1977年以来黄河临河段河岸冲淤变化及河道萎缩速率     

梅艳国  王随继 《地理学报》2016,71(9):1509-1519

不同时段河道的侧向侵蚀/加积面积变化的定量研究可以揭示河道的变化特征。以黄河临河段213 km长的河段为研究对象,利用1977年以来19个时段基于遥感影像绘制的河道平面形态图的面积变化来估算其4个亚河段（S1、S2、S3和S4）在不同时段的河岸侧向侵蚀/加积面积以及全河段的河道平均萎缩速率。研究结果表明,黄河临河段左右河岸在37年间都表现为侧向净加积,其4个亚河段左岸的侧向累计加积面积分别为33.16 km²、49.59 km²、29.52 km²和30.85 km²,其中1995-2000年的加积面积分别占到其总加积面积的85.5%、51.2%、47.2%和104.6%;右岸的侧向累计加积面积分别为30.83 km²、8.74 km²、26.44 km²和18.76 km²,而1995-2000年的加积面积分别占到其总加积面积的57.2%、111.9%、65.7%和61.6%。该河段河道面积1977-2001年具有减小趋势,2001年之后河道表现为侧向侵蚀、加积的交替变化,1977-2014年间河道平均萎缩速率为6.16 km²/yr。该河段河道平面形态值最明显的变化也发生在1990s,与1995年相比,2000年的河道长度增加了5.8%,河道面积减少了39.4%,河道平均宽度减小了42.8%,弯曲系数增加了6.6%。黄河临河段河道形态剧烈变化及河道严重萎缩都发生在1990s,这主要是黄河上游刘家峡和龙羊峡水库联合运行导致汛期水沙量大量减小所致,4个亚河段的河岸冲淤变化还受到局部河岸物质结构、护岸工程及水动力差异的影响。随着2000年后河流综合管理措施的调整,黄河临河段河道的上述变化趋势明显弱化,河流健康程度有所好转。  相似文献   

Nitrate transport in the unsaturated zone: a case study of the riverbank filtration system Karany,Czech Republic     

Frantisek Buzek  Renata Kadlecova  Ivana Jackova  Zdena Lnenickova 《水文研究》2012,26(5):640-651

Nitrate transport in the unsaturated zone of a riverbank filtration (RBF) system in Karany, Czech Republic, was studied. Previous study of the system estimated RBF recharge as 60% riverbank filtrate and 40% local groundwater contaminated by nitrates. Nitrate concentrations observed in RBF recently cannot be explained by simple groundwater contamination and a new conception of groundwater recharge is suggested. A two‐component model based on water ¹⁸O data modelled recharge of local groundwater. One component of groundwater recharge is rainfall and irrigation water moving through the unsaturated zone of the Quaternary sediments in piston flow. The second component is groundwater from the Cretaceous deposits with a free water table. Both the components of groundwater recharge have different nitrate concentrations, and resulting contamination of groundwater depends on the participation of water from Quaternary and Cretaceous deposits. Nitrates' origins and their mixing in the subsurface were traced by ¹⁵N data. Nitrate transport from the unsaturated zone is important and time variable source of groundwater contamination. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

Evaluation of high-flow rate continuous-flow centrifugation and filtration devices for sampling and concentrating fine-grained suspended sediment     

Masoud Goharrokhi  David A. Lobb  Philip N. Owens 《水文研究》2020,34(19):3882-3893

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Research and application of mud proportioning optimization of slurry balance shield in mudstone and gravel composite stratum     

SONG Yang  LI Ang  WANG Wei-yi  DU Chun-sheng  ZHANG Duo  FU Xing-xing 《岩土力学》2021,41(12):4054-4062

Slurry performance is one of the key factors to maintain the stability of excavation face when slurry balance shield is tunneling in complex strata. Based on the engineering background of slurry shield tunneling in mudstone and gravel composite stratum of Nanning Metro Line 5, the control variable method and the self-made slurry shield tunneling system are adopted to compare and select the mud admixture and to analyze the influence of the admixture amount and the formation composite ratio on the slurry relative density. Then, the mud permeability law and the dynamic and static mud film forming law under different formation composite ratios, swelling water ratios and slag dosages are analyzed comprehensively by factorial design. The results show that different admixtures have significant influence on the properties of bentonite slurry. Specifically, potassium methyl silicate and potassium chloride can effectively reduce the relative density of slurry, while sodium chloride and sodium silicate can promote the disintegration of mudstone in water. In addition, the slag admixture can effectively reduce the water filtration, improving the film quality and reducing the consumption of bentonite. When the cutter head speed is less than or equal to 2.5 r/min, the formation rate of mud film is greater than or equal to the failure rate so as to ensure the stability of driving face. The mud swelling water ratio suitable for mudstone and gravel composite stratum (composite ratio: 0?1) is 0.1?0.20, the residue content is 100?200 g/kg, and the potassium methyl silicate is 3.75%?7.50%.  相似文献   

水温、盐度和饵料密度对橄榄蚶滤水率的影响   总被引：1，自引：0，他引：1  

张媛  方建光  毛玉泽  梁峻  赵学伟 《海洋科学》2015,39(9):39-43

用实验生态学的方法研究了不同水温(15、20、25、30℃)、盐度(16、21、26、31、36)和饵料密度(0.5×104、1.5×104、2.5×104、3.5×104、5×104个/m L)对橄榄蚶(Estellarca olivacea)滤水率的影响。实验结果表明,以金藻作为饵料,水温、盐度、饵料密度对橄榄蚶的滤水率有显著影响(P0.05)。水温15~30℃、盐度16~36、饵料密度为0.5~5×104个/m L时,橄榄蚶的滤水率都呈峰值变化。水温25℃、盐度26、饵料密度3.5×104个/m L时,其滤水率分别达到最大值。在所研究的范围内,水温、盐度、饵料密度与滤水率之间分别满足函数关系:FRT=–0.3396T2+1.8937T+0.2728(R2=0.9857,P0.05);FRS=–0.3424S2+1.9626S+0.7112(R2=0.9683,P0.05);FRC=1.7395 C 0.4607,(R2=0.9062,P0.05)。  相似文献   

The progression of flow rates in variable declining rate filter systems     

Wojciech Dabrowski 《洁净——土壤、空气、水》2006,34(5):442-452

It has been demonstrated that the mathematical model of variable declining rate filters developed by Di Bernardo may be described by (z + 1) non‐linear equations, where z is the number of filters in a bank. Three approximate solutions to this system of equations have been developed and then verified by comparison with numerical solution and published experimental data. Two of these solutions appeared to be very accurate, while the third showed higher, but still acceptable errors of calculation. According to this approximation, flow rates through filters are elements of a geometric progression.  相似文献   

基于离散点绘制等高线算法的研究     

吕建升  须鼎兴 《现代测绘》2006,29(5):5-7

等高线图在实际工作中应用非常广泛，在离散点数据的基础上自动生成等高线图有许多算法。本文着重讨论了如何在采集离散点时加入编码的基础上，尽量减少或不进行人工干预，基于有约束的TIN构建方法一次性生成等高线图。实践表明该方法能够明显加快成图速度与提高等高线成图的精度。  相似文献   

潘晓川教授的反投影滤波(BPF)新型重建算法介绍   总被引：1，自引：2，他引：1  

李亮  陈志强  张丽  邢宇翔 《CT理论与应用研究》2006,15(3):68-73

计算机断面成像(CT)的精确重建方法一直是现代CT成像领域中一个活跃的研究方向。近几年,关于平行束、扇束、锥束CT精确重建的研究取得了一系列重要的突破和创新成果。本文主要介绍了美国芝加哥大学潘晓川教授为首的课题组提出的一类基于反投影卷积(BackprojectionFiltration:BPF)的CT精确重建算法。BPF算法最重要的贡献在于它成功地解决了从沿探测器方向截断的投影数据进行CT精确重建的问题;因此,通过BPF算法能够设计出针对目标的感兴趣区域成像策略,减少成像扫描、重建时间,辐照剂量和散射光子。  相似文献   

An investigation on dewatering kinetics of ultrafine coal     

D. Tao  B. K. Parekh  J. T. Liu  S. Chen 《International Journal of Mineral Processing》2003,70(1-4):235-249

Ultrafine coal dewatering is of great importance to the coal industry due to its impacts on the handling and utilization characteristics of coal products. Commercially available filtration techniques are either ineffective or costly for dewatering of ultrafine coal to the desired moisture level of about 20%. Considerable efforts have been devoted to understanding the dewatering process and developing new technologies for applications in the coal industry. Most of the previous work on ultrafine coal filtration was focused on the final filter cake moisture and few studies have been conducted to investigate the filtration kinetics. The present investigation was undertaken to better understand the kinetics of vacuum filtration of ultrafine coal under various conditions. The filtrate weight was continuously monitored using a precise load cell during the entire filtration process. Operating parameters such as vacuum pressure and reagent conditioning time were examined for their impacts on filtration kinetics. Use of cationic and anionic flocculants showed significant improvement in filtration kinetics. Kinetic data obtained from the study were used to determine the fundamental parameters of filtration such as cake permeability, specific cake resistance, and filter medium resistance using the integrated form of the Darcy's law.  相似文献   

桂北前寒武纪浅变质细碎屑岩型锑矿地质特征及成因     

王瑞湖 《矿产与地质》2002,16(4):212-216

桂北隆起区锑矿主要为产于前寒武纪浅变质细碎屑岩中的碎裂岩—石英脉型锑矿床 ,其成因与地下热水渗滤作用有关。其矿源来自于上地壳围岩 ,水源以大气降水为主、部分混染有变质水 ,硫源较复杂、具混合硫特征 ,热源由隐伏岩体、放射性元素和断裂磨擦提供。成矿流体为富含 CO2的 Na - K - Ca2 - SO42 -- Cl-型水溶液 ,成矿温度以 2 1 0～ 2 4 0℃为主 ,压力 1 0～ 38MPa,成矿时代为燕山期  相似文献