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1.
三峡水库蓄水运用后,泥沙淤积主要分布在常年库区的宽谷和弯道,峡谷则无累积性淤积。基于实测资料计算了三峡成库前（2001年）和成库后（2003-2011年）的挟沙力,结果表明挟沙力随着不同运行阶段坝前水位的抬高而逐步降低,宽谷河段降低幅度较大,峡谷河段降低幅度较小,泥沙淤积比率逐步增大。宽谷河段挟沙力普遍降至含沙量以下而发生淤积,峡谷河段挟沙力仍大于含沙量而无累积性淤积。流量越大,宽谷河段的挟沙力越小于含沙量,而峡谷河段的挟沙力越大于含沙量,表明宽谷河段淤积主要发生在汛期,而峡谷河段汛期以冲刷为主。由于细颗粒泥沙絮凝沉降以及黏性淤积物难以冲刷,恢复饱和系数淤积取1、冲刷取0.01得到的沿程淤积量计算值与实测值吻合较好。弯道河段计算的淤积量与实测值差异较大,表明弯道河段二维特征明显,利用一维的挟沙力计算淤积量不能适用。 相似文献
2.
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. 相似文献
3.
针对三峡水库近坝区细颗粒泥沙淤积特征,从过程机理出发,提出了深水库区细颗粒泥沙淤积过程的物理图形。采用临界坡度作为细颗粒淤积物失稳流动的判别标准,借鉴浅水流动模式,描述失稳后细颗粒淤积物重力驱动流动过程,通过耦合三维水沙数学模型,建立了细颗粒淤积物重力驱动流动的数值模拟方法,在此基础上对三峡水库近坝区细颗粒泥沙淤积形态进行了模拟研究。研究结果表明:水库蓄水运行初期近坝区细颗粒泥沙主要淤积在断面深槽内,且呈水平状,考虑重力驱动流动后的模拟结果与实测结果吻合较好,从而为进一步深入研究深水库区细颗粒泥沙运动特征提供了技术支撑。 相似文献
4.
受上游水沙条件和水库调度过程等影响,三峡水库实际淤积过程较为复杂。本文基于一维泥沙数学模型,分析上下游边界条件变化对三峡水库淤积特征的综合影响,建立入库沙量和汛期坝前水位与库区淤积的经验关系,讨论了其贡献及未来淤积趋势。结果表明：上游干支流入库沙量和汛期坝前水位是影响三峡水库淤积的主要因素,其变化均将造成库区淤积重心的偏移,变动回水区下段及常年回水区上段的泥沙分选及冲淤情况受影响最为明显;2013—2020年,干流来沙对三峡库区淤积的贡献减小(由65%减小至42%),支流来沙贡献逐步增大(由32%增大至56%);汛期坝前水位变化对该时段库区淤积较2003—2012年期间的影响已经较小(1.6%～1.8%);当遭遇平常水文年水沙过程,未来三峡水库泥沙淤积量约在0.5亿t/a左右;当遭遇不利洪水组合水文年,尤其是支流发生大规模强降雨使岷江和嘉陵江洪峰流量大于30 000 m3/s时,三峡水库泥沙淤积量约在1.6亿t/a左右。 相似文献
5.
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。 相似文献
6.
弯曲河流的河道冲淤变化在长时间尺度处于动态的平衡状况,其泥沙输移部分来自于凹岸冲刷与凸岸淤积的差值。2018年采用无人机航测获取黄河源典型弯曲河流(麦曲、哈曲、格曲和兰木错曲)连续弯道的低空影像数据,通过图像技术处理后生成高精度地形,进而提取单个弯道和连续弯道的断面地形,计算弯道凸、凹两侧断面面积和相邻断面间的差值。结果表明,凹岸侵蚀崩岸产生的泥沙量与凸岸点边滩淤积的泥沙量是不平衡的,即存在一个泥沙亏损量。对于单个弯道,兰木错曲单位河长的泥沙亏损量约为0.191 m^3,麦曲、哈曲和格曲单位河长的泥沙亏损量约为0.045 m^3,且相同河段的沿程亏损量具有不均匀性,其间接反映不同弯道横向的迁移速率具有差异性。 相似文献
7.
三峡库区絮凝现象是细颗粒泥沙淤积的重要原因,泥沙絮凝临界条件对三峡库区泥沙淤积规律和模拟具有重要意义。在三峡库区忠县和奉节河段开展泥沙絮凝的现场测量,基于声学多普勒流速仪（Acoustic Doppler Velocimeter,ADV）和泥沙采样测得同步的瞬时流速和含沙量,通过泥沙扩散理论反算现场泥沙沉速及絮团粒径,得到了三峡库区泥沙絮凝度及其与粒径、流速和含沙量的关系。结果表明:库区细颗粒泥沙发生絮凝,且多为中轻度絮凝,重度絮凝较少;库区泥沙絮凝的临界粒径约为0.018 mm,临界流速约为0.7 m/s,临界含沙量约为0.8 kg/m3。研究结果可为三峡库区泥沙的运动规律以及泥沙淤积模拟等提供一定的理论支撑。 相似文献
8.
近50年来长江水沙变化规律研究 总被引：5，自引：1，他引：4
较为系统地研究了近50年来长江流域不同河段、不同时段的水沙变化特性。从多年平均情况来看,长江上游水沙异源、不平衡现象十分突出,干流石鼓至宜昌沙量沿程增大,宜昌以下干流河道输沙量沿程减小,悬沙中值粒径也沿程变细;1991~2002年长江干流各站径流量变化不大,输沙量明显减少;2003～2010年长江上游来沙减小趋势仍然持续,加之三峡水库蓄水拦沙作用,坝下游输沙量大幅减小,悬移质泥沙粒径沿程变粗,至监利站粗沙量已基本恢复到蓄水前的水平。三峡水库蓄水运用后,长江中下游径流年内分配、泥沙来源和地区组成均发生新变化;荆江三口分流分沙量继续减小,洞庭湖湖区淤积减缓;三峡工程蓄水运用不仅改变了长江上游与中下游的冲淤环境,而且也进一步促进了长江中游江湖泥沙分配格局的调整。 相似文献
9.
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。 相似文献
10.
潮汐河口泥沙运动复杂多变, 科学划分泥沙运动形式并评估其对航道淤积的影响, 是厘清航道淤积泥沙来源、制定有效减淤措施的关键。基于长江口深水航道所处南港—北槽河段2015年和2018年洪季、枯季表层沉积物和近底悬沙的现场采样数据, 分析提出潮汐条件下推移质、悬移质和时推时悬泥沙3类泥沙运动形式的粒径划分方法, 量化3类泥沙对深水航道淤积的贡献比例。结果表明: 近底悬沙级配曲线上拐点粒径对泥沙由推移质向悬移质转化具有较好的指示意义; 长江口南港—北槽悬沙、底沙交换显著, 深水航道淤积物中除仅做推移质或悬移质运动的泥沙外, 还包括大量的时推时悬泥沙, 其在航道淤积泥沙中的占比最高, 约达50%~60%;南港段航道洪季、枯季推移质淤积占比分别为36%和26%, 高于悬移质的6%和13%;北槽段航道悬移质落淤泥沙占比为44%~48%, 明显较推移质3%~6%的占比高。3类泥沙运动形式粒径划分方法为深化潮汐河口泥沙运动规律认识、判别航道淤积泥沙来源提供了新途径。 相似文献
11.
梯级水库蓄水后，三峡水库入库泥沙大幅度减少，同时三峡水库洪峰沙峰传播特性发生变化，有必要研究新水沙条件下三峡水库洪峰沙峰异步特性变化及其原因，为深入认识水库洪峰沙峰异步特性机理和精细化减淤调度方式提供理论基础。采用实测资料分析法和理论分析法，以2003—2018年三峡水库实测水文资料为基础，对梯级水库蓄水后三峡水库洪峰沙峰异步特性变化进行分析，初步探讨这些变化的主要原因。结果表明：梯级水库蓄水后，三峡水库洪峰沙峰异步现象加剧，表现为入库滞后沙峰比例增加最多、库区洪峰传播时间减少以及沙峰传播时间增加。造成该现象的原因是入库泥沙来源发生变化、入库洪峰流量减少以及入库泥沙颗粒粗化。 相似文献
12.
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. 相似文献
13.
The erosion and deposition of debris flows at Jiangjia Gully in Dongchuan section of Yunnan province, southwestern China,
was surveyed at 12 cross sections from 1999 to 2003. Deposition occurred in most sections because of the low debris-flow magnitude.
The result was an increase in their elevations except for two sections at D17 and D19, where the channel was diverted in September
1999. As the annual sediment discharge of debris flow increased, the deposited volume decreased in the upper channel and increased
in the lower channel. In each debris flow event, the erosion or deposition at the upper and the lower channel were different,
but the eroded/deposited volume and the trend of erosion or deposition were similar between the neighboring sections. The
average elevation change of all cross sections between consecutive surveys can reasonably represent the debris flow influence
on the channel. Its relationship with the total sediment discharge between two surveys follows a three-stage pattern: when
debris flow magnitude is small, deposition in the channel increases with the magnitude. When the magnitude reaches a certain
level, the deposition begins to decrease and eventually erosion takes place. In three typical cross sections which had similar
channel width, the debris flow showed a clear trend that the deposited volume decreased, while the eroded volume increased
as the discharge of debris flow sediments increased. 相似文献
14.
对输沙水量的计算方法,黄河下游汛期、非汛期输沙水量的研究现状,水库对输沙水量的影响,输沙用水总量的研究现状等方面分别作了回顾。分析指出,输沙水量与来水含沙量、来水流量、河道冲淤、河床前期条件等有关。黄河下游各时期输沙水量不同,汛期最小,其余依次为非汛期、冬三月、凌汛期。水库调水调沙的同时也改变着黄河下游的输沙水量。利用水库群调水调沙,使小浪底水库以造床流量、高含沙水流输沙,是目前推荐的黄河下游节水减淤高效输沙入海的主要方式。提出了一些有待进一步研究的问题。 相似文献
15.
Overbank sedimentation rates were studied in former channels of three rivers in south-eastern France. Depth and spatial distribution of sediment, as well as geometry, hydrological connectivity and age of 39 lakes, were both measured and calculated. The mean sedimentation rate of lakes varied between 0 and 2·57 cm year−1 . Sedimentation rates are linked to water depth and often undergo a decreasing gradient from the downstream outlet to the inner part of the lake. Multiple regression modelling demonstrates that sediment depth is essentially a function of overbank flow frequency. The greater the difference between upstream and downstream overbank flow frequency, the faster the sedimentation rate. These differences in sedimentation rates also correspond to different former channel geometry: the rates are slower in narrow and straight channels (former braided, and point-bar backwater channels), and faster in large and sinuous channels (exhibiting meanders, anastomosing channels and coves). The suspended sediment flux is variable from one reach to another, the middle reach of the Rhône conveying more sediment than the upper reaches, the Doubs or the Ain reaches. The suspended sediment flux does not explain a statistical difference in lake sedimentation rates between the reaches, which also provide clear evidence of the importance of local connectivity controls. Sedimentation patterns were also complicated by temporal changes in lake connectivity associated with geomorphological or anthropogenic changes operating within the main channel. 相似文献