Estimation of dispersion in estuaries by a self-consistent method     

D.J. Gunn  O. Yenigun 《Estuarine, Coastal and Shelf Science》1985,21(2):257-272

Longitudinal and transverse dispersion in estuaries may be determined in principle by measuring the change in time of the concentration field of a water soluble dye. In practice, measurements may take the form of several sampling runs crossing the dye patch. The coefficients of dispersion are usually estimated from the second moments of the concentration field; the use of second moments, in particular, introduces errors because measurements at long times or distance are unduly emphasized.A self-consistent method, free of the disadvantages inherent in the use of higher moments, is described in which the distribution of concentration in space is related to the zeroth spatial moment of concentration. In this formulation, based upon sampling runs across the dye patch, the concentration field in the estuary may be directly and simply related to the dispersion coefficients in both the intercept and gradient of a linear graph.The methods are illustrated by the characterization of a series of experiments in the Inner Estuary of Milford Haven.  相似文献   

Seasonally Hypersaline Estuaries in Mediterranean-climate Regions     

J.L. Largier  J.T. Hollibaugh  S.V. Smith 《Estuarine, Coastal and Shelf Science》1997,45(6):789-797

Data collected in three Californian estuaries indicate that hypersaline conditions exist during the dry summers typical of a Mediterranean climate. The generalised seasonal and longitudinal hydrographic structures are described and explained. It is argued that this seasonal hypersalinity is common and that it represents a major class of estuaries. The observed accumulation of salt indicates surprisingly long residence times in small basins which have free exchange with the ocean. This semi-isolation of the inner basin leads to a large build-up or severe depletion of nutrients, pollutants and plankton in these systems. Of concern are the trends to increase pollutant loading in the same systems that are experiencing an increase in residence times owing to freshwater extraction in the watershed.  相似文献   

Strength Analysis of Turret Mooring Productive/Storage Tanker     

Zhang Shilian Jin Dexian Associate Professor 《中国海洋工程》1997,(3)

The longitudinal strength of turret mooring productive/storage tanker is studied.A numeri-cal example has been implemented according to the method presented in this paper to give practical il-lustration.From the results of the numerical example,it is concluded that the turret hole located near theforward of the amidships has small effect on the longitudinal strength of the ship hull.As for design ex-treme value of wave bending moment of storage tanker,statistic method is a more reasonablemethodology,especially with the consideration of the servere environmental conditions.The primary esti-mation of design section modulus of turret storage tanker can be determined by this design bending mo-ment.  相似文献   

国外海岸沙丘形成与演化的研究   总被引：13，自引：0，他引：13  

董玉祥 《海洋地质与第四纪地质》2001,21(2):93-98

自20世纪80年代以来，国外对海岸沙丘的研究已从主要对其地貌形态的研究转向海岸海丘与海岸变迁尤其是全球变化关系的研究上，海岸沙丘形成与演化的研究倍受关注，进行了大量研究并取得了一定的研究成果。这里介绍了国外在海岸沙丘形成与演化研究方面的主要进展及其成果，并以此探讨了国内今后开展海岸沙丘形成与演化研究的主要方向与问题。  相似文献   

青海共和盆地多石在沟河道沙丘现代风水交互过程   总被引：2，自引：0，他引：2       下载免费PDF全文

马玉凤  严平  宋阳  杜建会  朱孟郡  丁连刚 《第四纪研究》2008,28(4):695-701

选择青海共和盆地多石在沟河道中6道新月形沙丘链作为研究对象,采用Trimble4700DGPS与常规测量手段,结合野外风沙观测与自动气象站数据,初步观测分析了2006年多石在沟河道沙丘在不同季节的形态变化过程,计算出2006年风季前比雨季后多石在沟河道沙丘体积减小了548.3m³,风积量为2351m³,流水的蚀平量为2899m³,2006年风水两相营力对河道沙丘的侵蚀贡献率约为45%∶55%,流水的搬运作用强于风力的堆积作用。但从较长的时间尺度来看,研究区的风力侵蚀作用强于流水侵蚀作用,河道沙丘不断增大。多石在沟河道沙丘是一个典型的风水交互作用系统,河道成为风力与流水交互作用的"中转站",在风水的交替作用下,沉积物由风积环境进入流水环境中。  相似文献   

The gawler ranges,South Australia: an unusual volcanic massif     

E. M. Campbell  C. R. Twidale 《The Australian geographer》1991,22(1):24-33

The volcanic residuals of the Gawler Ranges together form an extensive massif that in its gross morphology differs markedly from most exposures of silicic volcanic rocks. The upland developed in two stages, the first involving differential fracture‐controlled subsurface weathering, the second the stripping of the regolith. As a result, an irregular weathering front was exposed, with domical projections prominent. These bornhardts are etch forms, and they are of considerable antiquity.

The differential weathering of the rock mass reflects the exploitation of various fracture systems by shallow groundwaters. Orthogonal fracture systems at various scales, sheet fractures and columnar joints control the morphology of the bornhardts in gross and in detail.

The exploitation of the structural base, which was established in the Middle Protero‐zoic, probably took place throughout the Late Proterozoic and the Palaeozoic, though only minor remnants of the Proterozoic land surface remain. The major landscape features developed during the Mesozoic. The weathering which initiated the bornhardts occurred in the Jurassic or earlier Mesozoic, and the landforms were exposed in Late Cretaceous to Early Tertiary times.

Though structural forms dominate the present landscape, some major and some minor landforms are best explained in terms of climatic changes of the later Cainozoic. The palaeodrainage system, established under humid conditions by the Early Tertiary, was alluviated during the Cainozoic arid phases, and salinas were formed. The sand dunes of the region also reflect this aridity.  相似文献   

库姆塔格沙漠"羽毛状沙丘"形态的示量特征   总被引：10，自引：2，他引：10  

刘虎俊  王继和  廖空太  郑庆中  张锦春  丁峰  唐进年  俄有浩  苏志珠  翟新伟  张国忠 《干旱区地理》2006,29(3):314-320

通过卫星照片判读和实地观测,库姆塔格沙漠的“羽毛状沙丘”由两种风沙地貌构成：东北-西南走向的新月形“沙垄”为“羽轴”；垄间分布的波状微起伏的“大沙波”为“羽枝”,“大沙波”与沙垄的夹角为75°～103°。二者组合成类似“羽毛”的风沙地貌。新月形“沙垄”由单个新月形沙丘的前一沙丘的迎风坡与后一沙丘东翼相连构成“沙垄”。组成“沙垄”的新月形沙丘的两翼平均长37．5m,翼间距30～66m,沙丘高3～19m；在所观测区域内,沙丘沙的分选性由南向北变差。新月形“沙垄”长为3～22km,垄间距为1～3km,其问分布浅色和暗色相间的波状微地貌,暗色部分平均宽24．3m,浅色部分的平均宽11．6m。暗色部分表层沙粒的粒径有60%在1．00～0．25mm之间,以暗色矿物为主,而浅色部分表层沙粒的粒径的90%在1．00～0．25mm之间,分选性相对暗色部分较好,以石英等浅色矿物为主。暗色和浅色微地貌成对出现,相对高差约7cm。这种波状微地貌在库姆塔格沙漠中北部重复出现,类似于风沙地貌分类的沙波,暂称其为“大沙波”。  相似文献   

A consideration of the dune:antidune transition in fine gravel   总被引：1，自引：0，他引：1  

Paul A. Carling  Andrey B. Shvidchenko† 《Sedimentology》2002,49(6):1269-1282

Hydraulic data defining the dune:antidune transition in fine gravel are compared with potential flow theory, and information is drawn from published experiments and field‐based studies. Attention is given to both transitional bedforms and the development of downstream‐migrating antidunes. In the latter case, most data pertain to sand beds and not to gravel. Empirical data provide some weak support for the theoretical notion that the transition occurs at progressively lower Froude numbers at greater relative depths. Although a critical Froude number of 0·84 may reasonably be applied for the beginning of the dune to antidune transformation, lag effects (and a possible depth limitation) ensure that transitional bedforms may persist across a broad range of Froude numbers from 0·5 to 1·8. This latter observation has great relevance for palaeohydraulic estimates derived from outcrop data. Whereas the application of theoretical bedform existence fields, based upon potential flow theory, to fine gravel was previously purely speculative, the addition of experimental and field data to these plots provides a degree of confidence in applying stability theory to practical geological problems. For the first time, laboratory data pertaining to downstream‐migrating gravel antidunes are compared with theory. These bedforms have been reported from certain experimental near‐critical flows above sand or gravel beds, but have been observed infrequently in natural streams. However, there are no detailed studies from natural rivers and only a few contentious identifications from outcrops. Nevertheless, the limited hydraulic data conform to theoretical expectations.  相似文献   

Do the Austrian blackfly fauna (Diptera: Simuliidae) support the typological approach of the EU water framework directive?     

Thomas Ofenbck  Otto Moog  Manfred Car 《Limnologica》2002,32(3):255

The Austrian blackfly fauna were analysed with regard to spatial (ecoregions, bioregions), vertical (altitude classes) and longitudinal zonation characteristics [stream order, biocoenotic (= fish) regions] on the basis of 2600 investigation sites. Of a total of 45 species recorded, Simulium ornatum, S. variegatum, S. argyreatum and S. reptans are the most common and most frequently distributed species, occurring in 60% of the investigated sites. Although the Austrian blackfly fauna seem to be quite well documented (on average one investigation site per 32 km²) the jackknife analyses indicates that there are still some fauna deficits. Whereas the species diversity of the main ecoregions is quite similar, the number of species differs clearly between the bioregions. Within the typological context of the Water Framework Directive, the Austrian Simuliidae confirm the bioregions as the most useful spatial units for river typology. A further optimisation in predicting a target list of blackfly species of a site can be achieved by subdividing the bioregions into either catchment area and altitude classes or into longitudinal zonation types (biocoenotic regions).  相似文献   

帕隆藏布河流纵剖面演化的最小功模式   总被引：3，自引：0，他引：3  

蒋忠信 《山地学报》2002,20(1):26-31

河流地貌最小功原理表明河流纵误时面形态将向力示使流速增大的方向演化，据此推导出矩形流域全程流速的平均值（u^-）与河流纵误时面形态指数（N）的关系式：u^∝-f(N)={1/2-1/[(N 1)(N 2)]}^1/2，f(N)被称为流速函数。这一最小功模式表明河流纵剖面演化方向是N由小变大。以西藏帕隆藏布中上游流域系统、干流全程及Ⅰ级阶地为例，由最小功模式计算的全程流速均值与实测值相吻合，从而检验了上述最小功原理和数学模式。  相似文献