Morphological responses and sediment processes following a typhoon‐induced dam failure,Dahan River,Taiwan

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.     

Jointly thinking the post-dam future: exchange of local and scientific knowledge on the lakes of the Lower Rufiji,Tanzania

Abstract

A 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. Acreman

Citation 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.     

铁岭柴河1#尾矿坝数值模拟及其稳定性分析

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。     

Textures and U-W-Sn-Mo signatures in hematite from the Olympic Dam Cu-U-Au-Ag deposit,South Australia: Defining the archetype for IOCG deposits

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.     

Incompressible SPH scour model for movable bed dam break flows

In this study an incompressible smoothed particle hydrodynamics (ISPH) approach coupled with the sediment erosion model is developed to investigate the sediment bed scour and grain movement under the dam break flows. Two-phase formulations are used in the ISPH numerical algorithms to examine the free surface and bed evolution profiles, in which the entrained sediments are treated as a different fluid component as compared with the water. The sediment bed erosion model is based on the concept of pick-up flow velocity and the sediment is initiated when the local flow velocity exceeds a critical value. The proposed model is used to reproduce the sediment erosion and follow-on entrainment process under an instantaneous dam break flow and the results are compared with those from the weakly compressible moving particle semi-implicit (WCMPS) method as well as the experimental data. It has been demonstrated that the two-phase ISPH model performed well with the experimental data. The study shows that the ISPH modelling approach can accurately predict the dynamic sediment scouring process without the need to use empirical sediment transport formulas.     

四川某水库右坝肩滑坡成因机制及稳定性分析

拟建水库右坝肩处于由砖红色砂岩夹薄层或透镜状泥岩、粉砂质泥岩构成的斜向V形河谷中,无明显断层构造,雨水充沛且存在一古滑坡,经过调查,滑坡主要由滑坡堆积体和滑动面以及其下方的扰动带组成,滑坡区发育的纵向和横向结构面以及岩层面构成一楔形槽。认为滑坡的成因是暴雨下楔形槽内控制的滑移-拉裂破坏。经过定性分析,古滑坡天然状态是稳定的。采用极限平衡法计算古滑坡在天然状态、地震作用以及暴雨等工况下的稳定系数分别为1.45、1.39及1.27,由此可知滑坡在天然状态下是稳定的,地震作用对其稳定性影响不大,但暴雨作用下滑坡的稳定性有所降低。最后通过数值模拟再现了现阶段古滑坡的应力应变场和变形破坏特征。     

An engineering geological appraisal of the Lakhwar Dam, Garhwal Himalaya, India

A 204 m high solid concrete gravity dam is proposed across the River Yamuna in Garhwal Himalaya, India. It will be located on dolerite rocks which have been intruded into the slates of Chandpur Formation. The present study includes the evaluation of the dam foundation by means of drifts, drill holes, water pressure tests and abutment slope stability studies. The water pressure test indicate the necessity of providing a grout curtain below the dam foundation. The analysis of the dam abutments for stability using the Limit equilibrium method indicates that the right abutment slope is kinematically unstable for plane failure mode. The plane failure analysis of the right abutment slope was carried out by modifying the Hoek and Bray (1981, Rock Slope Engineering, 3rd ed., Institute of Mining and Metallurgy, London) technique of plane failure analysis. The analysis reveals that right abutment slope may become unstable during the stripping operation. Based upon the analysis a safe cut slope design for the abutments have been suggested. Subsurface exploration by means of cross drift and drill holes has indicated a sheared contact of slate and dolerite in the foundation area. To avoid the settlement of the dam along this shear zone precautionary measures are suggested.     

后三峡工程时代的鄱阳湖湿地淹没动态演变

周期性的淹没或出露是洪泛型湖泊湿地的重要物理特征,湖泊湿地的淹没动态对其生态过程有显著影响。三峡工程运行以来,鄱阳湖湿地淹没动态发生了显著变化并引发了剧烈生态效应,而目前研究尚未对后三峡工程时代的鄱阳湖淹没动态演变进行系统量化,也制约了对其驱动下湖泊湿地生态系统演变原因与机制的了解。鉴于此,本研究结合水文站实测数据与遥感观测资料,以淹没开始时间、淹没结束时间以及淹没历时3个变量共同表征湖泊湿地淹没动态,从站点及全湖尺度分别对三峡工程运行后鄱阳湖湿地淹没动态的变化趋势、量级及显著性进行定量分析。结果表明:(1)2000—2020年间,鄱阳湖湿地淹没开始时间在64%的湖区被推迟,推迟速率约为1.10天/年;仅在入江水道及碟形湖小幅提前,且提前趋势并不显著;(2)鄱阳湖湿地淹没结束时间在72%的湖区显著提前,提前速率约为1.46天/年;仅在有闸控工程的碟形湖因延迟泄水而有所延迟;(3)受淹没开始时间推迟而结束时间提前的影响,鄱阳湖湿地淹没历时在70%的湖区显著缩短,缩短速率约为2.19天/年,而在有闸控工程的碟形湖则有所延长。本文从站点与全湖尺度分别给出了基于实测而非模型模拟的鄱阳湖淹没动态...     

三峡大坝上下游水质时空变化特征

为探索三峡大坝上下游（坝上99.9 km、坝下63.0 km、全长162.9 km）水质时空变化特征,运用主成分分析和方差分析对2016年近坝段水质时空变化特征进行了分析.主成分分析表明,水文因子流量（Q）、气温（T）、水位（Z）和水质因子（水温（WT）、pH、电导率（EC）、溶解氧（DO）、悬浮物（SS）、高锰酸盐指数（COD_Mn）、硫酸盐（SO₄^2-）、氟化物（F^-）、总硬度（T-Hard）、硝态氮（NO₃^--N）、总氮（TN）和硒（Se））的变化主导着研究区域水质变化;各采样点主成分得分和双因素方差分析结果显示研究区域水质因子时间变化主要呈现出季节和不同水库运行时期的差异.消落期（2-5月）,T-Hard、F^-、SO₄^2-和EC是影响河流水质变化的主导因子;汛期（7-8月）,Q、SS、COD_Mn、NO₃^--N、TN和Se是影响河流水质变化的主导因子;T和WT主导着汛末（9月）河流水质变化,并引起了DO等理化特性的变化;高水位运行期（12月）,Cl^-是影响河流水质变化的主导因子.现阶段,DO、有机污染物（COD_Mn）、无机盐（SO₄^2-和F^-）、营养盐类（NO₃^--N和TN）、类金属元素（Se）和水体的矿化程度（T-Hard）的变化主导着区域水质的变化,是三峡大坝近坝段水域水质的控制因子.方差分析表明,河流的理化特性（DO、pH和SS）、营养盐组分构成（NH₃-N和NO₃^--N）、无机盐类（EC和Cl^-）、石油类有机污染物及粪大肠菌群（FC）等指标在坝上与坝下断面存在显著性差异.气温、水温、降雨、含沙量的季节性影响因素和水库调度运行模式是影响近坝段水质时间差异的主要因子;空间差异主要受城区污染排放和三峡水库调度引起的坝上和坝下水文和水动力学条件差异影响.因此控制研究区域因人类活动等造成的外源性污染,并针对不同类污染物质的季节变化特征实施合理的水库运行方式是近坝段水质提升的关键.