Holocene loess in the middle reaches of the Yellow River

Holocene loess in the middle reaches of the Yellow River can be subdivided into three formations, which are composed commonly of upper loess and lower dark loessial soil (a kind of paleosol): the Xifeng Formation of Late Holocene, the Longxi Formation of Middle Holocene and the Luochuan Formation of Early Holocene. The layers of dark loessial soil at similar stratigraphic levels in different localities show such a change in age that samples from south are older than those from north, indicating a northward shift of the climate belt during pedogenesis.     

Impact of monsoonal climatic change on Holocene overbank flooding along Sushui River,middle reach of the Yellow River,China

In the semiarid loess regions, slackwater deposition of overbank flooding over the piedmont alluvial plains was episodic and alternated with dust accumulation and soil formation throughout the Holocene. The records of past hydrological events are therefore preserved within the architecture of loess and soils and are protected from subsequent erosion and destruction. Several Holocene loess–soil sequences with the deposits of overbank flooding over the semiarid piedmont alluvial plains in the southeast part of the middle reaches of the Yellow River drainage basin were investigated by field observation, OSL and C¹⁴ dating, measurement of magnetic susceptibility, particle-size distribution and chemical elements. This enables the reconstruction of a complete catalog of Holocene overbank flooding events at a watershed scale and an investigation of hydrological response to monsoonal climatic change as well. During the Holocene, there are six episodes of overbank flooding recorded over the alluvial plain. The first occurred at 11,500–11,000 a BP, i.e. the onset of the Holocene. The second took place at 9500–8500 a BP, immediately before the mid-Holocene Climatic Optimum. After an extended geomorphic stability and soil formation, the third overbank flooding episode came at about 3620–3520 a BP, i.e. the late stage of the mid-Holocene Climatic Optimum, and the floodwater inundated and devastated a Bronze-age town of the Xia Culture built on the alluvial plain, and therefore the town was abandoned for a period of ca 100 years. During the late Holocene, the alluvial plain experienced three episodes of overbank flooding at 2420–2170, 1860–1700 and 680–100 a BP, respectively. The occurrence of these overbank flooding episodes corresponds to the anomalous change in monsoonal climate in the middle reaches of the Yellow River drainage basin when rapid climate change or climatic decline occurs. During at least the last four episodes, both extreme floods and droughts occurred and climate departed from its normal condition, which was defined as a balanced change between the northwestern continental monsoon and southeastern maritime monsoon over time. Great floods occurred as a result of extreme rainstorms in summers caused by rare intensive meridianal airflows involving northwestward moving tropical cyclone systems from the Pacific. These results could be applied to improve our understanding of high-resolution climatic change, and of hydrological response to climatic change in the semiarid zones.     

长江中游地区暴雨过程的气候背景分析

通过用气候信号场研究长江中游地区暴雨发生的气候异常环境,提出了关于信号场的合成图的检验方法,应用到暴雨规律分析中。分析表明,暴雨与500hPa信号场中异常信号显著区的出现在我国东部上空,分布形势呈‘+-+'的波列是暴雨发生的重要征兆。     

黄河内蒙古河段河道冲淤演变与凌情响应机制

黄河上游内蒙古冲积性河道凌汛问题突出,研究河道冲淤演变与凌情响应机制可为该河段防凌减灾提供技术支持。根据内蒙古河段凌情、河道冲淤演变资料,分析凌情变化表征指标及与之密切相关的河道冲淤演变特征指标,研究河道冲淤演变特征指标与凌情变化表征指标的响应关系。结果表明:河道冲淤演变的特征指标平滩流量与凌情表征指标冰下过流能力、槽蓄水增量关系密切,冰下过流能力为平滩流量的1/5左右,随着平滩流量减小而减小,而槽蓄水增量随着平滩流量的减小而增大,有利内蒙古河段防凌的平滩流量宜不小于2 000 m3/s,槽蓄水增量宜不超过14亿m3。本研究成果可为内蒙古河段冰凌灾害防治提供参考。     

Holocene palaeoflood events recorded by slackwater deposits along the middle Beiluohe River valley,middle Yellow River basin,China

Palaeohydrological investigations were carried out in the middle Beiluohe River valley in the middle Yellow River basin. Palaeoflood slackwater deposits (SWDs) are natural records of overbank flooding and are often identified in the Holocene aeolian loess–soil profiles along the river valley. Three bedsets of palaeoflood SWDs were found within the mid‐Holocene Climatic Optimum palaeosol (S₀) on the right riverbank. Both the sedimentary and the analytical results, including magnetic susceptibility, grain‐size distribution and concentrations of chemical elements, indicate that these palaeoflood SWDs were deposited from the suspended sediment load of overbank flooding. We identified three episodes of extraordinary overbank flooding events. These hydro‐climatic events were dated to 7600–7400, 5800–5000 and 4200–4000 a BP, from optically stimulated luminescence (OSL) dating and pedostratigraphical correlation. The minimum flood peak discharges were estimated to have been between 12 600 and 14 100 m³ s^?1 using the slope–area method. These hydro‐climatic events are considered to be a regional expression of known climatic events and demonstrate that the mid‐Holocene climate was far from stable. These results show that the magnitudes of floods are highly sensitive to climate change in semi‐arid and sub‐humid regions with a monsoonal climate.     

黄河中游响应气候变化和地表相对抬升发育阶地研究

揭示河流系统响应气候变化和地表抬升的机制是理解流域地貌演化以及水系发育过程的基础,其核心难题是如何充分认识它们在阶地发育中扮演的角色.以往的研究倾向于分开讨论气候变化和地表抬升在河流阶地发育中的作用,认为河流堆积/侧蚀和下切行为分别与冰期和间冰期气候对应,或者将阶地作为地表抬升的直接证据.首先,从上下游河段对比的视角初...     

Phenomena and characteristics of barrier river reaches in the middle and lower Yangtze River,China

Alluvial river self-adjustment describes the mechanism whereby a river that was originally in an equilibrium state of sediment transport encounters some disturbance that destroys the balance and results in responses such as riverbed deformation. A systematic study of historical and recent aerial photographs and topographic maps in the Middle and Lower Reaches of the Yangtze River (MLYR) shows that river self-adjustment has the distinguishing feature of transferring from upstream to downstream, which may affect flood safety, waterway morphology, bank stability, and aquatic environmental safety over relatively long reaches downstream. As a result, it is necessary to take measures to control or block this transfer. Using the relationship of the occurrence time of channel adjustments between the upstream and downstream, 34 single-thread river reaches in the MLYR were classified into four types: corresponding, basically corresponding, basically not corresponding, not corresponding. The latter two types, because of their ability to prevent upstream channel adjustment from transferring downstream, are called barrier river reaches in this study. Statistics indicate that barrier river reaches are generally single thread and slightly curved, with a narrow and deep cross-sectional morphology, and without flow deflecting nodes in the upper and middle parts of reaches. Moreover, in the MLYR, barrier river reaches have a hydrogeometric coefficient of \({<}{4}\), a gradient \({>}\)1.2?, a silty clay content of the concave bank \({>}{9.5}\)%, and a median diameter of the bed sediment \({>}{0.158}\) mm. The barrier river reach mechanism lies in that can effectively centralise the planimetric position of the main stream from different upstream directions, meaning that no matter how the upper channel adjusts, the main stream shows little change, providing relatively stable inflow conditions for the lower reaches. Regarding river regulation, it is necessary to optimise the benefits of barrier river reaches; long river reaches without barrier properties should be systematically planned and regulated; drastic bank collapse and sandbar shrinking should be urgently controlled to prevent the loss of barrier effects.     

黄河中游黄土高原地质生态环境综合调查

黄土高原区资源丰富 ,生态环境脆弱 ,地质灾害多发性强 ,危害严重。治黄重点在中游 ,中游关键在地质生态环境的改善。笔者较系统论述了本区自然地理、国土资源、区域地质构造、新构造活动、地球物理场及深部构造特征 ,黄土高原隆升机制和地质灾害、生态环境问题 ,提出了基岩及第四纪地质、矿产和景观旅游资源、生态地质等地质生态综合调查的内容。     

Measuring individual vulnerability to floods in the lower and middle Grijalva River Basin,Tabasco, Mexico

Natural Hazards - We built an easy-to-interpret individual vulnerability index to floods that is amenable for empirical testing and may be adapted to any perceived hazard or ecological setting. An...     

黄河下游高含沙洪水过程一维水沙耦合数学模型

采用浑水控制方程,建立了基于耦合解法的一维非恒定非均匀沙数学模型,用于模拟高含沙洪水演进时的河床冲淤过程.然后采用黄河下游游荡段1977年7—8月实测高含沙洪水资料对该模型进行率定,基于水沙耦合解法的各水文断面流量、总含沙量及分组含沙量的计算过程与实测过程符合更好,计算的沿程最高水位及累计河段冲淤量与实测值也较为符合.最后还采用2004年8月高含沙洪水资料对该模型进行了验证.模型率定及验证计算结果表明,采用一维水沙耦合模型计算高含沙洪水过程,能取得较高的精度.     

Use of oxygen-18 isotope to quantify flows in the upriver and middle reaches of the Heihe River,Northwestern China

In recharge areas, the Heihe River flow was separated into components of ice-snowmelt and precipitation according to 14 gauging stations and to monthly hydrograph using oxygen-18. As shown by the result of the two-component mixing model, on average, 19.8% of the runoff comes from ice-snowmelt. At three stations which are closer to glaciers and with headstream of ice-snow melted water, the ice-snowmelt runoff is larger than 28% of stream water. In addition, because most of the ice-snowmelt infiltrates the groundwater, which later discharges into the river at mountain outlets, the ice-snowmelt percentage in runoff is lower than average at these stations with the elevation higher than 3,600 m. According to monthly hydrograph, the lowest percentage of ice-snowmelt in runoff is in July (6.46%), whereas during November it is the largest (26.1%). In the middle basin, the fraction of groundwater in runoff had a marked increase from 23.57% near Zhangye City to 60.28% near Gaotai City, and then a dramatic drop to 13.61% near Zhengyixia Station because of agricultural flood irrigation in Zhangye Basin.     

基于生态需水的黄河中游水平衡分析

为推动黄河流域生态保护及高质量发展,解决地表水资源供需矛盾,亟需开展水平衡分析,建立水平衡模型,为水资源合理分配提供参考依据。作为黄河的重要支流,沁河流域位于黄河中游末端,由于近年来上游调水政策的施行以及流域内生活、生产用水的增加,用水矛盾突出,出现了河道断流、入黄水量偏枯等问题。为保障河流生态环境健康,优化引沁入汾跨流域提水工程实施后的流域水资源供需平衡,以2021年为现状年,在“自然-人工”二元水循环研究理论的指导下,运用水平衡分析理论与方法,以河道内生态需水为保障基础,对沁河流域水资源需求、供水能力与供需平衡进行了分析与讨论。结果表明：（1）沁河流域水资源供给和需求在空间分布上具有分异性,上游山西省境内各河段河道内均能够保障适宜的生态需水量,下游河南省境内,仅可满足最小生态需水量;（2）沁河流域可供给水资源总量为10.04×108 m3,河道外生产、生活及生态用水总量为8.89×108 m3,剩余河道内水量仅为1.15×108 m3,仅可满足河流最小生态需水;（3）推算至2030年,流域内工业生产及生活取用地表水量将达到6.98×108 m3,河道外用水总量将达到9.81×108 m3,剩余水量无法满足最小生态需水。建议采用降低工业用水量、提高农田灌溉用水利用率、推广使用高效节水技术,进一步增强水资源的有效利用,改善流域生态环境。研究结果可为合理规划沁河流域水资源调度提供参考,也可为黄河中游水平衡分析提供范例。     

Accumulation of heavy metals in the lacustrine sediment of Longgan Lake, middle reaches of Yangtze River, China

Spatial and temporal distribution of heavy metals (Chromium, Copper, Nickel, Lead, and Zinc) in the sediment of Longgan Lake, middle reaches of Yangtze River, China were analyzed to discuss their enrichment characteristics and history in combination with geochronological data and to identify anthropogenic effects. The results showed that the enrichment state of heavy metals was higher in the western versus eastern lake area, although their concentrations behave in the opposite case, which demonstrated that stronger human activities existed in the western lake catchment. The enrichment history of heavy metals pointed out that prior to 1950, the enrichment state was lower in the ambient lake areas illustrating the natural effect on the lake; thereafter the human activities in the catchment enhanced markedly causing an increasing heavy metal enrichment. The increase of heavy metal enrichment in the 1970s occurred in the central lake areas. The temporal difference between the ambient and central areas elucidated that the heavy metal accumulation might be buffered by the lake before they entered the sediment. Correlation analysis revealed that there was a significant correlation between heavy metals in the sediment suggesting their similar sources. Heavy metals were distinctly related to aluminum, calcium, lithium, iron, and organic matters, which could denote their forms in the sediment.     

Ages and genesis of terrace flights in the middle reaches of the Yarlung Zangbo River,Tibetan Plateau,China

Field investigation has shown that the middle reaches of the Yarlung Zangbo River, in Tibet (known as the Bhramaputra River in reaches downstream) has 11 terraces. The ages of these terraces were determined as follows: T₁₁>2000 ka, T₁₀ = 1783 ka, T₉ = 1238 ka, T₈ = 683 ka, T₇ = 382 ka, T₆ = 150 ka, T₅ = 82 ka, T₄ = 67 ka, T₃ = 43 ka, T₂ = 28 ka and T₁ = 10 ka. These terraces formed during several stages of the Quaternary when the Tibetan Plateau was uplifting, recording tectonic–climatic cycles or subcycles of 1.2, 0.4, 0.1, 0.04 and 0.02 million years duration. The tectonic–climatic cycles identified by this study are correlated with red soil and palaeosol records. The preservation of the Oligocene to Early Miocene conglomeratic Dazhuka Formation, close to the present altitude of the main planation surface of the Tibetan Plateau and occurring only in the Yarlung Zangbo valley, suggests that this river has existed since at least 7 Ma. Discoveries of old and thick fluvial gravel layers extending to within 630 m of the valley floor show that the Yarlung Zangbo River was already incised by 2000 m or more below the surface of the Tibetan Plateau, that much of the incision from plateau to valley floor had been accomplished and that the plateau was already substantially uplifted prior to the Quaternary. In addition to its importance for understanding the evolution of the Tibetan Plateau, this study documents the impact of varying rates of tectonic uplift on river development.     

1849年长江中下游大水灾的时空分布及天气气候特征

清道光二十九年（1849年）长江中下游地区的大水灾,对民生造成了严重的影响。作者系统收集了档案、方志、日记和文集资料中关于该年份水灾的记载,以县级成灾分数资料为基础,重建了此次水灾的时空分布,并分析了形成这次水灾的天气气候特征。研究认为,该年度水灾基本在N28°～N33°间呈条状东西向分布,而以N31°一线的灾情最为严重;连续性的降水开始于5月18日左右,到7月18日才结束,中间还有3次持续各达10余天的强降雨过程;这次大水灾是全流域性的,涝灾大于洪灾,降水最集中区域为东部的太湖流域,这和有器测记录的几次长江全流域大洪水并不一致;本次大水灾的直接天气成因是梅雨期提前并超长,雨量明显偏大,持续时间长达62天左右,比有器测记录的更早、更长;当年夏季风应偏弱,副热带高压脊线位置异常偏南,且西风分支明显,经向环流发展,西风南支位置应该也异常偏南;夏季冷空气异常活跃可能是雨带长期在长江沿岸徘徊的真正原因。     

Groundwater flow and geochemistry in the lower reaches of the Yellow River: a case study in Shandang Province, China

Water samples were collected from the Yellow River and from wells for chemical and isotopic measurement in the counties of Yucheng and Qihe, to which 6–9×10⁸ m³ of water is diverted annually from the Yellow River. A zone of high electrical conductivity (EC) in groundwater corresponds well on the regional scale with a ridge in groundwater level, which is the main flow path through the region, but has a low gradient. The zone of highest EC along this ridge occurs at a position with the lowest ground altitude in the study area. The unique characteristic of the groundwater is the linear relationship among the principal anions as the result of mixing. The mixing effect is confirmed by its isotopic signature, which was then used to calculate the contributions from three sources: rainfall, old water, and diverted water with an average mixing rate of 18, 17, and 65%, respectively. As an indicator of water movement, Cl^– content varies across a wide range in the profile from 30–10 m with a maximum concentration at about 1.2 m depth. Concentrations are relatively stable at about 2 m, which is the average boundary of the saturated and unsaturated zone. The water from the Yellow River has proved to be dominant in mixing in the aquifer in terms of groundwater flow and geochemistry. Electronic Publication     

Analysis of non climatic origins of floods in the downstream part of the Kura River,Azerbaijan

Over the past century, there is an increased contribution of non climatic factors to the flood formation processes in the Kura River. Non climatic factors of floods refer to factors that are related to reductions in channel capacity and result in floods. More recently, there are numerous non climatic factors occurring in and around the Kura River basin that have increased the frequency of floods. Sediment accumulation in the riverbed over a long period of time has led to the reduction of channel capacity and has raised the elevation of the riverbed above the surrounding territory. It is illustrated that construction of dykes and levees do not actually prevent flooding, where hydrologic connections between groundwater and surface water are high, since infiltrated waters from channel results in raising of ground waters, causing an effect of “underground flood.” Since underground floods occur when water going from channels raises the level of ground waters, there is an urgent need to carefully investigate the groundwater–surface water connections. With the purpose of predicting floods, the authors suggest defining maximal acceptable flows (MAFs) rather than channel capacities. Results show that high rates of hydraulic conductivity of soils will decrease MAF rates. MAF computations before high-water season allow for further regulation of outlets further downstream in order to prevent flooding and enable flood forecasting. While the study focuses on a specific region, the overall approach suggested is generic and may be applied elsewhere.     

甘肃黑河中下游影响绿洲植被发育的某些因素

黑河下游额济纳绿洲区和中下游沿黑河干流河床附近的潜水位埋深较浅,是维系地表植被生长的重要因素。中游高台附近潜水位存在每年双峰值的变化,较之下游额济纳绿洲潜水位每年单峰值的变化更有利于植被的生长。在包气带剖面中,同一时刻水土势、含水量、含盐量随深度的变化趋势基本相同。采样点包气带土壤中易溶离子含量相对较低,全盐量小于5％,中游采样点土壤中以HCO3^-为主,下游以SO4^2-为主,由SO4^2-、Cl^-和Na^＋、Ca^2＋组成的盐类构成了包气带土壤中的主要盐分。土壤中易溶离子含量自地表至潜水面之间随深度总体上呈减小趋势。植被的根系分布对包气带土壤含水量、水土势和易溶离子含量随深度的分布有着重要的影响,在植物根系发育带的土壤中含水量、水土势和易溶离子含量升高。