浅水方程模拟中确定糙率的回归系数法

基于水流模拟本身就是模拟模型回归求真(即实体原型)过程的认识,从模拟模型和实体原型之间的相关关系出发,应用统计学中的线性回归分析方法,通过回归系数建立了模型与原型糙率系数之间的关系式,提出了二维浅水方程模拟中糙率确定的回归系数法。数值试验表明,该方法并不依赖于糙率系数的初值,具有稳定性好、收敛速度快的特点;对磨刀门水道水流的数值模拟应用显示,该方法能有效地改善模拟计算的精度,具有较好的适应能力,简便实用,为二维浅水流动模拟计算时率定糙率系数提供了一种有效途径。     

俯冲洋壳的折返及其相关问题讨论

大洋俯冲带中高压(HP)和超高压(UHP)岩石的折返机制一直以来都是俯冲工厂中最不为人知的问题之一.本文根据搜集全球折返到地表的洋壳榴辉岩基础数据(包括岩石学特征、峰期温压条件和折返P-T轨迹),初步探讨了洋壳榴辉岩的折返机制.根据峰期矿物组合、温压条件和对应的地温梯度,典型大洋俯冲带中的榴辉岩可以分为三类:含柯石英的UHP硬柱石榴辉岩(2.7～ 3.2GPa,470 ～ 610℃,5～7℃/km)、HP硬柱石榴辉岩(1.7～2.6GPa,360～ 620℃,5～8℃/km)和HP绿帘石榴辉岩(1.5 ～2.3 GPa,540 ～ 630℃,7～12℃/km).与大陆俯冲碰撞造山带中的HP-UHP榴辉岩相比,洋壳榴辉岩具有较低的峰期温压条件和较高的低密度含水矿物的含量,但是普遍缺失高密度的蓝晶石.已有的俯冲洋壳的折返模式都基于一个假设:洋壳榴辉岩密度比周围地幔大.因此,洋壳榴辉岩的折返必须借助于低密度的蛇纹岩或者变沉积岩.MORB体系的热力学模拟研究表明,俯冲洋壳的矿物组合、矿物含量和密度主要受低密度含水矿物(如硬柱石、绿泥石、蓝闪石和滑石等)的稳定性控制,并且在同等深度条件下,冷俯冲洋壳的密度低于热俯冲洋壳的密度.经历冷俯冲(～6℃/km)洋壳的密度在＜ 110～ 120km(P ＜3.3 ～ 3.6GPa)的深度仍小于周围地幔,但是经历热俯冲(～ 1O℃/km)洋壳的密度在＞60km(P＞1.8GPa)的深度就已经超过周围地幔.结合高温高压实验资料和地球物理观察数据,我们认为在＞120km的深度,俯冲基性洋壳本身密度大于周围地幔,不存在低密度的地幔楔蛇纹岩(蛇纹石已发生分解),并且大洋板块的俯冲角度突然增大可能阻碍了更深部的低密度变沉积岩的折返.以上这三个方面的原因可能导致现今折返到地表的洋壳榴辉岩和变沉积岩的形成深度普遍小于120km.折返过程中硬柱石脱水分解会导致洋壳密度增大,退变形成的蓝晶石榴辉岩的密度大于周围地幔,无法折返,这可能是全球洋壳榴辉岩中普遍缺失蓝晶石的主要原因.     

苏里格大气田多成因河道砂体的分布模式研究

以鄂尔多斯盆地苏里格大气田二叠系下石盒子组盒8段河道砂体为研究对象,开展盒8段河道砂体成因类型及分布模式的研究。详细的岩心观察和相标志研究表明,盒8下段为辫状河砂体,盒8上段为曲流河砂体,局部发育网状河砂体。岩性、岩相与砂体的含气性的关系密切,含气砂体与砂岩中的粗岩相单元有良好的对应关系,粗岩相主要发育在高能辫状水道、心滩及曲流河下部边滩内。河道砂体分布模式研究表明,盒8下段发育高能辫状河砂体与低能辫状河砂体模式,盒8上段具有北部网状河、南部曲流河的分布模式。     

一种改进的GNSS／INS非相干深组合导航

针对GNSS／INS非相干深组合导航中通道滤波器状态模型中信号幅值估测不准而导致跟踪环路观测噪声较大的问题,提出了一种改进的GNSS／INS非相干深组合导航方法。该方法通过去除通道滤波器中信号幅值状态变量,增加载波相位变化率加速度误差,重新设计了通道滤波器数学模型。仿真结果表明：相比于传统的非相干深组合导航方法,这种滤波器的跟踪性能与导航精度有了进一步提高。     

矿产资源运输通道概述

全球矿产资源垄断格局使得中国很多重要进口矿产资源来源较为集中,而中国对进口资源的运输通道控制力较弱,影响矿产资源供应安全。本文对中国矿产资源管道运输、海运及陆运进行了概述,分析目前存在的问题,并提出建议：开辟多元进口油气运输通道,加强科技创新,降低远距离运输安全风险;北极航线的开辟将使世界矿产资源贸易和战略格局产生重大调整;加快推进＂丝绸之路经济带＂和＂海上丝绸之路＂等。     

Temporal and spatial changes of the basal channel of the Getz Ice Shelf in Antarctica derived from multi-source data

Basal melting is an important factor affecting the stability of the ice shelf. The basal channel is formed from uneven melting, which also has an important impact on the stability of the ice shelf. Therefore, it has important scientific value to study the basal channel changes. This study combined datasets of Mosaics of Antarctica, Reference Elevation Model of Antarctica (REMA) and Operation IceBridge to study the temporal and spatial changes of basal channels at the Getz Ice Shelf in Antarctica. The relationships between the cross-sectional area and width of basal channel and those of its corresponding surface depression were statistically analyzed. Then, the changes of the basal channels of Getz Ice Shelf were derived from the ICESat observations and REMA digital elevation models (DEMs). After a detailed analysis of the factors affecting the basal channel changes, we found that the basal channels of Getz Ice Shelf were mainly concentrated in the eastern of the ice shelf, and most of them belonged to the ocean-sourced basal channel. From 2009 to 2016, the total length of the basal channel has increased by approximately 60 km. Affected by the warm Circumpolar Deep Water (CDW), significant changes in the basal channel occurred in the middle reaches of the Getz Ice Shelf. The change of the basal channels at the edge of the Getz Ice Shelf is significantly weaker than that in its middle and upper reaches. Especially in 2005–2012, the eastward wind on the ocean wind field and the westward wind around the continental shelf caused the invasion and upwelling of CDW. Meanwhile, the continuous warming of deep seawater also caused the deepening of the basal channel. During from 2012 to 2020, the fluctuations of the basal channels seem to be caused by the changes in temperature of CDW.     

Architecture,formation and implication of active structure-controlled intraslope channel system southeast offshore Sendai,Tohoku, Japan

Located off the Pacific coast of central Tohoku (NE Japan), the Ishinomaki slope channel (ISC) provides an excellent opportunity to study a structure-controlled intraslope channel and downslope sedimentation along the active margin. The seismic reflection data across ISC show an extensive basal surface and overlying channel complexes between the basement structures of the Abukuma ridge to the south and Kitakami massif to the north, indicating that the formation of the intraslope basin, channelization of ISC and sedimentation of the downstream channel-lobe transition zone (CLTZ) are very likely to be structure-controlled. The oblique channel stacking pattern, faulting of the seafloor and subsurface Abukuma ridge in the upper and lower domains of ISC, collectively suggest that ISC has migrated northward and is currently under the influence of active compression. Differences in styles of accommodation space between the upper and lower domains of ISC suggest that differential subsidence occurred along the strike-slip tectonic line. Based on the regional strike-slip tectonic line, we propose that a Kitakami-Abukuma ridge existed before the formation of ISC. The strike-slip faulting divided the Kitakami-Abukuma ridge into the Kitakami massif to the north and the Abukuma ridge to the south, and an intervening fault trough as the precursor of the intraslope basin and ISC. As the subduction of the Pacific Plate and associated compressional events continued, the Abukuma ridge was reactivated to narrow the intraslope basin into a confined channel. Located near the epicentre of the devastating 2011 Tohoku earthquake event, the ISC, downstream CLTZ and underlying intraslope basin provide information on active basement structure and the evolving sediment routing system on the tectonically active margin.     

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Edelvang, Karen; Larsen, Michael; Pejrup, Morten: Tidal Variation in Field Settling Velocities of Suspended Sediment in a Tidal Channel. Geografisk Tidsskrift 92:116–121. Copenhagen 1992.

Particles of silt and clay may form large, low density floes when suspended in salt water. The sediment floes have settling velocities much higher than the single small particles constituting them and therefore, the flocculation process may strongly influence the transport of cohesive sediment in estuarine environments. will be described in this paper, the field settling velocities of suspended sediment were investigated in a large tidal channel with tidal current velocities up to 1.3 m/s and depths of about 10 m. The analyses of suspended sediment were made on both bottom and surface samples. For the bottom samples, equivalent median fall diameters in the range 26–98 μm were measured. For surface samples, the range was 15–40 μm. During most of the tidal period, the occurrence of much larger settling diameters near the bottom was due to the suspension of individual sand and silt particles. For the investigated periods, high-tide was the only possible time to observe flocculation influencing the vertical distribution of finegrained sediment in the water column.     

Hydrologic and geomorphic flow thresholds in the Lower Brazos River,Texas, USA

Abstract

River science and management often require a design or reference discharge. The common (and sometimes unavoidable) use of such discharges may, however, obscure the fact that the magnitude and frequency of critical flows can differ due to various hydrological, geomorphological, and ecological criteria. Threshold stages and discharges were identified for six lower Brazos River, Texas gaging stations corresponding to thalweg connectivity, bed inundation, high sub-banktop flows, channel–floodplain connectivity (CFC), and overbank flooding. Critical flows were also identified for estimated thresholds for sandy bedform and medium gravel mobility, critical specific stream power for potential channel modifications, and cohesive-bank channel erosion. These thresholds have variable relationships to mean, median, and maximum flows. For four of the six stations, daily recurrence probabilities for all but flood flows are at least 1%, and as high as 11%. All stations achieve channel–floodplain connectivity at stages less than banktop. Estimated threshold flows for sediment mobility and channel erosion occur relatively frequently, with daily probabilities of 2–77%. Critical flows for bank erosion occur least often, and for sandy bedform and gravel mobility most often. Thalweg connectivity is always maintained at all sites, while bed inundation flows have a daily probability of about 80% or more. Overall, results suggest that no single flow level is dominant in hydrological or geomorphic dynamics, and that the frequency of a given threshold varies considerably even along a single river. The results support the idea that multiple flow levels and ranges are necessary to create and maintain the hydrological, geomorphological, and ecological characteristics of rivers, and that no single flow level is a reliable determinant of fluvial state.

Editor Z.W. Kundzewicz; Associate editor Q. Zhang     

Geomorphic coupling between hillslopes and channels in the Swiss Alps

The coupling relationships between hillslope and channel network are fundamental for the understanding of mountainous landscapes' evolution. Here, we applied dendrogeomorphic methods to identify the hillslope–channel relationship and the sediment transfer dynamics within an alpine catchment, at the highest possible resolution. The Schimbrig catchment is located in the central Swiss Alps and can be divided into two distinct geomorphic sectors. To the east, the Schimbrig earth flow is the largest sediment source of the basin, while to the west, the Rossloch channel network is affected by numerous shallow landslides responsible for the supply of sediment from hillslopes to channels. To understand the connectivity between hillslopes and channels and between sources and sink, trees were sampled along the main Rossloch stream, on the Schimbrig earth flow and on the Rossloch depositional area. Geomorphic observations and dendrogeomophic results indicate different mechanisms of sediment production, transfer and deposition between upper and lower segments of the channel network. In the source areas (upper part of the Rossloch channel system), sediment is delivered to the channel network through slow movements of the ground, typical of earth flow, shallow landslides and soil creep. Contrariwise, in the depositional area (lower part of the channel network), the mechanisms of sediment transfer are mainly due to torrential activity, floods and debris flows. Tree analysis allowed the reconstruction of periods of high activity during the last century for the entire catchment. The collected dataset presents a very high temporal resolution but we encountered some limitations in establishing the source‐to‐sink connectivity at the catchment‐wide scale. Despite these uncertainties, for decennial timescales the results suggest a direct coupling between hillslopes and neighbouring channels in the Rossloch channel network, and a de‐coupling between sediment sources and sink farther downstream, with connections possible only during extraordinary events. Copyright © 2012 John Wiley & Sons, Ltd.