How does the bed surface impact low-magnitude bedload transport rates over gravel-bed rivers?     

Emeline Perret  Céline Berni  Benoît Camenen 《地球表面变化过程与地形》2020,45(5):1181-1197

Bedload transport is a complex phenomenon that is not well understood, especially for poorly sorted sediment and low transport rates, which is what is typically found in alpine gravel-bed rivers. In this paper, the interaction between bedload rate, bed stability and flow is investigated using flume experiments. Significant differences in bedload rates were observed for experiments conducted on beds formed with the same gravel material but presenting diverse arrangements and bedforms. Tests were performed under regimes of low transport rate, which are mainly controlled by gravel-bed roughness. Different scales of roughness were identified using the statistical characteristics of detailed bed elevation measurements: grain, structure and large bedform scales. The role played by these different roughness scales in bedload dynamics was examined. For quasi-flat beds, bed stability was quantified using a combination of bed surface criteria describing grain and structure scales. It was found that bed stability affects the bedload rate directly and not only through its influence on the flow or on the incipient motion. For beds with large bedforms, the analysis of bedload dynamics also showed the importance of accounting for effective bed shear stress distributions. An empirical bedload model for low transport regimes was suggested. Compared with previous formulae developed for alpine rivers, this model accounts for bed stability and distribution of effective bed shear stress. It significantly improves the understanding of gravel dynamics over complex beds such as arranged beds or those with large bedforms. However, further tests are needed to use the model outside the range of conditions of this study. © 2019 John Wiley & Sons, Ltd.  相似文献   

Geomorphic evolution of the Qingshuigou channel of the Yellow River Delta in response to changing water and sediment regimes and human interventions     

Shasha Han  Stephen Rice  Guangming Tan  Kairong Wang  Shan Zheng 《地球表面变化过程与地形》2020,45(10):2350-2364

Delta channels are important landforms at the interface of sediment transfer from terrestrial to oceanic realms and affect large, and often vulnerable, human populations. Understanding these dynamics is pressing because delta processes are sensitive to climate change and human activity via adjustments in, for example, mean sea level and water/sediment regimes. Data collected over a 40-year period along a 110-km distributary channel of the Yellow River Delta offer an ideal opportunity to investigate morphological responses to changing water and sediment regimes and intensive human activity. Complementary data from the delta front provide an opportunity to explore the interaction between delta channel geomorphology and delta-front erosion–accretion patterns. Cross-section dimensions and shape, longitudinal gradation and a sediment budget are used to quantify spatial and temporal morphological change along the Qingshuigou channel. Distinctive periods of channel change are identified, and analysis provides a detailed understanding of the temporal and spatial adjustments of the channel to specific human interventions, including two artificial channel diversions and changes in water and sediment supply driven by river management, and downstream delta-front development. Adjustments to the diversions included a short-lived period of erosion upstream and significant erosion in the newly activated channel, which progressed downstream. Channel geomorphology widened and deepened during periods when management increased water yield and decreased sediment supply, and narrowed and shallowed during periods when management reduced water yield and the sediment load. Changes along the channel are driven by both upstream and downstream forcing. Finally, there is some evidence that changing delta-front erosion–accretion patterns played an important role in the geomorphic evolution of the deltaic channel; an area that requires further investigation. © 2020 John Wiley & Sons, Ltd.  相似文献   

三门峡水库冲淤重心变化及其对潼关高程的影响     

何娟  郑珊  吴保生 《湖泊科学》2023,35(1):338-348

以往关于三门峡水库的研究多关注库区年际间的冲淤变化,而对汛期和非汛期库区冲淤分布研究较少。本文基于三门峡水库蓄清排浑运用以来1974 2018年实测水沙、断面及冲淤数据,研究汛期和非汛期库区冲淤重心的迁移、冲淤速率及其对潼关高程的影响。结果表明,蓄清排浑运用以来库区河道基本遵循汛期冲刷、非汛期淤积的演变规律。分别定义汛期最大冲刷速率和非汛期最大淤积速率发生的相邻两断面间的子河段为冲刷重心和淤积重心,汛期冲刷重心与非汛期淤积重心出现的位置基本对应,1974 2010年冲淤重心由距坝约90 km逐渐向坝前移动,平均下移速率约1～2km/a;2010年后冲淤重心逐渐上移,2017年位于坝上游约60～70 km,但冲淤强度明显减弱。淤积重心的位置主要受水库回水长度影响,冲刷重心主要与汛期水流能量相关,淤积重心位置迁移滞后于影响因子的变化约5年,而冲刷重心滞后时间约2年。潼关高程与潼关至太安段（潼太段）比降呈反比关系,比降越大,潼关高程越低,而当冲刷重心迁移至潼太段并影响其下段时,潼太段比降增大,利于潼关高程降低。1985年后回水范围和冲淤重心均位于潼关以下,潼关高程受冲淤重心影响较小。  相似文献   

托普台区块高渗透地层随钻堵漏剂配方优化          下载免费PDF全文

田建东  于培志  牟福权 《探矿工程》2015,42(7):10-13

托普台区块上部地层以砂泥岩层、砾质砂岩为主,容易发生漏点不明确、漏失段长的高渗透性漏失。通过对堵漏材料的配伍性评价及合理级配,优选出了一种适合高渗透性漏失地层的随钻堵漏剂。该堵漏剂对钻井液流变性影响小,可降低钻井液API滤失量,对沙床封堵后承压能力＞10 MPa,在TP328X井的应用表明,高强度弹性石墨颗粒复合凝胶堵漏对于高压差、高渗透漏失的工况,可以有效封堵漏层,特别适用于对于漏层不明、漏涌同层、裸眼等复杂井况。  相似文献   

Origin of mud in turbidites and hybrid event beds: Insight from ponded mudstone caps of the Castagnola turbidite system (north-west Italy)     

Marco Patacci  Mattia Marini  Fabrizio Felletti  Andrea Di Giulio  Massimo Setti  William McCaffrey 《Sedimentology》2020,67(5):2625-2644

The partitioning of different grain-size classes in gravity flow deposits is one of the key characteristics used to infer depositional processes. Turbidites have relatively clean sandstones with most of their clay deposited as part of a mudstone cap or as a distal mudstone layer, whereas sand-bearing debrites commonly comprise mixtures of sand grains and interstitial clay; hybrid event beds develop alternations of clean and dirty (clay-rich) sandstones in varying proportions. Analysis of co-genetic mudstone caps in terms of thickness and composition is a novel approach that can provide new insight into gravity flow depositional processes. Bed thickness data from the ponded Castagnola system show that turbidites contain more clay overall than do hybrid event beds. The Castagnola system is characterized by deposits of two very different petrographic types. Thanks to this duality, analyses of sandstone and mudstone composition allow inference of which proportion of the clay in each of the deposit types was acquired en route. In combination with standard sedimentological observations the new data allow insight into the likely characteristics of their parent flows. Clean turbidites were deposited by lower concentration, long duration, erosive, muddy turbidity currents which were more efficient at fractionating clay particles away from their basal layer. Hybrid event beds were deposited by shorter duration, higher-concentration, less-erosive sandier flows which were less efficient at clay fractionation. The results are consistent with data from other turbidite systems (for example, Marnoso-arenacea). The approach represents a new method to infer the controls on the degree of clay partitioning in gravity flow deposits.  相似文献   

矽卡岩型钨矿床成矿作用研究进展   总被引：4，自引：1，他引：3  

李佳黛  李晓峰 《矿床地质》2020,39(2):256-272

钨具有极高的熔点和硬度,是现代生活、工业、国防和高科技领域中不可或缺的基础材料。研究显示,矽卡岩型钨矿是世界钨矿床中最主要的类型,广泛分布于受俯冲影响的环太平洋大陆边缘和与碰撞有关的欧亚大陆内部古大陆边缘,形成时代集中在中生代和古生代。钨在岩浆演化过程中呈现不相容的特征,因此与钨矿化相关的岩浆岩演化程度较高,包括S型、A型以及高分异I型花岗岩。钨具有较高的流体亲和性,使其在熔-流体分异过程中倾向于富集在共存的流体相。钨在热液流体中以氯化物、氟化物和碳酸盐络合物,以及同多钨酸盐和杂多钨酸盐等形式迁移,主要受源岩、围岩成分和流体物化条件等因素影响。矽卡岩型钨矿的成矿作用存在多期次、多阶段演化特征,不同阶段的成矿流体的温度和盐度存在差异。白钨矿是矽卡岩型钨矿中主要的矿石矿物,其沉淀可能受到多种机制的影响,如降温、流体混合、流体沸腾及流体-围岩反应等。文章简要综述了世界矽卡岩型钨矿的时空分布、地质特征和相关成因矿物学研究,并重点总结了钨的成矿岩浆-热液体系特征,钨在岩浆-热液演化过程中的地球化学行为及其迁移和沉淀机制等方面的研究成果。文章指出,为了完善矽卡岩型钨矿的成矿和找矿勘查模型,应当加强矽卡岩型钨矿的成矿时代、成矿物质和流体来源以及成矿环境的精细研究。  相似文献   

Evaluation of the simple settling theory for predicting sediment deposition by overland flow     

L. Beuselinck  G. Govers    A. Steegen  P. B. Hairsine  J. Poesen   《地球表面变化过程与地形》1999,24(11):993-1007

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Variations in trace element geochemistry in the Seine River Basin based on floodplain deposits and bed sediments     

Arthur J. Horowitz  Michel Meybeck  Zayed Idlafkih  Erwan Biger 《水文研究》1999,13(9):1329-1340

Between 1990 and 1995 a series of bed sediment, suspended sediment and fresh floodplain samples were collected within the Seine River Basin, in France, to evaluate variations in trace element geochemistry. Average background trace element levels for the basin were determined from the collection and subsequent analyses of bed sediment samples from small rural watersheds and from a prehistoric (5000 BP) site in Paris. Concentrations are relatively low, and similar to those observed for fine‐grained bed sediments from unaffected areas in the United States and Canada. However, the concentrations are somewhat higher than the reference levels presently adopted by French water authorities for areas north of the Seine Basin, which have similar bedrock lithologies. Downstream trace element variations were monitored in 1994 and 1995 using fresh surficial floodplain samples that were collected either as dried deposits a few days after peak discharge, or immediately after peak discharge (under ≤30 cm of water). Chemical comparisons between fresh floodplain deposits, and actual suspended sediments collected during flood events, indicate that, with some caveats, the former can be used as surrogates for the latter. The floodplain sediment chemical data indicate that within the Seine Basin, from the relatively unaffected headwaters through heavily affected urban streams, trace element concentrations vary by as much as three orders of magnitude. These trace element changes appear to be the result of both increases in population as well as concomitant increases in industrial activity. (This article is a US government work and is in the public domain in the United States.)  相似文献   

MODELLING FLOOD HYDRAULICS AND OVERBANK DEPOSITION ON RIVER FLOODPLAINS     

A. P. Nicholas  D. E. WALLING 《地球表面变化过程与地形》1997,22(1):59-77

This paper outlines a numerical model for the prediction of floodplain inundation sequences, overbank deposition rates and deposit grain size distributions. The model has two main components: first, a simplified hydraulic scheme which predicts floodwater flow depths and velocities, and second, a sediment transport element which employs a mass balance relation describing suspended sediment dispersion by convective and diffusive processes and sediment deposition as a function of particle settling rates. These relationships are solved numerically on a finite difference grid that accurately replicates the complex topographic features typical of natural river floodplains. The model is applied to a 600 m reach of the River Culm, Devon, U.K. using data derived from a range of field and laboratory techniques. Continuous records of river stage and suspended sediment concentration provide the model's upstream boundary input requirements. These are supplemented by measurements of the in situ settling characteristics of the suspended sediment load. The model's sediment transport component is calibrated with the aid of a dataset of measured overbank deposition amounts derived from flood events over a 16 month period. The model is shown to predict complicated floodwater inundation sequences and patterns of suspended sediment dispersion and deposition, which are largely a product of the complex topography of the floodplain. These results compare favourably with observations of overbank processes and are an improvement over those of previous models which have employed relatively simple representations of floodplain geometry. © 1997 by John Wiley & Sons, Ltd.  相似文献   

Atmospheric deposition to watersheds in complex terrain     

GARY M. LOVETT  JONATHAN J. BOWSER  ERIC S. EDGERTON 《水文研究》1997,11(7):645-654

Single collection stations for wet or bulk deposition are generally inadequate to describe atmospheric inputs to watersheds in complex terrain. Atmospheric deposition is delivered by wet, dry and cloud deposition processes, and these processes are controlled by a wide range of landscape features, including canopy type and structure, topographic exposure, elevation and slope orientation. As a result, there can be a very high degree of spatial variability within a watershed, and a single sampling point, especially at low elevation, is unlikely to be representative. Atmospheric inputs at the watershed scale can be calculated from the whole watershed mass balance if the outputs and within-watershed sources and sinks are known with sufficient accuracy. Alternatively, indices of atmospheric deposition such as Pb accumulation in the forest floor and SO²⁻₄ flux in throughfall can be used to characterize patterns of total deposition, and these indices can be used to model deposition to the entire watershed based on known landscape features such as elevation and canopy type. © 1997 John Wiley & Sons, Ltd.  相似文献