Comparison with other work indicates that POC transport is ∼2% of the Changjiang POC input.  相似文献   

Problems with biogenic silica measurement in marginal seas   总被引：5，自引：0，他引：5  

S.M Liu  X.W YeJ Zhang  Y.F Zhao 《Marine Geology》2002,192(4):383-392

Surface sediment samples from the Bohai, Yellow Sea, and the Pacific were used to assess biogenic silica (BSi) content and to study uncertainties in BSi measurements. The contents of BSi in the Bohai and Yellow Sea are all less than 1%. The dissolution of BSi in sediments from the Bohai and Yellow Sea is very important to maintain high levels of silicate in the water column. The non-biogenic silica from clay minerals has an obvious effect on BSi of sediment samples in the Bohai and Yellow Sea with low BSi and high clay minerals. The solid to solution ratio was found to have a great influence on BSi measurement, which can induce uncertainties up to 75%. The effect of loss by sorption and centrifugation is negligible. Interlaboratory comparison of techniques for BSi measurement by the wet alkaline extraction technique of Mortlock and Froelich [Deep-Sea Res. 36 (1989) 1415-1426] with clay correction was suggested to give no significant differences. However, differences in sediment compositions and reagent to sample ratio may limit the application of the wet alkaline extraction method.  相似文献   

In-Situ Observation of Fluid Mud in the North Passage of Yangtze Estuary, China   总被引：1，自引：0，他引：1  

李九发  万新宁何青应铭  时连强S.M.Hutchinson 《中国海洋工程》2004,18(1):149-156

Observations of fluid mud were made in the lower North Passage of the Yangtze Estuary in February 2000, on 10 -11 August 2000, on 30 - 31 August 2000 (after two strong typhoons), on 21 - 24 August 2000 (neap tide) and on 3 -6 September 2000 (mean tide) respectively. In situ data show that the fluid mud in this area consists of fine cohesive sediment (median size 7.23 μm). The formation and movement of fluid mud varied during the neap-spring and flood-ebb tidal cycle. Observations suggest that fluid mud phenomena in this area may be categorised in a three-fold manner as slack water, storm and saltwedge features. The thickness of the fluid mud layer of slack water during the neap tide ranged from 0.2 to 0.96 m, whereas during the mean tide, the thickness ranged from 0.17 to 0.73 m, and the thickness of the fluid mud layer was larger during slack water than at the flood peak. Shoals cover an area of 800 km^2 with a water depth smaller than 5 m. Erosion of these extensive intertidal mudflats due to storm action provides an abundant sediment source. This is particularly significant in this estuary when the tidal level is lower than 5 m. The lower North Passage is a typical zone of saltwater wedging, so the saltwedge fluid mud has the most extensive spatial range in the estuary.  相似文献   

长江口拦门沙地区的泥沙运动规律   总被引：12，自引：0，他引：12  

潘定安  孙介民 《海洋与湖沼》1996,27(3):279-286

依据１９８８年７月和１２月水文观测资料，通过流，盐，沙的综合分析，认识到长江口拦门沙地区的泥沙运动有与河口其他地区不同的特点，泥沙输移在水平面上和垂直面上存在着多种循环，潮流和盐水截留大量泥沙积聚的拦门沙地区，河口在盐淡水交锋地带，除了涨，落急时段外，发现在转流时期泥沙也可能产生再悬浮，从而形成一个潮周期中出现３次或４次再悬浮的特殊规律。  相似文献   

GIS支持下的长江口拦门沙泥沙冲淤定量计算   总被引：23，自引：4，他引：23  

吴华林  沈焕庭  胡辉  张莉莉  黄清辉 《海洋学报》2002,24(2):84-93

依据1842～1997年10幅不同年代的长江口海图资料,利用地理信息系统和数字化仪进行处理,建立不同时期的长江口水下数字高程模型,以此作为基础资料,实现了从横剖面、深泓线纵剖面、平面变化等不同角度对长江口拦门沙地区滩槽演变、岸线侵蚀、沙岛形成与变迁等进行研究.通过计算河槽容积,实现了对不同时段泥沙冲淤量的计算.结果表明,155a来拦门沙总的趋势是不断淤积,但不同时期淤积速度大不一样,个别时期甚至会发生一定程度的冲刷,这主要与动力条件的波动有关.1842～1997年,共淤积泥沙38.10亿t,平均每年淤积0.246亿t,约占长江来沙的5%,年均淤厚为1.1cm泥沙淤积部位主要在九段沙、横沙及横沙东滩、崇明东滩三处.发生冲刷的范围较小,仅占总面积的21.4%,主要在北槽,北港上段和南槽局部也有轻微的冲刷发生.  相似文献   

长江口徐六泾悬浮细颗粒泥沙絮凝体特性   总被引：5，自引：1，他引：5       下载免费PDF全文

程江  何青  夏小明 《海洋与湖沼》2007,38(4):304-313

2003年6月14日-22日, 利用现场激光粒度仪LISST-100在不扰动颗粒物的情况下, 于长江口徐六泾定点连续观测了洪季大、小潮表层粘性悬浮细颗粒泥沙絮凝体的实有粒径、体积浓度, 配合OBS-3A现场测量的悬沙浓度计算了现场絮凝体的有效密度和静水沉速.观测结果显示, 徐六泾大、小潮表层絮凝体体积浓度、粒径、有效密度和静水沉速的平均值分别为98.0 μl/L、39.8 μm、1173 kg/m^3、1.14 mm/s和70.8 μl/L、64.4 μm、919 kg/m^3、2.32 mm/s.研究表明： ①长江口徐六泾表层絮凝体体积浓度主要受水流流速影响, 再悬浮现象明显, 体积浓度过程线滞后流速过程线, 落潮期间滞后10-30 min, 涨潮则滞后30-50 min; ②小于一定流速时絮凝体平均粒径随流速增大而增大, 大于一定流速时絮凝体平均粒径则随流速增大而减小, 徐六泾大、小潮表层絮凝体在50 cm/s的垂线平均流速时出现平均粒径与垂线平均流速关系的转折; ③徐六泾大、小潮表层絮凝体平均粒径在体积浓度75 μl/L时出现平均粒径与体积浓度关系的转折, 体积浓度小于75 μl/L时粒径随体积浓度增加而增大, 超过75 μl/L时粒径随体积浓度的增加变化不明显; ④絮凝体有效密度由粒径大小控制, 粒径大, 有效密度小, 反之亦然, 粒径和有效密度共同决定絮凝体静水沉速, 有效密度和沉速与平均粒径之间均存在良好的幂指数关系.  相似文献   

日本沼虾染色体及其核型的研究   总被引：23，自引：0，他引：23  

邱高峰  堵南山  赖伟 《海洋与湖沼》1994,25(5):493-498

于１９９２年３月在上海青县采集日本沼虾，以改进的空气干燥法研究精巢细胞染色体及核型，特别较详细地研究了减数分裂前期Ｉ染色体的行为。结果表明，日本沼虾染色体数ｎ＝５３，２ｎ＝１０４，共分为Ａ，Ｂ，Ｃ，Ｄ４个染色体组；核型组成是Ｎ＝３７Ｍ＋４ＳＴ＋１１Ｔ；初级精母细胞减数分裂前期Ｉ可分为细线期／偶线期，粗线期、双线期和终变期５个时期，双线期的二价体存在弥散阶段，减数分裂的同步率高，大多处于双线期，且双  相似文献