Flood-borne sediment analysis of the Hoanib River, northwestern Namibia

The suspended sediment contained in six flood events in the Hoanib River catchment during the wet season of 1999/2000 were analysed for volatile (or low molecular weight) fine particulate organic material (FPOM), higher molecular weight FPOM and the total organic carbon (TOC). Samples were evaporated to dryness at 80 °C, then heated in a high temperature oven to 250, 550 and 850 °C. The results show that the amount of sediment carried during the flood events varied between 1.54 and 31.27 g/L, with an average of 14.62 g/L. The amount of suspended sediment in the flood-waters (2.789–616.359×10⁶ kg) was found to be dependent on the timing and duration of the flood event. The largest percentage of organic material was found in the volatile FPOM fraction (5.77±6.26%), with lesser amounts being found in the higher molecular weight FPOM (3.36±0.62%) and TOC (4.93±1.86%) fractions.     

中国国际河流研究进展

1IntroductionThe increasing momentum of economic globalization and regional geopolitical cooperation no longer stand as the major drivers of a new world order. Resource and environmental diplomacy are now regarded as new elements establishing future international patterns. Transboundary resources and environmental issues in international river basins have attracted increasing global concern and professional attention. The impact of such issues penetrates into national security, international e…     

Further perspectives on the evolution of bed material waves in alluvial rivers

In one‐dimensional mathematical models of ?uvial ?ow, sediment transport and morphological evolution, the governing equations based on mass and momentum conservation laws constitute a hyperbolic system. Succinctly, the hyperbolic nature excludes dispersion or diffusion operators, which is well known in the context of differential equations. There is no doubt that the so‐called ‘dispersion’ argument for bed material wave evolution is questionable, as we have explicitly asserted. Surprisingly, in a recent communication, the authors of the ‘dispersion’ argument suggest that dispersion is not precluded in hyperbolic systems. We provide herein further perspectives to help explain that the dispersion argument is neither appropriate nor necessary for interpreting bed material wave evolution. Also the continuity equations involved are addressed to prompt wider understanding of their signi?cance. In particular, the continuity equation of the water–sediment mixture proposed by the authors of the ‘dispersion’ argument is proved to be incorrect, and inevitably their reasoning based on it is problematic. Copyright © 2005 John Wiley & Sons, Ltd.     

Particle clusters in gravel‐bed rivers: an experimental morphological approach to bed material transport and stability concepts

Structured gravel river beds clearly exert a major influence on bed stability. Indexing structural stability by field measurements of bed strength neglects the processes operating to entrain and transport bed material in different parts of each structure. This study takes a morphological approach to interpreting the critical processes, using particle tracing to determine the movement of individual cluster particles over a range of flood event magnitudes and durations. The experiment was carried out on the River South Tyne, UK; it uses flow hydrographs measured nearby and also benefits from previous studies of historical development, channel morphology and sediment transport at the same site. More than 30 clusters were monitored over a seven‐month period during which clusters occupied 7–16 per cent of the bed. Threshold flows delimiting three apparently contrasting bed sediment process regimes for cluster particles are tentatively set at 100 m³ s^?1 and 183 m³ s^?1; durations of flow at these levels are critical for cluster development, rather than flow peak values. Wake particles are transported most easily. Flow straightening in the wandering channel planform reduces the stability of clusters, since mechanical strength is markedly reduced by this change of direction. The overall area covered by clusters between significant transport events varies little, implying a dynamic equilibrium condition. Copyright © 2005 John Wiley & Sons, Ltd.     

三江并流形成时代的初步探讨

滇西北三江并流区是世界上独特的纵向岭谷地貌区、世界自然遗产地。金沙江、怒江、澜沧江3条大江的阶地、河谷主要沉积物均为中更新世以来所形成，说明三江并流这-独特地貌-水文现象形成于中更新世及以后的时间。中更新世昆黄运动是西南纵向岭谷乃至中国的地貌-河流发育重要转型事件，奠定了西南纵向岭谷区的自然地理格局，影响了三江并流区的现代地表过程和生态环境变化。     

Bar-top hollows: A new element in the architecture of sandy braided rivers

Discrete hollows in the bar tops of the South Saskatchewan River are described that form a newly-recognized morphological element of sandy braided rivers. These bar-top hollows, which are up to 1.7 m deep and may extend for 10–30 m down and across flow, have a circular to ovoid planform and are shown, through use of ground penetrating radar, to be filled by a series of distinct, often angle-of-repose, foresets. The hollows form by both erosion and bar-top deposition and may be generated by bar-tail accretion, cross-bar channel cutoff and subsequent fill or lateral accretion at the bar-head. Bar-top hollows occur in the upper part of the bar depositional sequence and may thus prove useful indicators for braid bar reconstruction in ancient sediments, and should not be confused with channel scour.     

Barium in Deccan Basalt Rivers: Its Abundance, Relative Mobility and Flux

The concentration of dissolved Ba in a number of rivers having their drainage almost entirely in Deccan Trap basalts has been measured. These results along with available data on the abundances of major elements in these waters, and on Ba and major elements in bed sediments of these rivers provide a measure of (i) the relative mobility of Ba during chemical weathering and erosion of basalts, particularly with respect to alkaline earths, Mg, Ca and Sr, and (ii) the flux of Ba out of the Deccan and its global significance. The concentration of dissolved Ba ranges from 8 to 105 nM. The average Ba/Mg*, Ba/Ca* and Ba/Sr (* is concentration corrected for atmospheric contribution) in waters is lower than the corresponding mean ratios in Deccan basalts, though they overlap within errors. Majority of the water samples, however, have ratios less than that in basalts. These findings can be interpreted as a cumulative effect of limited release/mobility of Ba during chemical weathering and erosion of basalts and its reactive behaviour in waters which promote its association with clays and oxy-hydroxides of Fe. These results also indicate that during chemical erosion of Deccan basalts, Ba is the least mobile among the alkaline earth elements. The abundance of Ba in sediments and their Ba/Al ratios relative to basalts are consistent with the above conclusion. Ba/Mg and Ba/Ca ratios in water and in sediments from the same location are strongly correlated; however, the mean ratios in waters are far less than those in sediments. This is a result of limited Ba mobility, effectively 5–6 times lower than that of Mg. The annual flux of dissolved Ba out of the Deccan Traps is ~1 × 10⁷ moles, ~ 0.2% of its global riverine transport to oceans. The contribution of dissolved Ba from Deccan Traps, seem lower than its aerial coverage, ~ 0.5% of the global drainage area; the potential causes for this could be the lower abundance of Ba in basalts relative to “average continental crust”, and its behaviour during chemical weathering and erosion.     

Placer formation in gravel-bedded rivers: A review

The literature on placer formation processes within fluvial systems is widespread and ranges between detailed laboratory studies of the hydrodynamic segregation processes through to the intuitive interpretation of the distribution of minerals within geological sections. However, there are few, if any, comprehensive reviews of the literature. Surprisingly, given the economic importance of placers, the theoretical framework relating to the hydrodynamics of physical grain sorting is not well developed and there are relatively few detailed laboratory hydraulic investigations to inform theory. In this wide-ranging review, the history of the development of principles of placer formation is explored as far as possible in a non-technical fashion. A consideration is given to the hydrodynamics of physical grain sorting above lower-stage and upper-stage bedforms and the typical internal sedimentary structures associated with placer concentrations are detailed. Finally, examples of the depositional environment of diamond, tin and gold placers are considered.     

西藏一江两河地区农业景观调整研究

西藏一江两河地区是经济快速发展地区,由于高寒和多风少雨,生态环境条件极其恶劣,景观系统抗御和修复干扰的能力微弱.因此,在该地区实施大农业开发工程不能走传统的开荒要粮的道路,而应实施农业景观调整规划,规划的重要内容有3项,即实施现代农业技术使现有的高产田改造成稳产高产田;使现有的大量中低产田改造成有灌排条件的高产田;选择干旱坡地、不平整土地和与当地农民生活相关不密切的旱地退耕还林还草.从而解决粮食需求问题,遏止生态环境急剧退化的趋势.     

ALTERATIONS OF RIVER MORPHOLOGY DUE TO VEGETATION ON SLOPES AND FLOOD PLAINS

LRESEarCHACTIVITIESCharaCtCriedcofunlinedalluvialriVersisthe~linteractionbettVeenwaterflowandmovableriVerbed.Sedimenttransport,bedresistanceandriVermorphologydecisivelydependontheflowconditionsandviceversathesefactorsgovernthehydraulicprocesses.EVenundersimplifiedconditions,e.g.inlaboratorytests,theseillteractionsareeXtremelycomplexandrelldsraliZationmakesengineeringproblemsevenmored~.TomaketheseprocessesmoreunderstandablecomprehensiVeresearchprojectswereconductedatseveralGermanuniv…