Flood risk assessment in Quzhou City (China) using a coupled hydrodynamic model and fuzzy comprehensive evaluation (FCE)

Natural Hazards - To evaluate urban flood risk while considering spatial and temporal characteristics, this paper establishes an assessment method based on a coupled hydrodynamic model and a fuzzy...     

土−水特征曲线测量过程中孔隙分布的演化规律探讨

测量了在宽广吸力范围内原状样和压实样的脱湿持水曲线,对比分析了单双峰结构持水性能的差异;并利用压汞试验测试两种土样在脱湿过程的孔隙分布,分析了两者的差异并探讨了脱湿过程孔隙的演化规律;在考虑收缩变形的基础上,基于孔隙分布曲线确定了土?水特征曲线的基本参数。试验结果表明：原状样在宽广吸力范围内基本上呈单峰孔隙结构;饱和压实样具有单峰孔隙结构,随着吸力的增加,双峰结构越来越明显,当吸力达到很大时,演化成完全双峰孔隙结构。原状样的持水曲线为经典的S形,而压实样的持水曲线在过渡段出现了水平台阶状;低吸力段,压实样的持水曲线低于原状样,而高吸力段,两者的持水曲线基本重合。基于孔隙分布曲线确定了控制持水曲线进气值和残余值的孔径,并计算出对应的吸力值,其值更符合实际物理意义。     

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

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.     

三峡工程运用后坝下游河道泥沙输移变化规律

三峡工程蓄水后"清水"下泄,坝下游河段将会长期处于严重不饱和状态,水流含沙量沿程恢复将会引起坝下游长距离冲刷,本文根据三峡工程蓄水前、后的实测资料分析了坝下游河道泥沙输移变化规律,探索不同粒径组沙量沿程恢复对河床冲刷的影响,得到以下结论:在蓄水初期d≤0.031 mm沙量恢复主要受河床补给与江湖入汇共同的影响,随着水库下泄该粒径组沙量递减,使得各站该粒径组年均输沙量均远小于蓄水前的水平,沙量恢复仍主要受河床补给与江湖入汇的影响,这是造成坝下游河道发生长距离冲刷的主要原因之一;在蓄水初期0.031 mmd≤0.125 mm沙量恢复主要受河床补给的影响,但江湖入汇的影响较大,随着河床补给量逐渐减少,各站该粒径组年均输沙量均小于蓄水前的水平,沙量恢复仍主要受河床补给的影响,江湖入汇的影响逐渐减小,这也是坝下游河道发生长距离冲刷的主要原因之一; d0.125 mm沙量恢复主要受河床补给的影响,蓄水初期该粒径组沙量在宜昌监利河段沿程恢复速率较快,且在监利站达到蓄水前的水平,随着时间推移,在宜昌监利河段沿程恢复且速率仍较快,在监利站达到最大值,其数值逐渐小于蓄水前的水平,这是造成坝下游河道冲刷重点集中在宜昌监利河段的主要原因.     

太湖水体和沉积物细菌群落分布格局及其驱动因素

水体和沉积物是湖泊生态系统中迥异但又紧密相连的两类生境,栖息在这两类生境中的细菌在维持生态系统平衡和驱动元素循环中起着关键性作用。为了探究湖泊水体和沉积物细菌群落的分布格局,本文对太湖四个湖区水体和沉积物中细菌群落进行调查,基于高通量测序技术和统计分析手段,分析这两类生境中的细菌群落组成和多样性水平、分布特征及其驱动因素。结果表明:放线菌门(Actinobacteria)、变形菌门(Proteobacteria)和蓝细菌门(Cyanobacteria)是水体细菌群落中最主要的细菌门,而沉积物中Proteobacteria占据优势地位。在两类生境中,太湖西部区域细菌群落丰富度和独特性(LCBD)相对较高,各区域群落结构表现出显著性差异。对水体而言,电导率、pH值、PC1(重金属组成)和沉积物孔隙度是驱动细菌丰富度的重要因子,PC1、水温及pH值是影响细菌群落LCBD的重要因子,而细菌网络复杂性随pH值的增加而增加,且在高pH环境中占主导地位;对沉积物而言,其丰富度和LCBD的重要影响因子均是沉积物中总磷和锂,细菌网络复杂性随金属元素施加的环境压力增大而降低,但随总磷、磷酸盐和铵态氮浓度的...     

Dynamic simulation of tropical coral reef ecosystem being disturbed by multiple situations

In consideration of the rapid degradation of coral reef ecosystems, the establishment of models is helpful to comprehend the degradation mechanism of coral reef ecosystems and predict the development process of coral reef communities. According to the characteristics of complex ecosystem of tropical coral reefs in China, the coral reef functional group is the core level variable; combined with the multiple feedback effects of coral reef functional groups and environmental changes, the study presents a coral reef ecosystem dynamics model with hermatypic corals as the core. Based on the simulation of the assumed initial value and the internal feedback of the system, the results show that in the basic simulation(relative health conditions), the coverage area of live corals and coral reefs generally decreased first and then increased, and increased by 4.67% and 6.38% between2010 and 2050, respectively. Based on the calibration model and the current situation of the studied area, the multi-factor disturbance effects of coral reef communities were simulated and explored by setting up three scenarios involving fishing policy, terrestrial deposition, and inorganic nitrogen emissions. Among them, in the single factor disturbance, the fishing policy exerts the most direct impact on the community decline; and the succession phenomenon is obvious; the terrestrial sedimentation has a faster and more integrated effect on the community decline; the effect of inorganic nitrogen emission on the community decline is relatively slow. In the double/multi-factor disturbance, the superimposed disturbance will aggravate the multi-source feedback effect of the coral reef communities development, accelerate the community decay rate, and make its development trajectory more complicated and diverse. This method provides a scientific and feasible method for simulating the damage of long-term coral reef community and exploring the development law and adaptive management of coral reef ecosystems. In the future, it can be further studied in the ecological restoration process and decisionmaking direction of coral reefs.     

Magnetic minerals in Mid-Pleistocene sediments on the Caiwei Guyot,Northwest Pacific and their response to the Mid-Brunhes climate event

Seamounts are ubiquitous topographic units in global oceans, and their influences on local oceanic circulation have attracted great attention in physical oceanography; however, previous efforts were less made in paleoclimatology and paleoceanography. The Caiwei Guyot in the Magellan Seamounts of the western Pacific is a typical seamount, and in this study, we investigate a well-dated sediment core by magnetic properties to reveal the relationship between deep-sea sedimentary processes and global climate changes. The principal results are as follows: (1) the dominant magnetic minerals in the sediments are low-coercivity magnetite in pseudo-single domain range, probably including a biogenic contribution; (2) the variabilities of magnetic parameters can be clustered into two sections at ～500 ka, and the differences between the two units are evident in amplitudes and means; (3) changes in the grainsize-dependent magnetic parameters can be well correlated to records of global ice volume and atmospheric CO2 in the middle Pleistocene. Based on these results, a close linkage was proposed between deep-sea sedimentary processes in the Caiwei Guyot and global climate changes. This linkage likely involves different roles of biogenic magnetite in the sediments between interglacial and glacial intervals, responding to changes in marine productivity and deep-sea circulation and displaying a major change in the Mid-Brunhes climate event. Therefore, we proposed that the sedimentary archives at the bottom of the Caiwei Guyot record some key signals of global climate changes, providing a unique window to observe interactions between various environmental systems on glacial-interglacial timescales.     

三种非线性时变识别方法的对比研究——以2021年日本福岛地震为例

利用2021年日本福岛地震(M_JMA 7.3)中6个KiK-net台站的观测记录,分别基于移动窗解卷积法、移动窗谱比法和移动窗自相关函数法对场地非线性时变过程进行研究,分析非线性发生的阈值和程度。研究表明：三种方法识别场地非线性时变特征的稳定性不同。移动窗解卷积法更容易获得较为稳定的土体非线性时变过程,但其反映的是地表至井下平均波速的变化,识别的非线性程度偏低。对于存在强波阻抗比的浅表层土体,移动窗谱比法和移动窗自相关函数法识别的非线性程度更强;对于较低波阻抗比的浅表层土体,则不容易识别出稳定的非线性时变结果。三种方法识别的非线性最强时刻基本一致,皆位于整条记录加速度峰值附近。基于三种方法识别的6个台站的非线性阈值约在40～140 gal,剪切波速下降比在16%～53%之间,场地非线性程度较明显。     

基于ECC的小雁塔抗震加固性能分析

高延性纤维增强水泥基复合材料(ECC)是一种高强度、高延性的新型建筑材料,在加固工程中具有广泛的应用前景。本文利用ECC的高延性和抗剪性,提出一种采用ECC面层加固小雁塔的保护方案,以提高古塔抗震性能;通过有限元软件ANSYS进行模拟分析,比较了小雁塔加固前后的地震响应。分析结果表明:采用ECC面层加固可显著增强塔身整体的延性和承载力,有效地提高塔体损伤容限,为ECC在古塔抗震加固的实际应用中提供借鉴,可作为古塔抗震保护的新途径。     

中晚全新世毛乌素沙地东南部气候变化过程

位于中国北方半干旱区的毛乌素沙地对气候变化响应敏感,是研究气候变化的理想区域。通过对毛乌素沙地东南部锦界剖面磁化率、有机质含量、CaCO₃含量的分析,重建了7.5 ka BP以来的气候变化过程。结果显示：中晚全新世毛乌素沙地东南部环境与气候变化可分为3个阶段：7.5～4.6 ka BP,夏季风占主导,气候暖湿,与全新世大暖期对应;4.6～3.3 ka BP,气候突变为干冷并波动频繁;3.3～2.5 ka BP气候以干冷为主。另外,存在5次千年尺度的干旱事件：7.0～6.8 ka BP、6.6～5.7 ka BP、4.6～4.1 ka BP、3.7～3.5 ka BP、3.3～2.5 ka BP。研究区气候变化与全球具有较好的一致性。