北黎湾及邻近海域潮流数值计算     

孙长青  赵可胜  郭耀同 《海洋科学》2004,28(11):44-48

建立北黎湾及邻近海域二维潮流数值模型,重现该海域潮波及潮流的分布规律,计算得到m1分潮和M2分潮的同潮时线与等振幅线、潮流椭圆,m1与M2合成的潮致欧拉余流、最大潮流和不同时刻潮流场分布。  相似文献   

长江口滨岸潮滩柱样沉积物与孔隙水中氮的垂直分布特征   总被引：4，自引：1，他引：3  

刘巧梅  刘敏  许世远  侯立军  欧冬妮 《海洋科学》2004,28(9):13-19

对长江口滨岸潮滩柱样沉积物及孔隙水中NH4^ -N、NO3^--N和NO2^--N的剖面进行了分析。结果表明,沉积物和孔隙水中NH4^ -N,NO3^--N和NO2^--N剖面分布基本一致,其中NH4^ -N含量最高,这说明有机质的降解反应主要是在缺氧或无氧环境中进行的;沉积物中有机质含量与NH4^ -N含量线性相关;NO3^--N和NO2^--N在剖面中以0～20cm变化剧烈,说明表层和深层有机质的降解程度发生改变。  相似文献   

渤海湾海域潮流数值计算   总被引：3，自引：1，他引：2  

孙长青  郭耀同  赵可胜 《海洋科学》2004,28(8):33-37

采用不规则三角形网格的分步杂交法,建立渤海湾海域二维变边界潮流数值模型,重现该海域潮波及潮流的时空分布,计算得到M2分潮和K1分潮的同潮时线与等振幅线、潮流椭圆及不同时刻潮流场分布。计算结果与实测资料对比验证吻合良好。  相似文献   

湄洲湾潮流数值计算   总被引：2，自引：2，他引：0  

孙长青  赵可胜  郭耀同 《海洋科学》2004,28(12):35-38

采用不规则三角形网格的分步杂交法,建立了湄洲湾海域二维变动边界潮流数值模型,通过计算得到最大潮流分布、同潮时线与等振幅线、潮流椭圆、潮致欧拉余流分布及不同时刻潮流场分布。  相似文献   

湛江近海M2分潮的数值模拟   总被引：1，自引：0，他引：1  

路泽廷  杨支中  沙文钰  朱首贤 《海洋通报》2004,23(5):18-24

利用潮汐模型,在高分辨率的自适应曲线网格下,采用潮汐调和常数作为控制模拟精度的方法,模拟了洪江附近海域M2分潮的运动特征。模拟所得的潮汐调和常数同实测值相比,误差较小。根据模拟结果绘制的M2分潮的同潮图,揭示了湛江附近海域M2分潮振幅和迟角的分布特征以及M2分潮的传播和发展规律。模拟得到的M2分潮分别在涨憩、落憩、涨急和落急几个典型时刻的流场,揭示了湛江附近海域M2分潮潮流的分布特征及其运动规律。  相似文献   

Ice fracturing during jökulhlaups: implications for englacial floodwater routing and outlet development     

Matthew J. Roberts  Andrew J. Russell  Fiona S. Tweed   skar Knudsen 《地球表面变化过程与地形》2000,25(13):1429-1446

Theoretical studies of glacial outburst floods (jökulhlaups) assume that: (i) intraglacial floodwater is transported efficiently in isolated conduits; (ii) intraglacial conduit enlargement operates proportionally to increasing discharge; (iii) floodwater exits glaciers through pre‐existing ice‐marginal outlets; and (iv) the morphology and positioning of outlets remains fixed during flooding. Direct field observations, together with historical jökulhlaup accounts, confirm that these theoretical assumptions are not always correct. This paper presents new evidence for spatial and temporal changes in intraglacial floodwater routing during jökulhlaups; secondly, it identifies and explains the mechanisms controlling the position and morphology of supraglacial jökulhlaup outlets; and finally, it presents a conceptual model of the controls on supraglacial outbursts. Field observations are presented from two Icelandic glaciers, Skeiðarárjökull and Sólheimajökull. Video footage and aerial photographs, taken before, during and after the Skeiðarárjökull jökulhlaup and immediately after the Sólheimajökull jökulhlaup, reveal changes in floodwater routing and the positioning and morphology of outlets. Field observations confirm that glaciers cannot transmit floodwater as efficiently as previously assumed. Rapid increases in jökulhlaup discharge generate basal hydraulic pressures in excess of ice overburden. Under these circumstances, floodwater can be forced through the surface of glaciers, leading to the development of a range of supraglacial outlets. The rate of increase in hydraulic pressure strongly influences the type of supraglacial outlet that can develop. Steady increases in basal hydraulic pressure can retro‐feed pre‐existing englacial drainage, whereas transient increases in pressure can generate hydraulic fracturing. The position and morphology of supraglacial outlets provide important controls on the spatial and temporal impact of flooding. The development of supraglacial jökulhlaup outlets provides a new mechanism for rapid englacial debris entrainment. Copyright © 2000 John Wiley & Sons, Ltd.  相似文献   

Assessing the relative contributions of the flood tide and the ebb tide to tidal channel network dynamics     

Liang Geng  Zheng Gong  Zeng Zhou  Stefano Lanzoni  Andrea D'Alpaos 《地球表面变化过程与地形》2020,45(1):237-250

Flood and ebb currents provide different contributions to the initiation and evolution of tidal channel networks, generating diverse network structures and channel cross-sections. In order to separate the effects of these contributions, a physical model of a sloping tidal-flat basin was set up in the laboratory. Depending on the degree of tidal asymmetry imposed offshore, either flood or ebb currents can be enhanced. The experimental results show that the ebb current has a higher capability to initiate and shape tidal networks than the flood current. Headward erosion is mainly induced by the ebb flow. The slightly inclined flat surface tends to reduce the energy of the flood current and to enhance the ebb current, thus prolonging the duration of morphodynamic activity as well as sediment motion. Overall, flood-dominated tides favour the formation of small-scale channel branches in the upper basin zone, while long lasting ebb-dominated tides result in more complex, wider and deeper tidal networks. © 2019 John Wiley & Sons, Ltd.  相似文献   

Forests and floods: Using field evidence to reconcile analysis methods     

James C. Bathurst  Barry Fahey  Andrés Iroumé  Julia Jones 《水文研究》2020,34(15):3295-3310

The extent to which forests, relative to shorter vegetation, mitigate flood peak discharges remains controversial and relatively poorly researched, with only a few significant field studies. Considering the effect purely of change of vegetation cover, peak flow magnitude comparisons for paired catchments have suggested that forests do not mitigate large floods, whereas flood frequency comparisons have shown that forests mitigate frequencies over all magnitudes of flood. This study investigates the apparent inconsistency using field-based evidence from four contrasting field programmes at scales of 0.34–3.1 km². Repeated patterns are identified that provide strong evidence of real effects with physical explanations. Magnitude and frequency comparisons are both relevant to the impact of forests on peak discharges but address different questions. Both can show a convergence of response between forested and grassland/logged states at the highest recorded flows but the associated return periods may be quite variable and are subject to estimation uncertainty. For low to moderate events, the forested catchments have a lower peak magnitude for a given frequency than the grassland/logged catchments. Depending on antecedent soil saturation, a given storm may nevertheless generate peak discharges of the same magnitude for both catchment states but these peaks will have different return periods. The effect purely of change in vegetation cover may be modified by additional forestry interventions, such as road networks and drainage ditches which, by effectively increasing the drainage density, may increase peak flows for all event magnitudes. For all the sites, forest cover substantially reduces annual runoff.  相似文献   

Event-based classification for global study of river flood generating processes     

Lina Stein  Francesca Pianosi  Ross Woods 《水文研究》2020,34(7):1514-1529

Better understanding of which processes generate floods in a catchment can improve flood frequency analysis and potentially climate change impacts assessment. However, current flood classification methods are either not transferable across locations or do not provide event-based information. We therefore developed a location-independent, event-based flood classification methodology that is applicable in different climates and returns a classification of all flood events, including extreme ones. We use precipitation time series and very simply modelled soil moisture and snowmelt as inputs for a decision tree. A total of 113,635 events in 4155 catchments worldwide were classified into one of five hydro-climatological flood generating processes: short rain, long rain, excess rainfall, snowmelt and a combination of rain and snow. The new classification was tested for its robustness and evaluated with available information; these two tests are often lacking in current flood classification approaches. According to the evaluation, the classification is mostly successful and indicates excess rainfall as the most common dominant process. However, the dominant process is not very informative in most catchments, as there is a high at-site variability in flood generating processes. This is particularly relevant for the estimation of extreme floods which diverge from their usual flood generation pattern, especially in the United Kingdom, Northern France, Southeastern United States, and India.  相似文献   

Wood retention at inclined racks: Effects on flow and local bedload processes     

Isabella Schalko 《地球表面变化过程与地形》2020,45(9):2036-2047

Large wood (LW) transport can increase greatly during floods, leading to accumulations at river infrastructures. To mitigate the potential flood hazard, racks are a common method to retain LW upstream of endangered settlements or infrastructures. The majority of LW retention racks consist of vertical bars and, therefore, disrupt bedload transport. It can be hypothesized that inclined racks reduce backwater rise and local scour, as wood will block the upper part of the rack, thereby increasing the open flow cross-section below the accumulation. Flume experiments were conducted under clear water conditions to analyse backwater rise and local scour as a function of (1) rack inclination, (2) hydraulic inflow condition, (3) uniform bed material, and (4) LW volume. In addition, the first experiments were performed under live bed scour conditions to study the effect of bedload transport on local scour and backwater rise. Based on the experiments, backwater rise and local scour decrease with decreasing rack angle to the horizontal. LW predominantly accumulated at the upper part of the rack, leading to an open flow cross-section below the accumulation. The effect of rack angle was included in existing design equations for backwater rise and local scour depth. In addition, the first experiments with bedload transport resulted in smaller backwater rise and local scour depth. This study contributes to an enhanced process understanding of wood retention and bedload transport at rack structures and an improved design of LW retention racks. © 2020 John Wiley & Sons, Ltd.  相似文献