Temporal and spatial variations in water flow and sediment load in Narmada River Basin, India: natural and man-made factors   总被引：1，自引：0，他引：1  

Harish Gupta  G. J. Chakrapani 《Environmental Geology》2005,48(4-5):579-589

The Narmada River flows through the Deccan volcanics and transports water and sediments to the adjacent Arabian Sea. In a first-ever attempt, spatial and temporal (annual, seasonal, monthly and daily) variations in water discharge and sediment loads of Narmada River and its tributaries and the probable causes for these variations are discussed. The study has been carried out with data from twenty-two years of daily water discharge at nineteen locations and sediment concentrations data at fourteen locations in the entire Narmada River Basin. Water flow in the river is a major factor influencing sediment loads in the river. The monsoon season, which accounts for 85 to 95% of total annual rainfall in the basin, is the main source of water flow in the river. Almost 85 to 98% of annual sediment loads in the river are transported during the monsoon season (June to November). The average annual sediment flux to the Arabian Sea at Garudeshwar (farthest downstream location) is 34.29×10⁶ t year⁻¹ with a water discharge of 23.57 km³ year⁻¹. These numbers are the latest and revised estimates for Narmada River. Water flow in the river is influenced by rainfall, catchment area and groundwater inputs, whereas rainfall intensity, geology/soil characteristics of the catchment area and presence of reservoirs/dams play a major role in sediment discharge. The largest dam in the basin, namely Sardar Sarovar Dam, traps almost 60–80% of sediments carried by the river before it reaches the Arabian Sea.  相似文献   

Snow loads on wire mesh and cable net rockfall slope protection systems     

Shanzhi Shu  Thomas C. Badger 《Engineering Geology》2005,81(1):15-31

Snow load on mesh systems is complicated by many factors. This paper presents field instrumentation data on snow load variation with temperature, snowfall and snow depth on a mesh system. It was found that snow load pattern on mesh systems changed with temperature even without variation in snow depth. It reached its maximum value when the temperature rose just above freezing to melt the interface. The field data was used to formulate appropriate snow load models for the various conditions of temperature in the field. The snow load models were used to study the performance of a number of mesh systems in North America and estimate the interface friction that was prevalent for the different surface conditions.  相似文献   

One-dimensional consolidation of soil under multistage load based on continuous drainage boundary     

Yi--> Tian  Wenbing Wu  Guosheng Jiang  M. Hesham El Naggar  Guoxiong Mei  Meijuan Xu  Rongzhu Liang 《国际地质力学数值与分析法杂志》2020,44(8):1170-1183

In engineering practice, a rapid loading rate can result in ground failure when the strength of soft soils is relatively low, and a multistage loading scheme is always utilized to deal with this situation. Firstly, under a multistage load and the continuous drainage boundary, an analytical solution of excess pore-water pressure and consolidation degree is obtained by virtue of the superposition formula of excess pore-water pressure, and a more general continuous drainage boundary under arbitrary time-dependent load is developed. Then, a comparison with existing analytical solutions is conducted to verify the present solution. A preliminary attempt on applying the continuous drainage boundary into the finite element model is made, and the feasibility of the numerical model for the one-dimensional consolidation under the continuous drainage boundary is verified by comparing the results calculated by FEM with that from present analytical solution. Finally, the consolidation behavior of soil is investigated in detail for different int erface parameters or loading scheme. The results show that, in land reclamation projects, a horizontal drain should be placed close to the boundary with a smaller interface parameter to improve the consolidation efficiency. The degree of consolidation is also related to the applied time-dependent load and interface parameters.  相似文献   

Multi‐temporal scale changes of streamflow and sediment load in a loess hilly watershed of China          下载免费PDF全文

Guangyao Gao  Ying Ma  Bojie Fu 《水文研究》2016,30(3):365-382

Global climate change and diverse human activities have resulted in distinct temporal–spatial variability of watershed hydrological regimes, especially in water‐limited areas. This study presented a comprehensive investigation of streamflow and sediment load changes on multi‐temporal scales (annual, flood season, monthly and daily scales) during 1952–2011 in the Yanhe watershed, Loess Plateau. The results indicated that the decreasing trend of precipitation and increasing trend of potential evapotranspiration and aridity index were not significant. Significant decreasing trends (p < 0.01) were detected for both the annual and flood season streamflow, sediment load, sediment concentration and sediment coefficient. The runoff coefficient exhibited a significantly negative trend (p < 0.01) on the flood season scale, whereas the decreasing trend on the annual scale was not significant. The streamflow and sediment load during July–August contributed 46.7% and 86.2% to the annual total, respectively. The maximum daily streamflow and sediment load had the median occurrence date of July 31, and they accounted for 9.7% and 29.2% of the annual total, respectively. All of these monthly and daily hydrological characteristics exhibited remarkable decreasing trends (p < 0.01). However, the contribution of the maximum daily streamflow to the annual total progressively decreased (?0.07% year^?1), while that of maximum daily sediment load increased over the last 60 years (0.08% year^?1). The transfer of sloping cropland for afforestation and construction of check‐dams represented the dominant causes of streamflow and sediment load reductions, which also made the sediment grain finer. Copyright © 2015 John Wiley & Sons, Ltd.  相似文献   

Effects of linear and exponential heterogeneity on the dynamic response of a moving load in an irregular isotropic half-space: a comparative study     

Abhishek Kumar Singh  Anirban Lakshman  Amares Chattopadhyay 《Geomechanics and Geoengineering》2016,11(3):201-218

Heterogeneity, being a trivial feature inside the earth or in a geostructure, makes a strong basis for its consideration in the study of geomechanics. Inclusion of the concept of heterogeneity along with irregularity in the medium brings a novelty to the existing literature related to the study of the moving load. The present study investigates the effects of linear and exponential heterogeneity on the dynamic response due to a normal load moving with constant velocity on a rough irregular heterogeneous isotropic half-space in a comparative approach. Expressions for both normal and shear stresses for either case of heterogeneity have been established in closed form. Substantial effects of the affecting parameters such as depth, irregularity factor, maximum depth of irregularity, frictional coefficient, linear heterogeneity parameter and exponential heterogeneity parameter on normal and shear stresses for both the cases of heterogeneity have been observed. Numerical computation has been carried out and the effects of said parameters have been meticulously examined by means of graphs. Moreover, different cases of heterogeneity and homogeneity along with various types of irregularity namely rectangular, parabolic and no irregularity are compared which serve as a focal theme of the study.  相似文献   

腐蚀管道在内压和轴向压力影响下的弯曲破坏     

高杰  李昕  周晶 《海洋工程》2016,34(6):74-82

运行在恶劣环境中的海底管道,往往受到内压、轴力和弯矩等复杂荷载的联合作用。腐蚀会导致管壁局部变薄,降低管道极限承载力。为保证管道安全高效运行,准确预测和分析复杂荷载作用下的塑性极限承载力和变形行为就显得尤为重要。考虑大应变和大变形、应力强化和材料非线性,运用数值仿真软件建立腐蚀缺陷管道的三维实体有限元模型,在全尺寸管道破坏试验验证的基础上,对腐蚀管道在内压、轴向压力和弯矩相互作用下的失效模式和极限弯矩承载力进行了相关研究,并进行了腐蚀缺陷几何参数的敏感性分析。研究结果表明:初始内压和初始轴向压力会显著降低腐蚀管道的极限弯矩承载力,并且影响最终的失效模式;在腐蚀缺陷几何尺寸参数中,腐蚀宽度比腐蚀深度和腐蚀长度的影响更大。  相似文献   

Field Evaluation of the Vertical Bearing Capacity of a Screw Pretensioned Spun High-Strength Concrete Pile     

Yongkyu Choi  Dong-Chul Kim  Tae-Hyung Kim 《Marine Georesources & Geotechnology》2016,34(5):474-485

This study has evaluated the vertical bearing capacity by conducting static load tests for noise-free and vibration-free screw pretensioned spun high-strength concrete (PHC) piles installed using two different methods (end-squirting shoe and pre-boring methods). Vertical bearing capacity differences seem to occur due to the displacement of soils near the external circumference of a pile, depending on the installation method. A method by which to evaluate the bearing capacity of screw concrete piles is suggested by considering the equations that already have been used to calculate the bearing capacity of piles. Based on static load tests and analysis, the pile installed using the end-squirting shoe method was assumed to be a bored pile and it was reasonable to use the equation proposed by the Japanese Geotechnical Society. At the same time, the pile installed using the pre-boring method was deemed a low soil displacement pile and so it was reasonable to apply the equations proposed for calculating the bearing capacity of the driven pile suggested by the Architectural Institute of Japan.  相似文献   

小秦岭太峪水系沉积物重金属污染生态危害评价     

张江华  王葵颖  徐友宁  吴耀国  陈华清 《地质通报》2018,37(12):2224-2232

以金矿开发影响的黄河二级支流太峪水系沉积物为研究对象,沿河采集16个表层沉积物样品,分层采集垂向剖面10件水库沉积物样品,测定了样品中重金属元素Hg、Pb、Cd、Cr、As、Cu和Zn的含量,采用Hakanson潜在生态指数法和Tomlinson污染负荷指数法评价重金属元素污染程度和潜在生态风险。结果表明,矿业活动是太峪水系沉积物重金属元素污染的主要因素;变异系数、富集系数和最高污染系数均反映Hg、Pb、Cd是太峪水系沉积物的特征污染重金属元素,Cr和As的质量分数接近地区背景值;太峪水系表层沉积物受到重金属元素的极强污染,山区段污染较山外更严重;整个流域的Hg、Pb、Cd具有很强的潜在生态危害,Cr、As、Zn的潜在生态危害轻微;太峪水系沉积物垂向各层沉积物都受到重金属元素的极强污染,生态问题以Hg、Pb、Cd的潜在生态危害为主,其污染和生态危害程度都高于流向上的沉积物。潜在生态危害指数评价突出了不同元素的毒性和危害程度,而污染负荷指数法侧重于样本空间上的污染程度,二者互补使用有利于实际问题的全面评价。  相似文献   

川西九龙地区锂铍矿区土壤重金属分布特征及生态风险评价   总被引：1，自引：0，他引：1  

于沨  王伟  于扬  王登红  刘善宝  高娟琴  吕秉廷  刘丽君 《岩矿测试》2021,(3):408-424

川西九龙地区是近年来中国关键矿产资源勘查的热点地区之一,区内锂铍等稀有金属矿产资源优势突出,有望逐步发展成为国家级大型资源基地。作为长江上游生态保护屏障,该区生态环境脆弱,面对矿业开发的巨大机遇,在当前"环保优先"的现实情况下,急需摸清该区环境家底,支撑国家能源战略发展。本文用ICP-MS方法检测了该区352件土壤样品中7种重金属元素(Cd、As、Pb、Cr、Cu、Ni、Zn)的含量,运用地累积指数法、污染负荷指数法、潜在生态风险指数法和健康风险评价模型,结合GIS空间分析,综合研究了该区土壤中重金属的空间分布特征和生态风险。结果表明:(1)研究区土壤7种重金属元素浓度的平均值均没有超过国家农用土壤污染风险筛选值。As和Pb平均含量低于四川省土壤背景值,Cd、Cr、Cu、Ni和Zn含量高于背景值,分别是背景值的2.44、1.04、1.15、1.28和1.17倍。(2)Cd、Pb、Cr、Cu、Ni和Zn六种重金属元素浓度的空间分布特征明显受到区内黑云母花岗岩的影响,Pb的高浓度中心以及Cr、Cu、Ni和Zn的低浓度中心与岩体的空间位置对应关系明显。(3)地累积指数法评价结果显示,研究区土壤区域整体上不存在重金属异常累积;污染负荷指数法评价结果显示污染负荷指数均小于1,不存在重金属的污染;除Cd存在轻微的潜在生态风险外,其余6种元素均不存在潜在生态风险。(4)健康风险评价模型分析结果显示,空间上,Cd元素的单元素潜在生态风险指数空间分布规律与岩体存在一定联系,无生态风险区域与黑云母花岗岩岩体位置对应。土壤中的重金属可以通过手口、呼吸和皮肤直接接触三种途径进入人体,其中手口途径是产生健康风险的最主要途径。在全部重金属元素产生的健康风险中,除Cr的手口途径会产生可以接受的正常的自然致癌风险外,其余元素均不存在致癌性和非致癌性。研究表明,当前研究区土壤不存在重金属污染,潜在危害程度较低,且不存在非致癌和致癌性风险。但基于土壤中重金属存在一定的累积效应,在今后矿业开发过程中要密切关注土壤重金属浓度的变化,防止重金属污染带来的风险。  相似文献   

土工试验规范变更对膨胀计算和判定的影响     

刘军  石鹏飞  孙凯 《岩土工程技术》2021,(2):134-136,F0003

对土工试验方法标准的新旧规范中无荷膨胀率和有荷膨胀率的变化内容进行对比分析,发现两者的计算公式发生显著变化,新规范的计算结果与旧规范相比,膨胀率明显变大,膨胀量随之增大,这将对工程勘察、设计、施工等产生明显影响。以某工程为例,新规范计算后地层总膨胀量由旧规范的16.7 mm变为51.8 mm,增加了2倍左右,地基土的胀缩等级由Ⅰ级变为Ⅱ级,地基基础设计等级由丙级变为乙级,地基处理措施和施工方案随之也发生改变。因此,工程技术人员对此应综合考虑,严谨对待。  相似文献