Assessment of intermediate fine sediment storage in a braided river reach (southern French Prealps)

This paper presents a field investigation on river channel storage of fine sediments in an unglaciated braided river, the Bès River, located in a mountainous region in the southern French Prealps. Braided rivers transport a very large quantity of bedload and suspended sediment load because they are generally located in the vicinity of highly erosive hillslopes. Consequently, these rivers play an important role because they supply and control the sediment load of the entire downstream fluvial network. Field measurements and aerial photograph analyses were considered together to evaluate the variability of fine sediment quantity stored in a 2·5‐km‐long river reach. This study found very large quantities of fine sediment stored in this reach: 1100 t per unit depth (1 dm). Given that this reach accounts for 17% of the braided channel surface area of the river basin, the quantities of fine sediment stored in the river network were found to be approximately 80% of the mean annual suspended sediment yields (SSYs) (66 200 t year^?1), comparable to the SSYs at the flood event scale: from 1000 t to 12 000 t depending on the flood event magnitude. These results could explain the clockwise hysteretic relationships between suspended sediment concentrations and discharges for 80% of floods. This pattern is associated with the rapid availability of the fine sediments stored in the river channel. This study shows the need to focus on not only the mechanisms of fine sediment production from hillslope erosion but also the spatiotemporal dynamics of fine sediment transfer in braided rivers. Copyright © 2010 John Wiley & Sons, Ltd.     

Does upward seepage of river water and storm water runoff determine water quality of urban drainage systems in lowland areas? A case study for the Rhine–Meuse delta

The water quality of urban drainage ditches in lowlands in the Rhine‐Meuse delta was analysed with principal component analysis (PCA) during a dry period and a rain storm, and related to the seepage of polluted river water and effective impervious area (EIA). This was done in order to test the hypothesis that seepage of river water and storm water runoff from impervious areas strongly determine the water quality of urban drainage systems along large lowland rivers. Our analysis revealed that upward seepage of groundwater originating from rivers Rhine and Meuse was positively correlated with nitrate, potassium, sodium and chloride and negatively correlated with alkalinity, calcium, magnesium and iron. EIA was correlated with very few environmental variables (i.e. phosphate, pH and iron in the dry period and iron during the rain storm). Nickel and zinc concentrations generally exceeded the maximum allowable concentrations (MAC), while lead and phosphorus concentrations were just above the nutrient standards and MAC in a few locations during the rain storm. To optimize water quality in urban water systems, attention should be paid to all sources of pollution and not only to EIA. The impact of local groundwater seepage originating from large rivers in lowlands on the chemistry of urban water systems is often underestimated and should be taken into account when assessing water quality and improving water quality status. Copyright © 2009 John Wiley & Sons, Ltd.     

惠民凹陷大芦家地区馆陶组三段沉积微相类型及空间展布

针对惠民凹陷大芦家地区各断块地层单元划分不一致,沉积相认识存在分歧等问题,依据旋回级次、旋回性质等,将馆陶组三段划分出2个四级旋回、4个五级旋回、16个六级旋回;并以岩芯及室内分析资料、测井资料等为主要依据,综合分析岩石类型、粒度及结构特征、垂向粒序变化、层理构造类型及自然电位曲线形态等。结果表明:惠民凹陷大芦家地区馆陶组三段主要发育冲积扇及辫状河;冲积扇主要发育辫流砂岛、辫流沟道、辫流带、漫流席状砂、远端砂丘等微相;辫状河主要发育心滩,辫状河道充填,天然堤、漫滩和道间洼地沉积,泛滥平原沉积,废弃河道等微相;2个四级旋回的沉积相类型及空间展布特征相似;第Ⅰ五级旋回在研究区中偏西部属冲积扇沉积,主要发育辫流砂岛、辫流沟道、辫流带微相,在东部属扇前平原沉积;第Ⅱ五级旋回早期以辫状河沉积为主,河道规模较大,仅在第Ⅱ1六级旋回的东北部位见冲积扇的辫流砂岛及辫流沟道微相;第Ⅱ五级旋回中期属辫状河沉积,河道规模减小,2个河道群自NW向SE方向流动;第Ⅱ五级旋回晚期河道规模更小,逐渐向曲流河沉积过渡。     

西峰油田三叠系延长组长2_2砂层组沉积相分析

通过对西峰油田三叠系延长组长22砂层组的泥岩颜色、岩石类型、沉积构造、生物化石、沉积层序以及单井相等的研究,认为延长组长22油层主要沉积相为正常三角洲沉积。三角洲平原是该区三角洲砂体堆积的主体。可进一步辨别出分流河道、天然堤、分流间湾及决口扇4个微相。     

黄河三角洲北部海域的冲淤演化与成因

利用8个典型的固定剖面资料,对坡度、水深、沉积物底质、单宽侵蚀量和淤积量进行了分析。研究表明:黄河改道后,CS5—CS8剖面的三角洲前缘和前三角洲的侵蚀较为剧烈,各剖面三角洲前缘侵蚀较为强烈;蚀淤泥沙在纵向上由三角洲前缘向前三角洲搬运,在横向上沿近岸向西北方向运移;近岸颗粒粗化较为显著,尤其是在废弃的流路入海口处。     

800年来苏北废黄河三角洲的演变模式

根据历史资料、数据和相关研究,结合研究区域背景,分析苏北废黄河三角洲的演变。结果显示,岸线演变在发育阶段和侵蚀阶段分别为向海延伸约90 km和侵蚀后退约22 km,面积相差约800 km2,三角洲地貌演变表现为岸线平直-曲折-平滑-平直的过程。在废三角洲陆海相互作用的基础上,运用演化模式分析三角洲的演变过程。该三角洲演变可以分为7个演变阶段,发育期在径流和潮流作用下以沙洲并陆淤积延伸方式进行,侵蚀期在波浪和潮流作用下以沙洲合并侵蚀后退和淤积外长交替侵蚀的方式。泥沙输运、人类活动和气候变化对废三角洲的演变有重要影响,巨量的来沙是三角洲发育的原因,泥沙平衡被打破是侵蚀的主要原因。发育期中,泥沙输运影响淤积速度和位置,人类活动和气候变化影响黄河河道迁移、输沙量和产沙量;侵蚀期中,泥沙输运影响侵蚀状态,人类活动在一定程度上影响海岸带冲/淤,气候变化将影响三角洲的演变趋势。     

江西省鄱阳湖信江决口三角洲沉积特征及模式

利用实地考察、浅钻孔、探槽及卫星影像等方法,对鄱阳湖信江决口三角洲进行了系统研究。该决口三角洲是洪水冲破信江西岸天然堤流入附近的河漫湖泊形成的,其平面形态为鸟足状,总体延伸方向与主河道近垂直。在横切剖面上整个决口三角洲沉积体呈透镜状覆盖在早期的湿地或河漫湖泊沉积之上。鄱阳湖信江决口三角洲可分为3个亚相:决口三角洲平原、决口三角洲前缘和决口前三角洲。决口三角洲平原主要发育决口河道、决口天然堤、废弃决口河道和湿地,其中决口河道又可以进一步划分为决口水道、边滩、汊口滩;决口三角洲前缘主要发育河口坝、支流间湾。河漫湖泊规模小、深度浅、波浪能量弱,对河口坝和决口河道砂体的改造较弱,不易形成连片分布的席状砂;决口前三角洲不发育。决口三角洲沉积受河流作用和河漫湖泊作用的共同控制,其演化可以划分为主河道天然堤生长阶段、决口初期阶段、进积分汊阶段及分汊—废弃阶段4个阶段。     

祁连山造山作用与岩石圈地幔的特型结构构造

本文探讨了祁连山地壳增厚与造山机制。提出新生代以来,由于印度地块向北推进,其延迟的远程效应使祁连地块内4条断裂再次活动,特别是23 Ma以来,分阶段的活动使上地壳缩短了30%,40 km厚的祁连地壳增加到57km厚;并通过柴达木地块下地壳物质的挤入,使祁连地块地壳厚度增加到现今的60~74 km;地壳质量基本平衡表明其下部地壳物质横向迁移较小,即走滑断裂带走的地壳物质较少。依据INDEPTH-V新的宽频地震调查成果,提出祁连地块下岩石圈地幔的复杂结构,南部来的昆仑岩石圈地幔(双层结构)与北部向南俯冲的阿拉善地块下的亚洲岩石圈地幔在祁连地块深部相碰撞,而柴达木—祁连岩石圈地幔则被保存在昆仑岩石圈与亚洲岩石圈地幔碰撞带之上,共形成一倒三角汇聚区;在柴北缘与中祁连北缘岩石圈地幔各出现一条北倾和南倾的正转换震相,可能是老俯冲带残存岩片的显示;在祁连地块岩石圈地幔的两端地壳底部还出现有"双"莫霍"现象",地表见有多条榴辉岩带。以上结果构成了高原最具特色的构造区。     

利用DS-InSAR技术监测黄河三角洲地表形变

针对黄河三角洲地区湿地及农田多、范围大,导致PS-InSAR技术难以获取高密度地表形变信息的问题,提出一种基于分布式目标InSAR（DS-InSAR）的黄河三角洲地表形变监测方法。该方法通过置信区间估计选取同质像元点,利用特征值分解方法计算主散射体对应相位值以达到相位优化的目的,再根据时空相干性确定分布式目标,最后建模解算时序地表形变信息。以26景Sentinel-1A影像为数据源,提取2019-12～2020-12期间黄河三角洲地区的地表沉降信息,与PS-InSAR方法结果相比,点位密度提高5.56倍;两种方法获取的同名点对形变速率的相关系数为0.727,说明两者具有很好的一致性。实验结果表明,研究区内存在4处明显沉降区域,最大沉降速率达-238 mm/a,经分析及实地调查验证,其主要影响因素为地下卤水及油气开采。     

阵发性洪水条件下辫状河型冲积扇构型研究:以准噶尔盆地西北缘现代白杨河冲积扇为例*

白杨河冲积扇是由阵发性洪水期的碎屑流沉积物与间洪期辫状河沉积物组成的复合型冲积扇,其构型与碎屑流扇的构型和河流型扇的构型有很大的不同。本研究选取准噶尔盆地西北缘干旱气候下发育的现代白杨河冲积扇作为解剖实例,对103个天然剖面和9个人工大型探槽进行了详细测量,在沉积微相及不同级别的沉积构型的观测和分析的基础上,分析了阵发性洪水条件下间歇性辫状河型冲积扇体的地貌单元的演化过程和沉积构型特征,研究不同流态的阵发性洪水条件下各种建造和改造机制,明确受阵发性洪水控制的间歇性辫状河型冲积扇的沉积特征,建立了其沉积构型模式。认为: 在洪水期,阵发性洪流(碎屑流)形成席状化的片流(或片洪)沉积,在洪退期,随着洪水强度的减弱,又转变为辫流沉积,而在间洪期,仍有持续的辫状流体(牵引流)在限制性的水道中流动,并对洪水期的碎屑流沉积物进行改造,形成了限制性的(条带状的)辫状河道沉积,2个时期的沉积物在时空上频繁叠置,形成了一种更加复杂的沉积构型。该模式对油田地下冲积扇砂砾储集层的成因识别、预测及对比具有一定的参考价值。