Comparison of depth-averaged concentration and bed load flux sediment transport models of dam-break flow

This paper presents numerical simulations of dam-break flow over a movable bed. Two different mathematical models were compared: a fully coupled formulation of shallow water equations with erosion and deposition terms(a depth-averaged concentration flux model), and shallow water equations with a fully coupled Exner equation(a bed load flux model). Both models were discretized using the cell-centered finite volume method, and a second-order Godunov-type scheme was used to solve the equations. The numerical flux was calculated using a Harten, Lax, and van Leer approximate Riemann solver with the contact wave restored(HLLC). A novel slope source term treatment that considers the density change was introduced to the depth-averaged concentration flux model to obtain higher-order accuracy. A source term that accounts for the sediment flux was added to the bed load flux model to reflect the influence of sediment movement on the momentum of the water. In a onedimensional test case, a sensitivity study on different model parameters was carried out. For the depth-averaged concentration flux model,Manning's coefficient and sediment porosity values showed an almost linear relationship with the bottom change, and for the bed load flux model, the sediment porosity was identified as the most sensitive parameter. The capabilities and limitations of both model concepts are demonstrated in a benchmark experimental test case dealing with dam-break flow over variable bed topography.

Rare earth elements distribution in marine sediments of Malaysia coasts

In the east coast Peninsular Malaysia region,sediments are transported by several rivers from the east Malaysia into the South China Sea estuary.In the vicinity of the five river estuaries core sediments were collected in order to investigate rare earth elements(REEs) profile.Core sediments were divided into strata of between 2 to 4 cm intervals and prepared for analyzing by ICP-AES.REE concentrations of 54.3 μg/gr at 24–26 cm in EC4 increased to 114.1 μg/gr at 20–22 cm in EC5.The measured concentration of ...

Quantitative Application Study on Remote Sensing of Suspended Sediment

Quantitative application on remote sensing of suspended sediment is an important aspect of the engineering application of remote sensing study. In this paper, the Xiamen Bay is chosen as the study area. Eleven different phases of the remote sensing data are selected to establish a quantitative remote sensing model to map suspended sediment by using remote sensing images and the quasi-synchronous measured sediment data. Based on empirical statistics developed are the conversion models between instantaneous suspended sediment concentration and tidally-averaged suspended sediment concentration as well as the conversion models between surface layer suspended sediment concentration and＂ the depth-averaged suspended sediment concentration. On this basis, the quantitative application integrated model on remote sensing of suspended sediment is developed. By using this model as well as multi-temporal remote sensing images, multi-year averaged suspended sediment concentration of the Xiamen Bay are predicted. The comparison between model prediction and observed data shows that the multi-year averaged suspended sediment concentration of studied sites as well as the concentration difference of neighboring sites can be well predicted by the remote sensing model with an error rate of 21.61% or less, which can satisfy the engineering requirements of channel deposition calculation.

A Study on Description Methods of Sediment Transport Modulus in Small Watersheds

[Objective]This study aimed to clear the advantages,disadvantages and applicability of various analysis methods to assess sediment transport modulus in small watersheds using the multi-year observation data. [Method]Four methods,including the statistical eigenvalues,depolarized arithmetic mean,frequency of erosion intensity and box-whisker plots were applied into calculation of sediment transport modulus in four small watersheds,and then the results of the methods were compared to to filter a method with the widest applicability and scientific validity. [Result] The statistical arithmetic mean and median could hardly represent the concentration and general level of multi-year sediment transport modulus. Although the depolarized arithmetic mean had the tendency of reflecting the general level of data,it lost the extreme value and its information for making decision. The frequency of erosion intensity grade reflected the distribution of data in intensity classification. Box-whisker plot could show the concentration,dispersion and the number of abnormal data. [Conclusion] Multiple methods can be combined to comprehensively and objectively characterize the multi-year sand transport modulus due to their advantages and disadvantages. Additionally,box-whisker plot has good objectivity and applicability in displaying the multi-year data of small watershed.

Simulating cross-sectional geometry of the main channel in response to changes in water and sediment in Lower Yellow River

To understand the non-equilibrium morphological adjustment of a river in response to environmental changes,it is essential to(i)accurately identify how past conditions of water and sediment have impacted current morphological adjustment of the river,and(ii)establish a corresponding simulation for non-equilibrium conditions.Based on discharge and suspended sediment concentration(SSC)as well as 82 cross-sectional data items for the Huayuankou-Lijin reach of the Lower Yellow River in the period 1965-2015,the process of adjustment of the geometry of the main channel(area,width,depth,and geomorphic coefficient),and its responses to changes in discharge and SSC for different reaches are statistically analyzed.Following this,a delayed response model(DRM)of the geometry of the main channel subjected to variations in discharge and SSC is established using a multi-step analytical model,with the discharge and SSC as the main controlling factors.The results show that the area,width,and depth of the main channel decreased initially,then increased,decreased again,and finally increased again.These features of the geometry of the channel were positively correlated with the 4-year moving average discharge and negatively with the 4-year moving average SSC.The geomorphic coefficient for the Huayuankou-Sunkou reach exhibited a trend of decrease,whereas that of the Sunkou-Lijin reach decreased initially,then increased,decreased again,and finally increased again.Except for the Huayuankou-Gaocun reach in 1965-1999,the coefficient was negatively correlated with the 4-year moving average discharge and positively with SSC.The simulated values of the morphological parameters of the main channel for all sub-reaches obtained using the DRM agreed well with the measured values.This indicates that the DRM can be used to simulate the process of response of the cross-sectional geometry of the main channel to variations in the water and sediment.The results of the model show that the adjustment of the geometry of the main channel was affected by the discharge and the SSC at present(30%)as well as for the previous 7 years(70%).The proposed model offers insights into the mechanism whereby past water and sediment influence the current morphological adjustment of the river,and provides an effective method for predicting the magnitude and trend of the geometry of the main channel under different flow conditions.

Average life of oxygen vacancies of quartz in sediments

Average life of oxygen vacancies of quartz in sediments is estimated by using the ESR (electron spin resonance) signals of E( centers from the thermal activation technique. The experimental results show that the second-order kinetics equation is more applicable to the life estimation compared with the first order equation. The average life of oxygen vacancies of quartz from 4895 to 4908 deep sediments in the Tarim Basin is about 1018 a at 27℃.

A re-evaluation of the average chain length of lacustrine sedimentary n-alkanes as a paleoproxy on the Qinghai-Tibet Plateau

Long-chain n-alkanes are one of the most common organic compounds in terrestrial plants and they are well-preserved in various geological archives.n-alkanes are relatively resistant to degradation and thus they can provide high-fidelity records of past vegetation and climate changes.Nevertheless,previous studies have shown that the interpretation of n-alkane proxies,such as the average chain length(ACL),is often ambiguous since this proxy depends on more than one variable.Both vegetation and climate could exert controls on the n-alkane ACL,and hence its interpretation requires careful consideration,especially in regions like the Qinghai-Tibet Plateau(QTP)where topography,biome type and moisture source are highly variable.To further evaluate the influences of vegetation and climate on the ACL in high-elevation lakes,we examined the n-alkane distributions of the surface sediments of 55 lakes across the QTP.Our results show that the ACL across a climatic gradient is significantly affected by precipitation,rather than by temperature.The positive correlation between ACL and precipitation may be because of the effect of microbial degradation during deposition.Finally,we suggest that more caution is needed in the interpretation of ACL data in different regions.

非硬化路面侵蚀产沙规律野外模拟试验

为了科学治理非硬化路面水土流失,采用野外放水冲刷试验,对非硬化路面侵蚀产沙规律进行了试验研究。结果表明,同一坡度不同放水流量与同一放水流量不同坡度条件下,非硬化路面产沙随时间的变化形式均有3种,分别为平缓型、多峰型和单峰型。对同一路面不同观测断面的产沙量分析发现,产沙量沿坡面的空间变化形式分别为波动式减小、逐渐式减小和先增大后减小。、得出平均含沙量与放水流量呈对数相关,产沙率与放水流量、平均含沙量与坡度、产沙率与坡度均呈直线相关。以期为非硬化路面的水土流失预测和治理提供科学依据。

长江上游主要支流水沙特性及其影响因素分析

雅砻江、岷江、嘉陵江和乌江的水沙特性是决定长江泥沙变异的关键因素之一,关乎三峡水库的合理运行,关系着长江流域水资源的合理开发利用及水生态平衡.本文基于2002—2016年期间,长江主要支流设置的桐子林、高场、北碚、武隆4所重要控制性水文站水文泥沙监测资料,深入系统地探讨水文泥沙参量的变化特征及其影响因素,借助统计软件SPSS进一步分析水文泥沙参量的相关性.研究结果表明:在时序上,各支流年均含沙量、年输沙量、年输沙模数降低22.57%~91.54%,年径流量雅砻江、岷江和乌江增大3.28%~17.96%,嘉陵江降低1.58%;嘉陵江和乌江的中值粒径增大50%~80%.水电站的修建导致年均含沙量、年输沙量、中值粒径、年输沙模数降低5%~79.34%;强降雨、滑坡、塌方、泥石流、溃坝等自然灾害以及人为诱发滑坡和向河道倾倒土石体致使年均含沙量、年输沙量、年输沙模数增大20%~702.94%.参数间相关性由强到弱排序为年均含沙量和年输沙量/年输沙模数,年径流量和年均含沙量,年径流量和年输沙量/年输沙模数,年均含沙量和中值粒径,中值粒径和年输沙量/年输沙模数,以及年径流量和中值粒径.研究成果将为长江支流梯级电站的规划设计、三峡水库的合理运行提供理论支撑.

运用主成分分析(PCA)评价海洋沉积物中重金属污染来源

测定了胶州湾表层沉积物中重金属和有机质的含量，并用平均富集因子（Average Enrichment Factors，AEF）进行污染状况评价，发现胶州湾表层沉积物重金属污染可分为3类：轻度污染（AEFs〈2），其中有Zn（AEF=1．11）、Pb（AEF=1．15）、Cr（AEF=1．52）、Mn（AEF=0．80）、Fe（AEF=0．45）；中度污染（AEFs=2-3），包括Cu（AEF=2．79）和Cd（AEF=2．52）；严重污染（AEFs〉3），主要有As（AEF=3．03）和Hg（AEF=8．08）．进一步通过主成分分析（Principal Component Analysis，PEA）研究沉积物中重金属的来源，发现前3个主成分的贡献率分别为52．61％、17．37％和15．60％，表明重金属主要有3个来源：工业排污、有机质降解、岩石的自然风化与侵蚀过程．PCA的聚类分析指出，本次研究中所调查的14个站位在污染程度上可分为5大类，此结果既反映了胶州湾表层沉积物近河口污染程度重远河口污染程度轻的特点，同时也支持了工业排污是沉积物中重金属污染主要来源的分析．

1950～2000年黄河入海水沙的逐日变化及其影响因素

对 195 0～ 2 0 0 0年的 5 1年黄河经利津水文站入海的逐日水沙实测资料进行统计分析 ,展示了黄河入海水沙的极端情况 ,如洪峰和沙峰等逐渐变少到消失的过程及逐日入海水沙量的变化规律 ,并对其影响因素进行了初步分析。结果显示 :在黄河年均入海水沙锐减的背景下 ,2 0世纪 90年代日均流量 <5 0 0m3 /s的天数增加到了是 2 0世纪 5 0年代的 3倍多 ;>2 0 0 0m3 /s的洪季流量由初期频发至 1997年消失 ;>40 0 0m3 /s的洪峰流量自 1989年以后消失 ;>60 0 0m3 /s的洪峰流量从 1986年就不再发生。 >5 0 0t/s的日均输沙率 (4 3 .2× 10 6t/d的沙峰 )都出现在 1989年以前 ;>70 0t/s的日均输沙率 (60 .5× 10 6t/d的沙峰 )出现在 1977年以前 ;含沙量 >80kg/m3 的历时和可能产生异重流的含沙量天数都逐步减少。进入 2 0世纪 90年代以来基本不存在大洪灾及由沙峰造成的河口河道快速堆积而使河流改道现象 ,引起这些变化的因素除降雨外主要为流域耗水量不断增加及大中型水库的建成运用等 ,黄河入海水沙的这种锐减及水沙峰的极端情况都会对河口演变和河口区的生态环境产生重要的影响。

垂向平均含沙量计算方法初探

从2种悬沙垂向分布公式出发,结合对数流速分布公式,导出2种常见垂向平均含沙量计算方法的比值关系表达式。讨论了2种方法的区别与联系:两者不一定相等,比值可以大于1,也可以小于1,当近底相对水深稍大(如大于0.01)时加权平均含沙量小于算术平均含沙量,与实际相符;2种垂向平均含沙量的差异主要由悬沙及流速垂向分布不均匀性引起。对2种方法的实际应用情况进行了初步分析。

流域年均含沙量的人工神经网络模型

本文引入人工神经网络BP网络模型对流域产沙进行了定量研究 .针对小流域的土壤、地质、地貌在一定的时间范围内具有相当稳定的特性 ,选取采伐面积、采伐量、降雨量和年均径流量这四个代表植被、气候的主要因子对流域年均含沙量进行了建模预测 .建模结果表明采伐面积、采伐量对流域产沙具有较强的延迟效应 ,得出的BP网络模型不仅拟合精度高 ,而且预测效果好 .

佛山水道底泥的污染物释放动态模拟

为定量评价底泥对上覆水水质的影响,给河道底泥整治工程方案的选择提供参考,采用佛山水道的污染底泥以COD、NH3-N和TP为研究对象,进行了污染物释放的动态模拟,并根据试验结果用平均值法计算了底泥污染物的释放量。结果表明,污染程度较高的底泥对上覆水中NH3-N、COD和TP浓度的贡献依次为0.65、4.25和0.067 mg/L,分别占Ⅳ类水质标准值的43.3%、14.2%和22.3%。这说明在外源污染被控制后,如果没有采取有效措施抑制底泥污染物的释放,很难使佛山水道的水质达到Ⅳ类标准。

黄河下游洪水冲淤特性及高效输沙研究

以黄河下游实测洪水资料为基础,对洪水冲淤特性及高效输沙过程进行了分析。结果表明:①洪水平均流量大于2 000 m3/s后,排沙比的大小主要取决于洪水平均含沙量的大小;②输沙水量与排沙比的关系因含沙量的不同而分带分布,同一含沙量级洪水的输沙水量随着排沙比的增大而减小,当排沙比达到一定程度后,随着排沙比的增大,输沙水量不再明显减小;③可以用平均流量为3 200 m3/s、平均含沙量为65 kg/m3的水沙搭配来代表黄河下游高效输沙洪水过程。

基于时间平均的海底沉积物声速预测

在海底沉积物声速预测中,把不同海域的物理性质完全不同的沉积物试验数据拟合出一个统一的方程存在不足,不但数据过于离散,而且方程中参量的物理意义不明确。借鉴Wyllie等建立的时间平均方程的思路,基于声传播过程中路程、时间和声速之间的基本关系,引入了表征固液双相之间的堆垒方式和耦合状态对声传播路径影响的耦合系数,建立了沉积物声速预测模型。将鹿回头外海、南海南部和北部的沉积物测量数据进行线性回归分析,分别得出适用于不同海域的沉积物声速预测模型,拟合的复相关系数较大,偏差较小,证明该模型能够反映声速随孔隙度的变化规律,且各参数物理意义明确,具有一定的研究和理论探索意义。

不同鳃片间距下的分离鳃内部流场三维数值模拟

为研究鳃片间距对分离鳃的速度场及泥沙分布特性的影响,采用Fluent软件中的层流模型和欧拉模型,运用Phase Coupled SIMPLE(PC-SIMPLE)算法,对不同鳃片间距下分离鳃的水沙两相流流场进行了静水沉降的三维数值模拟。根据数值计算结果,对速度场和含沙量分布特性进行了对比与分析。结果表明:不同鳃片间距下,分离鳃内部的速度场分布规律有所不同,鳃片间距越大,速度流场受到来自泥沙通道中的泥沙流与清水通道中的清水流影响就越大;鳃片间距越小,分离鳃的沉淀效果越好。以泥沙平均速度和清水平均速度作为考核指标,同时考虑分离鳃内部的流场特性、水沙分离效果与制作分离鳃的成本,则最佳鳃片间距为5 cm。

山东荣成湾月湖口门落潮干道的推移质输运

改进了Gao等 ( 1 994)方法 ,并用以计算潮汐汊道口门落潮干道的垂线平均流速。利用月湖潮汐汊道系统冬、夏季各一个月的潮位资料 ,计算落潮干道的潮流流速和推移质输运率。结果表明 ,流速的计算值和实测值呈良好的相关性 。

深海沉积物分类与命名的参数指标和主成分分析

对于南海中部（118个表层沉积物样,水深82~4 420 m）、东部（106个表层沉积物样,水深700~4 508 m）海域的表层沉积物的粒度资料按小于200 m,200~2 000 m,大于2 000 m水深段对水深、平均粒径、黏土含量进行统计分析,结果表明从陆架到陆坡再到深海,平均粒径和黏土含量随水深增加呈非常有规律的变化;把大于2 000 m水深区域再细分为大于2 500 m,大于3 000 m,大于3 500 m,结果表明平均粒径和黏土含量随水深增加几乎无变化,在南海中部水深大于2 000 m海域平均粒径为3.39~3.54μm,黏土平均含量为54.91%~55.47%;在南海东部水深大于2 000 m海域平均粒径为3.25~3.37μm,黏土平均含量为53.91%~54.56%。研究表明2 000 m水深具有划分深海沉积物的指示意义。南海中部水深大于2 000 m海域黏土平均含量为55.19%,平均粒径为3.39μm;在南海东部水深大于2 000 m海域黏土平均含量为53.91%,平均粒径为3.37μm;在南海中部、东部水深大于2 000 m海域平均粒径均小于4μm,黏土平均含量均大于50%,表明深海沉积物粒度特征是平均粒径小于4μm和黏土平均含量大于50%。黏土含量是非生物组分的代表和划分深海沉积物类型的一个独立参数,钙质生物和硅质生物组分是另外两个独立参数。南海东部海域表层沉积物中55种元素总含量为47.50%,硅、铝、钛、钠、钾、磷、钙、镁、铁、锰十种主元素含量为47.03%,其他45种元素含量为0.47%,虽然沉积物来源复杂、成因不同,但沉积物化学主成分并不复杂,主要由前10种主元素和氧元素组成。沉积物主元素铝、钙、硅分别富集于黏土、钙质沉积、硅质沉积中。通过建立沉积物生源组分与碳酸钙、三氧化二铝、二氧化硅的量化关系,可把碳酸钙、生物二氧化硅作为钙质生物和硅质生物的两个替代参数。

基于含沙量分段的人类活动对延河水沙变化的影响分析

采用延河甘谷驿水文站控制区1965-2002年降水量、径流量和输沙量资料,分析了人类活动对河流水沙变化的影响。与以往以年代为基准期的分段方法不同,本研究根据河流含沙量距平累计值变化特征,把延河水沙变化过程划分为5个时段,并以含沙量持续较高的时段Ⅰ(1965-1971年)为基期,分析了各时段径流量和输沙量的变化特征。以基期单位降水产沙量和产流量为参数,计算了各时段全年和汛期的计算输沙量和径流量。通过比较计算和实测的输沙量和径流量,分析了各时段人类活动对全年和汛期输沙量和径流量的影响。研究表明,根据含沙量距平累计值划分时段可以更好反映河流水沙变化特征:治理期人类活动平均减少年和汛期输沙量分别约50.3%和40.0%;而减少年和汛期径流量的幅度分别约为19.8%和34.2%。人类活动在时段Ⅱ(1971-1976年)和时段Ⅴ(1997-2001年)对水沙的影响较大,而在时段Ⅳ(1987-1996年)影响较小,且表现复杂。