New methodologies for investigating rillenkarren cross-sections: a case study at Lluc,Mallorca     

J. Crowther 《地球表面变化过程与地形》1998,23(4):333-344

Precise data on the detailed form of 108 rillenkarren (flute) cross-sections at Lluc have been obtained by digitizing photographic enlargements of profile gauge traces taken in the field. Such data enable morphometric analysis to be undertaken more rigorously and on a wider range of characteristics (e.g. flute and cusp asymmetry, surface roughness and the properties of vertical sections) than in previous studies. Methods for quantifying and investigating these characteristics are presented. Since many of the flutes were found to be asymmetrical, the two ‘sides’ of each flute have been analysed separately. Although most of the sides have characteristic parabolic profiles, about one-fifth are rectilinear in form. The parabolic sides are relatively smooth, and this is thought to be attributable to dissolution within the thin film of water present on the surface during rainfall and/or to the detachment of small protruding fragments of limestone (weathered loose by biological agencies) by raindrop impact. The rectilinear sides have distinctly rougher surfaces and are thought to be truncated or immature forms. Sets of rillenkarren on rock outcrops appear to be in dynamic equilibrium, maintaining their overall form over time, but changing in detail as cusp lines shift, existing flutes are captured and new ones are initiated. © 1998 John Wiley & Sons, Ltd.  相似文献   

Sensitivity of bed shear stress estimated from vertical velocity profiles: the problem of sampling resolution     

Pascale M. Biron  Stuart N. Lane  Andr G. Roy  Kate F. Bradbrook  Keith S. Richards 《地球表面变化过程与地形》1998,23(2):133-139

Bed shear stress in open channel flows is often estimated from the logarithmic vertical velocity profile. However, most measuring devices used in the field do not allow for flow velocity to be measured very close to the bed. The lack of near-bed measurements is a critical loss of information which may affect bed shear stress estimates. Detailed velocity profiles obtained from a field acoustic Doppler velocimeter over three different bed roughnesses clearly show that the inclusion of near-bed points is critical for the estimation of bed shear stress in a shallow river environment. Moreover, the results indicate that using the full flow depth instead of the bottom 20 per cent of the profile generates an underestimation of the shear stress when flow is uniform. © 1998 John Wiley & Sons, Ltd.  相似文献   

DTM resolution controls the accuracy of estimating surface runoff indicators in flat,lowland landscapes     

Peter Schaap  Ype van der Velde  Perry de Louw  Harm Bartholomeus 《水文研究》2024,38(5):e15173

Surface runoff plays an important role in contaminant transport, nutrient loss, soil erosion and peak discharges in streams and rivers. Because it is the result of a variety of complex hydrological processes, estimating surface runoff using physically based hydrological models is challenging. Upscaling of physical soil properties is necessary to cope with the limits of computational power in surface runoff modelling. In flat landscapes, the (micro)topographic surface controls the onset and progression of surface runoff on saturated soils during rain events. Therefore, its proper representation is crucial when attempting to model and predict surface runoff. In this study, the influence of microtopography (centimetre scale) on estimations of maximum depression storage (MDS), random roughness (RR) and the connectivity threshold (CT) is explored. These properties are selected because they often serve as surface runoff indicators in hydrological modelling. To characterize microtopography, a terrestrial laser scanner (TLS) is used to generate a digital terrain model (DTM) of the study site with a horizontal spatial resolution of 5 cm. MDS, RR and CT are then calculated and compared to the values generated from the publicly available Dutch national DTM dataset with a resolution of 50 cm. Our results show considerable differences in MDS, RR and CT when calculated for the different input resolution datasets. Using DTMs that do not sufficiently capture microtopography leads to underestimation of MDS and RR, and to overestimation of CT. Our findings indicate that surface runoff indicators, and thereby the surface runoff response of a saturated surface to rainfall events, are defined at scales smaller than the scales of typically available DTMs. Understanding surface runoff through modelling studies therefore requires a framework that accounts for this lack of information arising from using coarser resolution DTMs. We demonstrate a linear relationship between MDS values generated from the different resolution DTMs. This opens the possibility of using empirical scaling relationships between high- and lower-resolution DTMs to account for microtopography. Repetition of our measurements on similar surfaces would contribute to establishing such empirical scaling relationships. Our results should be seen as indicative of flat landscapes and surfaces where centimetre scale microtopography is relevant.  相似文献   

胜利油田浅海区域海底土层的液化判别方法分析   总被引：2，自引：0，他引：2  

牟晓东 《海洋科学进展》2006,24(2):220-227

针对胜利油田海上石油勘探开发区(埕岛油田)的海底饱和粉土(砂土)液化判别问题,结合工程研究实例,对土层液化判别的各种方法进行对比分析,指出了当前各种方法的局限性和不足,为海底土层的液化判别分析提供了新思路。  相似文献   

FIELD STUDIES OF SAND PATCH INITIATION PROCESSES ON THE NORTHERN MARGIN OF THE NAMIB SAND SEA     

NICHOLAS LANCASTER 《地球表面变化过程与地形》1996,21(10):947-954

Field studies of protodunes (sand patches) on the northern margin of the Namib Sand Sea suggest that they are initiated in a zone of spatially and temporally fluctuating winds on the distal plinth of one of the south–north linear dunes and migrate northward across granule to gravel substrates. The sand patches disperse as surface roughness increases in the net migration distance. Dispersal of the sand patches is also constrained by sand supply. These studies suggest the importance of interactions between surface and aerodynamic roughness, transport thresholds, and sand supply in the initiation of dunes.  相似文献   

基于人工神经网络的海底细粒土工程分类研究          下载免费PDF全文

杜星  孙永福  宋玉鹏  张牧子 《海洋科学进展》2021,39(1):110-117

海洋沉积物工程定名对于开展海洋工程建设具有重要作用,然而海底粉土和黏性土的定名受人为因素影响容易产生误差.使用人工神经网络的方法对黄河口埕岛海域284组细粒土数据进行了训练和学习,得到了只利用沉积物粒径质量分数进行定名的方法.结果表明,使用人工神经网络的方法能够有效地对沉积物进行工程定名.当网络含有5个输入层节点、9个...  相似文献   

沿岸流流速垂向分布的实验研究   总被引：1，自引：0，他引：1  

张振伟  邹志利 《海洋通报》2009,28(2)

进行了沿岸流模型实验,测量沿岸流流速的垂向分布.采用Faria等(1996)的方法对实验结果进行了分析,将水深分为上层和下层两部分:下层采用对数分布来表达沿岸流的垂向分布;上层考虑了波浪引起的自由表面的波动,使流速分布包括了修正的对数分布和质量输移速度两部分.对实验结果得到的相对粗糙度与sleath(1991)的经验公式结果进行了对比,也对摩阻流速结果与已有经验公式计算结果的进行了对比.  相似文献   

国际近海工程研究进展——第26届近海力学与极地工程国际会议海洋工程分会简介     

舒勰俊  江森汇 《海洋工程》2009,27(1):110-114

简要介绍了2007年6月在美国圣迭戈举行的第26届近海力学与极地工程国际会议海洋工程主题分会的概况,分别从船舶研究与实际运用、水下技术研究与进展、海洋建筑物、水动力理论研究与工程应用以及海底矿产和能源开发利用等方面叙述了国内外海洋工程的研究进展情况,为国内相关领域的研究提供有益参考.  相似文献   

波浪作用下黄河口粉土海床粗化室内模型试验研究   总被引：1，自引：0，他引：1       下载免费PDF全文

李晓东  刘红军  张民生  王秀海 《海洋科学》2009,33(6):46-50

利用室内水槽模型实验,对黄河口粉质海床土在波浪荷载下的粗化现象进行了研究,试验中观测了土体表层沉积物的变化,测量了土体内孔隙水压力及土的粒径变化,结合高密度电阻率法探测结果分析探讨了波浪作用下土体粗化机理.研究表明,波浪作用会使粉质海床土发生明显的粗化现象;土体液化是波浪导致粉土粗化的首要条件;土体内超孔隙水压力累积及消散是细颗粒物质迁移的主要动力.该结果对于研究黄河口粉土海床地貌的形成有一定参考意义.  相似文献   

台湾海域海面粗糙度及曳力系数的研究     

葛苏放  申双和  张新厂  潘玉萍 《海洋通报》2009,28(6)

利用福建沿海海域南日岛、金门岛与广东南澳岛的近海面气象、水文观测资料及台湾海峡西南部与南部的浮标观测资料,通过COARE(Coupled-Ocean Atmosphere Response Experiment)算法(V3.0),计算了台湾海域近海面空气动力粗糙度、曳力系数及海气表面动量通量,并研究它们关于水平风速的分布规律。结果得出:摩擦速度与10m风速基本上呈线性分布,线性拟合系数在0.042～0.045之间。曳力系数对10m风速的线性分布与过去研究结果相近,线性拟合系数在0.064～0.067之间。海面空气动力粗糙度对10m风速的线性拟合系数在0.053～0.058之间。海面动量通量与10m风速呈明显的二次关系,其线性与非线性拟合系数对于进一步了解台海地区大气湍流结构,建立和完善台海地区数值预报模式可提供重要的参数依据。  相似文献