黄河三角洲浅层地下水位年内变化特征及影响因素

基于黄河三角洲地区3个站位的1小时一次的浅层地下水位连续观测记录,将浅层地下水位与同时期ERA5高分辨率再分析实际蒸发量数据结合,并联合潮位、降水量和径流量等数据,通过快速傅里叶变换、时序分析等方法,分析并阐明了黄河三角洲地区浅层地下水位变化的特征及机制。结果表明：（1）不同的沉积环境导致了浅层地下水位整体变化的差异。表层沉积物渗透性相对较强区域,浅层地下水位波动剧烈;而表层沉积物透水性较差地区,浅层地下水位在6月中上旬存在低谷,但总体相对稳定;（2）潮汐对黄河三角洲浅层地下水位在水平方向的影响范围至少可达7km,但不超过15km。在其影响区域内,浅层地下水位波动滞后于潮汐的时间存在年内变化,分为两个时间上持续各6个月的区间,二者数值相差约12h;（3）降水量与实际蒸发量是黄河三角洲浅层地下水位升降最主要的影响因素。此外,农业活动也对浅层地下水位的变化有一定影响。对黄河三角洲浅层地下水位变化规律研究,能够为本地区土地盐碱化、海水入侵灾害防治与生态保护提供科学依据。     

GENERATION OF SYNTHETIC SEDIMENTGRAPHS

A procedure for deriving sedimentgraphs in watersheds is proposed. The method is based on the instantaneous unit hydrograph theory developed for flood prediction and on the convolution integral theory. This procedure could be applied to any watershed where basic physical information is available (areas, slopes, length of channels, soil type). A qualitative comparison between results obtained and those published previously produced satisfactory results. Thus it is possible to conclude that the procedure is adequate. However, it is also necessary to compare it with real field measurements.     

一种土的阻尼比近似计算方法

提出了一种用多边形逼近滞回曲线计算土的阻尼比的方法,该方法可直接利用试验数据进行计算,算法可重复利用,使得阻尼比的计算工作得以简化。将其与传统的椭圆拟合方法计算结果进行了对比,由于实测的滞回圈不是标准的椭圆,两者的计算结果存在一定的差异。     

Sediment dynamics of an allogenic river channel in a very arid environment

Despite a growing interest in the sediment dynamics of dryland rivers, most research has been based on ephemeral streams in endogenic hydrological systems (runoff and sediment transport determined by local precipitation). Less attention, however, has been paid to allogenic and perennial dryland rivers. Here, we report a case study on the suspended sediment dynamics of the Tarim River, an allogenic and perennial river flowing in a very arid environment in China, based on mean daily discharge and mean daily suspended sediment concentration (SSC) over the last 5 decades (1960–2011). Results reveal that discharge and SSCs are predominantly low and have distributions with large positive skewness. The SSC–discharge relationships can be fairly well generalized by power functions, with quite large scatter at extreme (low and high) flow conditions. Marked temporal and spatial variations were observed in the effective discharge for sediment transport. The frequency of the effective discharge ranged from 0.5% to 2% (or an average flow duration of 2–7 days/year), implying that moderate to high flows play an important role in sediment transport. The sediment rating curves show strong hysteresis effects, with 3 types of hysteresis loops observed, clockwise (the most predominant), anticlockwise, and figure of eight. The high potential for bank collapse near the peak and falling limb of the flood hydrograph is the major cause of anticlockwise and figure‐of‐eight hysteresis loops.     

Seismic demands on nonstructural components anchored to concrete accounting for structure-fastener-nonstructural interaction (SFNI)

This paper investigates the influence of the hysteretic shear behavior of postinstalled anchors in concrete on the seismic response of nonstructural components (NSCs) using numerical methods. The purpose of the investigation is to evaluate current design requirements for NSC and their anchorage. Current design guidelines and simplified methods, such as floor response spectra (FRS), typically approach the dynamics of the structure-fastener-NSC (SFN) system using simplified empirical formulae. These formulations decouple the structure from the NSC and neglect the behavior of the anchor connection, with the assumption of full rigidity. There is a lack of knowledge on the complex interaction between a host structure, the fastening system, and the NSC, herein referred to as structure-fastener-nonstructural interaction (SFNI). More specifically, it is important to investigate whether and how the actual hysteresis shear behavior that takes place in the anchorage could alter the seismic response of the SFN system and its components. Herein, the results of extensive nonlinear dynamic analyses (NLDA) with different models for the anchorage force-displacement relationship are presented and compared with those obtained with FRS procedures and current code provisions. The anchor models include (a) linear-elastic, (b) bilinear, and (c) a recently developed hysteresis rule. The results of the NLDA showed that the first two approaches are not able to reflect the behavior of an anchor loaded in dynamic shear. Moreover, when using the more refined hysteresis model, it appears that current code provisions might underestimate the component and anchor shear amplification factors for rigid NSC fixed to the host structure through anchors.     

Enhanced hysteresis of suspended sediment transport in response to upstream damming: An example of the middle Yangtze River downstream of the Three Gorges Dam

The peak in sediment transport in alluvial rivers generally lags behind the peak in discharge. It is thus not clear how the hysteresis in the sediment/discharge relationship may be impacted by damming, which can fundamentally alter the water and sediment regimes in the downstream reaches of the river. In this study, a total of 500 flood events in the Yichang–Chenglingji Reach (YCR) of the Middle Yangtze River immediately downstream of the Three Gorges Dam (TGD) are analysed to study the impacts of dam operations on the hysteresis of suspended sediment transport. Sediment rating curves, hysteresis patterns, as well as lag times, are investigated to determine the relationship between suspended sediment concentration (SSC) and flow discharge (Q) at different temporal scales, from inter-annual to individual flood events, for the pre- and post-TGD period from 1992 to 2002 and from 2003 to 2017, respectively. The results showed that the TGD operation decreased the frequency and magnitude of floods. The decrease in peak flow and increase in base flow weakened the flood contribution to the annual discharge by nearly 20%. However, the relative suspended sediment load contribution during flood events was much higher than the discharge contribution, and was little impacted by the dam. At seasonal and monthly scales, more than 80% of the suspended sediment was transported by ~65% of the water discharge in the summer and early autumn. The monthly SSC–Q relationship changed from a figure-eight to an anti-clockwise pattern after the construction of the TGD. For single flood events, the TGD operations significantly modified the downstream SSC–Q hysteresis patterns, increasing the frequency of anti-clockwise loops and the lag time between peak Q and peak SSC. These adjustments were mainly caused by differences in the propagation velocities of flood and sediment waves and the sediment ‘storage–mobilization–depletion’ process, whereas the influence of lateral diversions was small. © 2020 John Wiley & Sons, Ltd.     

基于变轴力柱恢复力模型的钢框筒地震反应分析

建立了考虑轴力变化影响的钢结构杆件的恢复力模型,介绍了模型构成和经试验比较得到的模型的适用性,采用这一模型,对钢框筒结构进行了多维地震作用下的非线性分析,对这类结构的弹塑性特征进行了考察。     

L波段与59-701探空系统相对湿度对比分析

通过统计全国探空系统早期换型时获取的59个高空站L波段雷达-GTS1型电子探空仪系统相对于59-701探空系统在1000 hPa到200 hPa之间各规定等压面相对湿度的差值,分析探空系统换型对于相对湿度一致性的影响。结果表明:GTS1型探空仪测得的相对湿度明显比59型探空仪低,且差值随高度增加而增大,近地层二者相对湿度差值低于5%,200 hPa高度二者差值达到20%以上;冬季两套探空系统相对湿度的差值明显大于夏季,且差值随高度分布情况不尽相同。分析表明:相对湿度差值的变化除了与探空仪施放过程中外界温度变化相关,还与湿度变化趋势和变化幅度密切相关,湿度传感器存在湿滞回线和滞后现象。分析还发现,太原无线电一厂与上海长望气象科技有限公司制造的59型探空仪的性能差异不明显,且GTS1型探空仪与59型探空仪的两种湿度传感器在白天受太阳辐射的残余影响差异也不明显。     

草甸草原降水特征与土壤水分对降水脉动响应——以呼伦贝尔草原额尔古纳市为例

利用额尔古纳牧业气象试验站降水量与土壤水分数据,通过降水与土壤水分动态变化及转化过程分析,确定土壤水分响应的降水临界值与不同降水级别引起土壤水分响应的概率,构建了降水过程量与土壤水分增量函数关系。结果表明：（1） 研究区降水量呈“先降后升”变化趋势,年内降水量呈单峰型分布。（2） 研究区以无降水天气为主,降水又以小降水事件占主导,大降水事件发生频次低、过程降水量大,小降水事件则相反。（3） 可以引起研究区0~50 cm各层土壤水分响应的降水临界值分别为8.1 mm、10.1 mm、19.0 mm、27.9 mm和31.6 mm,小雨仅能引起0~10 cm土壤水分响应的概率为28.6%,中雨不能引起40~50 cm土壤水分的响应。（4） 降水量与0~10 cm和10~20 cm土壤水分达到最大值时的滞后时间呈现出极显著负相关关系,与20~30 cm呈显著负相关关系,0~30 cm各层土壤水分达到最大值时的滞后时间与降水量符合幂函数关系。（5） 降水量和0~50 cm土壤水分增量均呈现出极显著正相关关系,降水量与0~10 cm和10~20 cm土壤水分增量符合线性关系,与20~30 cm、30~40 cm和40~50 cm土壤水分增量符合多项式关系。检验结果表明,构建的函数模型可以较好地模拟研究区0~30 cm各层水分增量。研究结果为地方政府抗旱减灾提供了科学依据。     

江汉盆地马王庙油田自生磁铁矿与烃运移相互关系研究

研究表明，已知油井M36井Ⅱ油组的含油层（位于Ⅱ油组的中—下部）中有明显呈规律分布的强磁性层。以平均值为例，含油岩层屑的饱和磁化强度Js=352.58A/m，饱和剩磁Jc=60.43A/m；而干层的Js=147.34A/m，Jr=22.09A/m。磁滞回线特征表明，含油层岩屑中以偏软的磁性矿物为主（平均矫顽力Hc=33.5mT，饱和磁场Hs=0.25T），而干层岩屑中主要为磁性偏碱的磁性矿物（Hc=44.2mT，H8=0.4T）。重矿物分析结果显示，干井M46井Ⅱ油组岩屑中含沙射影有较多的碎屑磁铁矿。磁学与矿物学参量的对应分析表明，含油层强磁性岩层的载体为自生成因的磁铁矿，而菱铁矿与黄铁矿为非磁性矿物，对Ⅱ油组岩层的磁性没有影响。由此，我们提出M36井含油层中的自生磁铁矿可能是原油的生物降解作用、碎屑矿物中高价铁的被置换及后期菱铁矿的氧化作用等多种不同时空条件下形成的产物。