DRY-SEASON VARIABILITY IN SUSPENDED SEDIMENT CONCENTRATIONS IN THE SOUTH PASSAGE OF THE CHANGJIANG ESTUARY

This paper reports the results of continuous monitoring of turbidity, water depth, salinity (using an Optical Backscatter Sensor (OBS)), and current velocity (using a Current meter (SLC9-2)) in the South Passage of the Changjiang Estuary over a spring–neap period in February 2003 (dry season). The turbidity measured via OBS was closely correlated with the suspended sediment concentration (SSC), which was highly variable. Over the study period, the SSC in the middle layer ranged from 110 to 1400 mg/l. The minimum SSC occurred during a late ebb tide, and the maximum SSC occurred during a late flood tide. On average, the SSC was 1.5 times higher during flood tide than during ebb tide. Vertically within the water column, SSC increased downward, with the ratio of SSC measured near the bed to that measured at the surface ranging from 1.90 to 18.3. The temporal variability in SSC is jointly governed by tides and wind-induced waves, whereas the vertical variability in SSC is attributed to the effect of gravity and vertical water circulation.     

The evolution of the Dutch and Belgian coasts and the role of sand supply from the North Sea

During the Holocene, the Dutch and Belgian coasts evolved, controlled by post-glacial eustatic sea-level rise, spatially varying vertical subsurface motions (glacio-isostatic crustal rebound, compaction, tectonics) and spatially varying sediment supply (mainly marine sand). The marine sand supply changed as the tidal dynamics and the wave climate changed due to the changing geometry and depth of the North Sea during the Holocene transgression. These changes influenced the coastal evolution. This study compares the results of separate numerical model calculations of the large-scale Holocene tide- and wave-induced sand transport in the southern North Sea with existing geological data of the Dutch and Belgian large-scale coastal evolution, resulting in a qualitatively good correlation. The large-scale coastal evolution is interpreted in terms of the oceanographical forcing, and an integrated conceptual model of the Holocene evolution of the Dutch and Belgian coasts is proposed. The large-scale wave-driven bed-load transport was an order of magnitude smaller than the tidal transports. The modelled tidal transport direction changed from onshore before 6 ka BP to along shore at present for the Zeeland and Holland coasts; the influence that waves may have had on the tidal transport by suspending sand gradually decreased. This change in direction caused the modelled tidal sand supply to the coast to decrease for the Belgian, Zeeland and Holland coasts. While the offshore area of the Holland coast remained a zone of (small) deposition due to decreasing northward sand transports, the offshore area of the Zeeland coast became increasingly erosional after 6 ka BP due to the encroaching divergence of the tidal transports. Due to uncertainty in the magnitude of the modelled sand transports, but robustness in the transport patterns, the focus is on the qualitative rather than the quantitative model results. When compared with the trend of closure, expansion and later erosion and reopening of the coast, the above decrease in sand supply must have been slow enough compared with the decrease in sea-level rise to cause a temporary sand surplus which decayed to a slight deficit as the decrease in supply and the rise in sea level continued. The Wadden Sea coast exchanged little or no sand with the adjacent deeper North Sea throughout the Holocene.     

原子吸收光谱法测定土壤和水系沉积物中的银

样品经四酸分解,1％的硝酸提取,2％硫脲定溶。石墨炉原子吸收测定样品中的银,方法检出限0．014ug/g,精密度（RSD,n=6）4％～16％;回收率为96％～104％。方法经国家一级标准物质验证,测定结果与标准值相符。     

SEDIMENT TRANSPORT IN THE YANGTZE RIVER ESTUARY

SEDIMENT TRANSPORT IN TIIE YANGTZE RIVER ESTUARYSHEN Zhigang'ANSTa^CTThe hy~ntalc and the sedimen tranSport Patter'nS within the estUaIy of the YangtZe mver arecomPlex because of intemehon of fluvial and the hdal forCes, depending on freshwate discharge andhdal range. Based on the data measuIed in meent years, thes papo discusses the characterishcs of flowand sNnt movemen in the tw forer EstUaIy and their iIifluences on the evolution of theestuaryKey W: YangtZe mver…     

EVOLUTIONAL CHARACTERISTICS OF HYPER－CONCENTRATED FLOW IN BRAIDED CHANNEL OF THE YELLOW RIVER

ＥＶＯＬＵＴＩＯＮＡＬＣＨＡＲＡＣＴＥＲＩＳＴＩＣＳＯＦＨＹＰＥＲ－ＣＯＮＣＥＮＴＲＡＴＥＤＦＬＯＷＩＮＢＲＡＩＤＥＤＣＨＡＮＮＥＬＯＦＴＨＥＹＥＬＬＯＷＲＩＶＥＲ￥ＱＩＰｕ；ＬＩＷｅｎｘｕｅ（Ｓｅｎｉｏｒｅｎｇｉｎｅｅｒ，ＩｎｓｔｉｔｕｔｅｏｆＨｙ...     

清水沟北汊流路入海泥沙对东营港影响的数值分析

本文用平面二维潮流泥沙数学模型,模拟了清水沟流路北汊入海口海域的潮流泥沙扩散和河口淤积延伸方向等问题。在此基础上从流速场分布,泥沙扩散浓度分布及淤积厚度零米线的范围及河口淤积延伸方向等方面探讨了入海泥沙对东营港的影响。结论认为如果按此口门入海,入海泥沙不会对黄河海港产生直接淤积影响。     

莱州湾东岸三山岛段砂质海岸沉积物运移动力机制

通过对三山岛岸段冬夏重复的地形测量和表层沉积物的粒度分析,研究了其地貌特征与地形变化规律、沉积物类型、粒度特征、运移趋势,并探讨了沉积物运移的动力机制。结果表明:该岸段可根据1985黄海高程-1.2m(低潮水位)和-6.5m(闭合深度)平面划分为海滩、水下岸坡和浅海陆架三个地貌单元,各地貌单元表层沉积物分布规律与地形变化特征区别显著。其中水下岸坡和浅海陆架地貌单元主要受潮流作用,海滩地貌单元主要受波浪作用。在西向落潮流和西南向潮余流的作用下,水下岸坡地貌单元发育一个中等规模潮流通道-沙脊沉积系统。表层沉积物以向西运移的趋势为主,少数滞留于西部潮流沙脊处,与地形"东侵西淤"的变化规律相符,这些西向运移的沉积物最终离开研究区,补给莱州浅滩。     

Hydraulics of sediment-laden sheetflow and the influence of simulated rainfall

Laminar sheetflows, transporting sediment at their capacity rates, both with and without rainfall disturbance, were investigated. Values of flow depth and relative submergence were very small. In the flows without rainfall, measured velocities exceeded the predictions of the smooth-surface, clear-water laminar model by an average of 12 per cent. Reduced flow resistance due to high sediment concentrations may explain this result. Velocities in the rainfall-disturbed flows were not significantly different from the predictions of the smooth-surface, clear-water model, and the velocity reduction due to rainfall was about 12 per cent. Although the uniformity of rainfall intensity under the single-nozzle rainfall simulator is high, variation of momentum and kinetic energy fluxes along the 1-5 m long flume was significant. The rainfall angle of incidence was highly correlated with deviations from expected flow velocities in the upper and lower sections of the flume.     

Structure,composition and bulk properties of upland stream gravels

Upland gravel-bedded streams in the U.K. have received only scant attention from both hydrologists and sedimentologists, but are worthy of further investigation. The sedimentology of three small streams in Teesdale in the Pennines has been examined in detail. Grain-size characteristics, bedforms, structure, composition and packing characteristics of these deposits are described, and compared where appropriate with published information. It is argued that a fuller appreciation of gravel bed composition and morphology should eventually contribute to an improved understanding of sediment transport and deposition mechanisms, and, hence, to improved accuracy in sediment transport and deposition estimates.     

Characteristics and Influence of Phosphorus Accumulated in the Bed Sediments of a Stream Located in an Agricultural Watershed

We investigated the accumulation and influence of bioavailable P (BAP) in sediments of a stream located in an agricultural area of the Lake Mendota watershed in Wisconsin, USA. During hydrologic events, the stream carried high concentrations of suspended sediment (up to 250 mg/l) and BAP (up to 2.5 mg/l). Bed sediments were highly enriched in BAP, as inventories of BAP in the top 10 cm of sediment ranged from 143 to 14,500 μg P/cm². Space variations in BAP inventories were related to site-specific hydrodynamics and geochemical factors, including iron (Fe; r ² = 0.71) and aluminum (Al; r ² = 0.54) concentrations. Most sites behaved as potential sinks for dissolved reactive phosphate during hydrologic events and potential sources during base-flow periods. Through the combination of site-specific factors and geochemical controls, Dorn Creek modifies the amount, timing, and composition of P delivered from the watershed to downstream sites and water bodies.