Analytical Study of Longitudinal Mass Flux Due to the Shear Effect in a Tidal Basin     

Hidekazu Yasuda 《Journal of Oceanography》2004,60(3):587-596

The fundamental nature of the mass flux due to the shear effect is examined analytically in a basin with steady and oscillatory currents to promote a better understanding of the mass transport process in coastal waters. The currents are given from solutions of the simplified motion equation so as to be consistent with the diffusion equation. The matter concentration used is given by an analytical solution of the diffusion equation with the settling flux term contained. Mass flux, yielding the depth-averaged dispersion coefficient, is rather varied vertically in both steady and oscillatory currents. In the oscillatory current with a Stokes layer in particular, the vertical profile of flux is more complicated and even negative flux is induced near the basin floor. This negative flux does not necessarily yield a negative value of the vertically averaged dispersion coefficient. The exact dispersion coefficient given by the flux analysis is realized only in the steady state of the matter concentration distribution, though we can scarcely observe the steady state in the actual sea. The vertically uniform longitudinal dispersion coefficient at the stationary stage is shown to be caused from the vertical complexity of mass flux by the action of the vertical diffusing and the settling flux. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

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

Tony Butt  Jon MilesPeter Ganderton  Paul Russell 《Marine Geology》2002,192(4):419-424

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.  相似文献   

Contrasts in sedimentation flux below the southern California Current in late 1996 and during the El Niño event of 1997–1998     

Norman Silverberg  Aida Martínez  Sergio Aguíiga  Jos D. Carriquiry  Nancy Romero  Evgeni Shumilin  Soledad Cota 《Estuarine, Coastal and Shelf Science》2004,59(4):575-587

The vertical flux of particulate matter at 330 m depth in San Lázaro Basin off southern Baja California ranged from 63 to 587 mg m⁻² d⁻¹ between August and November 1996. Organic carbon contents were between 5.6 and 14.8%, yielding flux rates of 9–40 mgC m⁻² d⁻¹. In December 1997 and January 1998, at the height of the strong El Niño event, the respective fluxes (47–202 mg m⁻² d⁻¹ and 3–8 mgC m⁻² d⁻¹) were comparable. The February–June 1998 records, however, revealed sharply reduced mass (1–6 mg m⁻² d⁻¹) and organic carbon (0.2–0.8 mgC m⁻² d⁻¹) fluxes. The organics collected in 1996 were predominantly autochthonous (δ¹³C=−22‰; C/N=8). The variations in δ¹⁵N (8.3–11.0‰) suggest an alternation of new and regenerated production, possibly associated with fluctuations in the intensity of deep mixing during that autumn. The relatively high organic matter fluxes in December 1997 appear to be associated with regenerated production. The average composition from February to June 1998 (δ¹³C=−23.6‰; ¹⁵N=11.7‰; C/N=10.5) indicates degraded material of marine origin. The maximum δ¹⁵N value found (14‰) suggests that deeper, denitrified waters were brought to the surface and possibly advected laterally. Regime changes in the waters of the basin occur at 6–10 week intervals, evidenced by concurrent shifts in most of the measured parameters, including fecal pellet types and metal chemistry. The marine snow-dominated detritus collected showed a shift from a mixed diatom-rich-radiolarian-coccolith assemblage in late 1996 to a coccolith-dominated assemblage, including the contents of fecal pellets, during the 1997–1998 El-Niño period. T–S profiles, plankton analysis and chlorophyll contents of the upper water column indicated that the strong phytoplankton bloom, normally associated with seasonal upwelling along the Pacific coast of Baja, did not occur during the spring of 1998. The persistence of oligotrophic conditions during the 1997–1998 El Niño event favored the dominance of nanoplankton and reduced the vertical flux of particles.  相似文献   

考虑桩身压缩的综合系数法计算超长桩基础沉降   总被引：1，自引：0，他引：1  

张忠苗  杨淼  房凯 《岩土力学》2012,33(3):793-798

实测表明,超长桩基础的桩身压缩量占总沉降量很大比例,因此,等代墩基法刚性体的假定不符合实际,需要一种考虑桩身压缩量的方法来计算超长桩基础沉降。通过对现有超长桩实测数据的分析,得到了嵌岩桩桩身压缩系数拟合方程,同时得出了非嵌岩桩桩身压缩系数约为0.5;推出桩侧沉降比和桩端沉降比,并编制了Matlab计算程序。最后通过工程实例计算考虑桩身压缩的超长桩基础沉降,计算结果与实测结果相吻合。  相似文献   

不同光强下小球藻纵向沉降及悬浮特性研究     

卢金锁  张博  张旭 《海洋科学》2013,37(9):54-60

通过用自制沉降柱研究小球藻(Chlorella vulgaris)在表层不同光强作用下纵向沉降特性以及分布规律, 为进一步了解水库中小球藻的纵向分布提供参考。实验室培养的小球藻按其直径可分为小于4.5 μm、4.5～5.5 μm、大于5.5 μm 3 个等级, 不同粒径的小球藻在不同光强的作用下沉速不同; 实验条件下小球藻的沉速分布在0.1～468.2 μm/s, 均值为32.8 μm/s; 小球藻的沉降速度随沉降柱表层光强增强而降低, 无光状态下时沉速是表层光强为10 000 lx 的2～3 倍; 小球藻直径大小与沉速呈正相关, 直径4.5～5.5 μm 的小球藻沉速是3.5～4.5 μm 的5~6 倍; 沉降稳定后实验柱中小球藻从表层至底层粒径逐渐变大, 除底层外小球藻在纵向峰值随光强增加而向下延伸, 如实验柱表层光强为1 000 lx 和4 000 lx时小球藻峰值出现实验柱表层, 而表层光强为7 000 lx 和10 000 lx 的实验峰值分别出现在水下300 mm和600 mm 处。  相似文献   

Using a Lagrangian model to estimate source regions of particles in sediment traps     

ZhongFeng Qiu  A. M. Doglioli  F. Carlotti 《中国科学:地球科学(英文版)》2014,57(10):2447-2456

A Lagrangian model is used to evaluate source regions of particles collected in the sediment traps at the DYFAMED(Dynamique des Flux Atmosphériques en Méditerranée) station by tracking particles backwards from March 1 to August 31, 2001. The analysis suggests that source regions depend on the flow fields, the settling speed of the particles, and the deployment depths of the traps. Monthly variation is observed in the distribution patterns of source regions, which is caused by the currents. The source regions are located around the traps and up to hundreds of kilometers away. As the settling speed increases with the particle diameters, the distance to the source regions decreases. The vertical flux can be approximately estimated in 1D for the particles with diameters larger than 500 μm. Furthermore, traps moored at various depths at the DYFAMED can collect particles that originated from different regions in the Ligurian Sea.  相似文献   

Modelling suspended sediment concentration and load in a transport‐limited alluvial gully in northern Queensland,Australia          下载免费PDF全文

Calvin W. Rose  Jeffrey G. Shellberg  Andrew P. Brooks 《地球表面变化过程与地形》2015,40(10):1291-1303

Alluvial gullies are often formed in dispersible sodic soils along steep banks of incised river channels. Field data collected by Shellberg et al. (Earth Surface Processes and Landforms 38: 1765–1778, 2013) from a gully outlet in northern Australia showed little hysteresis between water discharge and fine (<63 µm) and coarse (>63 µm) suspended sediment, indicating transport‐limited rather than source‐limited conditions. The major source of the fine (silt/clay) component was the sodic soils of upstream gully scarps, and the coarser (sand) component was sourced locally from channel bed material. In this companion paper at the same study site, a new method was developed for combining the settling velocity characteristics of these two sediment source components to estimate the average settling velocity of the total suspended sediment. This was compared to the analysis of limited sediment samples collected during flood conditions. These settling velocity data were used in the steady‐state transport limit theory of Hairsine and Rose (Water Resources Research 28: 237–243, 245–250, 1992) that successfully predicted field data of concentrations and loads at a cross‐section, regardless of the complexity of transport‐limited upstream sources (sheet erosion, scalds, rills, gullies, mass failure, bank and bed erosion, other disturbed areas). The analysis required calibration of a key model parameter, the fraction of total stream power (F ≈ 0.025) that is effective in re‐entraining sediment. Practical recommendations are provided for the prediction of sediment loads from other alluvial gullies in the region with similar hydrogeomorphic conditions, using average stream power efficiency factors for suspended silt/clay (F_w ≈ 0.016) and sand (F_s ≈ 0.038) respectively, but with no requirement for field data on sediment concentrations. Only basic field data on settling velocity characteristics from soil samples, channel geometry measurements, estimates of water velocity and discharge, and associated error margins are needed for transport limit theory predictions of concentration and load. This theory is simpler than that required in source‐limited situations. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

AlCl₃对细颗粒泥沙絮凝沉降的影响   总被引：1，自引：0，他引：1       下载免费PDF全文

陈洪松  邵明安 《水科学进展》2001,12(4):445-449

铝类絮凝剂对细颗粒泥沙絮凝沉降有重要作用,常应用于浑水澄清、农业污水处理等研究中。在AlCl₃浓度为0～1.7mmol/L,泥沙浓度为10g/L时,用吸管法研究了AlCl₃对细颗粒泥沙絮凝沉降的影响,结果表明:在液面下同一深度,泥沙浓度随时间呈指数衰减;悬液经多次搅拌后再沉降,其沉速减缓;当AlCl₃浓度为0.9～1.7mmol/L时,出现明显的清浑水交界面,交界面随时间等速下降,平均沉速为4.756cm/min,对应的絮团平均粒径为0.0315mm;土娄土絮凝临界粒径为0.027mm。  相似文献   

通过比降观测浅析三姓浅滩的水文特性     

续庆义  李振波  朱洪刚 《测绘与空间地理信息》2001,24(4):47-48

通过把比降测量的观测成果进行科学的分析 ,得出泥沙淤积的原因 ,并提出了有关的航道测量、整治工程的一些建议  相似文献   

Hydrodynamic behaviour of Taupo 1800a pumice: implications for the sedimentology of remobilized pyroclasts   总被引：1，自引：0，他引：1  

V. Manville  B. Segschneider†  J. D. L. White† 《Sedimentology》2002,49(5):955-976

Abstract Large‐scale explosive eruptions from silicic caldera volcanoes can generate huge volumes of pyroclastic material in terrestrial and marine environments. On land, erosion, remobilization and redeposition of this debris is predominantly carried out by running water in the form of precipitation run‐off. Conversely, in the submarine realm, both primary emplacement and subsequent remobilization are influenced by the presence of water as a transporting medium. Despite this, and the number of studies devoted to volcaniclastic sedimentation, relatively little attention has been paid to the hydrodynamic behaviour of the particles themselves, which ought to underpin any assessment of transport or depositional process. This is crucial, as many volcanic particles exhibit variable density: according to composition and as functions of differing degrees of vesiculation and the extent to which pore space is filled by water and/or gaseous phases during transport and deposition. Investigation of the physical and hydrodynamic properties of Taupo 1800a pumice, with reference to sedimentary facies developed during the eruption aftermath, shows that, although buoyant when dry, when sufficiently waterlogged, cool pumice clasts will sink and behave more like quartzo‐feldspathic material. Saturation is apparently achieved by a combination of rapid capillary flooding of large interconnected vesicles and slower diffusional air–water exchange in smaller pores. Low saturated pumice densities result in lower settling velocities and easier entrainment by tractional currents than those for equivalent‐sized quartzo‐feldspathic or crystal/lithic particles. Fine‐grained pumice is conversely harder to entrain because of the frictional interlocking of angular particles. These unusual properties of temporary buoyancy, variable saturation, low density and size‐dependent cohesion complicate interpretations of the depositional setting and energy of pumiceous sediments and give rise to several unique facies. These findings have implications not only for the analysis of remobilized pyroclastic facies in terrestrial and marine environments, but also for primary depositional processes during subaqueous explosive volcanism.  相似文献