Seasonal variation of suspended-sediment transport through the southern Bohai Strait

Based on field observations made in winter 2006 and summer 2007 and on multiscene MODerate resolution Imaging Spectrometer (MODIS) imagery, the seasonal variation of suspended-sediment transport in the southern Bohai Strait and its possible mechanisms are examined. The field observations in two different seasons allow an exponential empirical model to be used to retrieve suspended-sediment concentration (SSC) from MODIS imagery. Both the field-survey data and the MODIS-derived SSC show that the sediment transport in the southern Bohai Strait has a significant seasonal variation due to the seasonally varying thermohaline structure of the water column and the hydrodynamics resulting from the seasonally alternating monsoons. The SSC in winter is approximately 3–10 times higher than in summer. Considering the seasonal variation of water flux (WF) and SSC, the annual sediment flux (SSF) through the southern Bohai Strait is estimated to be approximately 40.0 Mt yr⁻¹, about 4–8 times previous estimates, which did not take into account seasonal variation. Although the Huanghe (Yellow River) discharges a large amount of sediment in the summer, the SSF through the southern Bohai Strait in the winter (∼32.0 Mt) is about 4 times greater than it is in the summer. The strong seasonal variability of SSF through the southern Bohai Strait indicates that strong resuspension along the coast of the Huanghe delta in winter and enhanced longshore transport by coastal currents due to winter monsoon activity might be the major mechanisms of cross-strait transport of sediment in winter.     

On the criteria for the initiation of motion in tidal inlets,deterministic and stochastic approaches

Details are given herein of the refinement and application of a three-dimensional layer integrated numerical model to predict morphological changes in tidal basins. The solution of governing differential equations, which consist of the conservation of mass and momentum for the hydrodynamics, the transport equation for the suspended sediment fluxes and the sediment mass conservation equation for the bed level changes are carried out by the use of Alternating Direction Implicit (ADI) Finite Difference Method (FDM). The model includes different criteria for the initiation of motion namely Shields (1936, Application of Similarity Principles and Turbulence Research to Bed load Movement, Hydrodynamics Laboratory, California Institute of Technology, Pub. No. 167), Kolahdoozan (1999, Numerical Modelling of Geomorphological Processes in Estuarine Waters, PhD Thesis, Department of Civil and Environmental Engineering, University of Bradford, Bradford, UK, 288) and Zanke (2003, On the Influence of Turbulence on the Initiation of Sediment Motion, International Journal of Sediment Research, 18(1), 17–31), to compare different aspects of flow conditions. As the flow is highly turbulent with the random nature of its components, many researchers have tried to express sediment transport processes by using stochastic approaches. In the current study both deterministic and stochastic methods are included in the numerical model to evaluate their accuracy and efficiency. To validate the numerical model results, laboratory measurements are used, with these being obtained from an earlier experimental program undertaken by the authors. Results of a short term bed level changes in a laboratory model harbor are included for the model verification purposes. Comparisons are undertaken using different criteria for the initiation of motion, with the results highlighting that the unsteadiness in the flow parameters included in the numerical model has a major effect on the bed level changes inside the harbor, in compare with the turbulence structure of the flow. The model is then applied to a real case study of the Humber Estuary, located in the UK, with comparisons being undertaken for different criteria for the initiation of motion, using both deterministic and stochastic approaches for the long term bed level predictions.     

放射性废物处置研究进展

放射性废物的处置是制约核能可持续发展的关键因素,目前已成为国际社会关注的热点问题之一.针对处置场地核素运移污染的风险问题,对放射性废物的处置及其选址、核素运移试验和核素运移模型进行了回顾和论述.指出采用多重屏障系统进行放射性废物的处置,其安全性是可以得到保障的;处置场的选址应遵循就近原则,并应从环境水文地质的角度来构建...     

River adjustment to changes in sediment load: The effects of tin mining on the Ringarooma River,Tasmania, 1875–1984

The mining of alluvial tin in the Ringarooma basin began in 1875, reached a peak in 1900–20, and had virtually ceased by 1982. During that time 40 million m³ of mining waste were supplied to the main river, quickly replacing the natural bed material and requiring major adjustments to the channel. Based on estimates of sediment supply from more than 50 widely scattered mines and the frequency of flows capable of transporting the introduced load, the river's transport history is reconstructed using a mass-conservation model. Because of the lengthy time period (110 years) and river distance (75 km) involved, the model cannot predict detailed change but it does reproduce the main pattern of sediment movement in which successive phases of aggradation and degradation progress downstream. Peak storage is predicted in that part of the river where braiding and anastomosis are best developed. Aggradation was most rapid in the upper reaches close to major supply points, becoming slower and later with distance downstream. Channel width increased by up to 300 per cent where the valley floor was broad and braiding became relatively common. Bridges had frequently to be replaced. While bed levels were still rising in lower reaches, degradation began in upper ones, notably after 1950, and by 1984 had progressed downriver over 30 km. Rates of incision reached 0·5 m yr^?1, especially in the early 1970s when record high flows occurred. As a result of degradation the bed material became gravelly through either reexposure of the original bed or lag concentration of coarser fractions. Also a narrower unbraided channel has developed. The river is beginning to heal itself and upper reaches now have reasonably stable beds but at least another 50 years will be required for the river to cleanse its channel of mining debris.     

Use of deuterated water as a conservative artificial groundwater tracer

Conservative tracers are necessary to obtain groundwater transport velocities at the field scale. Deuterated water is an effective tracer for this purpose due to its similarity to water, chemical stability, non-reactivity, ease of handling and sampling, relatively neutral buoyancy, and reasonable price. Reliable detection limits of 0.1 mg deuterium/L may be obtained in field tests. A field example is presented in which deuterated water, bromide, and pentafluorobenzoic acid are used as groundwater tracers. Deuterated water appeared to be transported conservatively, producing almost identical breakthrough curves as that of other soluble tracers. Electronic Publication     

日照帆船港工程泥沙运移物模试验研究

通过动床波浪输沙模型试验,研究了日照帆船港3种设计方案的泥沙运移情况.通过分析试验结果,预报了常浪和大浪作用下工程区的冲淤分布.结果表明,日照帆船港工程的建设不会对邻近海岸产生大的影响,航道和港池均不会出现大的淤积.但是,为防止堤脚冲刷,应在挡沙坝堤脚处设置护脚结构.     

时间矩在地下水相关参数确定中的应用

应用矩分析方法定量分析示踪剂数据需要一系列严格的步骤,包括数据标准化,浓度衰减的校正,去卷积,外推和积分。正确的分析,可以得出示踪剂扫描孔隙体积、流体几何和流体速度等场地的特殊信息,有助于了解库区边界的特征。通过实例分析,结果表明：采用时间矩方法确定地下水有关参数时,效果良好。     

大陆深部地壳物质成分识别方法综述

本文系统总结了大陆深部地壳物质成分识别研究方法和元素丰度合理性检验的方法,以期为大陆深部地壳物质成分探测提供技术方法体系。深部地壳物质成分识别的主要方法有:①因构造运动抬升出露到地表的中下地壳剖面;②地表出露的高级变质地体;③产于火山岩中的深部地壳捕掳体,如麻粒岩捕掳体;④地球物理测深资料与深部岩石物理性质的高温高压实验测定结果之间的拟合和⑤壳源岩浆岩源区地球化学示踪。元素丰度合理性检验的方法主要有地表热流和元素比值法。     

台湾海峡西南部海域春季悬浮体及沉积物来源与输运机制

台湾海峡作为连接东海和南海的重要通道,其悬浮体和沉积物的来源和输运格局非常复杂。2005年4~5月利用带有浊度传感器和荧光传感器的SD204型CTD对台湾海峡西南部海域627个站位的悬浮体特性进行了综合调查,并采集了底层沉积物。在室内分别利用英国Marlvern公司生产的Mastersizer 2000型激光粒度仪和德国ELEMENTOR公司生产的ELEMENTOR varioELIII型元素分析仪对表层沉积物进行了粒度分析和沉积物碳、氮含量测定,结果表明,台湾海峡西南部海域春季受粤东沿岸流、韩江冲淡水、九龙江冲淡水及台湾海峡混合水影响,其中粤东沿岸流在向北输运过程中影响强度逐渐减弱,韩江冲淡水影响范围较大,并且在西南季风的控制下向东北方向输运;长时间尺度的沉积物输运格局表明,近岸沉积物由岸向海输运,远海地区沉积物由海向岸输运,并且在汕尾南部海域、南澳岛东南部海域形成了沉积物的汇聚区,沉积物以陆源为主;表层沉积物的输运过程受控于区域内水团、悬浮体分布及运动格局;在春季上升流形成早期尽管叶绿素荧光值相对较低,但其对表层沉积物的输运过程起着非常重要的控制作用。     

Transfort of oxygen,nutrients and carbonates by the Kuroshio Current

Measured concentrations of dissolved oxygen, phosphate, silicate, total alkalinity and calculated total CO₂ in a section between 121° E and 125° E across the Kuroshio near 22° N off Taiwan and the geostrophic velocity were used to estimate the gross transport of oxygen, nutrients and carbonates. The flux of dissolved oxygen is 6.7×10⁶ mol/s northward and 0.9×10⁶ mol/s southward. The net flux equals 5.8×10⁶ mol/s down-stream. The northward flux of phosphate is 22.6×10³ mol/s; the southward flux is 1.4×10³ mol/s. The net phosphate flux is 21.2×10³ mol/s northward. The flux of silicate is 967×10³ northward and 59×10³ mol/s southward; the net transport is 908×10³ mol/s down-stream. The flux of alkalinity is 75.5×10⁶ mol/s northward, and 10.8×10⁶ mol/s southward, the net flux is 64.7×10⁶ mol/s northward. For total CO₂ the transport is 73.4×10⁶ mol/s northward and 10.8×10⁶ mol/s southward, or a net transport of 62.6×10⁶ mol/s horthward.