Dynamics of cobbles in the shoaling region of a surf zone

The motion of large bottom particles (cobbles/mines) was studied in the laboratory under simulated surf conditions. A series of experiments was conducted in a large wave tank, 32×0.9×1.8 m, equipped with a computer-controlled wave maker and a sloping beach. As a first step, a solid impermeable beach with artificial roughness was used in the experiments. Cobbles of different size were placed along the floor and their evolution with time was studied and compared with the model predictions. Onshore and offshore mean motions of cobbles, as well as steady oscillations with zero mean displacement, were observed for different conditions. To explain the results of observations a theoretical model was advanced. The model takes into account all main governing parameters (size and density of cobbles, bottom slope, dynamic and static friction at the bottom, background flow characteristics, etc.). Standard parameterizations were used for a pressure accelerating term, drag, lift and other nonlinear forces. For the range of parameters used in the experiments, satisfactory agreement between the measured and calculated values of the cobble displacements as a function of time was obtained. The model is practically insensitive to the vertical accelerating pressure term but sensitive to the dynamic and static friction. One of the most important variables in the model, which is known with the least accuracy, is the virtual mass coefficient for disk-shaped cobbles moving with variable velocity along a solid boundary.     

Large-scale experiments on beach profile evolution and surf and swash zone sediment transport induced by long waves,wave groups and random waves

New large-scale laboratory data are presented on the influence of long waves, bichromatic wave groups and random waves on sediment transport in the surf and swash zones. Physical model testing was performed in the large-scale CIEM wave flume at UPC, Barcelona, as part of the SUSCO (swash zone response under grouping storm conditions) experiment in the Hydralab III program (Vicinanza et al., 2010). Fourteen different wave conditions were used, encompassing monochromatic waves, bichromatic wave groups and random waves. The experiments were designed specifically to compare variations in beach profile evolution between monochromatic waves and unsteady waves with the same mean energy flux. Each test commenced with approximately the same initial profile. The monochromatic conditions were perturbed with free long waves, and then subsequently substituted with bichromatic wave groups with different bandwidth and with random waves with varying groupiness. Beach profile measurements were made at half-hourly and hourly intervals, from which net cross-shore transport rates were calculated for the different wave conditions. Pairs of experiments with slightly different bandwidth or wave grouping show very similar net cross-shore sediment transport patterns, giving high confidence to the data set. Consistent with recent small-scale experiments, the data clearly show that in comparison to monochromatic conditions the bichromatic wave groups reduce onshore transport during accretive conditions and increase offshore transport during erosive conditions. The random waves have a similar influence to the bichromatic wave groups, promoting offshore transport, in comparison to the monochromatic conditions. The data also indicate that the free long waves promote onshore transport, but the conclusions are more tentative as a result of a few errors in the test schedule and modifications to the setup which reduced testing time. The experiments suggest that the inclusion of long wave and wave group sediment transport is important for improved near-shore morphological modeling of cross-shore beach profile evolution, and they provide a very comprehensive and controlled series of tests for evaluating numerical models. It is suggested that the large change in the beach response between monochromatic conditions and wave group conditions is a result of the increased significant and maximum wave heights in the wave groups, as much as the presence of the forced and free long waves induced by the groupiness. The equilibrium state model concept can provide a heuristic explanation of the influence of the wave groups on the bulk beach profile response if their effective relative fall velocity is larger than that of monochromatic waves with the same incident energy flux.     

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...     

Morphodynamics and cobbles behavior in and near the surf zone

The evolution of an initially flat sandy slope and the dynamics of large objects (cobbles/mines) emplaced on it are studied in a laboratory wave tank under simulated surf conditions. Upon initiation of wave forcing, the initially flat beach undergoes bedform changes before reaching a quasi-steady morphology characterized by a system of sand ripples along the slope and a large bar near the break point. Although the incoming wave characteristics are held fixed, the bottom morphology never reaches a strict steady state, but rather slowly changes due to the migration of ripples and bar transformation. When the wave characteristics are changed, the bedform adjusts to a new quasi-steady state after a suitable adjustment time. Studies conducted by placing model cobbles/mines on the evolving sandy bottom subjected to wave forcing show four distinct scenarios: (i) periodic cobble oscillations with zero mean displacement and small scour around the cobbles, (ii) mean onshore motion of relatively light cobbles, (iii) periodic burial of relatively heavy cobbles when their sizes are comparable to those of sand ripples, and (iv) the burial of relatively large cobbles under the bar, when the bar migrates due to changes of incoming waves. Quantitative data on the characteristics and dynamics of the bedform, including ripple-formation front propagating down the slope, ripple growth and drift, and flow around ripples, are presented. Physical explanations are provided for the observations.     

黄河三角洲埕岛近岸海域悬浮泥沙运动

根据1998年9月8日和1999年3月19日两次对埕北海域进行的10个站位的同步海流、悬浮泥沙观测资料,进行该海区的悬浮泥沙输运趋势分析,发现该海区含沙量较大。从整个海区来看,底层含沙量大于表层含沙量,该海区泥沙含量普遍表现为东南部的泥沙含量高于西北部的泥沙含量;由单宽输沙量的计算及有关资料分析可以得出,秋季泥沙运移趋势是由东南向到西北向,而春季泥沙的运移趋势是由东北向到西南向;含沙量是随流速的加大而增加,含沙量的峰值稍滞后于流速的峰值;该海区为冲蚀海区,悬浮泥沙产生的平均年7中刷量为2cm／a,在本海区的地形塑造中占次要地位。     

从频域分析波动输运过程的时均通量

本文提出悬沙输运时均通量可在频域上用共谱密度函数表达。据此分析了长周期和12h,6h等潮周期波动分量对河口、潮汐通道及浅滩区悬沙净输运的重要贡献。文章还讨论了它们的形成机制和从频域上分解扩散系数的可能。     

东海混浊海域悬沙浓度的三维数值模拟及与观测的比较

借助ECOMSED模式进行了东海混浊水海域三维悬浮泥沙输运的数值模拟,其中水动力模拟中考虑了潮汐,海流（包括黑潮,长江径流等）及风场的作用,输运模型中考虑了粘性泥沙的絮凝、粘性和非粘性泥沙的再悬浮等过程。另外,在沉积输运模式中,增加了波浪的作用,使沉积输运模拟更完善,并与2006年8月份在长江口外海域获得的走航断面及定...     

A new formula for the total longshore sediment transport rate

A new predictive formula for the total longshore sediment transport (LST) rate was developed from principles of sediment transport physics assuming that breaking waves mobilize the sediment, which is subsequently moved by a mean current. Six high-quality data sets on hydrodynamics and sediment transport collected during both field and laboratory conditions were employed to evaluate the predictive capability of the new formula. The main parameter of the formula (a transport coefficient), which represents the efficiency of the waves in keeping sand grains in suspension, was expressed through a Dean number based on dimensional analysis. The new formula yields predictions that lie within a factor of 0.5 to 2 of the measured values for 62% of the data points, which is higher than other commonly employed formulas for the LST rate such as the CERC equation or the formulas developed by Inman–Bagnold and Kamphuis, respectively. The new formula is well suited for practical applications in coastal areas, as well as for numerical modeling of sediment transport and shoreline change in the nearshore.     

A simple method for calibrating optical backscatter sensors in high concentrations of non-cohesive sediments

A new method is introduced for calibrating optical backscatter sensors for suspended quartz sand concentrations of up to 200 kg m⁻³. Due to the high settling velocity of quartz sand in water, considerable difficulties have arisen in the past to maintain a spatially and temporally homogeneous suspension suitable for calibration. Traditional methods are clumsy and prone to errors. Here, the sediment is calibrated in glycerol, a clear fluid with a higher viscosity than water. The settling velocity is reduced by three orders of magnitude. An empirical relationship is obtained which is used to correct for any optical differences in response of the sensors in the two fluids. Any extra errors introduced by calibrating with a different fluid from that found in the field are outweighed by the simplicity and reliability of this method.     

旌式泥沙捕获器的研制和施测

介绍了旌式泥沙捕获器的研制，以及该仪器在破波带泥沙垂直分布、破波带泥沙搬运机制和海岸带泥沙输运速率和通量研究中的应用；详细描述了旌式泥沙捕获器在破波带泥沙观测中的安装和施测要点。     

Erosional and depositional patterns in the Valencia Channel mouth: An example of a modern channel-lobe transition zone

Recent deep-towed, high resolution sidescan sonar records and seismic profiles have been collected on the lower Valencia Fan (Northwestern Mediterranean). Three morphological zones, channelled, transition and unchannelled, have been recognized in the Valencia Channel mouth. Sonographs from the transition zone show a progresive transversal gradation from depositional to erosional bedforms. This asymmetry may be due to the lateral inputs of sediment flows from the rhone deep-sea fan and to the effect of the Coriolis force, which could have diverted the flows to the southwest. Bedforms recorded in the study area include trains of starved ripples and dunes, sand ribbons, and fields of elongated scours. Most morphological features, bedforms and seismic characteristics of the Valencia Channel mouth are typical of channel-lobe transition zones.     

长江河口最大浑浊带的悬沙输移特征

根据１９８８年洪、枯季在和长江口南、北槽进行的最大浑浊带专项水文观测的资料,对悬沙输移的分项因子进行研究。结果表明,长江口最大浑浊带的悬沙输移过程存在明显的潮泵效应及强烈的悬沙、底沙双向交换;长江口南、北槽之间存在一个大尺度的平面环向悬沙输移,同时南、北槽自身还有次一级尺度的槽内平面环向悬沙输移。本文还探讨了最大浑浊带与拦门浅滩相互影响、彼此制约的关系。     

Determination and control of longshore sediment transport: A case study

The fishery harbor of Karaburun coastal village is located at the south west coast of the Black Sea. The significant waves coming from north eastern direction cause considerable rate of sediment transport along 4 km sandy beach towards the fishery harbor in the region. The resulting sediment deposition near and inside the harbor entrance prevents the boat traffic and cause a vital problem for the harbor operations. In order to determine the level and reasons of the sediment transport, the long-term observations of shoreline changes, the long-term statistical analysis of wind and wave characteristics in the region, and sediment properties have been performed. The data obtained from observations, measurements and analysis were discussed. The long-term statistics of deep water significant wave heights for each direction was discussed by comparing the results obtained from different data sources and methods. For shoreline evolution, the numerical study using one-line model was applied to describe the shoreline changes with respect to probable wave conditions. Initial shoreline was obtained from the digitized image in 1996 since there was no previous shoreline measurement of the site. The results were compared using the techniques of remote sensing obtained from sequent images using IKONOS and IRS1C/D satellites.     

大沽河口悬浮泥沙遥感模式实验研究

河口悬浮泥沙反射率渡谱特性研究是悬浮泥沙遥感定量分析的基础工作。不同水域悬浮泥沙物质成份、粒径分布和浓度的不同,其相应的反射率波谱特性也有所差异。对此,国内外尚未建立起具有普适型的算法模式,用以处理不同水域的悬浮泥沙遥感问题。鉴于此,我们于1991年9月6～11日对胶州湾大沽河口区进行了现场悬浮泥沙波谱特性实验。由此建立了大沽河口悬浮泥沙落度SSC与陆地卫星TM_3和TM_4渡段相应的光谱反射率之间的数学模式。经过相关分析和误差分析的检验证明,由模式计算所得结果是令人满意的。     

南黄海海水中悬浮体分布的水动力因素统计分析

以1983年11月和1984年7月的南黄海中美沉积动力学联合调查的悬浮体原始资料为基础,同时结合南黄海水文气象资料,对该海域进行了悬浮体沉积动力学分区。通过对悬浮体含量与水文气象因素的统计分析,得知潮流因子是决定南黄海海水中悬浮体平面分布的主要相关因子,但冬季风暴对悬浮体含量的普遍提高具有决定性的影响,且风因子在冬季对悬浮体含量的提高在整个研究区内的表现并不均匀,它同其他扰动因子一起,在一定程度上破坏了海水中悬浮体含量与潮流之间的相关性。