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101.
随着三峡水库的运用,其下游的造床流量发生变化,研究坝下游造床流量的变化特性及主要影响因素对河道的冲淤特性及河床演变机理研究有着重要意义。根据1981—2015年的资料,采用平滩水位法、马卡维耶夫法和流量保证率法计算三峡水库蓄水前后宜昌、枝城、沙市、监利、螺山、汉口、九江、大通各站的造床流量。结果表明:①马卡维耶夫法同时考虑了流量过程和输沙能力的影响,计算结果相对合理。②蓄水后各站造床流量减小3 000~6 000 m3/s,符合坝下游主要冲淤变形部位由平滩河槽调整为中枯水河槽的变化特性,反映了结果的合理性。具体来看,时间上,2009年以后造床流量的减小趋势更为明显;空间上,从绝对值来看,以监利站为转折点,从宜昌至大通呈先减小后增大的趋势。③造床流量对来水量和洪峰流量的响应较为敏感,与之呈正相关关系。 相似文献
102.
R. Woodall 《Australian Journal of Earth Sciences》2013,60(3):231-237
Vision is concerned with making observations: quantitative observations such as measurements, and observations of form and pattern. Vision is perception: an awareness of the significance of observations and insight or intuition. We live and work with limited vision. 相似文献
103.
Hossein Saadat Robert Bonnell Forood Sharifi Guy Mehuys Mohammad Namdar Sasan Ale-Ebrahim 《Geomorphology》2008,100(3-4):453-464
The Iranian Soil and Water Research Institute has been involved in mapping the soils of Iran and classifying landforms for the last 60 years. However, the accuracy of traditional landform maps is very low (about 55%). To date, aerial photographs and topographic maps have been used for landform classification studies. The principal objective of this research is to propose a quantitative approach for landform classification based on a 10-m resolution digital elevation model (DEM) and some use of an Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) image. In order to extract and identify the various landforms, slope, elevation range, and stream network pattern were used as basic identifying parameters. These are extractable from a DEM. Further, ASTER images were required to identify the general outline shape of a landform type and the presence or absence of gravel. This study encompassed a relatively large watershed of 451 183 ha with a total elevation difference of 2445 m and a variety of landforms from flat River Alluvial Plains to steep mountains. Classification accuracy ranged from 91.8 to 99.6% with an average of 96.7% based upon extensive ground-truthing. Since similar digital and ASTER image information is available for Iran, an accurate landform map can now be produced for the whole country. The main advantages of this approach are accuracy, lower demands on time and funds for field work and ready availability of required data for many regions of the world. 相似文献
104.
Seasonal variations of sediment discharge from the Yangtze River before and after impoundment of the Three Gorges Dam 总被引：14，自引：0，他引：14
Over the past decades, > 50,000 dams and reforestation on the Yangtze River (Changjiang) have had little impact on water discharge but have drastically altered annual and particularly seasonal sediment discharge. Before impoundment of the Three Gorges Dam (TGD) in June 2003, annual sediment discharge had decreased by 60%, and the hysteresis of seasonal rating curves in the upper reaches at Yichang station had shifted from clockwise to counterclockwise. In addition, the river channel in middle-lower reaches had changed from depositional to erosional in 2002.During the four years (2003–2006) after TGD impoundment, ~ 60% of sediment entering the Three Gorges Reservoir was trapped, primarily during the high-discharge months (June–September). Although periodic sediment deposition continues downstream of the TGD, during most months substantial erosion has occurred, supplying ~ 70 million tons per year (Mt/y) of channel-derived sediment to the lower reaches of the river. If sand extraction (~ 40 Mt/y) is taken into consideration, the river channel loses a total of 110 Mt/y. During the extreme drought year 2006, sediment discharge in the upper reaches drastically decreased to 9 Mt (only 2% of its 1950–1960s level) because of decreased water discharge and TGD trapping. In addition, Dongting Lake in the middle reaches, for the first time, changed from trapping net sediment from the mainstem to supplying 14 Mt net sediment to the mainstem. Severe channel erosion and drastic sediment decline have put considerable pressure on the Yangtze coastal areas and East China Sea. 相似文献
105.
2008年5月12日14时28分汶川发生8级地震,造成通讯中断,为了及时了解紫坪铺水库大坝受损情况,发震后不到半小时就出发,距发生8级地震后不到3小时到达水库大坝,用相机记录下大坝受损情况,向大坝上的相关领导和业主汇报8级地震情况及其与紫坪铺水库大坝的位置关系,当天返回省地震局后立即向相关领导和部门汇报。2008年2月14日21时36分都江堰市发生3．3级地震,2月15日组织去现场工作,现场调查认为,地震中心点董家山隧道口的烈度为Ⅳ度;发震构造为龙门山前山断裂。 相似文献
106.
107.
Morphological responses and sediment processes following a typhoon‐induced dam failure,Dahan River,Taiwan 
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下载免费PDF全文 The rates and styles of channel adjustments following an abrupt and voluminous sediment pulse are investigated in the context of site and valley characteristics and time‐varying sediment transport regimes. Approximately 10.5 x 106 m3 of stored gravel and sand was exposed when Barlin Dam failed during Typhoon WeiPa in 2007. The dam was located on the Dahan River, Taiwan, a system characterized by steep river gradients, typhoon‐ and monsoon‐driven hydrology, high, episodic sediment supply, and highly variable hydraulic conditions. Topography, bulk sediment samples, aerial photos, and simulated hydraulic conditions are analyzed to investigate temporal and spatial patterns in morphology and likely sediment transport regimes. Results document the rapid response of the reservoir and downstream channel, which occurred primarily through incision and adjustment of channel gradient. Hydraulic simulations illustrate how the dominant sediment transport regime likely varies between study periods with sediment yield and caliber and with the frequency and duration of high flows. Collectively, results indicate that information on variability in sediment transport regime, valley configuration, and distance from the dam is needed to explain the rate and pattern of morphological changes across study periods. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
108.
S. Duvail A.B. Mwakalinga A. Eijkelenburg O. Hamerlynck K. Kindinda A. Majule 《水文科学杂志》2014,59(3-4):713-730
AbstractA large dam is planned at Stiegler’s Gorge in Tanzania. The change in the Rufiji River flood pattern will affect downstream ecosystems. This paper concentrates on the highly productive floodplain lakes that play a vital role in local livelihoods. A participatory monitoring system with village-based observers collected water level, rainfall, fisheries and food data from 2001 to 2011. Water balances of the lakes show dependence on the Rufiji River flood, with varying vulnerability. With the dam design flood of 2500 m3 s-1, lakes with a high threshold and small catchment will dry out quickly. Lakes with a lower threshold and substantial catchment are more robust but may still dry out during prolonged local drought. Analysis of rainfall (1923–2012) indicates a recent decrease. The data were analysed through feedback workshops with local observers, government technical staff and researchers. Through this collaborative approach, local capacity in preparing for the post-dam future was enhanced.
Editor D. Koutsoyiannis; Guest editor M. AcremanCitation Duvail, S., Mwakalinga, A.B., Eijkelenburg, A., Hamerlynck, O., Kindinda, K., and Majule, A., 2014. Jointly thinking the post-dam future: exchange of local and scientific knowledge on the lakes of the Lower Rufiji, Tanzania. Hydrological Sciences Journal, 59 (3–4), 713–730. 相似文献
109.
铁岭柴河1#尾矿坝数值模拟及其稳定性分析 总被引：1，自引：0，他引：1
铁岭柴河1#尾矿坝位于辽宁省开原市靠山镇猴石社区的关门山沟内,由初期坝和尾矿堆积坝组成。本文在该尾矿坝现场勘察的基础上,将坝体实测主轴剖面进行合理地概化和延伸,建立有限差分数值模型,并以Duncan—Chang双曲线模型来反映尾矿坝岩土体应力—应变本构关系,对处于正常运行条件下的坝体进行数值分析,从而揭露坝体内部应力状态,同时在数值分析结果的基础上,采用基于极限平衡理论的条分法——Fellenius法和Biship法对尾矿坝的稳定性进行计算,从而实现对尾矿坝稳定性的定量分析,对尾矿库的安全生产具有重要指导意义。 相似文献
110.
The textural characteristics and trace element geochemistry of hematite with U-W-Sn-Mo signatures from the Cu-U-Au-Ag orebody at Olympic Dam, South Australia, are documented. Olympic Dam is the archetype for iron-oxide copper–gold (IOCG) deposits where hematite is by far the most abundant mineral in the orebody. The deposit is located within hematite-bearing breccias (>5% Fe) hosted by the ∼1.6 Ga Roxby Downs Granite (RDG). Although such breccias are mostly derived from RDG, they also include volcanic clasts and sedimentary rocks. Samples cover the ∼6 km strike length and ∼2 km vertical extent of mineralisation, including hematite from the aforementioned lithologies. Hematite with U-W-Sn-Mo (‘granitophile’ elements) signatures is recognised throughout all lithologies and parts of the deposit. Hematite enriched in granitophile elements is represented by a variety of textures, of which zoned hematite, defined by oscillatory zonation patterns, is the most prominent and can be tied to the age of the RDG, and thus initiation of the IOCG system as confirmed by published U-Pb geochronology. Other categories of hematite with granitophile signatures include hematite resulting from replacement of pre-existing minerals (e.g., carbonates and feldspars), as well as replacement of previous oscillatory-zoned hematites. Matrix and vacuole filling hematite from volcanoclastic-dominated intervals also carry ‘granitophile’ signatures. In addition, some colloform types which likely post-date primary IOCG mineralisation are also rich in ‘granitophile’ elements. Trace element mapping and spot analysis by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) defines complex trace element signatures of hematite, which, in addition to the ‘granitophile’ elements, also comprise rare earth elements, high field strength elements, chalcogens and transition metals.The distinct geochemical signature, characterised by enrichment in the ‘granitophile’ elements (up to wt% levels of U and W within individual zones, and up to thousands of ppm Mo and Sn) prevails throughout the hematite in the deposit irrespective of textures. Iron-oxides have been repeatedly formed, reworked and overprinted by subsequent cycles of brecciation, fluid-mineral reaction, remobilization, element redistribution and recrystallisation. Coupled dissolution-replacement reactions are discussed as having played a major role in the modification of textural and geochemical patterns in hematite, but also allow for widespread preservation of primary geochemical signatures. Despite its simple chemistry, the crystal-structural modularity of hematite can adapt and retain evolving fluid signatures. The reported trace element signatures are fully concordant with conceptual frameworks for the genesis of IOCG systems, and may be an inherent, albeit hitherto under-reported characteristic of other IOCG systems. Hematite is probably by far the most important W-, Sn- and Mo-bearing phase in the deposit by mass. 相似文献