整治工程影响下的河口拦门沙航道回淤特征及成因——以射阳港航道为例

通过不同时期实测地形资料,对比分析射阳港拦门沙航道一期整治工程建设后航道的回淤分布特征;利用实测水文泥沙资料和潮流数学模型计算分析射阳河口拦门沙航道开挖后的水流、含沙量特征;探讨了射阳港拦门沙航道淤积的泥沙来源和淤积成因。研究表明:航道开挖后沿程普遍淤积,尤其是口门及堤根区段航道淤积严重。导致航道淤积的主要原因为:有掩护航道内涨潮流速大、落潮流速小,口门外高含沙量水体进入航道后泥沙很难被带出航道,导致航道内普遍淤积;口门内2 km范围内回淤较大是由于越堤流输沙和口门内侧涨潮期间存在明显回流;导堤根部航道段回淤较大是由于射阳河与黄沙港河汇流后河道放宽,落潮期间出河口的水体挟沙力突然降低。     

三峡水库运行初期的泥沙淤积特点

针对三峡蓄水运行后的泥沙淤积问题,基于实测资料,采用输沙率法和断面法分析了三峡水库运行初期的泥沙淤积特点.结果表明:三峡水库2003—2013年泥沙淤积总量为15.31亿t,平均排沙比为24.5%,均较论证阶段降低;库区泥沙淤积主要分布在常年回水区的宽谷和弯道河段,宽谷段全断面发生淤积、弯道断面流速较小一侧淤积、峡谷无累积性淤积;常年库区近坝段泥沙淤积速度逐年减小,而上段泥沙淤积速度则呈增大趋势;淤积物粒径沿程分选不明显,常年回水区淤积物中值粒径多在0.01 mm以下.库区峡谷段深泓线无明显变化、尚未出现泥沙淤积三角洲、库尾泥沙淤积上延和尾水抬高不明显,据此初步推断峡谷河段存在富余挟沙力而成为局部侵蚀基准面,整个库区将无统一平衡比降的趋势.     

水沙调节后三峡工程变动回水区泥沙冲淤变化

长江上游溪洛渡、向家坝等水电工程的建设,改变了进入三峡水库变动回水区及库区的水沙环境。上游水库水沙调节后,变动回水区的泥沙淤积情况将会发生相应变化。在分析三峡工程变动回水区水沙特性的基础上,应用建立的适合多连通域的贴体正交曲线坐标系下的二维水沙数学模型,根据三峡工程初步设计阶段选定的1961-1970年(简称60系列)及上游水库水沙调节后的水文系列及相应进出口边界条件,预测了重庆主城区河段100年泥沙冲淤的时空变化规律。研究表明,60水沙系列条件下,该河段淤积比较严重,淤积主要位于岸线凹凸不平的弯沱、回流区及河道的宽浅河段;上游水沙调节后,仅局部岸线凹凸不平的弯沱有少量泥沙淤积,主城区川江段的淤积量仅为60系列的17.4%,嘉陵江段仅为60系列的10.3%,这对三峡水库有效库容的保持及主城区河段岸线利用有利。     

卵石沙洲发育与冲刷试验

沙洲是塑造分汊型河道最重要的形态因子,其发育与蚀退由于上游来水来沙变化呈现冲淤交替,从而影响分汊河道输水输沙平衡.通过单个卵石沙洲的淤积和冲刷试验,揭示不同加沙速率、粒径和来流量条件下,沙洲淤积和冲刷规律,并建立简化理论模型分析沙洲淤积速率.结果表明,4组加沙试验中,分流点后出现明显淤积下延至洲头,左汊和右汊成为输沙通道,洲尾中心线两侧的左右汊道有泥沙淤积,洲尾未出现淤积.7组清水冲刷试验中,洲头最先承受冲刷和蚀退,并沿洲体冲刷延伸,洲头冲刷的泥沙沿左右汊水流带到下游,洲尾未出现明显冲刷.卵石沙洲以洲头淤积为主导发育模式,泥沙粒径、洲头坡角和分流角是决定淤积速率的关键因子.     

三峡水库蓄水初期近坝区淤积形态成因初步分析

三峡水库蓄水运用后,库区泥沙淤积将显著增加.基于三维水沙数值模型及实测资料分析,对水库蓄水初期近坝区泥沙淤积形态的成因进行了初步探讨.研究结果表明坝前淤积形态的成因既与坝前水流流态的三维特性有关,又与水库蓄水初期坝前淤积物颗粒特性有关.水库蓄水初期沉积在近坝区的泥沙颗粒较细,初始干容重较低,使得淤积物表现出一定的浮泥特性.坝前淤积总量较大主要是宽谷河段水流特性造成的;而基底深槽处淤积物厚度较大、淤积面呈水平状的主要原因则是浮泥状淤积物在重力作用下向河底运动、并沿深泓线在基底深槽中汇集.     

海啸波作用下泥沙运动——Ⅰ.岸滩剖面变化分析

在波浪水槽实验的基础上,对海啸波作用下的岸滩剖面演变规律开展研究。实验采用1/10~1/20的组合坡度,考虑3种不同的水深,选取N波作为入射波,同时采用规则波和非规则波进行对比研究。实验对波高、波浪的上爬、回落和水跃过程、每个波作用后的地形进行了测量和记录。研究结果表明,水动力特性的不同造成了N波与规则波和不规则波作用下不同的岸滩剖面演变特点。N波作用下发生了明显的岸滩冲刷和淤积,水流回落时滩肩发生冲刷,高速薄层回流和出渗水流作用是滩肩冲刷的主要原因,离岸区水跃发生水流挟沙力降低,泥沙淤积呈沙坝剖面。     

坝后淤积条件下泥石流冲击拦挡坝动力响应研究

拦挡坝有效库容和泥石流冲击力是泥石流实体拦挡坝设计的重要指标,现有实体拦挡坝在泥石流反复冲击作用下淤积甚至填满,会对坝体调控能力产生重要影响.为此,基于理论分析和物理模型试验,开展坝后淤积条件下泥石流冲击实体拦挡坝动力响应研究,推导坝后淤积条件下泥石流速度衰减率、坝体拦挡率的无量纲计算公式,并建立考虑空间分布特性的坝后淤积条件下泥石流冲击力计算模型.结果表明：泥石流速度衰减率和坝体拦挡率与淤积体高度/淤积长度比值和泥石流相对容重呈正相关;泥石流冲击力静动荷载组合计算模型能较好反映坝后淤积条件下泥石流冲击力的组成和分布特征.上述研究可为泥石流实体拦挡坝工程设计提供理论及技术支持.     

塔里木河干流上游中、下段河床淤积和耗水对生态环境的影响

塔里木河干流上游中、下段河床一直呈淤积状态, 新渠满站1965-2007年总淤积厚度达120 cm, 平均年淤积3.0 cm. 其中: 1965-1990年25 a淤积50 cm, 年均淤积2.0 cm, 1991-2007年17 a中河床淤积加快, 总淤积70 cm, 年均淤积4.7 cm. 由于河床淤积, 河道行洪断面缩水, 洪水漫溢不断增大, 导致上游段耗水量呈不断增加趋势, 2001年起上游段己成为干流最大的耗水区. 阿克苏河、和田河和叶尔羌河3条源流出山口多年平均年输沙量为6310×10~4t, 进入塔里木河干流龙头站--阿拉尔站多年平均年输沙量为2050×10~4t, 干流上游段多年平均年泥沙淤积量为1462×10~4t, 占塔里木河阿拉尔站多年平均年输沙量的71.3%, 是干流最大的泥沙淤积区, 也是现今最大的洪水漫溢区和耗水区. 塔里木河干流上、中、 下游各水文点年输沙量呈急剧減少趋势, 泥沙淤积河道主要是上游段的沙雅二牧场至英巴扎318 km河段. 塔里木河上游段河长495 km, 多年平均区间耗水量14.48×10~8m~3, 占阿拉尔站多年径流量的31.5%;中游河长398 km, 多年平均区间耗水量24.84×10~8m~3, 占阿拉尔站年径流量的54.0%;下游河长428 km, 多年平均区耗水量6.68×10~8m~3, 占阿拉尔站年径流量的 14.5%. 上、 中游段多年平均区间耗水量39.32×10~8m~3, 占阿拉尔站年径流量的85.5%. 上游耗水量从2001年起成为塔里木河干流最大的耗水区, 导致2002、 2005和2006年上、中游耗水量达到50.0×10~8m~3, 占阿拉尔站年径流量的88%, 成为历史最大值.     

黄河万家寨水利枢纽淤积形态分析

以万家寨水利枢纽2000年至2010年泥沙淤积测量资料为基础,通过分析近年泥沙淤积变化情况及目前水库横、纵断面形态,得出万家寨水库目前纵向淤积为三角洲淤积形态淤积,主要表现为:淤积位于966 m以下,横向淤积坝前段淤积面平行抬高,库尾段近年来有明显冲刷。     

渤海湾天津滨海新区围海造陆前后海底冲淤变化

天津滨海新区2009—2010年实施了共计超过420 km2的围海造陆工程围堤建设,必然对该区的流场和侵蚀淤积产生影响.本文以2006—2009年海底地形地貌为本底,对比分析2015年海底地形地貌实测水深与浅地层剖面数据,结果显示,围海造陆外围海底冲淤与海底地形发生显著调整,呈现出北部淤积南部侵蚀的整体格局.淤积区主要...     

小浪底水库淤积形态数值模拟

水库淤积形态是影响库容分布、水库排沙的一项重要因素。小浪底水库近坝段淤积泥沙粒径极细,具有流动性,针对其细颗粒泥沙淤积特点,揭示了水库细颗粒淤积物的流变特性与流型特征;通过引入水、淤积物、床面之间的界面受力分析,构建了细颗粒淤积物失稳流动描述模式,并与水沙输移模型相耦合,建立了考虑细颗粒淤积物流动特性的水库淤积形态模拟方法,在此基础上对小浪底水库淤积形态进行了验证分析。研究结果表明:低密度细颗粒淤积物为宾汉型流体,淤积平衡坡降较小,当其密度大于1.25 g/cm 3后,流动性快速减弱;考虑细颗粒淤积物流动特征的水库淤积形态模拟结果与实测结果吻合较好。研究成果可为水库淤积形态形成机理及其对水沙调控的响应研究提供技术支撑。     

小浪底水库淤积形态数值模拟

水库淤积形态是影响库容分布、水库排沙的一项重要因素。小浪底水库近坝段淤积泥沙粒径极细,具有流动性,针对其细颗粒泥沙淤积特点,揭示了水库细颗粒淤积物的流变特性与流型特征;通过引入水、淤积物、床面之间的界面受力分析,构建了细颗粒淤积物失稳流动描述模式,并与水沙输移模型相耦合,建立了考虑细颗粒淤积物流动特性的水库淤积形态模拟方法,在此基础上对小浪底水库淤积形态进行了验证分析。研究结果表明:低密度细颗粒淤积物为宾汉型流体,淤积平衡坡降较小,当其密度大于1.25 g/cm³后,流动性快速减弱;考虑细颗粒淤积物流动特征的水库淤积形态模拟结果与实测结果吻合较好。研究成果可为水库淤积形态形成机理及其对水沙调控的响应研究提供技术支撑。     

Changes in fine sediment size distributions due to interactions with streambed sediments

In the classical view of fine sediment transport and deposition in streams, particles are expected to be removed from flowing water simply by direct sedimentation onto the streambed. However, recent research has demonstrated that fine sediments can propagate into pore spaces in the streambed due to hyporheic exchange and be removed by a combination of physical and chemical processes. This behaviour can significantly alter fine sediment size distributions during in-stream sediment transport because the physical transport of fine particles and their attachment to bed sediment grains are both a function of the particle size. Herein, we present model simulations for deposition of suspended sediments with a bimodal size distribution. We also applied this approach to analyse the results of laboratory flume observations of suspended sediment deposition. Results from model simulations and flume experiments clearly show that the rate of particle deposition increases with increasing particle size. Thus, the larger particles are preferentially removed from mixtures and there is a fining of the mixed suspensions over time. Both particle deposition mechanisms, i.e. particle sedimentation and filtration, contribute to the fining of the mixed fine particle suspensions over time, and their effects are clearly demonstrated using the fundamental process-based model. These results clearly demonstrate the effects of stream-subsurface exchange on the temporal evolution of the suspended fine sediment size distribution in downstream transport.     

青藏高原东南部贡嘎山海螺沟冰川冰下沉积物形成与变形

冰岩界面的冰川动力学是冰川系统的重要组成部分, 海螺沟冰川地处温暖湿润的海洋环境, 冰川运动速度较快, 冰川底部接近压融点, 是研究冰下过程的较理想地点. 在海螺沟冰川大型磨光面上浅显侵蚀坑内发现了碎屑物质. 对碎屑物质理化特征研究表明: 粒度特征、地球化学与石英砂SEM 分析表明沉积在冰岩界面上的物质来自于冰川底部的底碛层, 而不是冰上环境的产物. 偏光显微镜下观察到的冰下沉积物呈现出一系列塑性变形(微旋转、褶皱)和脆性变形(线性结构、支撑结构、断层)微观结构和构造. 两种变形结构的存在是碎屑物质在形成过程中其含水量波动情况的反映. 冰下碎屑物质是冰下融出、滞碛作用的共同产物. 在整个冰下碎屑物质形成与变形过程中, 由于冰下水系季节性变化带来的冰岩界面上冰川融水含量的波动起了决定性作用.     

黄河下游限制弯曲段河道冲淤数学模型

模型对黄河下游特有的来水来沙条件及河床边界条件下的河道冲淤规律进行了模拟。根据不平衡输沙理论,结合天然河道实际情况,将河道断面进行滩槽划分,采用综合阻力公式反映水沙条件变化,沉速计算考虑了含沙量特别是细颗粒影响,模型可应用于高含沙水流。验证结果与实测资料基本符合。     

The Rio Dell Formation: a Plio-Pleistocene basin slope deposit in Northern California

The Rio Dell Formation (Pleistocene and Pliocene), exposed south of Eureka, California, is a prograded sequence of basinal turbidites overlain by basin slope and shelf deposits. The slope deposits studied in the Centerville Beach section accumulated in a steadily shallowing environment delineated by analysis of palaeobathymetrically significant benthonic foraminiferal biofacies in turn suggesting deposition at depths of 1000–100 m. Lower slope deposits interfinger with basinal turbidites derived from the Eel River delta to the north. Slumped blocks of silty mudstone, and associated silt and mud beds, are common. The middle slope deposits are mudstones; coarser sediments bypassed this zone. Mudstones and muddy siltstones alternate on the upper slope. Shallow depressions, probably slump scars, that have been rapidly filled by upper slope sediment are common. The transition to shelf deposits is marked by an increase in sediment grain size, in the degree of oxidation, and in the abundance of megafossils. High percentages of benthonic foraminifera displaced from shelf depths indicate that resedimentation processes are most important on the upper slope.     

鄂尔多斯盆地陇东地区延长组重力流沉积特征及其模式

利用岩心、测井资料和重力流沉积理论,系统研究了鄂尔多斯盆地陇东地区延长组重力流沉积特征及其沉积模式。该区重力流沉积物可分为浊积岩、砂质碎屑流沉积物、泥质碎屑流沉积物和滑塌岩。其中,浊积岩发育正粒序;砂质碎屑流沉积物以冻结块状沉积为特征;泥质碎屑流沉积物以泥质为主,内部含少量砂质颗粒和砂质团块;滑塌岩发育包卷层理等液化构造。不同重力流沉积物发育程度差异明显,浊积岩和砂质碎屑流沉积物的钻遇井数最多,泥质碎屑流沉积物最少。在重力流单期沉积厚度方面,砂质碎屑流沉积物单期沉积厚度平均为0.986m,明显高于其他类型;浊流沉积厚度最低,平均厚度为0.414m。本区重力流是由三角洲前缘沉积物失稳滑塌所致,砂质碎屑流沉积物和浊积岩是主要的重力流沉积类型,其次为滑塌岩和泥质碎屑流沉积物。砂质碎屑流沉积物主要发育于北东向曲流河三角洲前缘前方的深水区;浊积岩主要发育于西部、西南部和南部物源形成的辫状河三角洲前缘前方的深水区域;泥质碎屑流沉积物和富含泥砾砂质碎屑流沉积物在平面分布极少,且规律不明显。     

Linking submarine channel–levee facies and architecture to flow structure of turbidity currents: insights from flume tank experiments

Submarine leveed channels are sculpted by turbidity currents that are commonly highly stratified. Both the concentration and the grain size decrease upward in the flow, and this is a fundamental factor that affects the location and grain size of deposits around a channel. This study presents laboratory experiments that link the morphological evolution of a progressively developing leveed channel to the suspended sediment structure of the turbidity currents. Previously, it was difficult to link turbidity current structure to channel–levee development because observations from natural systems were limited to the depositional products while experiments did not show realistic morphodynamics due to scaling issues related to the sediment transport. This study uses a novel experimental approach to overcome scaling issues, which results in channel inception and evolution on an initially featureless slope. Depth of the channel increased continuously as a result of levee aggradation combined with varying rates of channel floor aggradation and degradation. The resulting levees are fining upward and the grain‐size trend in the levee matches the upward decrease in grain size in the flow. It is shown that such deposit trends can result from internal channel dynamics and do not have to reflect upstream forcing. The suspended sediment structure can also be linked to the lateral transition from sediment bypass in the channel thalweg to sediment deposition on the levees. The transition occurs because the sediment concentration is below the flow capacity in the channel thalweg, while higher up on the channel walls the concentration exceeds capacity resulting in deposition of the inner levee. Thus, a framework is provided to predict the growth pattern and facies of a levee from the suspended sediment structure in a turbidity current.     

An equation of state for biologically active lake sediments and its implications for interpretations of sediment data

The aim of this work is to link physical sediment parameters to biological parameters by an equation of state, which describes how the given variables interact in biologically active deposits from accumulation areas, i.e. lake areas where fine material is being continuously deposited. In the model the following parameters are utilized: sediment depth, rate of deposition, degree of compaction, bulk density, water content, net biotransport, upward biotransport, downward biotransport, and substrate decomposition. The equation of state has been empirically tested with data from Lake Ekoln and Lake Vänern, Sweden. The model enables determinations of age frequency distributions for arbitrary sediment layers, and it has been shown that, for example, the sediment layer 12-13 cm in Lake Ekoln has a median age of 15.3 years and that the deposits from the median year only constitutes about 15% of the total amount of material in this particular sediment layer. The spread due to bioturbation is considerable and the range at this sediment layer is 22 years. A mechanism to explain secondary lamination is introduced and discussed in the light of the results from the model.     

Quartzite development in early Palaeozoic nearshore marine environments

Quartzites are especially characteristic of Proterozoic and Cambro‐Ordovician shallow marine strata, whereas equivalent age fluvial deposits are commonly arkosic. The absence of land vegetation in the pre‐Silurian influenced weathering processes and styles of fluvial deposition. It may also have had an impact on shallow marine sedimentation. Two field studies from the English Channel region are presented to investigate the processes leading to quartzite formation. On Alderney, nearshore marine and fluvial facies occur interbedded on a metre scale and are interpreted to represent deposition on the lower reaches of an alluvial plain, and in beach and upper shoreface environments. The marine and fluvial sandstones display marked differences in textural and mineralogical maturity, pointing to a process of sediment maturation by the destruction of feldspar and labile grains at the shoreline. At Erquy, fully mature, marine quartzites occur bounded above and below by alluvial deposits via sharp or erosional surfaces, and are interpreted to represent high energy, storm and tidally influenced lower shoreface and inner shelf deposits. A model for quartzite development is proposed where, under a cool climate, frequent storms in un‐vegetated, tectonically rejuvenated uplands provided an abundance of arkosic sand to fluvial basins and clastic shorelines. The model proposes that the marine basins were subject to high wave energies, frequent storm events and tidal currents. These were conditions conducive to transforming arkosic sand to quartz‐rich sand by the attrition of feldspar at the shoreline and in the shallow marine environment. On sediment burial, further feldspar destruction occurred during diagenesis. The proposed model highlights the potential for a step change in sediment maturity to occur at the shoreline in early Palaeozoic depositional systems tracts.