STABILITY OF GRAVEL BED RIVERS BASED ON SIEVE ANALYSIS DATA   总被引：1，自引：0，他引：1  

Andreas DITTRICH Institute of Water Resources Management  Hydraulic  Rural Engineering  University of Karlsruhe  Germany. 《国际泥沙研究》2001,16(2)

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Multiple thread flow and channel bifurcation in a braided river: Brahmaputra–Jamuna River, Bangladesh     

W. Roy Richardson  Colin R. Thorne 《Geomorphology》2001,38(3-4)

Considerable progress has been made recently in characterising the patterns displayed by the anabranches of braided rivers. However, the physical processes of sediment scour, transfer and deposition that govern the generation and evolution of anabranch channels remain largely unexplained. Direct measurement of three-dimensional flow fields and morphological evolution of the anabranches in the braided Brahmaputra–Jamuna River, Bangladesh, were undertaken to investigate the interactions between fluvial processes and anabranch morphology. These data were used to elucidate the circumstances leading to the bifurcation of a single channel, which is a topic of fundamental importance to understanding the physical processes responsible for braiding. Results indicate that division of the velocity field into multiple threads within a single channel precedes a division in the cross-sectional morphology of the channel and appears to be a necessary prerequisite for development of a bifurcation. An empirical relationship was established to discriminate between channels with single and multi-thread velocity fields, based on the depth-to-width ratio and specific energy of the flow at a representative channel cross-section. This function requires further validation, but could be used to predict the conditions under which a single channel is likely to bifurcate to produce two anabranches.  相似文献   

甘肃省主要河流径流时空分布规律及演变趋势分析   总被引：21，自引：0，他引：21  

胡兴林 《地球科学进展》2000,15(5):516-521

通过对甘肃省主要河流径流时空分布规律的分析研究,得出干旱缺水的主要原因是各河年径流丰水时段很短,一般只有2～3年;枯水时段很长,可达7～26年;祁连山区许多河流多年均值基本稳定。并预测从1998年开始至2009年,全省诸河水量从枯水年代转向平水到偏丰的年代;建议全省必须树立长期抗旱的思想,水资源利用必须进行系统分析优化配置。  相似文献   

Estuarine Physical Processes Research: Some Recent Studies and Progress   总被引：2，自引：0，他引：2  

R. J. Uncles 《Estuarine, Coastal and Shelf Science》2002,55(6):829

The literature on estuarine physical studies is vast, diverse and contains many valuable case studies in addition to pure, process-based research. This essay is an attempt to summarize both some of the more recent studies that have been undertaken during the last several years, as well as some of the trends in research direction and progress that they represent. The topics covered include field and theoretical studies on hydrodynamics, turbulence, salt and fine sediment transport and morphology. The development and ease-of-application of numerical and analytical models and technical software has been essential for much of the progress, allowing the interpretation of large amounts of data and assisting with the understanding of complex processes. The development of instrumentation has similarly been essential for much of the progress with field studies. From a process viewpoint, much more attention is now being given to interpreting intratidal behaviour, including the effects of tidal straining and suspended fine sediment on water column stratification, stability and turbulence generation and dissipation. Remote sensing from satellites and aircraft, together with fast sampling towed instruments and high frequency radar now provide unique, frequently high resolution views of spatial variability, including currents, frontal and plume phenomena, and tidal and wave-generated turbidity. Observations of fine sediment characteristics (floc size, aggregation mechanisms, organic coatings and settling velocity) are providing better parameterizations for sediment transport models. These models have enhanced our understanding both of the estuarine turbidity maximum and its relationship to fronts and intratidal hydrodynamic and sedimentological variability, as well as that of simple morphological features such as intertidal mudflats. Although few, interdisciplinary studies to examine the relationships between biology and estuarine morphology show that bivalve activity and the surface diatom biofilm on an intertidal mudflat can be important in controlling the erosion of the surface mud layer.  相似文献   

Tidal mixing and trapping in mangrove swamps     

Eric Wolanski  Peter Ridd 《Estuarine, Coastal and Shelf Science》1986,23(6)

Lateral trapping in mangrove swamps is a dominant process controlling longitudinal mixing in mangrove-fringed tidal rivers. In the dry season, the effective value of the longitudinal diffusivity is increased by the trapping effect by typically two orders of magnitude, from its value in the absence of swamps. In the wet season, freshwater is trapped within the swamp and the adjoining boundary in the tidal river, for long periods following the passage of a short-lived flood. This may have important ecological implications. A fluid-mud layer appears to be created by strong tidal currents over colloidal mangrove mud.  相似文献   

Determination of bankfull discharge magnitude and frequency: comparison of methods on 16 gravel‐bed river reaches     

O. Navratil  M‐B. Albert  E. Hrouin  J‐M. Gresillon 《地球表面变化过程与地形》2006,31(11):1345-1363

Bankfull discharge is identified as an important parameter for studying river morphology, sediment motion, flood dynamics and their ecological impacts. In practice, the determination of this discharge and its hydrological characteristics is not easy, and a choice has to be made between several existing methods. To evaluate the impact of the choice of methods, five bankfull elevation definitions and four hydrological characterizations (determination of duration and frequency of exceedance applied to instantaneous or mean daily data) were compared on 16 gravel‐bed river reaches located in France (the catchment sizes vary from 10 km² to 1700 km²). The consistency of bankfull discharge estimated at reach scale and the hydraulic significance of the five elevation definitions were examined. The morphological definitions (Bank Inflection, Top of Bank) were found more relevant than the definitions based on a geometric criterion. The duration of exceedance was preferred to recurrence intervals (partial duration series approach) because it is not limited by the independency of flood events, especially for low discharges like those associated with the Bank Inflection definition. On average, the impacts of the choice of methods were very important for the bankfull discharge magnitude (factor of 1·6 between Bank Inflection and Top of Bank) and duration of exceedance or frequency (respectively a factor 1·8 and 1·9 between mean daily and instantaneous discharge data). The choice of one combination of methods rather than another can significantly modify the conclusions of a comparative analysis in terms of bankfull discharge magnitude and its hydrological characteristics, so that one must be cautious when comparing results from different studies that use different methods. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

天山北坡中段主要河流的枯季径流分析     

葛新娟  尤平达  吉锦环  胡莲连 《干旱区地理》2006,29(3):338-341

枯水径流是构成河川径流年内分配的重要组成部分,在水资源评价、生态环境及工程水文分析计算中是必不可少的,它是河川径流的一种特殊形态。研究区域地处新疆经济社会发展的中心地带—天山北坡经济带,是水资源紧缺地区,对其枯季径流进行较深入的分析研究,有其重要的现实意义。对天山北坡中段主要河流的冬季、枯水期、最小月和最小日平均流量作了初步分析,并提出某些区域性的基本规律。  相似文献   

The precision of sampling grain‐size percentiles using the Wolman method     

Julian C. Green 《地球表面变化过程与地形》2003,28(9):979-991

The precision of sampling different grain‐size percentiles in comparison to each other is of signi?cance for choosing which percentile is appropriate to characterize riverbed surface sediments. The traditional view, based on normal grain‐size distributions derived by the Wolman grid‐by‐number method, has identi?ed the median percentile as having the highest sampling precision. However, grain‐size distributions are highly variable and often fail to follow a theoretical distribution. This paper presents both theoretical and empirical techniques to determine the precision of sampling different percentiles. These methods are then applied to a range of natural distributions found in UK rivers. It is found that grains between the 66th and 91st percentiles are the most precisely sampled, with maximum precision obtained with the 73rd percentile. Copyright © 2003 John Wiley & Sons, Ltd.  相似文献   

Problems of reservoir sedimentation in China     

姜乃森  傅玲燕 《中国地理科学(英文版)》1998,8(2):117-125

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The environmental state of freshwater resources in Greece (rivers and lakes)   总被引：1，自引：0，他引：1  

N. T. Skoulikidis  I. Bertahas  T. Koussouris 《Environmental Geology》1998,36(1-2):1-17

 The dominant factor regulating Greek riverine dissolved inorganic solid concentrations is chemical weathering, which depends on catchment climate and petrography. The majority of Greek rivers are moderately polluted and only a few of them show significant human impact and an increase in pollutant concentrations over time. Due to droughts in recent years and anthropogenic influence, the mean annual riverine dissolved solid concentrations exhibit a general interannual increase and significant long-term variations in their intra-annual hydrochemical fluctuations. The shallow Greek lakes are eutrophic, while the deep ones are oligo-mesotrophic. The majority of the lakes are monomictic and show summer thermal stratification, while the shallow ones are characterized by anoxic hypolimnetic conditions. Catchment petrography is not a dominant factor in the composition of lake waters since biochemical processes prevail. The majority of Greek lakes are also moderately polluted and are characterized by phosphorous-limited photosynthesis. Received: 17 March 1997 · Accepted: 16 January 1998  相似文献