Seven decades of hydrogeomorphological changes in a near-natural (Sense River) and a hydropower-regulated (Sarine River) pre-Alpine river floodplain in Western Switzerland

Hydropower alteration of the natural flow and sediment regime can severely degrade hydromorphology, thereby threatening biodiversity and overall ecosystem processes of rivers and their floodplains. Using sequences of aerial images, we quantified seven decades (1938/1942–2013) of spatiotemporal changes in channel and floodplain morphology, as well as changes in the physical habitats, of three floodplain river reaches of the Swiss pre-Alps, two hydropower-regulated and one near-natural. In the Sarine River floodplain, within the first decades of hydropower impairment, the magnitude and frequency of flood events (Q₂, Q₁₀, Q₃₀) decreased substantially. As a result, the area of pioneer floodplain habitats that depend on flood activity and sediment dynamic, such as bare sediments, decreased dramatically by approximately 95%. However, by 2013 vegetated areas had generally increased in comparison to the pre-regulation period in 1943, indicating general vegetative colonization. Between 1943 and 2013, the active channel underwent essential narrowing (up to 62% width reduction in the residual flow reach) and habitat turnover rates were very low (5% of the total floodplain area changed habitat type five to six times). In contrast, from the 1950s onwards, the near-natural floodplain of the Sense River experienced recurrent narrowing and widening, and frequent changes between bare and vegetated areas, reflecting the shifting habitat mosaic concept typical for natural floodplains. In the three reaches investigated, we found that the active floodplain width and erosion of vegetated areas were primarily controlled by medium to large floods (Q₁₀, Q₃₀), which combined with reduced time intervals between ordinary floods ≥ Q₂ most likely mobilized streambed sediments and limited the ability of vegetation to establish itself on bare gravel bars within the parafluvial zone. These findings can contribute to restoration action plans such as controlled flooding and sediment replenishments in the Sarine and other floodplain rivers of the Alps. © 2020 John Wiley & Sons, Ltd.     

水系连通变异下荆南三口河系水文干旱识别与特征分析

为揭示水系连通变异下荆南三口河系水文干旱演变特征,运用荆南三口河系五站1956-2016年的月径流量数据,采用游程理论识别该河系水文干旱特征变量,并运用Kolmogorow-Smirnov优度检验法选出干旱历时、干旱强度和峰值的概率分布函数,构建出水文干旱特征联合分布Copula函数,对水系连通变异下该河系水文干旱特征进行深入研究。结果表明：① 1989年为荆南三口河系（1956-2016年）水系连通变异分割点;② 该河系连通性变异前后水文干旱特征均发生显著变化,水文干旱事件发生的次数增多,干旱历时增长,干旱强度增大,峰值增高;③ 各站点的相同单变量重现期下二维联合重现期在水系连通变异前基本上均比水系连通变异后长,二维同现重现期在水系连通变异前均比水系连通变异后短;④ 水系连通变异后,该河系水文干旱历时、干旱强度和峰值呈现增加趋势,且在相同单变量重现期的情况下,干旱历时更长,干旱强度更大,峰值更高;⑤ 水系连通变异后水文干旱特征的变化幅度与变异前存在差异,不同河系其水文干旱特征的变化幅度不同。     

黄土高原乡村体制转换与转型发展

农户生计方式的改变对研究黄土高原乡村转型发展具有重要意义。以黄土高原苹果优生区的彬县、长武县和旬邑县为研究区,从体制转换的视角出发,基于模糊层次分析、地理探测器和多元线性回归等算法,模拟乡村体制演化的路径,甄别影响乡村转型发展的微观要素,进一步揭示农户家庭体制转换与乡村转型发展之间的互馈机理。研究发现：① 在研究区内抽样选择的130个乡村中,传统农业体制型乡村共有27个,主要分布于黄土梁地貌类型区,新型农业体制型乡村共有96个,主要分布于黄土塬地貌类型区,非农体制型乡村共有7个,主要分布于河谷地貌类型区;② 当乡村地域系统由传统农业型体制向新型农业型体制转变,再至非农型体制的演化路径中,乡村转型发展度在三维空间坐标系中为倒“U”型变化趋势,乡村人口发展度在二维坐标系中表现为下凸递增趋势,乡村经济发展度在二维坐标系中表现为上凸递增趋势,农业经济发展度在二维坐标系中表现为倒“U”型发展趋势;③ 生计方式成为衔接农户家庭体制转换与乡村转型发展的控制性因素,在农户尺度上,由人力资本与自然资本决定,并直接影响到金融资本和物质资本,在村域尺度上,通过与乡村地域系统的人口、经济和农业等3个维度的响应,引导乡村转型发展过程。     

柴达木盆地风况及输沙势特征

利用柴达木盆地13个气象站的风资料,分析了盆地风况和输沙势的变化特征。结果表明：（1）盆地年平均风速2.0~4.4 m·s^-1,自盆地南、北边缘山地到盆地中部逐渐降低。盆地西部主风向为偏西风,风向较集中;东部主风向为偏东风,风向较分散。（2）盆地年平均起沙风速7.0~8.2 m·s^-1,起沙风频率5.1%~26.1%,主要发生在冬、春季,风向以WNW和W为主。（3）盆地输沙势34.0~462.3 VU,盆地西北部属于高风能环境,中部及东南部属于低-中风能环境,方向变率0.45~0.91,风况为窄单峰或宽单峰风况,盆地西北部和东南部差异较大,东部德令哈站与其他地区的合成输沙势方向相反。     

青海湖东岸沙地风沙活动特征

风况、输沙势和输沙量是评价区域风沙活动特征的重要指标。以青海湖东岸的克土沙区为研究区域,利用2013-2014年和2016-2017年风速风向数据及全方位集沙仪的集沙数据,比较分析本区的风沙活动特征。结果表明：（1）2013-2014年,研究区平均风速为2.79 m·s^-1,起沙风出现频率为6.76%;2016-2017年,研究区平均风速为2.63 m·s^-1,起沙风出现频率为6.13%;（2）起沙风风向均以WSW-WNW和ESE-SSE两个方向为主,偏西方向的起沙风增加而东南方向起沙风减少;（3）输沙势季节变化特征基本一致,均表现为春季输沙势最大,夏季输沙势最小;从输沙势年变化趋势来看,本区总体上属于低风能环境;（4）输沙量差异显著,2016-2017年观测点的输沙量比2013-2014年少77.18 kg,但输沙量分布的方向基本一致。植被盖度增加是输沙量减少的主要原因。     

山东鲁西地块断裂构造分布型式与中生代沉积-岩浆-构造演化序列

鲁西地块的断裂构造有两类不同分布型式:一类呈放射状分布, 由陡倾、基底右行韧性剪切带和盖层内复杂力学性质的断裂组成; 另一类呈环绕地块基底核部同心环状分布, 由3个主要盖层伸展拆离带组成, 主滑脱面分别位于古生界盖层与基底间的不整合面、石炭系与奥陶系之间的平行不整合面和中新生代断陷-沉积岩系与新生代火山-沉积物之间的断层。中生代构造变形样式可以分为3个层次:印支期褶皱-逆冲推覆构造、燕山中期NNE轴向的隔槽式箱状褶皱和燕山晚期NW、NNE向共轭正断-走滑断裂。相应地鲁西地块经历了3个成盆期, 即早-中侏罗世、早白垩世和晚白垩世, 这些中生代盆地在空间上的叠置导致了地块内部复杂的盆-山耦合关系。鲁西地块中生代有两个岩浆活动集中时期, 即早侏罗世(约190Ma)和早白垩世(132~110Ma)。综合沉积记录、岩浆活动和构造变形过程, 将鲁西地块中生代构造演化历史划分为6个阶段:晚三叠世挤压变形, 早、中侏罗世弱伸展作用, 中、晚侏罗世挤压变形与地壳增厚作用, 早白垩世大陆裂谷与地壳伸展作用, 早白垩世末期挤压变形与盆地反转事件和晚白垩世区域隆升。这些构造演化阶段和构造事件对研究和理解中生代构造体制和深部岩石圈动力学转换过程具有重要意义。      

水文频率分析述评

对水文频率分析研究进行了回顾与评述,分别对常遇的几个问题——频率曲线线型、经验频率公式、统计参数估计和特殊水文资料应用等作了叙述,总结了我国近50年来在频率分析上的主要成就以及对分析思路、研究探索、实际应用和实践经验等作出剖析。可以认为,现在已发展成一套具有中国特色的水文频率分析方法,为工程所需提供了科学依据,为水文学科的发展作出了贡献。     

Interannual and Decadal Sea-Level Variations along the Japanese Coast

Interannual (an annual to a decadal) and decadal sea-level variations along the Japanese coast have been investigated on the basis of monthly mean sea level during the period from 1951 to 1995. For the interannual variation, the Japanese coast is divided into six regions according to a regional similarity of sea level by using the cluster analysis, which is close to Tsumura's (1963) classification. The first mode of the Empirical Orthogonal Function (EOF) of the Interannual variation is the simultaneous rising and falling of the sea level along the Japanese coast. The first mode shows the largest variation in winter and has a negative correlation with the wintertime monsoon index; this suggests that the first mode is associated with a steric height change depending on the wintertime cooling intensity. The EOF second mode represents the Kuroshio large meander because strong negative eigenvectors are seen on the southeast coast of Japan and the time coefficient shows a high correlation with the Kushimoto-Uragami sea-level difference. For the decadal sea-level variation, the EOF first mode is a bi-decadal variation exhibiting simultaneous rising and falling of the sea level for the entire Japanese coast. The time coefficient of the first mode shows the first minimum in 1965, reaches a maximum in 1975, and decreases to the second minimum in 1984. The decrease from the mid-1970s and the increase from the mid-1980s to early 1990s correspond to the climatic regime shifts occurring in the same periods.     

Relic UHP Structures in Dabie-Sulu Region, China:Structural Expression and Geodynamic Significance

INTRODUCTIONIn recent years a num ber of detailed m ineralogical- petro-logical studies have been carried out on the UHP and HPmetamorphic belts in the Dabie- Sulu region,central China(see review papers by Jahn,1999;Ernst and L iou,1999;Wallis et al.,1999;Hacker et al.,1996 ;L iou et al.,1996 ;Cong et al.,1994) . Various tectonic evolution models for theUHP belt in the Dabie- Sulu region have been constructed(e.g.,Webb etal.,1999;Hacker et al.,1996 ;Cong et al.,1994) .However,as …     

近50年鄱阳湖形态和水情的变化及其与围垦的关系

根据1954、1957、1961、1965、1967、1976、1984年量测的鄱阳湖高程与面积、容积关系,分析鄱阳湖不同时期的形态参数及其变化特征;统计年最高水位的变化,用以揭示水情变化特点。利用典型年交叉调洪计算结果,探讨围垦对洪水位的影响;建立洪水位围垦效应与围垦面积的关系,用以反映洪水位围垦效应随围垦程度而变化的规律;根据退垦效益与退垦面积的关系和湖区大中型圩堤的堤高现状,确定鄱阳湖退垦还湖面积。