Challenges to the representation of suspended sediment transfer using a depth‐averaged flux          下载免费PDF全文

Chen Cheng  Huiming Huang  Chengyan Liu  Weimin Jiang 《地球表面变化过程与地形》2016,41(10):1337-1357

The sediment saturation recovery process (i.e. the adaptation of suspended sediment concentration [SSC] to local forcing) is the main feature of the non‐equilibrium suspended sediment transport (SST) frequently occurring in fluvial, estuarine and coastal waters. In order to quantitatively describe this phenomenon, a series solution is analytically derived, including the evolution of both vertical SSC profile and near‐bed sediment flux (NBSF), and is verified by net erosion and net deposition experiments, respectively. The results suggest that the sediment saturation recovery process involves vertically varying fluxes that are not represented correctly by depth‐averaging. Consequently, a vertical two‐dimensional (2D) combined scheme is established and applied respectively in to a dredged trench and to a sand wave feature to demonstrate this argument. By analyzing the variations of the calculated depth‐averaged SSC and NBSF we reveal that the equilibrium state presented by the sediment carrying capacity (SCC) form of the NBSF, which is usually applied in depth‐integrated SST models, lags behind the actual dynamic bed equilibrium state. Moreover, the key factor α, the so‐called saturation recovery coefficient within this form, is not only a function of local Rouse number but also is influenced by the local SSC profile. Finally, a three‐dimensional (3D) non‐orthogonal curvilinear body‐fitted SST model is developed and validated in the Yangtze estuary, China, combined with the in situ hourly hydrographic data from August 14–15, 2007 during spring tide in the wet season. Model results confirm that the vertically varying sediment saturation recovery process, the discrepancies between the actual and SCC form of NBSF and non‐constant value of α are significant in actual real geomorphic cases. The quantitative morphological change resulting from variations in environmental conditions may not be correctly represented by uncorrected depth‐integrated SST models if they do not treat the effects of vertical motion on the sediment saturation recovery process. Copyright © 2016 John Wiley & Sons, Ltd.  相似文献   

Climate change and coral reef bleaching: An ecological assessment of long-term impacts,recovery trends and future outlook   总被引：2，自引：0，他引：2  

Andrew C. Baker  Peter W. Glynn  Bernhard Riegl 《Estuarine, Coastal and Shelf Science》2008

Since the early 1980s, episodes of coral reef bleaching and mortality, due primarily to climate-induced ocean warming, have occurred almost annually in one or more of the world's tropical or subtropical seas. Bleaching is episodic, with the most severe events typically accompanying coupled ocean–atmosphere phenomena, such as the El Niño-Southern Oscillation (ENSO), which result in sustained regional elevations of ocean temperature. Using this extended dataset (25+ years), we review the short- and long-term ecological impacts of coral bleaching on reef ecosystems, and quantitatively synthesize recovery data worldwide. Bleaching episodes have resulted in catastrophic loss of coral cover in some locations, and have changed coral community structure in many others, with a potentially critical influence on the maintenance of biodiversity in the marine tropics. Bleaching has also set the stage for other declines in reef health, such as increases in coral diseases, the breakdown of reef framework by bioeroders, and the loss of critical habitat for associated reef fishes and other biota. Secondary ecological effects, such as the concentration of predators on remnant surviving coral populations, have also accelerated the pace of decline in some areas. Although bleaching severity and recovery have been variable across all spatial scales, some reefs have experienced relatively rapid recovery from severe bleaching impacts. There has been a significant overall recovery of coral cover in the Indian Ocean, where many reefs were devastated by a single large bleaching event in 1998. In contrast, coral cover on western Atlantic reefs has generally continued to decline in response to multiple smaller bleaching events and a diverse set of chronic secondary stressors. No clear trends are apparent in the eastern Pacific, the central-southern-western Pacific or the Arabian Gulf, where some reefs are recovering and others are not. The majority of survivors and new recruits on regenerating and recovering coral reefs have originated from broadcast spawning taxa with a potential for asexual growth, relatively long distance dispersal, successful settlement, rapid growth and a capacity for framework construction. Whether or not affected reefs can continue to function as before will depend on: (1) how much coral cover is lost, and which species are locally extirpated; (2) the ability of remnant and recovering coral communities to adapt or acclimatize to higher temperatures and other climatic factors such as reductions in aragonite saturation state; (3) the changing balance between reef accumulation and bioerosion; and (4) our ability to maintain ecosystem resilience by restoring healthy levels of herbivory, macroalgal cover, and coral recruitment. Bleaching disturbances are likely to become a chronic stress in many reef areas in the coming decades, and coral communities, if they cannot recover quickly enough, are likely to be reduced to their most hardy or adaptable constituents. Some degraded reefs may already be approaching this ecological asymptote, although to date there have not been any global extinctions of individual coral species as a result of bleaching events. Since human populations inhabiting tropical coastal areas derive great value from coral reefs, the degradation of these ecosystems as a result of coral bleaching and its associated impacts is of considerable societal, as well as biological concern. Coral reef conservation strategies now recognize climate change as a principal threat, and are engaged in efforts to allocate conservation activity according to geographic-, taxonomic-, and habitat-specific priorities to maximize coral reef survival. Efforts to forecast and monitor bleaching, involving both remote sensed observations and coupled ocean–atmosphere climate models, are also underway. In addition to these efforts, attempts to minimize and mitigate bleaching impacts on reefs are immediately required. If significant reductions in greenhouse gas emissions can be achieved within the next two to three decades, maximizing coral survivorship during this time may be critical to ensuring healthy reefs can recover in the long term.  相似文献   

提高机采水平的配套技术及应用     

张健泉  吴凤英  师清磊 《海洋地质译丛》2008,(4):70-72

随着濮城油田的持续性高速开发,油田综合含水逐渐上升,油水井井况进一步恶化,作为油田生产主体的机械采油井躺井频繁、管杆泵使用寿命缩短。近几年中原油田采油二厂濮城油田年平均躺井数达560井次之多,导致机械采油井维护费用增加,管杆泵投入增大,严重制约着油田的生产和经营。通过加缓蚀剂在油管内壁形成保护油膜,起到润滑作用;应用特殊抽油杆防腐止磨;应用尼龙扶正器对抽油杆体扶正,避免了钢体与钢体的硬磨;应用旋转井口通过地面人力转动改变油管与抽油杆的偏磨面;配合合理生产参数;各种配套技术的合理应用,使濮城油田躺井减少,避免了频繁作业,增加长寿井,管杆泵投入节约了19.3%。  相似文献   

低渗油藏采收率确定新方法     

黄小亮  ;唐海  ;吕栋梁  ;李仲  ;吕浙江  ;余贝贝 《海洋地质译丛》2008,(3):74-77

通过对油藏相渗曲线的归一化处理，利用达西定律理论，建立采油指数与含水率的关系；再通过油藏确定的单井经济极限采油量和油藏极限生产压差求出极限采油指数，从而得到极限含水率；最后以最终水驱体积波及系数与储层退汞效率计算出采收率。并以低渗透油藏为实例验证了该方法的正确与适用性，说明该方法对油田开发中确定低渗油藏采收率具有科学的指导意义。  相似文献   

The effects of beach nourishment on the sandy-beach amphipod Exoediceros fossor: impact and recovery in Botany Bay, New South Wales, Australia     

Alan R. Jones  Anna Murray  Theresa A. Lasiak  & Robin E. Marsh 《Marine Ecology》2008,29(S1):28-36

Beach nourishment is increasingly being implemented to address problems of erosion. However, the ecological consequences of nourishment are poorly understood, especially in Australia. In Botany Bay, sand was piped from an intertidal borrow area at Elephant's Trunk to nourish the nearby eroding beach at Towra Point. The effects on an intertidal exoedicerotid amphipod, Exoediceros fossor (Stimpson, 1856), were examined using a beyond-BACI (Before–After, Control–Impact) sampling design. Sampling was conducted before and after engineering operations at sites within the borrow and nourishment locations and multiple control locations. Hypotheses concerning impact and recovery were tested using asymmetrical ANOVAs and two-tailed F-tests. These examined the effects on abundance and spatial variability, respectively. The impact of the engineering operations on abundance was very large at both borrow and nourishment locations. However, recovery started within several weeks and, using space × time interactions as a criterion, appeared to be complete within a year. This conclusion is made cautiously because of low statistical power and because other criteria for recovery suggest that it was not complete at some sites. As beach erosion is likely to increase in severity with rising sea levels and greater storm surges associated with climate change, management authorities will need a better understanding of the ecological effects of beach nourishment.  相似文献   

正理庄高89-1区块CO2混相驱参数优化数值模拟研究     

史华 《海洋地质译丛》2008,(1):68-73

为了确保高89-1区块CO2混相驱项目的顺利实施,依据该区块的精细油藏描述成果,在优化适于CO2混相驱模型基础上,建立了符合油藏地质特点的三维地质模型。在此基础上对开发指标进行计算,对五个参数（井网、开发方式、压力水平、注入量和采油速度）进行优化,并提出了推荐方案,预测采收率可达23.10%,比弹性开采方式提高15.16%。  相似文献   

低轨卫星初始状态误差对反演地球重力场的影响     

张兴福  沈云中 《测绘科学》2009,34(3)

基于动力学法反演地球重力场的基本理论,研究了卫星初始状态向量误差对应用低轨卫星精密轨道数据反演地球重力场的影响。在仅考虑低轨卫星初始状态误差的情况下进行了模拟计算,结果表明:在利用低轨卫星精密轨道数据反演地球重力场时,卫星初始状态向量误差需要重新进行估计;在目前的轨道精度水平下,若不顾及误差方程二次项的影响,反演弧长不宜过长;卫星初始状态速度误差(约1.5mm/s)的影响要大于位置误差(约10 cm)的影响。  相似文献   

Assessing the extent of mangrove change caused by Cyclone Vance in the eastern Exmouth Gulf, northwestern Australia   总被引：1，自引：1，他引：0  

E.I. Paling  H.T. Kobryn  G. Humphreys   《Estuarine, Coastal and Shelf Science》2008,77(4):603-613

Changes in mangal area were quantified in the eastern Exmouth Gulf over six years (1999–2004) after Cyclone Vance using Landsat TM satellite imagery and aerial photography. Vance was the strongest tropical cyclone ever to impact the Australian mainland before 2006 and produced wind gusts of more than 280 km h⁻¹. Image data were processed using ENVI™ and IDRISI™ software. Three sets of Landsat TM images from 1999 (a few days before the cyclone), 2002 and 2004 were used, along with 2004 digital aerial photography. A ‘common’ subset of 904 km² was selected from all images and classification was developed using ISODATA™ unsupervised classification to identify spectrally distinct areas followed by principal component analysis (PCA), vegetation indices and supervised classification. Some 12,800 ha of mangrove habitat was present before the cyclone and approximately 5700 ha (44%) was removed by it. Most mangroves lost (74%) between 1999 and 2004 were converted either to bare sediment or to live saltmarshes and this occurred mostly between 1999 and 2002. Five basic categories of damage were conspicuous from imagery and field observations, and evidence suggests that much of the loss was due to the longer term consequences of sediment deposition or smothering, rather than the immediate effects of wind or waves. Mangroves exhibited accelerated recovery between 2002 and 2004, and around 1580 ha regenerated during this time, amounting to a return of 68% of their former coverage. At this recovery rate we estimate that they should have returned to their pre-cyclone area by 2009. Over half of the saltmarsh habitats (54%) were removed by the cyclone (4060 ha) but their recovery has been far more rapid than mangroves. After 5 years, saltmarshes had returned to 87% of their previous area. The 5700 ha of mangrove habitat damaged by Cyclone Vance exceeds any anthropogenic impact that has ever taken place in Western Australia by several orders of magnitude.  相似文献   

汶川科学钻探PDC取心钻头有限元分析          下载免费PDF全文

唐胜利 《地质与勘探》2014,50(3):577-582

汶川地震断裂带科学钻探项目是在龙门山"北川-映秀"断裂及龙门山前缘安县-灌县断裂附近实施5口科学群钻,由于所实施的5个钻孔都位于地震断裂带上,地层十分松软破碎,普通取心钻进的取心率低、岩心扰动大。为解决该问题,设计并采用了一种超前式隔水防冲蚀PDC取心钻头,取得了良好的效果,提高了岩心采取率,并保证了岩心的原状性。论文通过UG建立的实体模型导入ANSYS Workbench下的CFX流场分析和Steady-Thermal稳定热分析模块,分析了该钻头的井底流场分布、大小以及钻头的冷却效果,并计算孔底有效排粉的最低泵量,以确定超前式隔水防冲蚀PDC取心钻头取心钻进时保证取心率和岩心原状性要求的最优泵量。  相似文献   

Further discussion on the intercomparison of the trace metal concentrations and particle size of fluvial sediment recovered from two centrifuge systems     

S. Santiago  R. L. Thomas  J.-L. Loizeau  P.-Y. Favarger  J.-P. Vernet 《水文研究》1990,4(3):283-287

A single large volume water sample taken at the mouth of the Upper Rhone River on Lake Geneva was processed directly in parallel through two continuous flow centrifuges, a Westphalia and an Alfa-Laval. Sediment was recovered from the Westphalia, and separately from the bowl and brass core of the Alfa-Laval. The three sediment samples were analyzed for particle size and the following elements: Zn, Cu, Mn, Cr, P, Co, B, V, Be, Sr, Na, Pb, Ni, Ba, Fe, Ca, and Mg. Results indicate that the particle size recovery of both machines is similar when sediment from the brass core and bowl of the Alfa-Laval are combined, and that the recovery for all elements other than Cu, V, B, and Pb are the same when the particle size differences are taken into account. Sediment from the Alfa-Laval brass core is clearly contaminated by Cu, B and is also elevated in V and Pb but not to a significant extent. The sediment recovered from the bowl of the Alfa-Laval is contaminated only with Cu, with a 10 ppm increase over the 52 ppm recovered in the Westphalia sediment. Operating procedures involve the discarding of the brass core sediment and the mixing of the Alfa-Laval bowl sediment with that from the Westphalia. The consequent increase in Cu is estimated at less than 5 ppm or within the confidence level of the analysis. These procedures are recommended to all operators of non modified Alfa-Laval units.  相似文献